Bio


The Jackson lab examines the different ways that people affect the Earth. We seek to produce the building blocks of basic scientific knowledge and to use that knowledge to guide policy solutions for global warming, energy extraction, and other environmental issues.We're currently examining the effects of climate change and droughts on forest mortality and grassland ecosystems. Recently we've also published the first studies looking at fracking and drinking water quality and mapped thousands of natural gas leaks across cities such as Boston and Washington, D.C.

Academic Appointments


Projects


  • Research Project, Stanford University

    Location

    Argentina

  • Research Project, Stanford University

    Location

    Uruguay

  • Research Project, Stanford University

    Location

    Peru

2014-15 Courses


Postdoctoral Advisees


Journal Articles


  • Noble gases identify the mechanisms of fugitive gas contamination in drinking-water wells overlying the Marcellus and Barnett Shales PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Darrah, T. H., Vengosh, A., Jackson, R. B., Warner, N. R., Poreda, R. J. 2014; 111 (39): 14076-14081
  • Biophysical forcings of land-use changes from potential forestry activities in North America ECOLOGICAL MONOGRAPHS Zhao, K., Jackson, R. B. 2014; 84 (2): 329-353

    View details for DOI 10.1890/12-1705.1

    View details for Web of Science ID 000335859700007

  • Natural Gas Pipeline Leaks Across Washington, DC ENVIRONMENTAL SCIENCE & TECHNOLOGY Jackson, R. B., Down, A., Phillips, N. G., Ackley, R. C., Cook, C. W., Plata, D. L., Zhao, K. 2014; 48 (3): 2051-2058

    Abstract

    Pipeline safety in the United States has increased in recent decades, but incidents involving natural gas pipelines still cause an average of 17 fatalities and $133 M in property damage annually. Natural gas leaks are also the largest anthropogenic source of the greenhouse gas methane (CH4) in the U.S. To reduce pipeline leakage and increase consumer safety, we deployed a Picarro G2301 Cavity Ring-Down Spectrometer in a car, mapping 5893 natural gas leaks (2.5 to 88.6 ppm CH4) across 1500 road miles of Washington, DC. The δ(13)C-isotopic signatures of the methane (-38.2‰ ± 3.9‰ s.d.) and ethane (-36.5 ± 1.1 s.d.) and the CH4:C2H6 ratios (25.5 ± 8.9 s.d.) closely matched the pipeline gas (-39.0‰ and -36.2‰ for methane and ethane; 19.0 for CH4/C2H6). Emissions from four street leaks ranged from 9200 to 38,200 L CH4 day(-1) each, comparable to natural gas used by 1.7 to 7.0 homes, respectively. At 19 tested locations, 12 potentially explosive (Grade 1) methane concentrations of 50,000 to 500,000 ppm were detected in manholes. Financial incentives and targeted programs among companies, public utility commissions, and scientists to reduce leaks and replace old cast-iron pipes will improve consumer safety and air quality, save money, and lower greenhouse gas emissions.

    View details for DOI 10.1021/es404474x

    View details for Web of Science ID 000331015100083

    View details for PubMedID 24432903

  • The environmental costs and benefits of fracking Annual Review of Environment and Resources Jackson, R. B., Vengosh, A., Carey, J. W., Davies, R. J., Darrah, T. H., O'Sullivan, F., Petrón, G. 2014; 39: 327-362
  • Fungal Community Responses to Past and Future Atmospheric CO2 Differ by Soil Type APPLIED AND ENVIRONMENTAL MICROBIOLOGY Procter, A. C., Ellis, J. C., Fay, P. A., Polley, H. W., Jackson, R. B. 2014; 80 (23): 7364-7377
  • New Tracers Identify Hydraulic Fracturing Fluids and Accidental Releases from Oil and Gas Operations ENVIRONMENTAL SCIENCE & TECHNOLOGY Warner, N. R., Darrah, T. H., Jackson, R. B., Millot, R., Kloppmann, W., Vengosh, A. 2014; 48 (21): 12552-12560

    View details for DOI 10.1021/es5032135

    View details for Web of Science ID 000344449100010

  • Role of aquaporin activity in regulating deep and shallow root hydraulic conductance during extreme drought TREES-STRUCTURE AND FUNCTION Johnson, D. M., Sherrard, M. E., Domec, J., Jackson, R. B. 2014; 28 (5): 1323-1331
  • Oil and gas wells and their integrity: Implications for shale and unconventional resource exploitation MARINE AND PETROLEUM GEOLOGY Davies, R. J., Almond, S., Ward, R. S., Jackson, R. B., Adams, C., Worrall, F., Herringshaw, L. G., Gluyas, J. G., Whitehead, M. A. 2014; 56: 239-254
  • Air impacts of increased natural gas acquisition, processing, and use: a critical review. Environmental science & technology Moore, C. W., Zielinska, B., Pétron, G., Jackson, R. B. 2014; 48 (15): 8349-8359

    Abstract

    During the past decade, technological advancements in the United States and Canada have led to rapid and intensive development of many unconventional natural gas plays (e.g., shale gas, tight sand gas, coal-bed methane), raising concerns about environmental impacts. Here, we summarize the current understanding of local and regional air quality impacts of natural gas extraction, production, and use. Air emissions from the natural gas life cycle include greenhouse gases, ozone precursors (volatile organic compounds and nitrogen oxides), air toxics, and particulates. National and state regulators primarily use generic emission inventories to assess the climate, air quality, and health impacts of natural gas systems. These inventories rely on limited, incomplete, and sometimes outdated emission factors and activity data, based on few measurements. We discuss case studies for specific air impacts grouped by natural gas life cycle segment, summarize the potential benefits of using natural gas over other fossil fuels, and examine national and state emission regulations pertaining to natural gas systems. Finally, we highlight specific gaps in scientific knowledge and suggest that substantial additional measurements of air emissions from the natural gas life cycle are essential to understanding the impacts and benefits of this resource.

    View details for DOI 10.1021/es4053472

    View details for PubMedID 24588259

  • Risks and risk governance in unconventional shale gas development. Environmental science & technology Small, M. J., Stern, P. C., Bomberg, E., Christopherson, S. M., Goldstein, B. D., Israel, A. L., Jackson, R. B., Krupnick, A., Mauter, M. S., Nash, J., North, D. W., Olmstead, S. M., Prakash, A., Rabe, B., Richardson, N., Tierney, S., Webler, T., Wong-Parodi, G., Zielinska, B. 2014; 48 (15): 8289-8297

    Abstract

    A broad assessment is provided of the current state of knowledge regarding the risks associated with shale gas development and their governance. For the principal domains of risk, we identify observed and potential hazards and promising mitigation options to address them, characterizing current knowledge and research needs. Important unresolved research questions are identified for each area of risk; however, certain domains exhibit especially acute deficits of knowledge and attention, including integrated studies of public health, ecosystems, air quality, socioeconomic impacts on communities, and climate change. For these, current research and analysis are insufficient to either confirm or preclude important impacts. The rapidly evolving landscape of shale gas governance in the U.S. is also assessed, noting challenges and opportunities associated with the current decentralized (state-focused) system of regulation. We briefly review emerging approaches to shale gas governance in other nations, and consider new governance initiatives and options in the U.S. involving voluntary industry certification, comprehensive development plans, financial instruments, and possible future federal roles. In order to encompass the multiple relevant disciplines, address the complexities of the evolving shale gas system and reduce the many key uncertainties needed for improved management, a coordinated multiagency federal research effort will need to be implemented.

    View details for DOI 10.1021/es502111u

    View details for PubMedID 24983403

  • A critical review of the risks to water resources from unconventional shale gas development and hydraulic fracturing in the United States. Environmental science & technology Vengosh, A., Jackson, R. B., Warner, N., Darrah, T. H., Kondash, A. 2014; 48 (15): 8334-8348

    Abstract

    The rapid rise of shale gas development through horizontal drilling and high volume hydraulic fracturing has expanded the extraction of hydrocarbon resources in the U.S. The rise of shale gas development has triggered an intense public debate regarding the potential environmental and human health effects from hydraulic fracturing. This paper provides a critical review of the potential risks that shale gas operations pose to water resources, with an emphasis on case studies mostly from the U.S. Four potential risks for water resources are identified: (1) the contamination of shallow aquifers with fugitive hydrocarbon gases (i.e., stray gas contamination), which can also potentially lead to the salinization of shallow groundwater through leaking natural gas wells and subsurface flow; (2) the contamination of surface water and shallow groundwater from spills, leaks, and/or the disposal of inadequately treated shale gas wastewater; (3) the accumulation of toxic and radioactive elements in soil or stream sediments near disposal or spill sites; and (4) the overextraction of water resources for high-volume hydraulic fracturing that could induce water shortages or conflicts with other water users, particularly in water-scarce areas. Analysis of published data (through January 2014) reveals evidence for stray gas contamination, surface water impacts in areas of intensive shale gas development, and the accumulation of radium isotopes in some disposal and spill sites. The direct contamination of shallow groundwater from hydraulic fracturing fluids and deep formation waters by hydraulic fracturing itself, however, remains controversial.

    View details for DOI 10.1021/es405118y

    View details for PubMedID 24606408

  • Priming of soil organic carbon decomposition induced by corn compared to soybean crops SOIL BIOLOGY & BIOCHEMISTRY Mazzilli, S. R., Kemanian, A. R., Ernst, O. R., Jackson, R. B., Pineiro, G. 2014; 75: 273-281
  • The integrity of oil and gas wells. Proceedings of the National Academy of Sciences of the United States of America Jackson, R. B. 2014; 111 (30): 10902-10903

    View details for DOI 10.1073/pnas.1410786111

    View details for PubMedID 25009178

  • Impacts of climate change drivers on C-4 grassland productivity: scaling driver effects through the plant community JOURNAL OF EXPERIMENTAL BOTANY Polley, H. W., Derner, J. D., Jackson, R. B., Wilsey, B. J., Fay, P. A. 2014; 65 (13): 3415-3424

    Abstract

    Climate change drivers affect plant community productivity via three pathways: (i) direct effects of drivers on plants; (ii) the response of species abundances to drivers (community response); and (iii) the feedback effect of community change on productivity (community effect). The contribution of each pathway to driver-productivity relationships depends on functional traits of dominant species. We used data from three experiments in Texas, USA, to assess the role of community dynamics in the aboveground net primary productivity (ANPP) response of C4 grasslands to two climate drivers applied singly: atmospheric CO2 enrichment and augmented summer precipitation. The ANPP-driver response differed among experiments because community responses and effects differed. ANPP increased by 80-120g m(-2) per 100 μl l(-1) rise in CO2 in separate experiments with pasture and tallgrass prairie assemblages. Augmenting ambient precipitation by 128mm during one summer month each year increased ANPP more in native than in exotic communities in a third experiment. The community effect accounted for 21-38% of the ANPP CO2 response in the prairie experiment but little of the response in the pasture experiment. The community response to CO2 was linked to species traits associated with greater soil water from reduced transpiration (e.g. greater height). Community effects on the ANPP CO2 response and the greater ANPP response of native than exotic communities to augmented precipitation depended on species differences in transpiration efficiency. These results indicate that feedbacks from community change influenced ANPP-driver responses. However, the species traits that regulated community effects on ANPP differed from the traits that determined how communities responded to drivers.

    View details for DOI 10.1093/jxb/eru009

    View details for Web of Science ID 000339953400009

    View details for PubMedID 24501178

  • Nitrogen Fertilization Has a Stronger Effect on Soil Nitrogen-Fixing Bacterial Communities than Elevated Atmospheric CO2 APPLIED AND ENVIRONMENTAL MICROBIOLOGY Berthrong, S. T., Yeager, C. M., Gallegos-Graves, L., Steven, B., Eichorst, S. A., Jackson, R. B., Kuske, C. R. 2014; 80 (10): 3103-3112

    Abstract

    Biological nitrogen fixation is the primary supply of N to most ecosystems, yet there is considerable uncertainty about how N-fixing bacteria will respond to global change factors such as increasing atmospheric CO2 and N deposition. Using the nifH gene as a molecular marker, we studied how the community structure of N-fixing soil bacteria from temperate pine, aspen, and sweet gum stands and a brackish tidal marsh responded to multiyear elevated CO2 conditions. We also examined how N availability, specifically, N fertilization, interacted with elevated CO2 to affect these communities in the temperate pine forest. Based on data from Sanger sequencing and quantitative PCR, the soil nifH composition in the three forest systems was dominated by species in the Geobacteraceae and, to a lesser extent, Alphaproteobacteria. The N-fixing-bacterial-community structure was subtly altered after 10 or more years of elevated atmospheric CO2, and the observed shifts differed in each biome. In the pine forest, N fertilization had a stronger effect on nifH community structure than elevated CO2 and suppressed the diversity and abundance of N-fixing bacteria under elevated atmospheric CO2 conditions. These results indicate that N-fixing bacteria have complex, interacting responses that will be important for understanding ecosystem productivity in a changing climate.

    View details for DOI 10.1128/AEM.04034-13

    View details for Web of Science ID 000335386200017

    View details for PubMedID 24610855

  • Contrasting hydraulic architecture and function in deep and shallow roots of tree species from a semi-arid habitat ANNALS OF BOTANY Johnson, D. M., Brodersen, C. R., Reed, M., Domec, J., Jackson, R. B. 2014; 113 (4): 617-627

    Abstract

    Despite the importance of vessels in angiosperm roots for plant water transport, there is little research on the microanatomy of woody plant roots. Vessels in roots can be interconnected networks or nearly solitary, with few vessel-vessel connections. Species with few connections are common in arid habitats, presumably to isolate embolisms. In this study, measurements were made of root vessel pit sizes, vessel air-seeding pressures, pit membrane thicknesses and the degree of vessel interconnectedness in deep (approx. 20 m) and shallow (<10 cm) roots of two co-occurring species, Sideroxylon lanuginosum and Quercus fusiformis.Scanning electron microscopy was used to image pit dimensions and to measure the distance between connected vessels. The number of connected vessels in larger samples was determined by using high-resolution computed tomography and three-dimensional (3-D) image analysis. Individual vessel air-seeding pressures were measured using a microcapillary method. The thickness of pit membranes was measured using transmission electron microscopy.Vessel pit size varied across both species and rooting depths. Deep Q. fusiformis roots had the largest pits overall (>500 µm) and more large pits than either shallow Q. fusiformis roots or S. lanuginosum roots. Vessel air-seeding pressures were approximately four times greater in Q. fusiformis than in S. lanuginosum and 1·3-1·9 times greater in shallow roots than in deep roots. Sideroxylon lanuginosum had 34-44 % of its vessels interconnected, whereas Q. fusiformis only had 1-6 % of its vessels connected. Vessel air-seeding pressures were unrelated to pit membrane thickness but showed a positive relationship with vessel interconnectedness.These data support the hypothesis that species with more vessel-vessel integration are often less resistant to embolism than species with isolated vessels. This study also highlights the usefulness of tomography for vessel network analysis and the important role of 3-D xylem organization in plant hydraulic function.

    View details for DOI 10.1093/aob/mct294

    View details for Web of Science ID 000332251700005

    View details for PubMedID 24363350

  • China's fuel gas sector: History, current status, and future prospects UTILITIES POLICY Yang, C., Zhou, Y., Jackson, R. B. 2014; 28: 12-21
  • Geophysical subsurface imaging for ecological applications NEW PHYTOLOGIST Jayawickreme, D. H., Jobbagy, E. G., Jackson, R. B. 2014; 201 (4): 1170-1175

    Abstract

    Ecologists, ecohydrologists, and biogeochemists need detailed insights into belowground properties and processes, including changes in water, salts, and other elements that can influence ecosystem productivity and functioning. Relying on traditional sampling and observation techniques for such insights can be costly, time consuming, and infeasible, especially if the spatial scales involved are large. Geophysical imaging provides an alternative or complement to traditional methods to gather subsurface variables across time and space. In this paper, we review aspects of geophysical imaging, particularly electrical and electromagnetic imaging, that may benefit ecologists seeking clearer understanding of the shallow subsurface. Using electrical resistivity imaging, for example, we have been able to successfully show the effect of land-use conversions to agriculture on salt mobilization and leaching across kilometer-long transects and to depths of tens of meters. Recent advances in ground-penetrating radar and other geophysical imaging methods currently provide opportunities for subsurface imaging with sufficient detail to locate small (≥5 cm diameter) animal burrows and plant roots, observe soil-water and vegetation spatial correlations in small watersheds, estuaries, and marshes, and quantify changes in groundwater storage at local to regional scales using geophysical data from ground- and space-based platforms. Ecologists should benefit from adopting these minimally invasive, scalable imaging technologies to explore the subsurface and advance our collective research.

    View details for DOI 10.1111/nph.12619

    View details for Web of Science ID 000338510200013

    View details for PubMedID 24649489

  • Betting on Negative Emissions Nature Climate Change Fuss, S., Canadell, J. G., Peters, G. P., Tavoni, M., Andrew, R. M., Ciais, P., Jackson, R. B., Jones, C. D., Kraxner, F., Nakicenovic, N., Le Quere, C., Raupach, M. R., Sharifi, A., Smith, P., Yamagata, Y. 2014; 4: 850-853

    View details for DOI 10.1038/nclimate2392

  • Shifting carbon pools along a plant cover gradient in woody encroached savannas of central Argentina Forest Ecology and Management González-Roglich, M., Swenson, J. J., Jobbágy, E. G., Jackson, R. B. 2014; 331: 71–78
  • Land-use and topography shape soil and groundwater salinity in central Argentina AGRICULTURAL WATER MANAGEMENT Nosetto, M. D., ACOSTA, A. M., Jayawickreme, D. H., Ballesteros, S. I., Jackson, R. B., Jobbagy, E. G. 2013; 129: 120-129
  • Impacts of Shale Gas Wastewater Disposal on Water Quality in Western Pennsylvania ENVIRONMENTAL SCIENCE & TECHNOLOGY Warner, N. R., Christie, C. A., Jackson, R. B., Vengosh, A. 2013; 47 (20): 11849-11857

    Abstract

    The safe disposal of liquid wastes associated with oil and gas production in the United States is a major challenge given their large volumes and typically high levels of contaminants. In Pennsylvania, oil and gas wastewater is sometimes treated at brine treatment facilities and discharged to local streams. This study examined the water quality and isotopic compositions of discharged effluents, surface waters, and stream sediments associated with a treatment facility site in western Pennsylvania. The elevated levels of chloride and bromide, combined with the strontium, radium, oxygen, and hydrogen isotopic compositions of the effluents reflect the composition of Marcellus Shale produced waters. The discharge of the effluent from the treatment facility increased downstream concentrations of chloride and bromide above background levels. Barium and radium were substantially (>90%) reduced in the treated effluents compared to concentrations in Marcellus Shale produced waters. Nonetheless, (226)Ra levels in stream sediments (544-8759 Bq/kg) at the point of discharge were ~200 times greater than upstream and background sediments (22-44 Bq/kg) and above radioactive waste disposal threshold regulations, posing potential environmental risks of radium bioaccumulation in localized areas of shale gas wastewater disposal.

    View details for DOI 10.1021/es402165b

    View details for Web of Science ID 000326123600060

    View details for PubMedID 24087919

  • Shale Gas Extraction in North Carolina: Research Recommendations and Public Health Implications ENVIRONMENTAL HEALTH PERSPECTIVES Down, A., Armes, M., Jackson, R. B. 2013; 121 (10): A292-A293

    View details for DOI 10.1289/ehp.1307402

    View details for Web of Science ID 000325152400001

    View details for PubMedID 24218671

  • Increasing atmospheric CO2 reduces metabolic and physiological differences between isoprene- and non-isoprene-emitting poplars. New phytologist Way, D. A., Ghirardo, A., Kanawati, B., Esperschütz, J., Monson, R. K., Jackson, R. B., Schmitt-Kopplin, P., Schnitzler, J. 2013; 200 (2): 534-546

    Abstract

    Isoprene, a volatile organic compound produced by some plant species, enhances abiotic stress tolerance under current atmospheric CO2 concentrations, but its biosynthesis is negatively correlated with CO2 concentrations. We hypothesized that losing the capacity to produce isoprene would require stronger up-regulation of other stress tolerance mechanisms at low CO2 than at higher CO2 concentrations. We compared metabolite profiles and physiological performance in poplars (Populus × canescens) with either wild-type or RNAi-suppressed isoprene emission capacity grown at pre-industrial low, current atmospheric, and future high CO2 concentrations (190, 390 and 590 ppm CO2 , respectively). Suppression of isoprene biosynthesis led to significant rearrangement of the leaf metabolome, increasing stress tolerance responses such as xanthophyll cycle pigment de-epoxidation and antioxidant levels, as well as altering lipid, carbon and nitrogen metabolism. Metabolic and physiological differences between isoprene-emitting and suppressed lines diminished as growth CO2 concentrations rose. The CO2 dependence of our results indicates that the effects of isoprene biosynthesis are strongest at pre-industrial CO2 concentrations. Rising CO2 may reduce the beneficial effects of biogenic isoprene emission, with implications for species competition. This has potential consequences for future climate warming, as isoprene emitted from vegetation has strong effects on global atmospheric chemistry.

    View details for DOI 10.1111/nph.12391

    View details for PubMedID 23822651

  • Increasing atmospheric CO2 reduces metabolic and physiological differences between isoprene- and non-isoprene-emitting poplars NEW PHYTOLOGIST Way, D. A., Ghirardo, A., Kanawati, B., Esperschuetz, J., Monson, R. K., Jackson, R. B., Schmitt-Kopplin, P., Schnitzler, J. 2013; 200 (2): 534-546

    View details for DOI 10.1111/nph.12391

    View details for Web of Science ID 000324621600024

  • COMMENTARY: China's synthetic natural gas revolution NATURE CLIMATE CHANGE Yang, C., Jackson, R. B. 2013; 3 (10): 852-854
  • Geochemical and isotopic variations in shallow groundwater in areas of the Fayetteville Shale development, north-central Arkansas APPLIED GEOCHEMISTRY Warner, N. R., Kresse, T. M., Hays, P. D., Down, A., Karr, J. D., Jackson, R. B., Vengosh, A. 2013; 35: 207-220
  • Increased stray gas abundance in a subset of drinking water wells near Marcellus shale gas extraction PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Jackson, R. B., Vengosh, A., Darrah, T. H., Warner, N. R., Down, A., Poreda, R. J., Osborn, S. G., Zhao, K., Karr, J. D. 2013; 110 (28): 11250-11255

    Abstract

    Horizontal drilling and hydraulic fracturing are transforming energy production, but their potential environmental effects remain controversial. We analyzed 141 drinking water wells across the Appalachian Plateaus physiographic province of northeastern Pennsylvania, examining natural gas concentrations and isotopic signatures with proximity to shale gas wells. Methane was detected in 82% of drinking water samples, with average concentrations six times higher for homes <1 km from natural gas wells (P = 0.0006). Ethane was 23 times higher in homes <1 km from gas wells (P = 0.0013); propane was detected in 10 water wells, all within approximately 1 km distance (P = 0.01). Of three factors previously proposed to influence gas concentrations in shallow groundwater (distances to gas wells, valley bottoms, and the Appalachian Structural Front, a proxy for tectonic deformation), distance to gas wells was highly significant for methane concentrations (P = 0.007; multiple regression), whereas distances to valley bottoms and the Appalachian Structural Front were not significant (P = 0.27 and P = 0.11, respectively). Distance to gas wells was also the most significant factor for Pearson and Spearman correlation analyses (P < 0.01). For ethane concentrations, distance to gas wells was the only statistically significant factor (P < 0.005). Isotopic signatures (δ(13)C-CH4, δ(13)C-C2H6, and δ(2)H-CH4), hydrocarbon ratios (methane to ethane and propane), and the ratio of the noble gas (4)He to CH4 in groundwater were characteristic of a thermally postmature Marcellus-like source in some cases. Overall, our data suggest that some homeowners living <1 km from gas wells have drinking water contaminated with stray gases.

    View details for DOI 10.1073/pnas.1221635110

    View details for Web of Science ID 000321827000027

    View details for PubMedID 23798404

  • Hydraulic limits on maximum plant transpiration and the emergence of the safety-efficiency trade-off NEW PHYTOLOGIST Manzoni, S., Vico, G., Katul, G., Palmroth, S., Jackson, R. B., Porporato, A. 2013; 198 (1): 169-178

    Abstract

    Soil and plant hydraulics constrain ecosystem productivity by setting physical limits to water transport and hence carbon uptake by leaves. While more negative xylem water potentials provide a larger driving force for water transport, they also cause cavitation that limits hydraulic conductivity. An optimum balance between driving force and cavitation occurs at intermediate water potentials, thus defining the maximum transpiration rate the xylem can sustain (denoted as E(max)). The presence of this maximum raises the question as to whether plants regulate transpiration through stomata to function near E(max). To address this question, we calculated E(max) across plant functional types and climates using a hydraulic model and a global database of plant hydraulic traits. The predicted E(max) compared well with measured peak transpiration across plant sizes and growth conditions (R = 0.86, P < 0.001) and was relatively conserved among plant types (for a given plant size), while increasing across climates following the atmospheric evaporative demand. The fact that E(max) was roughly conserved across plant types and scales with the product of xylem saturated conductivity and water potential at 50% cavitation was used here to explain the safety-efficiency trade-off in plant xylem. Stomatal conductance allows maximum transpiration rates despite partial cavitation in the xylem thereby suggesting coordination between stomatal regulation and xylem hydraulic characteristics.

    View details for DOI 10.1111/nph.12126

    View details for Web of Science ID 000315440400018

    View details for PubMedID 23356378

  • Mapping urban pipeline leaks: Methane leaks across Boston ENVIRONMENTAL POLLUTION Phillips, N. G., Ackley, R., Crosson, E. R., Down, A., Hutyra, L. R., Brondfield, M., Karr, J. D., Zhao, K., Jackson, R. B. 2013; 173: 1-4

    Abstract

    Natural gas is the largest source of anthropogenic emissions of methane (CH(4)) in the United States. To assess pipeline emissions across a major city, we mapped CH(4) leaks across all 785 road miles in the city of Boston using a cavity-ring-down mobile CH(4) analyzer. We identified 3356 CH(4) leaks with concentrations exceeding up to 15 times the global background level. Separately, we measured δ(13)CH(4) isotopic signatures from a subset of these leaks. The δ(13)CH(4) signatures (mean = -42.8‰ ± 1.3‰ s.e.; n = 32) strongly indicate a fossil fuel source rather than a biogenic source for most of the leaks; natural gas sampled across the city had average δ(13)CH(4) values of -36.8‰ (± 0.7‰ s.e., n = 10), whereas CH(4) collected from landfill sites, wetlands, and sewer systems had δ(13)CH(4) signatures ~20‰ lighter (μ = -57.8‰, ± 1.6‰ s.e., n = 8). Repairing leaky natural gas distribution systems will reduce greenhouse gas emissions, increase consumer health and safety, and save money.

    View details for DOI 10.1016/j.envpol.2012.11.003

    View details for Web of Science ID 000313845500001

    View details for PubMedID 23174345

  • The effects of shale gas exploration and hydraulic fracturing on the quality of water resources in the United States PROCEEDINGS OF THE FOURTEENTH INTERNATIONAL SYMPOSIUM ON WATER-ROCK INTERACTION, WRI 14 Vengosh, A., Warner, N., Jackson, R., Darrah, T. 2013; 7: 863-866
  • Elevated growth temperatures alter hydraulic characteristics in trembling aspen (Populus tremuloides) seedlings: implications for tree drought tolerance PLANT CELL AND ENVIRONMENT Way, D. A., Domec, J., Jackson, R. B. 2013; 36 (1): 103-115

    Abstract

    Although climate change will alter both soil water availability and evaporative demand, our understanding of how future climate conditions will alter tree hydraulic architecture is limited. Here, we demonstrate that growth at elevated temperatures (ambient +5 °C) affects hydraulic traits in seedlings of the deciduous boreal tree species Populus tremuloides, with the strength of the effect varying with the plant organ studied. Temperature altered the partitioning of hydraulic resistance, with greater resistance attributed to stems and less to roots in warm-grown seedlings (P < 0.02), and a 46% (but marginally significant, P = 0.08) increase in whole plant conductance at elevated temperature. Vulnerability to cavitation was greater in leaves grown at high than at ambient temperatures, but vulnerability in stems was similar between treatments. A soil-plant-atmosphere (SPA) model suggests that these coordinated changes in hydraulic physiology would lead to more frequent drought stress and reduced water-use efficiency in aspen that develop at warmer temperatures. Tissue-specific trade-offs in hydraulic traits in response to high growth temperatures would be difficult to detect when relying solely on whole plant measurements, but may have large-scale ecological implications for plant water use, carbon cycling and, possibly, plant drought survival.

    View details for DOI 10.1111/j.1365-3040.2012.02557.x

    View details for Web of Science ID 000311974000007

    View details for PubMedID 22690910

  • The Structure, Distribution, and Biomass of the World's Forests ANNUAL REVIEW OF ECOLOGY, EVOLUTION, AND SYSTEMATICS, VOL 44 Pan, Y., Birdsey, R. A., Phillips, O. L., Jackson, R. B. 2013; 44: 593-?
  • Reply to Engelder: Potential for fluid migration from the Marcellus Formation remains possible PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Warner, N. R., Jackson, R. B., Darrah, T. H., Osborn, S. G., Down, A., Zhao, K., White, A., Vengosh, A. 2012; 109 (52): E3626-E3626
  • China's coal price disturbances: Observations, explanations, and implications for global energy economies ENERGY POLICY Yang, C., Xuan, X., Jackson, R. B. 2012; 51: 720-727
  • Revised calibration of the MBT-CBT paleotemperature proxy based on branched tetraether membrane lipids in surface soils GEOCHIMICA ET COSMOCHIMICA ACTA Peterse, F., van der Meer, J., Schouten, S., Weijers, J. W., Fierer, N., Jackson, R. B., Kim, J., Damste, J. S. 2012; 96: 215-229
  • Assessing the potential of wildfires as a sustainable bioenergy opportunity GLOBAL CHANGE BIOLOGY BIOENERGY Veron, S. R., Jobbagy, E. G., Di Bella, C. M., Paruelo, J. M., Jackson, R. B. 2012; 4 (6): 634-641
  • Soil-mediated effects of subambient to increased carbon dioxide on grassland productivity NATURE CLIMATE CHANGE Fay, P. A., Jin, V. L., Way, D. A., Potter, K. N., Gill, R. A., Jackson, R. B., Polley, H. W. 2012; 2 (10): 742-746
  • Shifts in soil organic carbon for plantation and pasture establishment in native forests and grasslands of South America GLOBAL CHANGE BIOLOGY Eclesia, R. P., Jobbagy, E. G., Jackson, R. B., Biganzoli, F., Pineiro, G. 2012; 18 (10): 3237-3251
  • The impact of geologic variability on capacity and cost estimates for storing CO2 in deep-saline aquifers ENERGY ECONOMICS Eccles, J. K., Pratson, L., Newell, R. G., Jackson, R. B. 2012; 34 (5): 1569-1579
  • Geochemical evidence for possible natural migration of Marcellus Formation brine to shallow aquifers in Pennsylvania PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Warner, N. R., Jackson, R. B., Darrah, T. H., Osborn, S. G., Down, A., Zhao, K., White, A., Vengosh, A. 2012; 109 (30): 11961-11966

    Abstract

    The debate surrounding the safety of shale gas development in the Appalachian Basin has generated increased awareness of drinking water quality in rural communities. Concerns include the potential for migration of stray gas, metal-rich formation brines, and hydraulic fracturing and/or flowback fluids to drinking water aquifers. A critical question common to these environmental risks is the hydraulic connectivity between the shale gas formations and the overlying shallow drinking water aquifers. We present geochemical evidence from northeastern Pennsylvania showing that pathways, unrelated to recent drilling activities, exist in some locations between deep underlying formations and shallow drinking water aquifers. Integration of chemical data (Br, Cl, Na, Ba, Sr, and Li) and isotopic ratios ((87)Sr/(86)Sr, (2)H/H, (18)O/(16)O, and (228)Ra/(226)Ra) from this and previous studies in 426 shallow groundwater samples and 83 northern Appalachian brine samples suggest that mixing relationships between shallow ground water and a deep formation brine causes groundwater salinization in some locations. The strong geochemical fingerprint in the salinized (Cl > 20 mg/L) groundwater sampled from the Alluvium, Catskill, and Lock Haven aquifers suggests possible migration of Marcellus brine through naturally occurring pathways. The occurrences of saline water do not correlate with the location of shale-gas wells and are consistent with reported data before rapid shale-gas development in the region; however, the presence of these fluids suggests conductive pathways and specific geostructural and/or hydrodynamic regimes in northeastern Pennsylvania that are at increased risk for contamination of shallow drinking water resources, particularly by fugitive gases, because of natural hydraulic connections to deeper formations.

    View details for DOI 10.1073/pnas.1121181109

    View details for Web of Science ID 000306992700025

    View details for PubMedID 22778445

  • The hydrologic consequences of land cover change in central Argentina AGRICULTURE ECOSYSTEMS & ENVIRONMENT Nosetto, M. D., Jobbagy, E. G., Brizuela, A. B., Jackson, R. B. 2012; 154: 2-11
  • Analytical models of soil and litter decomposition: Solutions for mass loss and time-dependent decay rates SOIL BIOLOGY & BIOCHEMISTRY Manzoni, S., Pineiro, G., Jackson, R. B., Jobbagy, E. G., Kim, J. H., Porporato, A. 2012; 50: 66-76
  • Ecosystem Impacts of Geoengineering: A Review for Developing a Science Plan AMBIO Russell, L. M., Rasch, P. J., Mace, G. M., Jackson, R. B., Shepherd, J., Liss, P., Leinen, M., Schimel, D., Vaughan, N. E., Janetos, A. C., Boyd, P. W., Norby, R. J., Caldeira, K., Merikanto, J., Artaxo, P., Melillo, J., Morgan, M. G. 2012; 41 (4): 350-369

    Abstract

    Geoengineering methods are intended to reduce climate change, which is already having demonstrable effects on ecosystem structure and functioning in some regions. Two types of geoengineering activities that have been proposed are: carbon dioxide (CO(2)) removal (CDR), which removes CO(2) from the atmosphere, and solar radiation management (SRM, or sunlight reflection methods), which reflects a small percentage of sunlight back into space to offset warming from greenhouse gases (GHGs). Current research suggests that SRM or CDR might diminish the impacts of climate change on ecosystems by reducing changes in temperature and precipitation. However, sudden cessation of SRM would exacerbate the climate effects on ecosystems, and some CDR might interfere with oceanic and terrestrial ecosystem processes. The many risks and uncertainties associated with these new kinds of purposeful perturbations to the Earth system are not well understood and require cautious and comprehensive research.

    View details for DOI 10.1007/s13280-012-0258-5

    View details for Web of Science ID 000304617700004

    View details for PubMedID 22430307

  • Global resorption efficiencies and concentrations of carbon and nutrients in leaves of terrestrial plants ECOLOGICAL MONOGRAPHS Vergutz, L., Manzoni, S., Porporato, A., Novais, R. F., Jackson, R. B. 2012; 82 (2): 205-220
  • Common bacterial responses in six ecosystems exposed to 10 years of elevated atmospheric carbon dioxide ENVIRONMENTAL MICROBIOLOGY Dunbar, J., Eichorst, S. A., Gallegos-Graves, L. V., Silva, S., Xie, G., Hengartner, N. W., Evans, R. D., Hungate, B. A., Jackson, R. B., Megonigal, J. P., Schadt, C. W., Vilgalys, R., Zak, D. R., Kuske, C. R. 2012; 14 (5): 1145-1158

    Abstract

    Six terrestrial ecosystems in the USA were exposed to elevated atmospheric CO(2) in single or multifactorial experiments for more than a decade to assess potential impacts. We retrospectively assessed soil bacterial community responses in all six-field experiments and found ecosystem-specific and common patterns of soil bacterial community response to elevated CO(2) . Soil bacterial composition differed greatly across the six ecosystems. No common effect of elevated atmospheric CO(2) on bacterial biomass, richness and community composition across all of the ecosystems was identified, although significant responses were detected in individual ecosystems. The most striking common trend across the sites was a decrease of up to 3.5-fold in the relative abundance of Acidobacteria Group 1 bacteria in soils exposed to elevated CO(2) or other climate factors. The Acidobacteria Group 1 response observed in exploratory 16S rRNA gene clone library surveys was validated in one ecosystem by 100-fold deeper sequencing and semi-quantitative PCR assays. Collectively, the 16S rRNA gene sequencing approach revealed influences of elevated CO(2) on multiple ecosystems. Although few common trends across the ecosystems were detected in the small surveys, the trends may be harbingers of more substantive changes in less abundant, more sensitive taxa that can only be detected by deeper surveys. Representative bacterial 16S rRNA gene clone sequences were deposited in GenBank with Accession No. JQ366086–JQ387568.

    View details for DOI 10.1111/j.1462-2920.2011.02695.x

    View details for Web of Science ID 000302934000004

    View details for PubMedID 22264231

  • Conversion of Tallgrass Prairie to Woodland: Consequences for Carbon and Nitrogen Cycling AMERICAN MIDLAND NATURALIST McCulley, R. L., Jackson, R. B. 2012; 167 (2): 307-321
  • The potential of waste-to-energy in reducing GHG emissions CARBON MANAGEMENT Chandel, M. K., Kwok, G., Jackson, R. B., Pratson, L. F. 2012; 3 (2): 133-144

    View details for DOI 10.4155/CMT.12.11

    View details for Web of Science ID 000315238200010

  • Contribution of Various Carbon Sources Toward Isoprene Biosynthesis in Poplar Leaves Mediated by Altered Atmospheric CO2 Concentrations PLOS ONE Trowbridge, A. M., Asensio, D., Eller, A. S., Way, D. A., Wilkinson, M. J., Schnitzler, J., Jackson, R. B., Monson, R. K. 2012; 7 (2)

    Abstract

    Biogenically released isoprene plays important roles in both tropospheric photochemistry and plant metabolism. We performed a (13)CO(2)-labeling study using proton-transfer-reaction mass spectrometry (PTR-MS) to examine the kinetics of recently assimilated photosynthate into isoprene emitted from poplar (Populus × canescens) trees grown and measured at different atmospheric CO(2) concentrations. This is the first study to explicitly consider the effects of altered atmospheric CO(2) concentration on carbon partitioning to isoprene biosynthesis. We studied changes in the proportion of labeled carbon as a function of time in two mass fragments, M41(+), which represents, in part, substrate derived from pyruvate, and M69(+), which represents the whole unlabeled isoprene molecule. We observed a trend of slower (13)C incorporation into isoprene carbon derived from pyruvate, consistent with the previously hypothesized origin of chloroplastic pyruvate from cytosolic phosphenolpyruvate (PEP). Trees grown under sub-ambient CO(2) (190 ppmv) had rates of isoprene emission and rates of labeling of M41(+) and M69(+) that were nearly twice those observed in trees grown under elevated CO(2) (590 ppmv). However, they also demonstrated the lowest proportion of completely labeled isoprene molecules. These results suggest that under reduced atmospheric CO(2) availability, more carbon from stored/older carbon sources is involved in isoprene biosynthesis, and this carbon most likely enters the isoprene biosynthesis pathway through the pyruvate substrate. We offer direct evidence that extra-chloroplastic rather than chloroplastic carbon sources are mobilized to increase the availability of pyruvate required to up-regulate the isoprene biosynthesis pathway when trees are grown under sub-ambient CO(2).

    View details for DOI 10.1371/journal.pone.0032387

    View details for Web of Science ID 000302916100077

    View details for PubMedID 22384238

  • A Global Analysis of Groundwater Recharge for Vegetation, Climate, and Soils VADOSE ZONE JOURNAL Kim, J. H., Jackson, R. B. 2012; 11 (1)
  • China's growing methanol economy and its implications for energy and the environment ENERGY POLICY Yang, C., Jackson, R. B. 2012; 41: 878-884
  • The carbon balance of South America: a review of the status, decadal trends and main determinants BIOGEOSCIENCES Gloor, M., Gatti, L., Brienen, R., Feldpausch, T. R., Phillips, O. L., Miller, J., Ometto, J. P., ROCHA, H., Baker, T., de Jong, B., Houghton, R. A., Malhi, Y., Aragao, L. E., Guyot, J., Zhao, K., Jackson, R., Peylin, P., Sitch, S., Poulter, B., Lomas, M., Zaehle, S., Huntingford, C., Levy, P., Lloyd, J. 2012; 9 (12): 5407-5430
  • N2 fixation estimates in real-time by cavity ring-down laser absorption spectroscopy Oecologia Cassar, N., Bellenger, J., Karr, J., Jackson, R. B. 2012; 168:335-342
  • The effect of hydraulic lift on organic matter decomposition, soil nitrogen cycling, and nitrogen acquisition by a grass species OECOLOGIA Armas, C., Kim, J. H., Bleby, T. M., Jackson, R. B. 2012; 168 (1): 11-22

    Abstract

    Hydraulic lift (HL) is the passive movement of water through plant roots, driven by gradients in water potential. The greater soil-water availability resulting from HL may in principle lead to higher plant nutrient uptake, but the evidence for this hypothesis is not universally supported by current experiments. We grew a grass species common in North America in two-layer pots with three treatments: (1) the lower layer watered, the upper one unwatered (HL), (2) both layers watered (W), and (3) the lower layer watered, the upper one unwatered, but with continuous light 24 h a day to limit HL (no-HL). We inserted ingrowth cores filled with enriched-nitrogen organic matter ((15)N-OM) in the upper layer and tested whether decomposition, mineralization and uptake of (15)N were higher in plants performing HL than in plants without HL. Soils in the upper layer were significantly wetter in the HL treatment than in the no-HL treatment. Decomposition rates were similar in the W and HL treatments and lower in no-HL. On average, the concentration of NH(4)(+)-N in ingrowth cores was highest in the W treatment, and NO(3)(-)-N concentrations were highest in the no-HL treatment, with HL having intermediate values for both, suggesting differential mineralization of organic N among treatments. Aboveground biomass, leaf (15)N contents and the (15)N uptake in aboveground tissues were higher in W and HL than in no-HL, indicating higher nutrient uptake and improved N status of plants performing HL. However, there were no differences in total root nitrogen content or (15)N uptake by roots, indicating that HL affected plant allocation of acquired N to photosynthetic tissues. Our evidence for the role of HL in organic matter decomposition and nutrient cycling suggests that HL could have positive effects on plant nutrient dynamics and nutrient turnover.

    View details for DOI 10.1007/s00442-011-2065-2

    View details for Web of Science ID 000299058100002

    View details for PubMedID 21766189

  • Shallow groundwater quality and geochemistry in the Fayetteville Shale gas-production area, north-central Arkansas, 2011. U.S. Geological Survey Scientific Investigations Report 2012–5273 Kresse, T., Warner, N. R., Hays, P. D., Down, A., Vengosh, A., Jackson, R. B. 2012; 2012–5273
  • Soil C and N changes with afforestation of grasslands across gradients of precipitation and plantation age ECOLOGICAL APPLICATIONS Berthrong, S. T., Pineiro, G., Jobbagy, E. G., Jackson, R. B. 2012; 22 (1): 76-86

    Abstract

    Afforestation, the conversion of unforested lands to forests, is a tool for sequestering anthropogenic carbon dioxide into plant biomass. However, in addition to altering biomass, afforestation can have substantial effects on soil organic carbon (SOC) pools, some of which have much longer turnover times than plant biomass. An increasing body of evidence suggests that the effect of afforestation on SOC may depend on mean annual precipitation (MAP). The goal of this study was to test how labile and bulk pools of SOC and total soil nitrogen (TN) change with afforestation across a rainfall gradient of 600-1500 mm in the Rio de la Plata grasslands of Argentina and Uruguay. The sites were all former grasslands planted with Eucalyptus spp. Overall, we found that afforestation increased (up to 1012 kg C x ha(-1) x yr(-1)) or decreased (as much as 1294 kg C x ha(-1) x yr(-1)) SOC pools in this region and that these changes were significantly related to MAP. Drier sites gained, and wetter sites lost, SOC and TN (r2 = 0.59, P = 0.003; and r2 = 0.57, P = 0.004, respectively). Labile C and N in microbial biomass and extractable soil pools followed similar patterns to bulk SOC and TN. Interestingly, drier sites gained more SOC and TN as plantations aged, while losses reversed as plantations aged in wet sites, suggesting that plantation age in addition to precipitation is a critical driver of changes in soil organic matter with afforestation. This new evidence implies that longer intervals between harvests for plantations could improve SOC storage, ameliorating the negative trends found in humid sites. Our results suggest that the value of afforestation as a carbon sequestration tool should be considered in the context of precipitation and age of the forest stand.

    View details for Web of Science ID 000301095600007

    View details for PubMedID 22471076

  • Considering shale gas extraction in North Carolina: lessons from other states Duke Environmental Law and Policy Forum Adair, S., Rainey Pearson, B., Monast, J., Vengosh, A., Jackson, R. B. 2012; 22:257-301
  • Beyond Bacteria: A Study of the Enteric Microbial Consortium in Extremely Low Birth Weight Infants PLOS ONE Latuga, M. S., Ellis, J. C., Cotton, C. M., Goldberg, R. N., Wynn, J. L., Jackson, R. B., Seed, P. C. 2011; 6 (12)

    Abstract

    Extremely low birth weight (ELBW) infants have high morbidity and mortality, frequently due to invasive infections from bacteria, fungi, and viruses. The microbial communities present in the gastrointestinal tracts of preterm infants may serve as a reservoir for invasive organisms and remain poorly characterized. We used deep pyrosequencing to examine the gut-associated microbiome of 11 ELBW infants in the first postnatal month, with a first time determination of the eukaryote microbiota such as fungi and nematodes, including bacteria and viruses that have not been previously described. Among the fungi observed, Candida sp. and Clavispora sp. dominated the sequences, but a range of environmental molds were also observed. Surprisingly, seventy-one percent of the infant fecal samples tested contained ribosomal sequences corresponding to the parasitic organism Trichinella. Ribosomal DNA sequences for the roundworm symbiont Xenorhabdus accompanied these sequences in the infant with the greatest proportion of Trichinella sequences. When examining ribosomal DNA sequences in aggregate, Enterobacteriales, Pseudomonas, Staphylococcus, and Enterococcus were the most abundant bacterial taxa in a low diversity bacterial community (mean Shannon-Weaver Index of 1.02 ± 0.69), with relatively little change within individual infants through time. To supplement the ribosomal sequence data, shotgun sequencing was performed on DNA from multiple displacement amplification (MDA) of total fecal genomic DNA from two infants. In addition to the organisms mentioned previously, the metagenome also revealed sequences for gram positive and gram negative bacteriophages, as well as human adenovirus C. Together, these data reveal surprising eukaryotic and viral microbial diversity in ELBW enteric microbiota dominated bytypes of bacteria known to cause invasive disease in these infants.

    View details for DOI 10.1371/journal.pone.0027858

    View details for Web of Science ID 000298163600007

    View details for PubMedID 22174751

  • Sources of increased N uptake in forest trees growing under elevated CO2: results of a large-scale N-15 study GLOBAL CHANGE BIOLOGY Hofmockel, K. S., Gallet-Budynek, A., McCarthy, H. R., Currie, W. S., Jackson, R. B., Finzi, A. C. 2011; 17 (11): 3338-3350
  • Reply to Davies: Hydraulic fracturing remains a possible mechanism for observed methane contamination of drinking water PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Jackson, R. B., Osborn, S. G., Vengosh, A., Warner, N. R. 2011; 108 (43): E872-E872
  • Changes in hydrology and salinity accompanying a century of agricultural conversion in Argentina ECOLOGICAL APPLICATIONS Jayawickreme, D. H., Santoni, C. S., Kim, J. H., Jobbagy, E. G., Jackson, R. B. 2011; 21 (7): 2367-2379

    Abstract

    Conversions of natural woodlands to agriculture can alter the hydrologic balance, aquifer recharge, and salinity of soils and groundwater in ways that influence productivity and sustainable land use. Using a land-use change chronosequence in semiarid woodlands of Argentina's Espinal province, we examined the distribution of moisture and solutes and estimated recharge rates on adjacent plots of native woodlands and rain-fed agriculture converted 6-90 years previously. Soil coring and geoelectrical profiling confirmed the presence of spatially extensive salt accumulations in dry woodlands and pervasive salt losses in areas converted to agriculture. A 1.1-km-long electrical resistivity transect traversing woodland, 70-year-old agriculture, and woodland, for instance, revealed a low-resistivity (high-salinity) horizon between approximately 3 m and 13 m depth in the woodlands that was virtually absent in the agricultural site because of leaching. Nine-meter-deep soil profiles indicated a 53% increase in soil water storage after 30 or more years of cultivation. Conservative groundwater-recharge estimates based on chloride tracer methods in agricultural plots ranged from approximately 12 to 45 mm/yr, a substantial increase from the <1 mm/yr recharge in dry woodlands. The onset of deep soil moisture drainage and increased recharge led to >95% loss of sulfate and chloride ions from the shallow vadose zone in most agriculture plots. These losses correspond to over 100 Mg of sulfate and chloride salts potentially released to the region's groundwater aquifers through time with each hectare of deforestation, including a capacity to increase groundwater salinity to >4000 mg/L from these ions alone. Similarities between our findings and those of the dryland salinity problems of deforested woodlands in Australia suggest an important warning about the potential ecohydrological risks brought by the current wave of deforestation in the Espinal and other regions of South America and the world.

    View details for Web of Science ID 000296139200003

    View details for PubMedID 22073629

  • Responses of soil cellulolytic fungal communities to elevated atmospheric CO2 are complex and variable across five ecosystems ENVIRONMENTAL MICROBIOLOGY Weber, C. F., Zak, D. R., Hungate, B. A., Jackson, R. B., Vilgalys, R., Evans, R. D., Schadt, C. W., Megonigal, J. P., Kuske, C. R. 2011; 13 (10): 2778-2793

    Abstract

    Elevated atmospheric CO(2) generally increases plant productivity and subsequently increases the availability of cellulose in soil to microbial decomposers. As key cellulose degraders, soil fungi are likely to be one of the most impacted and responsive microbial groups to elevated atmospheric CO(2). To investigate the impacts of ecosystem type and elevated atmospheric CO(2) on cellulolytic fungal communities, we sequenced 10,677 cbhI gene fragments encoding the catalytic subunit of cellobiohydrolase I, across five distinct terrestrial ecosystem experiments after a decade of exposure to elevated CO(2). The cbhI composition of each ecosystem was distinct, as supported by weighted Unifrac analyses (all P-values; < 0.001), with few operational taxonomic units (OTUs) being shared across ecosystems. Using a 114-member cbhI sequence database compiled from known fungi, less than 1% of the environmental sequences could be classified at the family level indicating that cellulolytic fungi in situ are likely dominated by novel fungi or known fungi that are not yet recognized as cellulose degraders. Shifts in fungal cbhI composition and richness that were correlated with elevated CO(2) exposure varied across the ecosystems. In aspen plantation and desert creosote bush soils, cbhI gene richness was significantly higher after exposure to elevated CO(2) (550 µmol mol(-1)) than under ambient CO(2) (360 µmol mol(-1) CO(2)). In contrast, while the richness was not altered, the relative abundance of dominant OTUs in desert soil crusts was significantly shifted. This suggests that responses are complex, vary across different ecosystems and, in at least one case, are OTU-specific. Collectively, our results document the complexity of cellulolytic fungal communities in multiple terrestrial ecosystems and the variability of their responses to long-term exposure to elevated atmospheric CO(2).

    View details for DOI 10.1111/j.1462-2920.2011.02548.x

    View details for Web of Science ID 000295971300014

    View details for PubMedID 21883796

  • The potential impacts of climate-change policy on freshwater use in thermoelectric power generation ENERGY POLICY Chandel, M. K., Pratson, L. F., Jackson, R. B. 2011; 39 (10): 6234-6242
  • Reply to Saba and Orzechowski and Schon: Methane contamination of drinking water accompanying gas-well drilling and hydraulic fracturing PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Osborn, S. G., Vengosh, A., Warner, N. R., Jackson, R. B. 2011; 108 (37): E665-E666
  • A synthesis of current knowledge on forests and carbon storage in the United States ECOLOGICAL APPLICATIONS McKinley, D. C., Ryan, M. G., Birdsey, R. A., Giardina, C. P., Harmon, M. E., Heath, L. S., Houghton, R. A., Jackson, R. B., Morrison, J. F., Murray, B. C., Pataki, D. E., Skog, K. E. 2011; 21 (6): 1902-1924

    Abstract

    Using forests to mitigate climate change has gained much interest in science and policy discussions. We examine the evidence for carbon benefits, environmental and monetary costs, risks and trade-offs for a variety of activities in three general strategies: (1) land use change to increase forest area (afforestation) and avoid deforestation; (2) carbon management in existing forests; and (3) the use of wood as biomass energy, in place of other building materials, or in wood products for carbon storage. We found that many strategies can increase forest sector carbon mitigation above the current 162-256 Tg C/yr, and that many strategies have co-benefits such as biodiversity, water, and economic opportunities. Each strategy also has trade-offs, risks, and uncertainties including possible leakage, permanence, disturbances, and climate change effects. Because approximately 60% of the carbon lost through deforestation and harvesting from 1700 to 1935 has not yet been recovered and because some strategies store carbon in forest products or use biomass energy, the biological potential for forest sector carbon mitigation is large. Several studies suggest that using these strategies could offset as much as 10-20% of current U.S. fossil fuel emissions. To obtain such large offsets in the United States would require a combination of afforesting up to one-third of cropland or pastureland, using the equivalent of about one-half of the gross annual forest growth for biomass energy, or implementing more intensive management to increase forest growth on one-third of forestland. Such large offsets would require substantial trade-offs, such as lower agricultural production and non-carbon ecosystem services from forests. The effectiveness of activities could be diluted by negative leakage effects and increasing disturbance regimes. Because forest carbon loss contributes to increasing climate risk and because climate change may impede regeneration following disturbance, avoiding deforestation and promoting regeneration after disturbance should receive high priority as policy considerations. Policies to encourage programs or projects that influence forest carbon sequestration and offset fossil fuel emissions should also consider major items such as leakage, the cyclical nature of forest growth and regrowth, and the extensive demand for and movement of forest products globally, and other greenhouse gas effects, such as methane and nitrous oxide emissions, and recognize other environmental benefits of forests, such as biodiversity, nutrient management, and watershed protection. Activities that contribute to helping forests adapt to the effects of climate change, and which also complement forest carbon storage strategies, would be prudent.

    View details for Web of Science ID 000294155900003

    View details for PubMedID 21939033

  • A Large and Persistent Carbon Sink in the World's Forests SCIENCE Pan, Y., Birdsey, R. A., Fang, J., Houghton, R., Kauppi, P. E., Kurz, W. A., Phillips, O. L., Shvidenko, A., Lewis, S. L., Canadell, J. G., Ciais, P., Jackson, R. B., Pacala, S. W., McGuire, A. D., Piao, S., Rautiainen, A., Sitch, S., Hayes, D. 2011; 333 (6045): 988-993

    Abstract

    The terrestrial carbon sink has been large in recent decades, but its size and location remain uncertain. Using forest inventory data and long-term ecosystem carbon studies, we estimate a total forest sink of 2.4 ± 0.4 petagrams of carbon per year (Pg C year(-1)) globally for 1990 to 2007. We also estimate a source of 1.3 ± 0.7 Pg C year(-1) from tropical land-use change, consisting of a gross tropical deforestation emission of 2.9 ± 0.5 Pg C year(-1) partially compensated by a carbon sink in tropical forest regrowth of 1.6 ± 0.5 Pg C year(-1). Together, the fluxes comprise a net global forest sink of 1.1 ± 0.8 Pg C year(-1), with tropical estimates having the largest uncertainties. Our total forest sink estimate is equivalent in magnitude to the terrestrial sink deduced from fossil fuel emissions and land-use change sources minus ocean and atmospheric sinks.

    View details for DOI 10.1126/science.1201609

    View details for Web of Science ID 000294000400048

    View details for PubMedID 21764754

  • Earth Stewardship: science for action to sustain the human-earth system ECOSPHERE Chapin, F. S., Power, M. E., Pickett, S. T., Freitag, A., Reynolds, J. A., Jackson, R. B., Lodge, D. M., Duke, C., Collins, S. L., Power, A. G., Bartuska, A. 2011; 2 (8)
  • Atmospheric CO2 and soil extracellular enzyme activity: a meta-analysis and CO2 gradient experiment ECOSPHERE Kelley, A. M., Fay, P. A., Polley, H. W., Gill, R. A., Jackson, R. B. 2011; 2 (8)
  • Methane contamination of drinking water accompanying gas-well drilling and hydraulic fracturing PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Osborn, S. G., Vengosh, A., Warner, N. R., Jackson, R. B. 2011; 108 (20): 8172-8176

    Abstract

    Directional drilling and hydraulic-fracturing technologies are dramatically increasing natural-gas extraction. In aquifers overlying the Marcellus and Utica shale formations of northeastern Pennsylvania and upstate New York, we document systematic evidence for methane contamination of drinking water associated with shale-gas extraction. In active gas-extraction areas (one or more gas wells within 1 km), average and maximum methane concentrations in drinking-water wells increased with proximity to the nearest gas well and were 19.2 and 64 mg CH(4) L(-1) (n = 26), a potential explosion hazard; in contrast, dissolved methane samples in neighboring nonextraction sites (no gas wells within 1 km) within similar geologic formations and hydrogeologic regimes averaged only 1.1 mg L(-1) (P < 0.05; n = 34). Average δ(13)C-CH(4) values of dissolved methane in shallow groundwater were significantly less negative for active than for nonactive sites (-37 ± 7‰ and -54 ± 11‰, respectively; P < 0.0001). These δ(13)C-CH(4) data, coupled with the ratios of methane-to-higher-chain hydrocarbons, and δ(2)H-CH(4) values, are consistent with deeper thermogenic methane sources such as the Marcellus and Utica shales at the active sites and matched gas geochemistry from gas wells nearby. In contrast, lower-concentration samples from shallow groundwater at nonactive sites had isotopic signatures reflecting a more biogenic or mixed biogenic/thermogenic methane source. We found no evidence for contamination of drinking-water samples with deep saline brines or fracturing fluids. We conclude that greater stewardship, data, and-possibly-regulation are needed to ensure the sustainable future of shale-gas extraction and to improve public confidence in its use.

    View details for DOI 10.1073/pnas.1100682108

    View details for Web of Science ID 000290719600025

    View details for PubMedID 21555547

  • Enhanced isoprene-related tolerance of heat- and light-stressed photosynthesis at low, but not high, CO2 concentrations OECOLOGIA Way, D. A., Schnitzler, J., Monson, R. K., Jackson, R. B. 2011; 166 (1): 273-282

    Abstract

    The principal function of isoprene biosynthesis in plants remains unclear, but emission rates are positively correlated with temperature and light, supporting a role for isoprene in maintaining photosynthesis under transient heat and light stress from sunflecks. Isoprene production is also inversely correlated with CO(2) concentrations, implying that rising CO(2) may reduce the functional importance of isoprene. To understand the importance of isoprene in maintaining photosynthesis during sunflecks, we used RNAi technology to suppress isoprene production in poplar seedlings and compared the responses of these transgenic plants to wild-type and empty-vector control plants. We grew isoprene-emitting and non-emitting trees at low (190 ppm) and high (590 ppm) CO(2) concentrations and compared their photosynthetic responses to short, transient periods of high light and temperature, as well as their photosynthetic thermal response at constant light. While there was little difference between emitting and non-emitting plants in their photosynthetic responses to simulated sunflecks at high CO(2), isoprene-emitting trees grown at low CO(2) had significantly greater photosynthetic sunfleck tolerance than non-emitting plants. Net photosynthesis at 42°C was 50% lower in non-emitters than in isoprene-emitting trees at low CO(2), but only 22% lower at high CO(2). Dark respiration rates were significantly higher in non-emitting poplar from low CO(2), but there was no difference between isoprene-emitting and non-emitting lines at high CO(2). We propose that isoprene biosynthesis may have evolved at low CO(2) concentrations, where its physiological effect is greatest, and that rising CO(2) will reduce the functional benefit of isoprene in the near future.

    View details for DOI 10.1007/s00442-011-1947-7

    View details for Web of Science ID 000289442000026

    View details for PubMedID 21380850

  • Biophysical considerations in forestry for climate protection FRONTIERS IN ECOLOGY AND THE ENVIRONMENT Anderson, R. G., Canadell, J. G., Randerson, J. T., Jackson, R. B., Hungate, B. A., Baldocchi, D. D., Ban-Weiss, G. A., Bonan, G. B., Caldeira, K., Cao, L., Diffenbaugh, N. S., Gurney, K. R., Kueppers, L. M., Law, B. E., Luyssaert, S., O'Halloran, T. L. 2011; 9 (3): 174-182

    View details for DOI 10.1890/090179

    View details for Web of Science ID 000289377800019

  • Response to Comment on "Potential Impacts of Leakage from Deep CO2 Geosequestration on Overlying Freshwater Aquifers" ENVIRONMENTAL SCIENCE & TECHNOLOGY Little, M. G., Jackson, R. B. 2011; 45 (7): 3175-3176

    View details for DOI 10.1021/es200421f

    View details for Web of Science ID 000288841500100

  • Increases in the flux of carbon belowground stimulate nitrogen uptake and sustain the long-term enhancement of forest productivity under elevated CO2 ECOLOGY LETTERS Drake, J. E., Gallet-Budynek, A., Hofmockel, K. S., Bernhardt, E. S., Billings, S. A., Jackson, R. B., Johnsen, K. S., Lichter, J., McCarthy, H. R., McCormack, M. L., Moore, D. J., Oren, R., Palmroth, S., Phillips, R. P., Pippen, J. S., Pritchard, S. G., Treseder, K. K., Schlesinger, W. H., DeLucia, E. H., Finzi, A. C. 2011; 14 (4): 349-357

    Abstract

    The earth's future climate state is highly dependent upon changes in terrestrial C storage in response to rising concentrations of atmospheric CO₂. Here we show that consistently enhanced rates of net primary production (NPP) are sustained by a C-cascade through the root-microbe-soil system; increases in the flux of C belowground under elevated CO₂ stimulated microbial activity, accelerated the rate of soil organic matter decomposition and stimulated tree uptake of N bound to this SOM. This process set into motion a positive feedback maintaining greater C gain under elevated CO₂ as a result of increases in canopy N content and higher photosynthetic N-use efficiency. The ecosystem-level consequence of the enhanced requirement for N and the exchange of plant C for N belowground is the dominance of C storage in tree biomass but the preclusion of a large C sink in the soil.

    View details for DOI 10.1111/j.1461-0248.2011.01593.x

    View details for Web of Science ID 000288211000004

    View details for PubMedID 21303437

  • Water subsidies from mountains to deserts: their role in sustaining groundwater-fed oases in a sandy landscape ECOLOGICAL APPLICATIONS Jobbagy, E. G., Nosetto, M. D., Villagra, P. E., Jackson, R. B. 2011; 21 (3): 678-694

    Abstract

    In arid regions throughout the world, shallow phreatic aquifers feed natural oases of much higher productivity than would be expected solely from local rainfall. In South America, the presence of well-developed Prosopis flexuosa woodlands in the Monte Desert region east of the Andes has puzzled scientists for decades. Today these woodlands provide crucial subsistence to local populations, including descendants of the indigenous Huarpes. We explore the vulnerability and importance of phreatic groundwater for the productivity of the region, comparing the contributions of local rainfall to that of remote mountain recharge that is increasingly being diverted for irrigated agriculture before it reaches the desert. We combined deep soil coring, plant measurements, direct water-table observations, and stable-isotopic analyses (2H and 18O) of meteoric, surface, and ground waters at three study sites across the region, comparing woodland stands, bare dunes, and surrounding shrublands. The isotopic composition of phreatic groundwaters (delta2H: -137 per thousand +/- 5 per thousand) closely matched the signature of water brought to the region by the Mendoza River (-137 per thousand +/- 6 per thousand), suggestin that mountain-river infiltration rather than in situ rainfall deep drainage (-39 per thousand +/- 19 per thousand) was the dominant mechanism of recharge. Similarly, chloride mass balances determined from deep soil profiles (> 6 m) suggested very low recharge rates. Vegetation in woodland ecosystems, where significant groundwater discharge losses, likely >100 mm/yr occurred, relied on regionally derived groundwater located from 6.5 to 9.5 m underground. At these locations, daily water-table fluctuations of 10 mm, and stable-isotopic measurements of plant water, indicated groundwater uptake rates of 200-300 mm/yr. Regional scaling suggests that groundwater evapotranspiration reaches 18-42 mm/yr across the landscape, accounting for 7 17% of the Mendoza River flow regionally. Our study highlights the reliance of ecosystem productivity in natural oases on Andean snowmelt, which is increasingly being diverted to one of the largest irrigated regions of the continent. Understanding the ecohydrological coupling of mountain and desert ecosystems here and elsewhere should help managers balance production agriculture and conservation of unique woodland ecosystems and the rural communities that rely on them.

    View details for Web of Science ID 000290661300004

    View details for PubMedID 21639036

  • Increasing Forest Carbon Sequestration through Cooperation and Shared Strategies between China and the United States ENVIRONMENTAL SCIENCE & TECHNOLOGY Shao, G., Dai, L., Dukes, J. S., Jackson, R. B., Tang, L., Zhao, J. 2011; 45 (6): 2033-2034

    View details for DOI 10.1021/es200147k

    View details for Web of Science ID 000288146200001

    View details for PubMedID 21309612

  • Research frontiers in the analysis of coupled biogeochemical cycles FRONTIERS IN ECOLOGY AND THE ENVIRONMENT Finzi, A. C., Cole, J. J., Doney, S. C., Holland, E. A., Jackson, R. B. 2011; 9 (1): 74-80

    View details for DOI 10.1890/100137

    View details for Web of Science ID 000286845400011

  • Opportunities and barriers to pumped-hydro energy storage in the United States RENEWABLE & SUSTAINABLE ENERGY REVIEWS Yang, C., Jackson, R. B. 2011; 15 (1): 839-844
  • Earth stewardship: a strategy for social–ecological transformation to reverse planetary degradation Journal of Environmental Studies and Sciences Chapin III, F. S., Pickett, S. T., Power, M. E., Jackson, R. B., Carter, D. M., Duke, C. 2011; 1: 44-53
  • A U.S. Carbon Cycle Science Plan U.S. Carbon Cycle Science Program, Washington, DC Michalak, A. M., Jackson, R. B., Marland, G., Sabine, C. L. 2011
  • Potential Impacts of Leakage from Deep CO2 Geosequestration on Overlying Freshwater Aquifers ENVIRONMENTAL SCIENCE & TECHNOLOGY Little, M. G., Jackson, R. B. 2010; 44 (23): 9225-9232

    Abstract

    Carbon Capture and Storage may use deep saline aquifers for CO(2) sequestration, but small CO(2) leakage could pose a risk to overlying fresh groundwater. We performed laboratory incubations of CO(2) infiltration under oxidizing conditions for >300 days on samples from four freshwater aquifers to 1) understand how CO(2) leakage affects freshwater quality; 2) develop selection criteria for deep sequestration sites based on inorganic metal contamination caused by CO(2) leaks to shallow aquifers; and 3) identify geochemical signatures for early detection criteria. After exposure to CO(2), water pH declines of 1-2 units were apparent in all aquifer samples. CO(2) caused concentrations of the alkali and alkaline earths and manganese, cobalt, nickel, and iron to increase by more than 2 orders of magnitude. Potentially dangerous uranium and barium increased throughout the entire experiment in some samples. Solid-phase metal mobility, carbonate buffering capacity, and redox state in the shallow overlying aquifers influence the impact of CO(2) leakage and should be considered when selecting deep geosequestration sites. Manganese, iron, calcium, and pH could be used as geochemical markers of a CO(2) leak, as their concentrations increase within 2 weeks of exposure to CO(2).

    View details for DOI 10.1021/es102235w

    View details for Web of Science ID 000284523400070

    View details for PubMedID 20977267

  • Water uptake and hydraulic redistribution across large woody root systems to 20 m depth PLANT CELL AND ENVIRONMENT Bleby, T. M., McElrone, A. J., Jackson, R. B. 2010; 33 (12): 2132-2148

    Abstract

    Deep water uptake and hydraulic redistribution (HR) are important processes in many forests, savannas and shrublands. We investigated HR in a semi-arid woodland above a unique cave system in central Texas to understand how deep root systems facilitate HR. Sap flow was measured in 9 trunks, 47 shallow roots and 12 deep roots of Quercus, Bumelia and Prosopis trees over 12 months. HR was extensive and continuous, involving every tree and 83% of roots, with the total daily volume of HR over a 1 month period estimated to be approximately 22% of daily transpiration. During drought, deep roots at 20 m depth redistributed water to shallow roots (hydraulic lift), while after rain, shallow roots at 0-0.5 m depth redistributed water among other shallow roots (lateral HR). The main driver of HR appeared to be patchy, dry soil near the surface, although water may also have been redistributed to mid-level depths via deeper lateral roots. Deep roots contributed up to five times more water to transpiration and HR than shallow roots during drought but dramatically reduced their contribution after rain. Our results suggest that deep-rooted plants are important drivers of water cycling in dry ecosystems and that HR can significantly influence landscape hydrology.

    View details for DOI 10.1111/j.1365-3040.2010.02212.x

    View details for Web of Science ID 000284166500011

    View details for PubMedID 20716068

  • Estimation of long-term basin scale evapotranspiration from streamflow time series WATER RESOURCES RESEARCH Palmroth, S., Katul, G. G., Hui, D., Mccarthy, H. R., Jackson, R. B., Oren, R. 2010; 46
  • Opportunities and Constraints for Forest Climate Mitigation BIOSCIENCE Jackson, R. B., Baker, J. S. 2010; 60 (9): 698-707
  • Interactions of the carbon cycle, human activity, and the climate system: a research portfolio CURRENT OPINION IN ENVIRONMENTAL SUSTAINABILITY Canadell, J. G., Ciais, P., Dhakal, S., Dolman, H., Friedlingstein, P., Gurney, K. R., Held, A., Jackson, R. B., Le Quere, C., Malone, E. L., Ojima, D. S., Patwardhan, A., Peters, G. P., Raupach, M. R. 2010; 2 (4): 301-311
  • Amino acid abundance and proteolytic potential in North American soils OECOLOGIA Hofmockel, K. S., Fierer, N., Colman, B. P., Jackson, R. B. 2010; 163 (4): 1069-1078

    Abstract

    Studies of nitrogen (N) cycling have traditionally focused on N mineralization as the primary process limiting plant assimilation of N. Recent evidence has shown that plants may assimilate amino acids (AAs) directly, circumventing the mineralization pathway. However, the general abundance of soil AAs and their relative importance in plant N uptake remains unclear in most ecosystems. We compared the concentrations and potential production rates of AAs and NH(4) (+), as well as the edaphic factors that influence AA dynamics, in 84 soils across the United States. Across all sites, NH(4) (+) and AA-N comprised similar proportions of the total bioavailable N pool (approximately 20%), with NO(3) (-) being the dominant form of extractable N everywhere but in tundra and boreal forest soils. Potential rates of AA production were at least comparable to those of NH(4) (+) production in all ecosystems, particularly in semi-arid grasslands, where AA production rates were six times greater than for NH(4) (+) (P < 0.01). Potential rates of proteolytic enzyme activity were greatest in bacteria-dominated soils with low NH(4) (+) concentrations, including many grassland soils. Based on research performed under standardized laboratory conditions, our continental-scale analyses suggest that soil AA and NH(4) (+) concentrations are similar in most soils and that AAs may contribute to plant and microbial N demand in most ecosystems, particularly in ecosystems with N-poor soils.

    View details for DOI 10.1007/s00442-010-1601-9

    View details for Web of Science ID 000280083300023

    View details for PubMedID 20349250

  • Pursuing Geoengineering for Atmospheric Restoration ISSUES IN SCIENCE AND TECHNOLOGY Jackson, R. B., Salzman, J. 2010; 26 (4): 67-76
  • Greater seed production in elevated CO2 is not accompanied by reduced seed quality in Pinus taeda L. GLOBAL CHANGE BIOLOGY Way, D. A., LaDeau, S. L., McCarthy, H. R., Clark, J. S., Oren, R., Finzi, A. C., Jackson, R. B. 2010; 16 (3): 1046-1056
  • Stoichiometric controls on carbon, nitrogen, and phosphorus dynamics in decomposing litter ECOLOGICAL MONOGRAPHS Manzoni, S., Trofymow, J. A., Jackson, R. B., Porporato, A. 2010; 80 (1): 89-106
  • Hydraulic lift and tolerance to salinity of semiarid species: consequences for species interactions OECOLOGIA Armas, C., Padilla, F. M., Pugnaire, F. I., Jackson, R. B. 2010; 162 (1): 11-21

    Abstract

    The different abilities of plant species to use ephemeral or permanent water sources strongly affect physiological performance and species coexistence in water-limited ecosystems. In addition to withstanding drought, plants in coastal habitats often have to withstand highly saline soils, an additional ecological stress. Here we tested whether observed competitive abilities and C-water relations of two interacting shrub species from an arid coastal system were more related to differences in root architecture or salinity tolerance. We explored water sources of interacting Juniperus phoenicea Guss. and Pistacia lentiscus L. plants by conducting physiology measurements, including water relations, CO2 exchange, photochemical efficiency, sap osmolality, and water and C isotopes. We also conducted parallel soil analyses that included electrical conductivity, humidity, and water isotopes. During drought, Pistacia shrubs relied primarily on permanent salty groundwater, while isolated Juniperus plants took up the scarce and relatively fresh water stored in upper soil layers. As drought progressed further, the physiological activity of Juniperus plants nearly stopped while Pistacia plants were only slightly affected. Juniperus plants growing with Pistacia had stem-water isotopes that matched Pistacia, unlike values for isolated Juniperus plants. This result suggests that Pistacia shrubs supplied water to nearby Juniperus plants through hydraulic lift. This lifted water, however, did not appear to benefit Juniperus plants, as their physiological performance with co-occurring Pistacia plants was poor, including lower water potentials and rates of photosynthesis than isolated plants. Juniperus was more salt sensitive than Pistacia, which withstood salinity levels similar to that of groundwater. Overall, the different abilities of the two species to use salty water appear to drive the outcome of their interaction, resulting in asymmetric competition where Juniperus is negatively affected by Pistacia. Salt also seems to mediate the interaction between the two species, negating the potential positive effects of an additional water source via hydraulic lift.

    View details for DOI 10.1007/s00442-009-1447-1

    View details for Web of Science ID 000271736100002

    View details for PubMedID 19730891

  • Re-assessment of plant carbon dynamics at the Duke free-air CO2 enrichment site: interactions of atmospheric [CO2] with nitrogen and water availability over stand development NEW PHYTOLOGIST Mccarthy, H. R., Oren, R., Johnsen, K. H., Gallet-Budynek, A., Pritchard, S. G., Cook, C. W., LaDeau, S. L., Jackson, R. B., Finzi, A. C. 2010; 185 (2): 514-528

    Abstract

    *The potential for elevated [CO(2)]-induced changes to plant carbon (C) storage, through modifications in plant production and allocation of C among plant pools, is an important source of uncertainty when predicting future forest function. Utilizing 10 yr of data from the Duke free-air CO(2) enrichment site, we evaluated the dynamics and distribution of plant C. *Discrepancy between heights measured for this study and previously calculated heights required revision of earlier allometrically based biomass determinations, resulting in higher (up to 50%) estimates of standing biomass and net primary productivity than previous assessments. *Generally, elevated [CO(2)] caused sustained increases in plant biomass production and in standing C, but did not affect the partitioning of C among plant biomass pools. Spatial variation in net primary productivity and its [CO(2)]-induced enhancement was controlled primarily by N availability, with the difference between precipitation and potential evapotranspiration explaining most interannual variability. Consequently, [CO(2)]-induced net primary productivity enhancement ranged from 22 to 30% in different plots and years. *Through quantifying the effects of nutrient and water availability on the forest productivity response to elevated [CO(2)], we show that net primary productivity enhancement by elevated [CO(2)] is not uniform, but rather highly dependent on the availability of other growth resources.

    View details for DOI 10.1111/j.1469-8137.2009.03078.x

    View details for Web of Science ID 000272893800016

    View details for PubMedID 19895671

  • Root responses along a subambient to elevated CO2 gradient in a C3–C4 grassland Global Change Biology Anderson, L. J., Derner, J. D., Polley, H. W., Gordon, W. S., Eissenstat, D. M., Jackson, R. B. 2010; 16: 454-468
  • Increased belowground biomass and soil CO2 fluxes after a decade of carbon dioxide enrichment in a warm-temperate forest ECOLOGY Jackson, R. B., Cook, C. W., Pippen, J. S., Palmer, S. M. 2009; 90 (12): 3352-3366

    Abstract

    Atmospheric CO2 concentrations have risen 40% since the start of the industrial revolution. Beginning in 1996, the Duke Free-Air CO2 Enrichment experiment has exposed plots in a loblolly pine forest to an additional 200 microL/L CO2 compared to trees growing in ambient CO2. This paper presents new belowground data and a synthesis of results through 2008, including root biomass and nutrient concentrations, soil respiration rates, soil pore-space CO2 concentrations, and soil-solution chemistry to 2 m depth. On average in elevated CO2, fine-root biomass in the top 15 cm of soil increased by 24%, or 59 g/m2 (26 g/m2 C). Coarse-root biomass sampled in 2008 was twice as great in elevated CO2 and suggests a storage of approximately 20 g C x m(-2) x yr(-1). Root C and N concentrations were unchanged, suggesting greater belowground plant demand for N in high CO2. Soil respiration was significantly higher by 23% on average as assessed by instantaneous infrared gas analysis and 24-h integrated estimates. N fertilization decreased soil respiration and fine-root biomass by approximately 10-20% in both ambient and elevated CO2. In recent years, increases in root biomass and soil respiration grew stronger, averaging approximately 30% at high CO2. Peak changes for root biomass, soil respiration, and other variables typically occurred in midsummer and diminished in winter. Soil CO2 concentrations between 15 and 100 cm depths increased 36-60% in elevated CO2. Differences from 30 cm depth and below were still increasing after 10 years' exposure to elevated CO2, with soil CO2 concentrations >10000 microL/L higher at 70- and 100-cm depths, potentially influencing soil acidity and rates of weathering. Soil solution Ca2+ and total base cation concentrations were 140% and 176% greater, respectively, in elevated CO2 at 200 cm depth. Similar increases were observed for soil-solution conductivity and alkalinity at 200 cm in elevated CO2. Overall, the effect of elevated CO2 belowground shows no sign of diminishing after more than a decade of CO2 enrichment.

    View details for Web of Science ID 000272700800008

    View details for PubMedID 20120805

  • CO2 emissions from forest loss (vol 2, pg 737, 2009) NATURE GEOSCIENCE van der Werf, G. R., MORTON, D. C., DeFries, R. S., Olivier, J. G., Kasibhatla, P. S., Jackson, R. B., Collatz, G. J., Randerson, J. T. 2009; 2 (12): 829-829

    View details for DOI 10.1038/ngeo720

    View details for Web of Science ID 000272239400013

  • A global meta-analysis of soil exchangeable cations, pH, carbon, and nitrogen with afforestation ECOLOGICAL APPLICATIONS Berthrong, S. T., Jobbagy, E. G., Jackson, R. B. 2009; 19 (8): 2228-2241

    Abstract

    Afforestation, the conversion of non-forested lands to forest plantations, can sequester atmospheric carbon dioxide, but the rapid growth and harvesting of biomass may deplete nutrients and degrade soils if managed improperly. The goal of this study is to evaluate how afforestation affects mineral soil quality, including pH, sodium, exchangeable cations, organic carbon, and nitrogen, and to examine the magnitude of these changes regionally where afforestation rates are high. We also examine potential mechanisms to reduce the impacts of afforestation on soils and to maintain long-term productivity. Across diverse plantation types (153 sites) to a depth of 30 cm of mineral soil, we observed significant decreases in nutrient cations (Ca, K, Mg), increases in sodium (Na), or both with afforestation. Across the data set, afforestation reduced soil concentrations of the macronutrient Ca by 29% on average (P < 0.05). Afforestation by Pinus alone decreased soil K by 23% (P < 0.05). Overall, plantations of all genera also led to a mean 71% increase of soil Na (P < 0.05). Mean pH decreased 0.3 units (P < 0.05) with afforestation. Afforestation caused a 6.7% and 15% (P < 0.05) decrease in soil C and N content respectively, though the effect was driven principally by Pinus plantations (15% and 20% decrease, P < 0.05). Carbon to nitrogen ratios in soils under plantations were 5.7-11.6% higher (P < 0.05). In several regions with high rates of afforestation, cumulative losses of N, Ca, and Mg are likely in the range of tens of millions of metric tons. The decreases indicate that trees take up considerable amounts of nutrients from soils; harvesting this biomass repeatedly could impair long-term soil fertility and productivity in some locations. Based on this study and a review of other literature, we suggest that proper site preparation and sustainable harvest practices, such as avoiding the removal or burning of harvest residue, could minimize the impact of afforestation on soils. These sustainable practices would in turn slow soil compaction, erosion, and organic matter loss, maintaining soil fertility to the greatest extent possible.

    View details for Web of Science ID 000271874300020

    View details for PubMedID 20014590

  • Future land use and land cover influences on regional biogenic emissions and air quality in the United States ATMOSPHERIC ENVIRONMENT Chen, J., Avise, J., Guenther, A., Wiedinmyer, C., Salathe, E., Jackson, R. B., Lamb, B. 2009; 43 (36): 5771-5780
  • CO2 emissions from forest loss NATURE GEOSCIENCE van der Werf, G. R., MORTON, D. C., DeFries, R. S., Olivier, J. G., Kasibhatla, P. S., Jackson, R. B., Collatz, G. J., Randerson, J. T. 2009; 2 (11): 737-738

    View details for DOI 10.1038/ngeo671

    View details for Web of Science ID 000271388500004

  • Afforestation Alters the Composition of Functional Genes in Soil and Biogeochemical Processes in South American Grasslands APPLIED AND ENVIRONMENTAL MICROBIOLOGY Berthrong, S. T., Schadt, C. W., Pineiro, G., Jackson, R. B. 2009; 75 (19): 6240-6248

    Abstract

    Soil microbes are highly diverse and control most soil biogeochemical reactions. We examined how microbial functional genes and biogeochemical pools responded to the altered chemical inputs accompanying land use change. We examined paired native grasslands and adjacent Eucalyptus plantations (previously grassland) in Uruguay, a region that lacked forests before European settlement. Along with measurements of soil carbon, nitrogen, and bacterial diversity, we analyzed functional genes using the GeoChip 2.0 microarray, which simultaneously quantified several thousand genes involved in soil carbon and nitrogen cycling. Plantations and grassland differed significantly in functional gene profiles, bacterial diversity, and biogeochemical pool sizes. Most grassland profiles were similar, but plantation profiles generally differed from those of grasslands due to differences in functional gene abundance across diverse taxa. Eucalypts decreased ammonification and N fixation functional genes by 11% and 7.9% (P < 0.01), which correlated with decreased microbial biomass N and more NH(4)(+) in plantation soils. Chitinase abundance decreased 7.8% in plantations compared to levels in grassland (P = 0.017), and C polymer-degrading genes decreased by 1.5% overall (P < 0.05), which likely contributed to 54% (P < 0.05) more C in undecomposed extractable soil pools and 27% less microbial C (P < 0.01) in plantation soils. In general, afforestation altered the abundance of many microbial functional genes, corresponding with changes in soil biogeochemistry, in part through altered abundance of overall functional gene types rather than simply through changes in specific taxa. Such changes in microbial functional genes correspond with altered C and N storage and have implications for long-term productivity in these soils.

    View details for DOI 10.1128/AEM.01126-09

    View details for Web of Science ID 000270113200024

    View details for PubMedID 19700539

  • Ecohydrology in a human-dominated landscape ECOHYDROLOGY Jackson, R. B., Jobbagy, E. G., Nosetto, M. D. 2009; 2 (3): 383-389

    View details for DOI 10.1002/eco.81

    View details for Web of Science ID 000271491500018

  • Reciprocal influence of crops and shallow ground water in sandy landscapes of the Inland Pampas FIELD CROPS RESEARCH Nosetto, M. D., Jobbagy, E. G., Jackson, R. B., Sznaider, G. A. 2009; 113 (2): 138-148
  • Primary Productivity and Water Balance of Grassland Vegetation on Three Soils in a Continuous CO2 Gradient: Initial Results from the Lysimeter CO2 Gradient Experiment ECOSYSTEMS Fay, P. A., Kelley, A. M., Procter, A. C., Hui, D., Jin, V. L., Jackson, R. B., Johnson, H. B., Polley, H. W. 2009; 12 (5): 699-714
  • Sheep Grazing Decreases Organic Carbon and Nitrogen Pools in the Patagonian Steppe: Combination of Direct and Indirect Effects ECOSYSTEMS Golluscio, R. A., Austin, A. T., Garcia Martinez, G. C., Gonzalez-Polo, M., Sala, O. E., Jackson, R. B. 2009; 12 (4): 686-697
  • Risks to forest carbon offset projects in a changing climate FOREST ECOLOGY AND MANAGEMENT Galik, C. S., Jackson, R. B. 2009; 257 (11): 2209-2216
  • Leaf isoprene emission rate as a function of atmospheric CO2 concentration GLOBAL CHANGE BIOLOGY Wilkinson, M. J., Monson, R. K., Trahan, N., Lee, S., Brown, E., Jackson, R. B., Polley, H. W., Fay, P. A., Fall, R. 2009; 15 (5): 1189-1200
  • Grazing effects on belowground C and N stocks along a network of cattle exclosures in temperate and subtropical grasslands of South America GLOBAL BIOGEOCHEMICAL CYCLES Pineiro, G., Paruelo, J. M., Jobbagy, E. G., Jackson, R. B., Oesterheld, M. 2009; 23
  • Physical and Economic Potential of Geological CO2 Storage in Saline Aquifers ENVIRONMENTAL SCIENCE & TECHNOLOGY Eccles, J. K., Pratson, L., Newell, R. G., Jackson, R. B. 2009; 43 (6): 1962-1969

    Abstract

    Carbon sequestration in sandstone saline reservoirs holds great potential for mitigating climate change, but its storage potential and cost per ton of avoided CO2 emissions are uncertain. We develop a general model to determine the maximum theoretical constraints on both storage potential and injection rate and use it to characterize the economic viability of geosequestration in sandstone saline aquifers. When applied to a representative set of aquifer characteristics, the model yields results that compare favorably with pilot projects currently underway. Over a range of reservoir properties, maximum effective storage peaks at an optimal depth of 1600 m, at which point 0.18-0.31 metric tons can be stored per cubic meter of bulk volume of reservoir. Maximum modeled injection rates predict minima for storage costs in a typical basin in the range of $2-7/ ton CO2 (2005 U.S.$) depending on depth and basin characteristics in our base-case scenario. Because the properties of natural reservoirs in the United States vary substantially, storage costs could in some cases be lower or higher by orders of magnitude. We conclude that available geosequestration capacity exhibits a wide range of technological and economic attractiveness. Like traditional projects in the extractive industries, geosequestration capacity should be exploited starting with the low-cost storage options first then moving gradually up the supply curve.

    View details for DOI 10.1021/es801572e

    View details for Web of Science ID 000264108800050

    View details for PubMedID 19368199

  • Set-asides can be better climate investment than corn ethanol ECOLOGICAL APPLICATIONS Pineiro, G., Jobbagy, E. G., Baker, J., Murray, B. C., Jackson, R. B. 2009; 19 (2): 277-282

    Abstract

    Although various studies have shown that corn ethanol reduces greenhouse gas (GHG) emissions by displacing fossil fuel use, many of these studies fail to include how land-use history affects the net carbon balance through changes in soil carbon content. We evaluated the effectiveness and economic value of corn and cellulosic ethanol production for reducing net GHG emissions when produced on lands with different land-use histories, comparing these strategies with reductions achieved by set-aside programs such as the Conservation Reserve Program (CRP). Depending on prior land use, our analysis shows that C releases from the soil after planting corn for ethanol may in some cases completely offset C gains attributed to biofuel generation for at least 50 years. More surprisingly, based on our comprehensive analysis of 142 soil studies, soil C sequestered by setting aside former agricultural land was greater than the C credits generated by planting corn for ethanol on the same land for 40 years and had equal or greater economic net present value. Once commercially available, cellulosic ethanol produced in set-aside grasslands should provide the most efficient tool for GHG reduction of any scenario we examined. Our results suggest that conversion of CRP lands or other set-aside programs to corn ethanol production should not be encouraged through greenhouse gas policies.

    View details for Web of Science ID 000263719400001

    View details for PubMedID 19323189

  • Assessing interactive responses in litter decomposition in mixed species litter PLANT AND SOIL Hui, D., Jackson, R. B. 2009; 314 (1-2): 263-271
  • Soil carbon sequestration in a pine forest after 9 years of atmospheric CO2 enrichment GLOBAL CHANGE BIOLOGY Lichter, J., Billings, S. A., Ziegler, S. E., Gaindh, D., Ryals, R., Finzi, A. C., Jackson, R. B., Stemmler, E. A., Schlesinger, W. H. 2008; 14 (12): 2910-2922
  • Protecting climate with forests ENVIRONMENTAL RESEARCH LETTERS Jackson, R. B., Randerson, J. T., Canadell, J. G., Anderson, R. G., Avissar, R., Baldocchi, D. D., Bonan, G. B., Caldeira, K., Diffenbaugh, N. S., Field, C. B., Hungate, B. A., Jobbagy, E. G., Kueppers, L. M., Nosetto, M. D., Pataki, D. E. 2008; 3 (4)
  • Stream acidification and base cation losses with grassland afforestation WATER RESOURCES RESEARCH Farley, K. A., Pineiro, G., Palmer, S. M., Jobbagy, E. G., Jackson, R. B. 2008; 44
  • The global stoichiometry of litter nitrogen mineralization SCIENCE Manzoni, S., Jackson, R. B., Trofymow, J. A., Porporato, A. 2008; 321 (5889): 684-686

    Abstract

    Plant residue decomposition and the nutrient release to the soil play a major role in global carbon and nutrient cycling. Although decomposition rates vary strongly with climate, nitrogen immobilization into litter and its release in mineral forms are mainly controlled by the initial chemical composition of the residues. We used a data set of approximately 2800 observations to show that these global nitrogen-release patterns can be explained by fundamental stoichiometric relationships of decomposer activity. We show how litter quality controls the transition from nitrogen accumulation into the litter to release and alters decomposers' respiration patterns. Our results suggest that decomposers lower their carbon-use efficiency to exploit residues with low initial nitrogen concentration, a strategy used broadly by bacteria and consumers across trophic levels.

    View details for DOI 10.1126/science.1159792

    View details for Web of Science ID 000258077700042

    View details for PubMedID 18669860

  • Regional patterns and controls of ecosystem salinization with grassland afforestation along a rainfall gradient GLOBAL BIOGEOCHEMICAL CYCLES Nosetto, M. D., Jobbagy, E. G., Toth, T., Jackson, R. B. 2008; 22 (2)
  • Nonlinear root-derived carbon sequestration across a gradient of nitrogen and phosphorous deposition in experimental mesocosms GLOBAL CHANGE BIOLOGY Bradford, M. A., Fierer, N., Jackson, R. B., Maddox, T. R., Reynolds, J. F. 2008; 14 (5): 1113-1124
  • Measuring uncertainty in estimates of biodiversity loss: The example of biodiversity intactness variance BIOLOGICAL CONSERVATION Hui, D., Biggs, R., Scholes, R. J., Jackson, R. B. 2008; 141 (4): 1091-1094
  • Fine-root respiration in a loblolly pine (Pinus taeda L.) forest exposed to elevated CO2 and N fertilization Plant Cell and Environment Drake, J. E., Stoy, P. C., Jackson, R. B., DeLucia, E. H. 2008; 31: 1663-1672
  • Fine root dynamics in a loblolly pine forest are influenced by free-air-CO2-enrichment: a six-year-minirhizotron study Global Change Biology Pritchard, S. G., Strand, A. E., McCormack, M. L., Davis, M. A., Finzi, A. C., Jackson, R. B., Matamala, R., Rogers, H. H., Oren, R. 2008; 14: 588-602
  • Hydraulic traits are influenced by phylogenetic history in the drought-resistant, invasive genus Juniperus (Cupressaceae) American Journal of Botany Willson, C. J., Manos, P. S., Jackson, R. B. 2008; 95: 299-314
  • Uncertainty in allometric exponent estimation: A case study in scaling metabolic rate with body mass JOURNAL OF THEORETICAL BIOLOGY Hui, D., Jackson, R. B. 2007; 249 (1): 168-177

    Abstract

    Many factors could influence the allometric scaling exponent beta estimation, but have not been explored systematically. We investigated the influences of three factors on the estimate of beta based on a data set of 626 species of basal metabolic rate and mass in mammals. The influence of sampling error was tested by re-sampling with different sample sizes using a Monte Carlo method. Small random errors were introduced to measured data to examine their influence on parameter estimations. The influence of analysis method was also evaluated by applying nonlinear and linear regressions to the original data. Results showed that a relative large sample size was required to lower statistical inference errors. When sample size n was 10% of the base population size (n=63), 35% of the samples supported beta=2/3, 39% supported beta=3/4, and 15% rejected beta=0.711, even though the base population had a beta=0.711. The controversy surrounding the estimation of beta in the literature could be partially attributable to such small sample sizes in many studies. Measurement errors in body mass and base metabolic rate, especially in body mass, could largely increase alpha and beta errors. Analysis methods also affected parameter estimations. Nonlinear regressions provided better estimates of the scaling exponent that were significantly higher than these commonly estimated by linear regressions. This study demonstrated the importance of the quantity and quality of data as well as analysis method in power law analysis, raising caution in interpreting power law results. Meta-data synthesis using data from independent studies seems to be a proper approach in the future, but caution should be taken to make sure that such measurements are made using similar protocols.

    View details for DOI 10.1016/j.jtbi.2007.07.003

    View details for Web of Science ID 000250847700015

    View details for PubMedID 17720203

  • Metagenomic and small-subunit rRNA analyses reveal the genetic diversity of bacteria, archaea, fungi, and viruses in soil APPLIED AND ENVIRONMENTAL MICROBIOLOGY Fierer, N., Breitbart, M., Nulton, J., Salamon, P., Lozupone, C., Jones, R., Robeson, M., Edwards, R. A., Felts, B., Rayhawk, S., Knight, R., Rohwer, F., Jackson, R. B. 2007; 73 (21): 7059-7066

    Abstract

    Recent studies have highlighted the surprising richness of soil bacterial communities; however, bacteria are not the only microorganisms found in soil. To our knowledge, no study has compared the diversities of the four major microbial taxa, i.e., bacteria, archaea, fungi, and viruses, from an individual soil sample. We used metagenomic and small-subunit RNA-based sequence analysis techniques to compare the estimated richness and evenness of these groups in prairie, desert, and rainforest soils. By grouping sequences at the 97% sequence similarity level (an operational taxonomic unit [OTU]), we found that the archaeal and fungal communities were consistently less even than the bacterial communities. Although total richness levels are difficult to estimate with a high degree of certainty, the estimated number of unique archaeal or fungal OTUs appears to rival or exceed the number of unique bacterial OTUs in each of the collected soils. In this first study to comprehensively survey viral communities using a metagenomic approach, we found that soil viruses are taxonomically diverse and distinct from the communities of viruses found in other environments that have been surveyed using a similar approach. Within each of the four microbial groups, we observed minimal taxonomic overlap between sites, suggesting that soil archaea, bacteria, fungi, and viruses are globally as well as locally diverse.

    View details for DOI 10.1128/AEM.00358-07

    View details for Web of Science ID 000250700600042

    View details for PubMedID 17827313

  • Aquaporin-mediated changes in hydraulic conductivity of deep tree roots accessed via caves PLANT CELL AND ENVIRONMENT McElrone, A. J., Bichler, J., Pockman, W. T., Addington, R. N., Linder, C. R., Jackson, R. B. 2007; 30 (11): 1411-1421

    Abstract

    Although deep roots can contribute substantially to whole-tree water use, little is known about deep root functioning because of limited access for in situ measurements. We used a cave system on the Edwards Plateau of central Texas to investigate the physiology of water transport in roots at 18-20 m depth for two common tree species, Quercus fusiformis and Bumelia lanuginosa. Using sap flow and water potential measurements on deep roots, we found that calculated root hydraulic conductivity (RHC) fluctuated diurnally for both species and decreased under shading for B. lanuginosa. To assess whether these dynamic changes in RHC were regulated during initial water absorption by fine roots, we used an ultra-low flowmeter and hydroxyl radical inhibition to measure in situ fine root hydraulic conductivity (FRHC) and aquaporin contribution to FRHC (AQPC), respectively. During the summer, FRHC and AQPC were found to cycle diurnally in both species, with peaks corresponding to the period of highest transpirational demand at midday. During whole-tree shade treatments, B. lanuginosa FRHC ceased diurnal cycling and decreased by 75 and 35% at midday and midnight, respectively, while AQPC decreased by 41 and 30% during both time periods. A controlled growth-chamber study using hydroponically grown saplings confirmed daily cycling and shade-induced reductions in FRHC and AQPC. Winter measurements showed that the evergreen Q. fusiformis maintained high FRHC and AQPC throughout the year, while the deciduous B. lanuginosa ceased diurnal cycling and exhibited its lowest annual values for both parameters in winter. Adjustments in FRHC and AQPC to changing canopy water demands may help the trees maintain the use of reliable water resources from depth and contribute to the success of these species in this semi-arid environment.

    View details for DOI 10.1111/j.1365-3040.2007.01714.x

    View details for Web of Science ID 000249826400006

    View details for PubMedID 17897411

  • Environmental controls on the landscape-scale biogeography of stream bacterial communities ECOLOGY Fierer, N., Morse, J. L., Berthrong, S. T., Bernhardt, E. S., Jackson, R. B. 2007; 88 (9): 2162-2173

    Abstract

    We determined the biogeographical distributions of stream bacteria and the biogeochemical factors that best explained heterogeneity for 23 locations within the Hubbard Brook watershed, a 3000-ha forested watershed in New Hampshire, USA. Our goal was to assess the factor, or set of factors, responsible for generating the biogeographical patterns exhibited by microorganisms at the landscape scale. We used DNA fingerprinting to characterize bacteria inhabiting fine benthic organic matter (FBOM) because of their important influence on stream nutrient dynamics. Across the watershed, streams of similar pH had similar FBOM bacterial communities. Streamwater pH was the single variable most strongly correlated with the relative distance between communities (Spearman's p = 0.66, P < 0.001) although there were other contributing factors, including the quality of the fine benthic organic matter and the amount of dissolved organic carbon and nitrogen in the stream water (P < 0.05 for each). There was no evidence of an effect of geographic distance on bacterial community composition, suggesting that dispersal limitation has little influence on the observed biogeographical patterns in streams across this landscape. Cloning and sequencing of small-subunit rRNA genes confirmed the DNA fingerprinting results and revealed strong shifts among bacterial groups along the pH gradient. With an increase in streamwater pH, the abundance of acidobacteria in the FBOM bacterial community decreased (from 71% to 38%), and the abundance of proteobacteria increased (from 11% to 47%). Together these results suggest that microorganisms, like "macro"-organisms, do exhibit biogeographical patterns at the landscape scale and that these patterns may be predictable based on biogeochemical factors.

    View details for Web of Science ID 000249500900003

    View details for PubMedID 17918395

  • Effects of elevated atmospheric carbon dioxide on amino acid and NH4+-N cycling in a temperate pine ecosystem GLOBAL CHANGE BIOLOGY Hofmockel, K. S., Schlesinger, W. H., Jackson, R. B. 2007; 13 (9): 1950-1959
  • Increases in nitrogen uptake rather than nitrogen-use efficiency support higher rates of temperate forest productivity under elevated CO2 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Finzi, A. C., Norby, R. J., Calfapietra, C., Gallet-Budynek, A., Gielen, B., Holmes, W. E., Hoosbeek, M. R., Iversen, C. M., Jackson, R. B., Kubiske, M. E., Ledford, J., Liberloo, M., Oren, R., Polle, A., Pritchard, S., Zak, D. R., Schlesinger, W. H., Ceulemans, R. 2007; 104 (35): 14014-14019

    Abstract

    Forest ecosystems are important sinks for rising concentrations of atmospheric CO(2). In previous research, we showed that net primary production (NPP) increased by 23 +/- 2% when four experimental forests were grown under atmospheric concentrations of CO(2) predicted for the latter half of this century. Because nitrogen (N) availability commonly limits forest productivity, some combination of increased N uptake from the soil and more efficient use of the N already assimilated by trees is necessary to sustain the high rates of forest NPP under free-air CO(2) enrichment (FACE). In this study, experimental evidence demonstrates that the uptake of N increased under elevated CO(2) at the Rhinelander, Duke, and Oak Ridge National Laboratory FACE sites, yet fertilization studies at the Duke and Oak Ridge National Laboratory FACE sites showed that tree growth and forest NPP were strongly limited by N availability. By contrast, nitrogen-use efficiency increased under elevated CO(2) at the POP-EUROFACE site, where fertilization studies showed that N was not limiting to tree growth. Some combination of increasing fine root production, increased rates of soil organic matter decomposition, and increased allocation of carbon (C) to mycorrhizal fungi is likely to account for greater N uptake under elevated CO(2). Regardless of the specific mechanism, this analysis shows that the larger quantities of C entering the below-ground system under elevated CO(2) result in greater N uptake, even in N-limited ecosystems. Biogeochemical models must be reformulated to allow C transfers below ground that result in additional N uptake under elevated CO(2).

    View details for DOI 10.1073/pnas.0706518104

    View details for Web of Science ID 000249187500030

    View details for PubMedID 17709743

  • Toward an ecological classification of soil bacteria ECOLOGY Fierer, N., Bradford, M. A., Jackson, R. B. 2007; 88 (6): 1354-1364

    Abstract

    Although researchers have begun cataloging the incredible diversity of bacteria found in soil, we are largely unable to interpret this information in an ecological context, including which groups of bacteria are most abundant in different soils and why. With this study, we examined how the abundances of major soil bacterial phyla correspond to the biotic and abiotic characteristics of the soil environment to determine if they can be divided into ecologically meaningful categories. To do this, we collected 71 unique soil samples from a wide range of ecosystems across North America and looked for relationships between soil properties and the relative abundances of six dominant bacterial phyla (Acidobacteria, Bacteroidetes, Firmicutes, Actinobacteria, alpha-Proteobacteria, and the beta-Proteobacteria). Of the soil properties measured, net carbon (C) mineralization rate (an index of C availability) was the best predictor of phylum-level abundances. There was a negative correlation between Acidobacteria abundance and C mineralization rates (r2 = 0.26, P < 0.001), while the abundances of beta-Proteobacteria and Bacteroidetes were positively correlated with C mineralization rates (r2 = 0.35, P < 0.001 and r2 = 0.34, P < 0.001, respectively). These patterns were explored further using both experimental and meta-analytical approaches. We amended soil cores from a specific site with varying levels of sucrose over a 12-month period to maintain a gradient of elevated C availabilities. This experiment confirmed our survey results: there was a negative relationship between C amendment level and the abundance of Acidobacteria (r2 = 0.42, P < 0.01) and a positive relationship for both Bacteroidetes and beta-Proteobacteria (r2 = 0.38 and 0.70, respectively; P < 0.01 for each). Further support for a relationship between the relative abundances of these bacterial phyla and C availability was garnered from an analysis of published bacterial clone libraries from bulk and rhizosphere soils. Together our survey, experimental, and meta-analytical results suggest that certain bacterial phyla can be differentiated into copiotrophic and oligotrophic categories that correspond to the r- and K-selected categories used to describe the ecological attributes of plants and animals. By applying the copiotroph-oligotroph concept to soil microorganisms we can make specific predictions about the ecological attributes of various bacterial taxa and better understand the structure and function of soil bacterial communities.

    View details for Web of Science ID 000247203100003

    View details for PubMedID 17601128

  • New directions in microbial ecology ECOLOGY Jackson, R. B., Fierer, N., Schimel, J. P. 2007; 88 (6): 1343-1344
  • Groundwater and soil chemical changes under phreatophytic tree plantations JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES Jobbagy, E. G., Jackson, R. B. 2007; 112 (G2)
  • Coupling diurnal cytosolic Ca2+ oscillations to the CAS-IP3 pathway in Arabidopsis SCIENCE Tang, R., Han, S., Zheng, H., Cook, C. W., Choi, C. S., Woerner, T. E., Jackson, R. B., Pei, Z. 2007; 315 (5817): 1423-1426

    Abstract

    Various signaling pathways rely on changes in cytosolic calcium ion concentration ([Ca2+]i). In plants, resting [Ca2+]i oscillates diurnally. We show that in Arabidopsis thaliana, [Ca2+]i oscillations are synchronized to extracellular Ca2+ concentration ([Ca2+]o) oscillations largely through the Ca2+-sensing receptor CAS. CAS regulates concentrations of inositol 1,4,5-trisphosphate (IP3), which in turn directs release of Ca2+ from internal stores. The oscillating amplitudes of [Ca2+]o and [Ca2+]i are controlled by soil Ca2+ concentrations and transpiration rates. The phase and period of oscillations are likely determined by stomatal conductance. Thus, the internal concentration of Ca2+ in plant cells is constantly being actively revised.

    View details for DOI 10.1126/science.1134457

    View details for Web of Science ID 000244752200037

    View details for PubMedID 17347443

  • Effects of elevated atmospheric CO2 on amino acid and NH4+-N cycling in a temperate pine ecosystem Global Change Biology Hofmockel, K. S., Schlesinger, W. H., Jackson, R. B. 2007; 13: 13:1950-1959
  • Inhibition of nitrification alters carbon turnover in the Patagonian steppe ECOSYSTEMS Austin, A. T., Sala, O. E., Jackson, R. B. 2006; 9 (8): 1257-1265
  • Predicting the temperature dependence of microbial respiration in soil: A continental-scale analysis GLOBAL BIOGEOCHEMICAL CYCLES Fierer, N., Colman, B. P., Schimel, J. P., Jackson, R. B. 2006; 20 (3)
  • Determinants of biodiversity change: Ecological tools for building scenarios ECOLOGY Sala, O. E., Jackson, R. B. 2006; 87 (8): 1875-1876
  • Xylem cavitation caused by drought and freezing stress in four co-occurring Juniperus species PHYSIOLOGIA PLANTARUM Willson, C. J., Jackson, R. B. 2006; 127 (3): 374-382
  • Functional coordination between leaf gas exchange and vulnerability to xylem cavitation in temperate forest trees PLANT CELL AND ENVIRONMENT Maherali, H., Moura, C. F., Caldeira, M. C., Willson, C. J., Jackson, R. B. 2006; 29 (4): 571-583

    Abstract

    We examined functional coordination among stem and root vulnerability to xylem cavitation, plant water transport characteristics and leaf traits in 14 co-occurring temperate tree species. Relationships were evaluated using both traditional cross-species correlations and phylogenetically independent contrast (PIC) correlations. For stems, the xylem tension at which 50% of hydraulic conductivity was lost (psi50) was positively associated (P < 0.001) with specific conductivity (K(S)) and with mean hydraulically weighted xylem conduit diameter (D(h-w)), but was only marginally (P = 0.06) associated with leaf specific conductivity (K(L)). The PIC correlation for each of these relationships, however, was not statistically significant. There was also no relationship between root psi50 and root K(S) in either cross-species or PIC analysis. Photosynthetic rate (A) and stomatal conductance (g(s)) were strongly and positively correlated with root psi50 in the cross-species analysis (P < 0.001), a relationship that was robust to phylogenetic correction (P < 0.01). A and g(s) were also positively correlated with stem psi50 in the cross-species analysis (P = 0.02 and 0.10, respectively). However, only A was associated with stem psi50 in the PIC analysis (P = 0.04). Although the relationship between vulnerability to cavitation and xylem conductivity traits within specific organs (i.e. stems and roots) was weak, the strong correlation between g(s) and root psi50 across species suggests that there is a trade-off between vulnerability to cavitation and water transport capacity at the whole-plant level. Our results were therefore consistent with the expectation of coordination between vulnerability to xylem cavitation and the regulation of stomatal conductance, and highlight the potential physiological and evolutionary significance of root hydraulic properties in controlling interspecific variation in leaf function.

    View details for DOI 10.1111/j.1365-3040.2005.01433.x

    View details for Web of Science ID 000236385900010

    View details for PubMedID 17080608

  • The diversity and biogeography of soil bacterial communities PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Fierer, N., Jackson, R. B. 2006; 103 (3): 626-631

    Abstract

    For centuries, biologists have studied patterns of plant and animal diversity at continental scales. Until recently, similar studies were impossible for microorganisms, arguably the most diverse and abundant group of organisms on Earth. Here, we present a continental-scale description of soil bacterial communities and the environmental factors influencing their biodiversity. We collected 98 soil samples from across North and South America and used a ribosomal DNA-fingerprinting method to compare bacterial community composition and diversity quantitatively across sites. Bacterial diversity was unrelated to site temperature, latitude, and other variables that typically predict plant and animal diversity, and community composition was largely independent of geographic distance. The diversity and richness of soil bacterial communities differed by ecosystem type, and these differences could largely be explained by soil pH (r(2) = 0.70 and r(2) = 0.58, respectively; P < 0.0001 in both cases). Bacterial diversity was highest in neutral soils and lower in acidic soils, with soils from the Peruvian Amazon the most acidic and least diverse in our study. Our results suggest that microbial biogeography is controlled primarily by edaphic variables and differs fundamentally from the biogeography of "macro" organisms.

    View details for DOI 10.1073/pnas.0507535103

    View details for Web of Science ID 000234727800024

    View details for PubMedID 16407148

  • Potential nitrogen constraints on soil carbon sequestration under low and elevated atmospheric CO2 ECOLOGY Gill, R. A., Anderson, L. J., Polley, H. W., Johnson, H. B., Jackson, R. B. 2006; 87 (1): 41-52

    Abstract

    The interaction between nitrogen cycling and carbon sequestration is critical in predicting the consequences of anthropogenic increases in atmospheric CO2 (hereafter, Ca). The progressive N limitation (PNL) theory predicts that carbon sequestration in plants and soils with rising Ca may be constrained by the availability of nitrogen in many ecosystems. Here we report on the interaction between C and N dynamics during a four-year field experiment in which an intact C3/C4 grassland was exposed to a gradient in Ca from 200 to 560 micromol/mol. There were strong species effects on decomposition dynamics, with C loss positively correlated and N mineralization negatively correlated with Ca for litter of the C3 forb Solanum dimidiatum, whereas decomposition of litter from the C4 grass Bothriochloa ischaemum was unresponsive to Ca. Both soil microbial biomass and soil respiration rates exhibited a nonlinear response to Ca, reaching a maximum at approximately 440 micromol/mol Ca. We found a general movement of N out of soil organic matter and into aboveground plant biomass with increased Ca. Within soils we found evidence of C loss from recalcitrant soil C fractions with narrow C:N ratios to more labile soil fractions with broader C:N ratios, potentially due to decreases in N availability. The observed reallocation of N from soil to plants over the last three years of the experiment supports the PNL theory that reductions in N availability with rising Ca could initially be overcome by a transfer of N from low C:N ratio fractions to those with higher C:N ratios. Although the transfer of N allowed plant production to increase with increasing Ca, there was no net soil C sequestration at elevated Ca, presumably because relatively stable C is being decomposed to meet microbial and plant N requirements. Ultimately, if the C gained by increased plant production is rapidly lost through decomposition, the shift in N from older soil organic matter to rapidly decomposing plant tissue may limit net C sequestration with increased plant production.

    View details for Web of Science ID 000236020000006

    View details for PubMedID 16634295

  • Geographical and interannual variability in biomass partitioning in grassland ecosystems: a synthesis of field data NEW PHYTOLOGIST Hui, D. F., Jackson, R. B. 2006; 169 (1): 85-93

    Abstract

    Biomass partitioning is an important variable in terrestrial ecosystem carbon modeling. However, geographical and interannual variability in f(BNPP), defined as the fraction of belowground net primary productivity (BNPP) to total NPP, and its relationship with climatic variables, have not been explored. Here we addressed these issues by synthesizing 94 site-year field biomass data at 12 grassland sites around the world from a global NPP database and from the literature. Results showed that f(BNPP) varied from 0.40 to 0.86 across 12 sites. In general, savanna and humid savanna ecosystems had smaller f(BNPP) but larger interannual variability in f(BNPP), and cold desert steppes had larger f(BNPP) but smaller interannual variability. While mean f(BNPP) at a site decreased significantly with increasing mean annual temperature and precipitation across sites, no consistent temporal response of f(BNPP) with annual temperature and precipitation was found within sites. Based on these results, both geographical variability in f(BNPP) and the divergent responses of f(BNPP) with climatic variables at geographical and temporal scales should be considered in global C modeling.

    View details for DOI 10.1111/j.1469-8137.2005.01569.x

    View details for Web of Science ID 000233530400010

    View details for PubMedID 16390421

  • Does nitrogen constrain carbon cycling, or does carbon input stimulate nitrogen cycling? ECOLOGY Luo, Y. Q., Field, C. B., Jackson, R. B. 2006; 87 (1): 3-4
  • Ecosystem changes associated with grazing in subhumid South American grasslands Journal of Vegetation Science Altesor, A., Piñeiro, G., Lezama, F., Jackson, R. B., Sarasola, M., Paruelo, J. M. 2006; 17: 323-332
  • Grassland afforestation: towards an integrative perspective of its ecological opportunities and costs Agrociencia Jobbágy, E. G., Vasallo, M., Farley, K. A., Piñeiro, G., Garbulsky, M. F., Nosetto, M. M., Jackson, R. B., Paruelo, J. M. 2006; 10: 109-124
  • Progressive nitrogen limitation of ecosystem processes under elevated CO2 in a warm-temperate forest ECOLOGY Finzi, A. C., Moore, D. J., DeLucia, E. H., Lichter, J., Hofmockel, K. S., Jackson, R. B., Kim, H. S., Matamala, R., McCarthy, H. R., Oren, R., Pippen, J. S., Schlesinger, W. H. 2006; 87 (1): 15-25

    Abstract

    A hypothesis for progressive nitrogen limitation (PNL) proposes that net primary production (NPP) will decline through time in ecosystems subjected to a step-function increase in atmospheric CO2. The primary mechanism driving this response is a rapid rate of N immobilization by plants and microbes under elevated CO2 that depletes soils of N, causing slower rates of N mineralization. Under this hypothesis, there is little long-term stimulation of NPP by elevated CO2 in the absence of exogenous inputs of N. We tested this hypothesis using data on the pools and fluxes of C and N in tree biomass, microbes, and soils from 1997 through 2002 collected at the Duke Forest free-air CO2 enrichment (FACE) experiment. Elevated CO2 stimulated NPP by 18-24% during the first six years of this experiment. Consistent with the hypothesis for PNL, significantly more N was immobilized in tree biomass and in the O horizon under elevated CO2. In contrast to the PNL hypothesis, microbial-N immobilization did not increase under elevated CO2, and although the rate of net N mineralization declined through time, the decline was not significantly more rapid under elevated CO2. Ecosystem C-to-N ratios widened more rapidly under elevated CO2 than ambient CO2 indicating a more rapid rate of C fixation per unit of N, a processes that could delay PNL in this ecosystem. Mass balance calculations demonstrated a large accrual of ecosystem N capital. Is PNL occurring in this ecosystem and will NPP decline to levels under ambient CO2? The answer depends on the relative strength of tree biomass and O-horizon N immobilization vs. widening C-to-N ratios and ecosystem-N accrual as processes that drive and delay PNL, respectively. Only direct observations through time will definitively answer this question.

    View details for Web of Science ID 000236020000004

    View details for PubMedID 16634293

  • Trading water for carbon with biological sequestration SCIENCE Jackson, R. B., Jobbagy, E. G., Avissar, R., Roy, S. B., Barrett, D. J., Cook, C. W., Farley, K. A., Le Maitre, D. C., McCarl, B. A., Murray, B. C. 2005; 310 (5756): 1944-1947

    Abstract

    Carbon sequestration strategies highlight tree plantations without considering their full environmental consequences. We combined field research, synthesis of more than 600 observations, and climate and economic modeling to document substantial losses in stream flow, and increased soil salinization and acidification, with afforestation. Plantations decreased stream flow by 227 millimeters per year globally (52%), with 13% of streams drying completely for at least 1 year. Regional modeling of U.S. plantation scenarios suggests that climate feedbacks are unlikely to offset such water losses and could exacerbate them. Plantations can help control groundwater recharge and upwelling but reduce stream flow and salinize and acidify some soils.

    View details for DOI 10.1126/science.1119282

    View details for Web of Science ID 000234275400039

    View details for PubMedID 16373572

  • Hydrological consequences of eucalyptus afforestation in the argentine pampas WATER RESOURCES RESEARCH Engel, V., Jobbagy, E. G., Stieglitz, M., Williams, M., Jackson, R. B. 2005; 41 (10)
  • From icy roads to salty streams PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Jackson, R. B., Jobbagy, E. G. 2005; 102 (41): 14487-14488

    View details for DOI 10.1073/pnas.0507389102

    View details for Web of Science ID 000232603600005

    View details for PubMedID 16203970

  • Effects of afforestation on water yield: a global synthesis with implications for policy GLOBAL CHANGE BIOLOGY Farley, K. A., Jobbagy, E. G., Jackson, R. B. 2005; 11 (10): 1565-1576
  • Responses of tropical native and invader C-4 grasses to water stress, clipping and increased atmospheric CO2 concentration OECOLOGIA Baruch, Z., Jackson, R. B. 2005; 145 (4): 522-532

    Abstract

    The invasion of African grasses into Neotropical savannas has altered savanna composition, structure and function. The projected increase in atmospheric CO(2) concentration has the potential to further alter the competitive relationship between native and invader grasses. The objective of this study was to quantify the responses of two populations of a widespread native C(4) grass (Trachypogon plumosus) and two African C(4) grass invaders (Hyparrhenia rufa and Melinis minutiflora) to high CO(2) concentration interacting with two primary savanna stressors: drought and herbivory. Elevated CO(2) increased the competitive potential of invader grasses in several ways. Germination and seedling size was promoted in introduced grasses. Under high CO(2), the relative growth rate of young introduced grasses was twice that of native grass (0.58 g g(-1) week(-1) vs 0.25 g g(-1) week(-1)). This initial growth advantage was maintained throughout the course of the study. Well-watered and unstressed African grasses also responded more to high CO(2) than did the native grass (biomass increases of 21-47% compared with decreases of 13-51%). Observed higher water and nitrogen use efficiency of invader grasses may aid their establishment and competitive strength in unfertile sites, specially if the climate becomes drier. In addition, high CO(2) promoted lower leaf N content more in the invader grasses. The more intensive land use, predicted to occur in this region, may interact with high CO(2) to favor the African grasses, as they generally recovered faster after simulated herbivory. The superiority of invader grasses under high CO(2) suggests further increases in their competitive strength and a potential increased rate of displacement of the native savannas in the future by grasslands dominated by introduced African species.

    View details for DOI 10.1007/s00442-005-0153-x

    View details for Web of Science ID 000232559900002

    View details for PubMedID 16003505

  • Elevated CO2 reduces disease incidence and severity of a red maple fungal pathogen via changes in host physiology and leaf chemistry GLOBAL CHANGE BIOLOGY McElrone, A. J., Reid, C. D., Hoye, K. A., Hart, E., Jackson, R. B. 2005; 11 (10): 1828-1836
  • Assessment of soil microbial community structure by use of taxon-specific quantitative PCR assays APPLIED AND ENVIRONMENTAL MICROBIOLOGY Fierer, N., Jackson, J. A., Vilgalys, R., Jackson, R. B. 2005; 71 (7): 4117-4120

    Abstract

    Here we describe a quantitative PCR-based approach to estimating the relative abundances of major taxonomic groups of bacteria and fungi in soil. Primers were thoroughly tested for specificity, and the method was applied to three distinct soils. The technique provides a rapid and robust index of microbial community structure.

    View details for DOI 10.1128/AEM.71.7.4117-4120.2005

    View details for Web of Science ID 000230445700091

    View details for PubMedID 16000830

  • Mapping the global distribution of deep roots in relation to climate and soil characteristics GEODERMA Schenk, H. J., Jackson, R. B. 2005; 126 (1-2): 129-140
  • Genetic variance and covariance for physiological traits in Lobelia: Are there constraints on adaptive evolution? EVOLUTION Caruso, C. M., Maherali, H., Mikulyuk, A., Carlson, K., Jackson, R. B. 2005; 59 (4): 826-837

    Abstract

    Physiological traits that control the uptake of carbon dioxide and loss of water are key determinants of plant growth and reproduction. Variation in these traits is often correlated with environmental gradients of water, light, and nutrients, suggesting that natural selection is the primary evolutionary mechanism responsible for physiological diversification. Responses to selection, however, can be constrained by the amount of standing genetic variation for physiological traits and genetic correlations between these traits. To examine the potential for constraint on adaptive evolution, we estimated the quantitative genetic basis of physiological trait variation in one population of each of two closely related species (Lobelia siphilitica and L. cardinalis). Restricted maximum likelihood analyses of greenhouse-grown half-sib families were used to estimate genetic variances and covariances for seven traits associated with carbon and water relations. We detected significant genetic variation for all traits in L. siphilitica, suggesting that carbon-gain and water-use traits could evolve in response to natural selection in this population. In particular, narrow-sense heritabilities for photosynthetic rate (A), stomatal conductance (gs), and water-use efficiency (WUE) in our L. siphilitica population were high relative to previous studies in other species. Although there was significant narrow-sense heritability for A in L. cardinalis, we detected little genetic variation for traits associated with water use (gs and WUE), suggesting that our population of this species may be unable to adapt to drier environments. Despite being tightly linked functionally, the genetic correlation between A and gs was not strong and significant in either population. Therefore, our L. siphilitica population would not be genetically constrained from evolving high A (and thus fixing more carbon for growth and reproduction) while also decreasing gs to limit water loss. However, a significant negative genetic correlation existed between WUE and plant size in L. siphilitica, suggesting that high WUE may be negatively associated with high fecundity. In contrast, our results suggest that any constraints on the evolution of photosynthetic and stomatal traits of L. cardinalis are caused primarily by a lack of genetic variation, rather than by genetic correlations between these functionally related traits.

    View details for Web of Science ID 000228734300010

    View details for PubMedID 15926692

  • Ecohydrological implications of woody plant encroachment ECOLOGY Huxman, T. E., Wilcox, B. P., Breshears, D. D., Scott, R. L., Snyder, K. A., Small, E. E., Hultine, K., Pockman, W. T., Jackson, R. B. 2005; 86 (2): 308-319
  • Ecohydrological control of deep drainage in arid and semiarid regions ECOLOGY Seyfried, M. S., Schwinning, S., Walvoord, M. A., Pockman, W. T., Newman, B. D., Jackson, R. B., Phillips, E. M. 2005; 86 (2): 277-287
  • Carbon cycling in soil FRONTIERS IN ECOLOGY AND THE ENVIRONMENT Johnston, C. A., Groffman, P., Breshears, D. D., Cardon, Z. G., Currie, W., Emanuel, W., Gaudinski, J., Jackson, R. B., Lajtha, K., Nadelhoffer, K., Nelson, D., Post, W. M., Retallack, G., Wielopolski, L. 2004; 2 (10): 522-528
  • Nutrient uptake as a contributing explanation for deep rooting in arid and semi-arid ecosystems OECOLOGIA McCulley, R. L., Jobbagy, E. G., Pockman, W. T., Jackson, R. B. 2004; 141 (4): 620-628

    Abstract

    Explanations for the occurrence of deep-rooted plants in arid and semi-arid ecosystems have traditionally emphasized the uptake of relatively deep soil water. However, recent hydrologic data from arid systems show that soil water potentials at depth fluctuate little over long time periods, suggesting this water may be rarely utilized or replenished. In this study, we examine the distributions of root biomass, soil moisture and nutrient contents to 10-m depths at five semi-arid and arid sites across southwestern USA. We couple these depth distributions with strontium (Sr) isotope data that show deep (>1 m) nutrient uptake is prevalent at four of the five sites. At all of the sites, the highest abundance of one or more of the measured nutrients occurred deep within the soil profile, particularly for P, Ca2+ and Mg2+. Phosphate contents were greater at depth than in the top meter of soil at three of five sites. At Jornada, for example, the 2-3 m depth increment had twice the extractable P as the top meter of soil, despite the highest concentrations of P occurring at the surface. The prevalence of such deep resource pools, and our evidence for cation uptake from them, suggest nutrient uptake as a complementary explanation for the occurrence of deep-rooted plants in arid and semi-arid systems. We propose that hydraulic redistribution of shallow surface water to deep soil layers by roots may be the mechanism through which deep soil nutrients are mobilized and taken up by plants.

    View details for DOI 10.1007/s00442-004-1687-z

    View details for Web of Science ID 000224999800008

    View details for PubMedID 15322902

  • Curbing the US carbon deficit PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Jackson, R. B., Schlesinger, W. H. 2004; 101 (45): 15827-15829

    Abstract

    The U.S. emitted approximately 1.58 petagrams (Pg) of fossil fuel carbon in 2001, approximately one-quarter of global CO(2) production. With climate change increasingly likely, strategies to reduce carbon emissions and stabilize climate are needed, including greater energy efficiency, renewable energy sources, geoengineering, decarbonization, and geological and biological sequestration. Two of the most commonly proposed biological strategies are restoring organic carbon in agricultural soils and using plantations to sequester carbon in soils and wood. Here, we compare scenarios of land-based sequestration to emissions reductions arising from increased fuel efficiency in transportation, targeting ways to reduce net U.S. emissions by 10% ( approximately 0.16 Pg of carbon per year). Based on mean sequestration rates, converting all U.S. croplands to no-till agriculture or retiring them completely could sequester approximately 0.059 Pg of carbon per year for several decades. Summary data across a range of plantations reveal an average rate of carbon storage an order of magnitude larger than in agricultural soils; in consequence, one-third of U.S. croplands or 44 million hectares would be needed for plantations to reach the target of approximately 0.16 Pg of carbon per year. For fossil fuel reductions, cars and light trucks generated approximately 0.31 Pg of carbon in U.S. emissions in 2001. To reduce net emissions by 0.16 Pg of carbon per year, a doubling of fuel efficiency for cars and light trucks is needed, a change feasible with current technology. Issues of permanence, leakage, and economic potentials are discussed briefly, as is the recognition that such scenarios are only a first step in addressing total U.S. emissions.

    View details for DOI 10.1073/pnas.0403631101

    View details for Web of Science ID 000225196800002

    View details for PubMedID 15514026

  • Nitric oxide represses the Arabidopsis floral transition SCIENCE He, Y. K., Tang, R. H., Hao, Y., Stevens, R. D., Cook, C. W., Am, S. M., Jing, L. F., Yang, Z. G., Chen, L. G., Guo, F. Q., Fiorani, F., Jackson, R. B., Crawford, N. M., Pei, Z. M. 2004; 305 (5692): 1968-1971

    Abstract

    The correct timing of flowering is essential for plants to maximize reproductive success and is controlled by environmental and endogenous signals. We report that nitric oxide (NO) repressed the floral transition in Arabidopsis thaliana. Plants treated with NO, as well as a mutant overproducing NO (nox1), flowered late, whereas a mutant producing less NO (nos1) flowered early. NO suppressed CONSTANS and GIGANTEA gene expression and enhanced FLOWERING LOCUS C expression, which indicated that NO regulates the photoperiod and autonomous pathways. Because NO is induced by environmental stimuli and constitutively produced, it may integrate both external and internal cues into the floral decision.

    View details for Web of Science ID 000224136000051

    View details for PubMedID 15448272

  • The uplift of soil nutrients by plants: Biogeochemical consequences across scales ECOLOGY Jobbagy, E. G., Jackson, R. B. 2004; 85 (9): 2380-2389
  • Terrestrial and freshwater biogeochemistry ECOLOGY Jackson, R. B., Hedin, L. O. 2004; 85 (9): 2353-2354
  • Variation in xylem structure and function in stems and roots of trees to 20 m depth NEW PHYTOLOGIST McElrone, A. J., Pockman, W. T., Martinez-Vilalta, J., Jackson, R. B. 2004; 163 (3): 507-517
  • Adaptive variation in the vulnerability of woody plants to xylem cavitation ECOLOGY Maherali, H., Pockman, W. T., Jackson, R. B. 2004; 85 (8): 2184-2199
  • Groundwater use and salinization with grassland afforestation GLOBAL CHANGE BIOLOGY Jobbagy, E. G., Jackson, R. B. 2004; 10 (8): 1299-1312
  • Disconnects in evaluating the relative effectiveness of conservation strategies CONSERVATION BIOLOGY Saterson, K. A., Christensen, N. L., Jackson, R. B., Kramer, R. A., Pimm, S. L., Smith, M. D., Wiener, J. B. 2004; 18 (3): 597-599
  • Comment on "A reservoir of nitrate beneath desert soils" SCIENCE Jackson, R. B., Berthrong, S. T., Cook, C. W., Jobbagy, E. G., McCulley, R. L. 2004; 304 (5667)

    View details for Web of Science ID 000220567900025

    View details for PubMedID 15060308

  • Regional feedbacks among fire, climate, and tropical deforestation JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES Hoffmann, W. A., Schroeder, W., Jackson, R. B. 2003; 108 (D23)
  • On the relationship between stomatal characters and atmospheric CO2 GEOPHYSICAL RESEARCH LETTERS Reid, C. D., Maherali, H., Johnson, H. B., Smith, S. D., Wullschleger, S. D., Jackson, R. B. 2003; 30 (19)
  • Defining a plant's belowground zone of influence ECOLOGY Casper, B. B., Schenk, H. J., Jackson, R. B. 2003; 84 (9): 2313-2321
  • Stomatal sensitivity to vapour pressure difference over a subambient to elevated CO2 gradient in a C-3/C-4 grassland PLANT CELL AND ENVIRONMENT Maherali, H., Johnson, H. B., Jackson, R. B. 2003; 26 (8): 1297-1306
  • Patterns and mechanisms of soil acidification in the conversion of grasslands to forests BIOGEOCHEMISTRY Jobbagy, E. G., Jackson, R. B. 2003; 64 (2): 205-229
  • Gender-specific floral and physiological traits: implications for the maintenance of females in gynodioecious Lobelia siphilitica OECOLOGIA Caruso, C. M., Maherali, H., Jackson, R. B. 2003; 135 (4): 524-531

    Abstract

    A common gender dimorphism in angiosperms is gynodioecy, in which hermaphrodites and females co-occur. Females are at an inherent disadvantage because they can transmit their genes only through ovule production. One mechanism by which females can compensate for the loss of male function is by producing more seeds than hermaphrodites. As such, females should: (1) increase resource uptake to support higher seed production; and (2) allocate resources saved by the loss of male function to seed production. To test this hypothesis, we measured physiological and floral traits of gynodioecious Lobelia siphilitica, controlling for both environmental and genetic variation through a comparison of greenhouse-grown siblings. Pre-reproductive females had 14% higher area-based (Z=2.14; P=0.04) and 32% higher mass-based (Z=1.96; P=0.05) photosynthetic rate than hermaphrodites, suggesting that they have increased carbon acquisition by altering photosynthetic physiology. Female L. siphilitica produced flowers with 4-8% smaller corollas than hermaphrodites (all P<0.05), suggesting that females allocate resources away from floral structures used for pollinator attraction. The genetic correlation between genders for four floral and four physiological traits was significantly less than one but greater than zero, indicating that the evolution of gender dimorphism in response to sex-differential selection will be constrained. The allocation of resources saved by the loss of male function has been viewed as the most important mechanism allowing females of gynodioecious species to support higher seed production. Our data suggest that increased resource acquisition by females at pre-reproductive stages can also contribute to the maintenance of gender dimorphism in gynodioecious species.

    View details for DOI 10.1007/s00442-003-1199-2

    View details for Web of Science ID 000183722700005

    View details for PubMedID 16228251

  • Positive feedbacks of fire, climate, and vegetation and the conversion of tropical savanna GEOPHYSICAL RESEARCH LETTERS Hoffmann, W. A., Schroeder, W., Jackson, R. B. 2002; 29 (22)
  • Meeting ecological and societal needs for freshwater ECOLOGICAL APPLICATIONS Baron, J. S., Poff, N. L., Angermeier, P. L., Dahm, C. N., Gleick, P. H., Hairston, N. G., Jackson, R. B., Johnston, C. A., Richter, B. D., Steinman, A. D. 2002; 12 (5): 1247-1260
  • Linking molecular insight and ecological research TRENDS IN ECOLOGY & EVOLUTION Jackson, R. B., Linder, C. R., Lynch, M., Purugganan, M., Somerville, S., Thayer, S. S. 2002; 17 (9): 409-414
  • Root production and demography in a california annual grassland under elevated atmospheric carbon dioxide GLOBAL CHANGE BIOLOGY Higgins, P. A., Jackson, R. B., Des Rosiers, J. M., Field, C. B. 2002; 8 (9): 841-850
  • Ecosystem carbon loss with woody plant invasion of grasslands NATURE Jackson, R. B., Banner, J. L., Jobbagy, E. G., Pockman, W. T., Wall, D. H. 2002; 418 (6898): 623-626

    Abstract

    The invasion of woody vegetation into deserts, grasslands and savannas is generally thought to lead to an increase in the amount of carbon stored in those ecosystems. For this reason, shrub and forest expansion (for example, into grasslands) is also suggested to be a substantial, if uncertain, component of the terrestrial carbon sink. Here we investigate woody plant invasion along a precipitation gradient (200 to 1,100 mm yr(-1)) by comparing carbon and nitrogen budgets and soil delta(13)C profiles between six pairs of adjacent grasslands, in which one of each pair was invaded by woody species 30 to 100 years ago. We found a clear negative relationship between precipitation and changes in soil organic carbon and nitrogen content when grasslands were invaded by woody vegetation, with drier sites gaining, and wetter sites losing, soil organic carbon. Losses of soil organic carbon at the wetter sites were substantial enough to offset increases in plant biomass carbon, suggesting that current land-based assessments may overestimate carbon sinks. Assessments relying on carbon stored from woody plant invasions to balance emissions may therefore be incorrect.

    View details for DOI 10.1038/nature00910

    View details for Web of Science ID 000177305600038

    View details for PubMedID 12167857

  • The global biogeography of roots ECOLOGICAL MONOGRAPHS Schenk, H. J., Jackson, R. B. 2002; 72 (3): 311-328
  • Rooting depths, lateral root spreads and below-ground/above-ground allometries of plants in water-limited ecosystems JOURNAL OF ECOLOGY Schenk, H. J., Jackson, R. B. 2002; 90 (3): 480-494
  • Nonlinear grassland responses to past and future atmospheric CO2 NATURE Gill, R. A., Polley, H. W., Johnson, H. B., Anderson, L. J., Maherali, H., Jackson, R. B. 2002; 417 (6886): 279-282

    Abstract

    Carbon sequestration in soil organic matter may moderate increases in atmospheric CO(2) concentrations (C(a)) as C(a) increases to more than 500 micromol mol(-1) this century from interglacial levels of less than 200 micromol mol(-1) (refs 1 6). However, such carbon storage depends on feedbacks between plant responses to C(a) and nutrient availability. Here we present evidence that soil carbon storage and nitrogen cycling in a grassland ecosystem are much more responsive to increases in past C(a) than to those forecast for the coming century. Along a continuous gradient of 200 to 550 micromol mol(-1) (refs 9, 10), increased C(a) promoted higher photosynthetic rates and altered plant tissue chemistry. Soil carbon was lost at subambient C(a), but was unchanged at elevated C(a) where losses of old soil carbon offset increases in new carbon. Along the experimental gradient in C(a) there was a nonlinear, threefold decrease in nitrogen availability. The differences in sensitivity of carbon storage to historical and future C(a) and increased nutrient limitation suggest that the passive sequestration of carbon in soils may have been important historically, but the ability of soils to continue as sinks is limited.

    View details for DOI 10.1038/417279a

    View details for Web of Science ID 000175592100045

    View details for PubMedID 12015601

  • Stomatal acclimation over a subambient to elevated CO2 gradient in a C-3/C-4 grassland PLANT CELL AND ENVIRONMENT Maherali, H., Reid, C. D., Polley, H. W., Johnson, H. B., Jackson, R. B. 2002; 25 (4): 557-566
  • Nitrogen controls on climate model evapotranspiration JOURNAL OF CLIMATE Dickinson, R. E., Berry, J. A., Bonan, G. B., Collatz, G. J., Field, C. B., Fung, I. Y., Goulden, M., Hoffmann, W. A., Jackson, R. B., Myneni, R., Sellers, P. J., Shaikh, M. 2002; 15 (3): 278-295
  • Using simple environmental variables to estimate below-ground productivity in grasslands GLOBAL ECOLOGY AND BIOGEOGRAPHY Gill, R. A., Kelly, R. H., Parton, W. J., Day, K. A., Jackson, R. B., Morgan, J. A., Scurlock, J. M., Tieszen, L. L., Castle, J. V., Ojima, D. S., Zhang, X. S. 2002; 11 (1): 79-86
  • Below-ground processes in gap models for simulating forest response to global change CLIMATIC CHANGE Wullschleger, S. D., Jackson, R. B., Currie, W. S., Friend, A. D., Luo, Y., Mouillot, F., Pan, Y., Shao, G. F. 2001; 51 (3-4): 449-473
  • Modeling root water uptake in hydrological and climate models BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY Feddes, R. A., Hoff, H., Bruen, M., Dawson, T., de Rosnay, P., Dirmeyer, O., Jackson, R. B., Kabat, P., Kleidon, A., Lilly, A., Pitman, A. J. 2001; 82 (12): 2797-2809
  • Water in a changing world ECOLOGICAL APPLICATIONS Jackson, R. B., Carpenter, S. R., Dahm, C. N., McKnight, D. M., Naiman, R. J., Postel, S. L., Running, S. W. 2001; 11 (4): 1027-1045
  • Gas exchange and photosynthetic acclimation over subambient to elevated CO2 in a C-3-C-4 grassland GLOBAL CHANGE BIOLOGY Anderson, L. J., Maherali, H., Johnson, H. B., Polley, H. W., Jackson, R. B. 2001; 7 (6): 693-707
  • The distribution of soil nutrients with depth: Global patterns and the imprint of plants BIOGEOCHEMISTRY Jobbagy, E. G., Jackson, R. B. 2001; 53 (1): 51-77
  • Plant physiological ecology: linking the organism to scales above and below - Ecological Society of America Meeting Snowbird, UT, USA, August 2000 NEW PHYTOLOGIST DeLucia, E. H., Coleman, J. S., Dawson, T. E., Jackson, R. B. 2001; 149 (1): 12-16
  • Water and tree-understory interactions: A natural experiment in a savanna with oak wilt ECOLOGY Anderson, L. J., Brumbaugh, M. S., Jackson, R. B. 2001; 82 (1): 33-49
  • Heterogenous soil-resource distribution and plant responses - from individual-plant growth to ecosystem functioning Progress in Botany Huber-Sannwald, E., Jackson, R. B. 2001; 62: 451-476
  • Reduction of isoprene emissions from live oak (Quercus fusiformis) with oak wilt TREE PHYSIOLOGY Anderson, L. J., Harley, P. C., Monson, R. K., Jackson, R. B. 2000; 20 (17): 1199-1203
  • Root water uptake and transport: using physiological processes in global predictions TRENDS IN PLANT SCIENCE Jackson, R. B., Sperry, J. S., Dawson, T. E. 2000; 5 (11): 482-488

    Abstract

    Plant water loss, regulated by stomata and driven by atmospheric demand, cannot exceed the maximum steady-state supply through roots. Just as an electric circuit breaks when carrying excess current, the soil-plant continuum breaks if forced to transport water beyond its capacity. Exciting new molecular, biophysical and ecological research suggests that roots are the weakest link along this hydraulic flow path. We attempt here to predict rooting depth and water uptake using the hydraulic properties of plants and the soil, and also to suggest how new physiological tools might contribute to larger-scale studies of hydraulic lift, the water balance and biosphere-atmosphere interactions.

    View details for Web of Science ID 000165268000017

    View details for PubMedID 11077257

  • A universal molecular method for identifying underground plant parts to species MOLECULAR ECOLOGY Linder, C. R., Moore, L. A., Jackson, R. B. 2000; 9 (10): 1549-1559

    Abstract

    As part of a large project to determine rooting depth and resource uptake on the Edwards Plateau of central Texas, we developed a DNA-based technique that allows the below-ground parts of all plants to be identified to the level of genus and usually to species. Identification is achieved by comparing DNA sequences of the internal transcribed spacer (ITS) region of the 18S-26S nuclear ribosomal DNA repeat, derived from below-ground plant material, with a reference ITS region database for plants at a site. The method works throughout plants because the plant ITS region can be PCR amplified using a set of universal primers. Congeneric species can usually be identified because the ITS region evolves relatively rapidly. In our study, all roots were easily identified to the level of genus; most congeneric species were identified solely by ITS sequence differences but some required a combination of ITS sequence data and above-ground surveys of species at a site. In addition to showing the feasibility and efficacy of our technique, we compare it with another DNA-based technique used to identify below-ground plant parts. Finally, we also describe a DNA extraction and purification technique that reliably provides high-quality DNA of sufficient quantity from roots so that PCR can be readily accomplished. Our technique should allow the below-ground parts of plants in any system to be identified and thereby open new possibilities for the study of below-ground plant communities.

    View details for Web of Science ID 000089998600010

    View details for PubMedID 11050550

  • Global patterns of root turnover for terrestrial ecosystems NEW PHYTOLOGIST Gill, R. A., Jackson, R. B. 2000; 147 (1): 13-31
  • Root dynamics and global change: seeking an ecosystem perspective NEW PHYTOLOGIST Norby, R. J., Jackson, R. B. 2000; 147 (1): 3-12
  • Vegetation-climate feedbacks in the conversion of tropical savanna to grassland JOURNAL OF CLIMATE Hoffmann, W. A., Jackson, R. B. 2000; 13 (9): 1593-1602
  • Elevated CO2 enhances resprouting of a tropical savanna tree OECOLOGIA Hoffmann, W. A., Bazzaz, F. A., Chatterton, N. J., Harrison, P. A., Jackson, R. B. 2000; 123 (3): 312-317
  • Global controls of forest line elevation in the northern and southern hemispheres GLOBAL ECOLOGY AND BIOGEOGRAPHY Jobbagy, E. G., Jackson, R. B. 2000; 9 (3): 253-268
  • The vertical distribution of soil organic carbon and its relation to climate and vegetation ECOLOGICAL APPLICATIONS Jobbagy, E. G., Jackson, R. B. 2000; 10 (2): 423-436
  • Belowground processes and global change ECOLOGICAL APPLICATIONS Jackson, R. B. 2000; 10 (2): 397-398
  • Belowground consequences of vegetation change and their treatment in models ECOLOGICAL APPLICATIONS Jackson, R. B., Schenk, H. J., Jobbagy, E. G., Canadell, J., Colello, G. D., Dickinson, R. E., Field, C. B., Friedlingstein, P., Heimann, M., Hibbard, K., Kicklighter, D. W., Kleidon, A., Neilson, R. P., Parton, W. J., Sala, O. E., Sykes, M. T. 2000; 10 (2): 470-483
  • Biodiversity - Global biodiversity scenarios for the year 2100 SCIENCE Sala, O. E., Chapin, F. S., Armesto, J. J., Berlow, E., Bloomfield, J., Dirzo, R., Huber-Sanwald, E., Huenneke, L. F., Jackson, R. B., Kinzig, A., Leemans, R., Lodge, D. M., Mooney, H. A., Oesterheld, M., Poff, N. L., Sykes, M. T., Walker, B. H., Walker, M., Wall, D. H. 2000; 287 (5459): 1770-1774
  • Carbon metabolism of the terrestrial biosphere: A multitechnique approach for improved understanding ECOSYSTEMS Canadell, J. G., Mooney, H. A., Baldocchi, D. D., Berry, J. A., Ehleringer, J. R., Field, C. B., Gower, S. T., Hollinger, D. Y., Hunt, J. E., Jackson, R. B., Running, S. W., Shaver, G. R., STEFFEN, W., Trumbore, S. E., Valentini, R., Bond, B. Y. 2000; 3 (2): 115-130
  • Nutrient concentrations in fine roots ECOLOGY Gordon, W. S., Jackson, R. B. 2000; 81 (1): 275-280
  • Ecosystem rooting depth determined with caves and DNA PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Jackson, R. B., Moore, L. A., Hoffmann, W. A., Pockman, W. T., Linder, C. R. 1999; 96 (20): 11387-11392

    Abstract

    Belowground vertical community composition and maximum rooting depth of the Edwards Plateau of central Texas were determined by using DNA sequence variation to identify roots from caves 5-65 m deep. Roots from caves were identified by comparing their DNA sequences for the internal transcribed spacer (ITS) region of the 18S-26S ribosomal DNA repeat against a reference ITS database developed for woody plants of the region. Sequencing the ITS provides, to our knowledge, the first universal method for identifying plant roots. At least six tree species in the system grew roots deeper than 5 m, but only the evergreen oak, Quercus fusiformis, was found below 10 m. The maximum rooting depth for the ecosystem was approximately 25 m. (18)O isotopic signatures for stem water of Q. fusiformis confirmed water uptake from 18 m underground. The availability of resources at depth, coupled with small surface pools of water and nutrients, may explain the occurrence of deep roots in this and other systems.

    View details for Web of Science ID 000082868500085

    View details for PubMedID 10500186

  • Downward flux of water through roots (ie inverse hydraulic lift) in dry Kalahari sands OECOLOGIA Schulze, E. D., Caldwell, M. M., Canadell, J., Mooney, H. A., Jackson, R. B., Parson, D., Scholes, R., Sala, O. E., Trimborn, P. 1998; 115 (4): 460-462
  • Ecosystem water fluxes for two grasslands in elevated CO2: a modeling analysis OECOLOGIA Jackson, R. B., Sala, O. E., Paruelo, J. M., Mooney, H. A. 1998; 113 (4): 537-546
  • The fate of carbon in grasslands under carbon dioxide enrichment NATURE Hungate, B. A., Holland, E. A., Jackson, R. B., Chapin, F. S., Mooney, H. A., Field, C. B. 1997; 388 (6642): 576-579
  • A global budget for fine root biomass, surface area, and nutrient contents PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Jackson, R. B., Mooney, H. A., Schulze, E. D. 1997; 94 (14): 7362-7366

    Abstract

    Global biogeochemical models have improved dramatically in the last decade in their representation of the biosphere. Although leaf area data are an important input to such models and are readily available globally, global root distributions for modeling water and nutrient uptake and carbon cycling have not been available. This analysis provides global distributions for fine root biomass, length, and surface area with depth in the soil, and global estimates of nutrient pools in fine roots. Calculated root surface area is almost always greater than leaf area, more than an order of magnitude so in grasslands. The average C:N:P ratio in living fine roots is 450:11:1, and global fine root carbon is more than 5% of all carbon contained in the atmosphere. Assuming conservatively that fine roots turn over once per year, they represent 33% of global annual net primary productivity.

    View details for Web of Science ID A1997XJ87600044

    View details for PubMedID 11038557

  • Photosynthetic electron transport in single guard cells as measured by scanning electrochemical microscopy PLANT PHYSIOLOGY Tsionsky, M., Cardon, Z. G., Bard, A. J., Jackson, R. B. 1997; 113 (3): 895-901
  • Plant competition underground ANNUAL REVIEW OF ECOLOGY AND SYSTEMATICS Casper, B. B., Jackson, R. B. 1997; 28: 545-570
  • Integrating resource heterogeneity and plant plasticity: Modelling nitrate and phosphate uptake in a patchy soil environment JOURNAL OF ECOLOGY Jackson, R. B., Caldwell, M. M. 1996; 84 (6): 891-903
  • Maximum rooting depth of vegetation types at the global scale OECOLOGIA Canadell, J., Jackson, R. B., Ehleringer, J. R., Mooney, H. A., Sala, O. E., Schulze, E. D. 1996; 108 (4): 583-595
  • A global analysis of root distributions for terrestrial biomes OECOLOGIA Jackson, R. B., Canadell, J., Ehleringer, J. R., Mooney, H. A., Sala, O. E., Schulze, E. D. 1996; 108 (3): 389-411
  • Rooting depth, water availability, and vegetation cover along an aridity gradient in Patagonia OECOLOGIA Schulze, E. D., Mooney, H. A., Sala, O. E., Jobbagy, E., Buchmann, N., Bauer, G., Canadell, J., Jackson, R. B., Loreti, J., Oesterheld, M., Ehleringer, J. R. 1996; 108 (3): 503-511
  • Elevated CO2 increases belowground respiration in California grasslands OECOLOGIA Luo, Y. Q., Jackson, R. B., Field, C. B., Mooney, H. A. 1996; 108 (1): 130-137
  • Nitrate and ammonium uptake for single- and mixed-species communities grown at elevated CO2 OECOLOGIA Jackson, R. B., Reynolds, H. L. 1996; 105 (1): 74-80
  • STOMATAL RESPONSES TO INCREASED CO2 - IMPLICATIONS FROM THE PLANT TO THE GLOBAL-SCALE PLANT CELL AND ENVIRONMENT Field, C. B., Jackson, R. B., Mooney, H. A. 1995; 18 (10): 1214-1225
  • CO2 ALTERS WATER-USE, CARBON GAIN, AND YIELD FOR THE DOMINANT SPECIES IN A NATURAL GRASSLAND OECOLOGIA Jackson, R. B., Sala, O. E., Field, C. B., Mooney, H. A. 1994; 98 (3-4): 257-262
  • Local regulation of mycorrhizal arbuscule frequency in enriched soil microsites Canadian Journal of Botany Duke, S. E., Jackson, R. B., Caldwell, M. M. 1994; 72: 998-1001
  • GEOSTATISTICAL PATTERNS OF SOIL HETEROGENEITY AROUND INDIVIDUAL PERENNIAL PLANTS JOURNAL OF ECOLOGY Jackson, R. B., Caldwell, M. M. 1993; 81 (4): 683-692
  • THE SCALE OF NUTRIENT HETEROGENEITY AROUND INDIVIDUAL PLANTS AND ITS QUANTIFICATION WITH GEOSTATISTICS ECOLOGY Jackson, R. B., Caldwell, M. M. 1993; 74 (2): 612-614
  • SHADING AND THE CAPTURE OF LOCALIZED SOIL NUTRIENTS - NUTRIENT CONTENTS, CARBOHYDRATES, AND ROOT UPTAKE KINETICS OF A PERENNIAL TUSSOCK GRASS OECOLOGIA Jackson, R. B., Caldwell, M. M. 1992; 91 (4): 457-462
  • KINETIC RESPONSES OF PSEUDOROEGNERIA ROOTS TO LOCALIZED SOIL ENRICHMENT PLANT AND SOIL Jackson, R. B., Caldwell, M. M. 1991; 138 (2): 231-238
  • EXPLOITATION OF PHOSPHATE FROM FERTILE SOIL MICROSITES BY 3 GREAT-BASIN PERENNIALS WHEN IN COMPETITION FUNCTIONAL ECOLOGY Caldwell, M. M., MANWARING, J. H., Jackson, R. B. 1991; 5 (6): 757-764
  • Nonsteady-state photosynthesis following an increase in photon flux density (PFD): effects of magnitude and duration of initial photon flux density Plant Physiology Jackson, R. B., Woodrow, I. E., Mott, K. A. 1991; 95: 498-503
  • RAPID PHYSIOLOGICAL ADJUSTMENT OF ROOTS TO LOCALIZED SOIL ENRICHMENT NATURE Jackson, R. B., MANWARING, J. H., Caldwell, M. M. 1990; 344 (6261): 58-60

    Abstract

    SOIL microsites rich in available nutrients are an important source of mineral nutrients for plants in many environments(1-5). Patchiness in nutrient availability below ground is analogous to resource availability in canopy gaps above ground(6). Although the physiological changes occurring in leaves exposed to sun and shade in canopy gaps are well known(7-9), we do not know any studies that show similar physiological changes in roots in enriched soil patches. Here we present evidence of large and rapid increases in the uptake kinetics of plant roots after creating nutrient-rich soil patches in the field. The mean rate of phosphate uptake at a given external phosphate concentration increased by as much as 80% for roots from enriched soil patches compared with roots of control patches treated with distilled water. The changes took place within days of patch treatment. This degree of plasticity was particularly notable for plants growing in soils of very low available phosphorus. These results showing rapid physiological plasticity of roots in fertile soil microsites have important implications for the theory and modelling of nutrient uptake in all soils.

    View details for Web of Science ID A1990CQ97200059

    View details for PubMedID 18278027

  • The timing and degree of root proliferation in fertile-soil microsites for three cold-desert perennials Oecologia Jackson, R. B., Caldwell, M. M. 1989; 81: 149-153

Books and Book Chapters


  • Weekend Mischief Jackson, R. Wordsong, Boyds Mills Press. 2010
  • Carbon and water tradeoffs in conversions to forests and shrublands Terrestrial Ecosystems in a Changing World Jackson, R. B., Farley, K. A., Hoffmann, W. A., Jobbagy, E. G., McCulley, R. L. Springer. 2007: 237-246
  • Animal Mischief Jackson, R. Wordsong, Boyds Mills Press. 2006
  • The Earth Remains Forever Jackson, R. University of Texas Press. 2002
  • Methods in Ecosystem Science edited by Sala, O. E., Jackson, R. B., Mooney, H. A., Howarth, R. W. Springer. 2000
  • The importance of root distributions for hydrology, biogeochemistry, and ecosystem functioning Integrating hydrology, ecosystem dynamics, and biogeochemistry in complex landscapes Jackson, R. B. John Wiley and Sons. 1999: 219-240
  • Desertification control to sequester C and mitigate the greenhouse effect: a commentary Carbon sequestration in soils: science, monitoring, and beyond Jackson, R. B. Batelle Press. 1999: 143-146
  • The structure and function of root systems Handbook of Functional Plant Ecology Jackson, R. B., Pockman, W. T., Hoffmann, W. A. Marcel Dekker. 1999: 195-220
  • Interactive effects of water stress and elevated CO2 on growth, photosynthesis, and water use efficiency Carbon Dioxide and Environmental Stress Hsiao, T. C., Jackson, R. B. Academic Press. 1999: 3-31
  • The soil system Global Biodiversity Assessment Anderson, J. M., Cuevas, E., Chapin III, F. S., Hobbs, R. J., Pitelka, L. F., Jackson, R. B. Cambridge University Press. 1995: 406-412

Conference Proceedings


  • Detecting changes in soil carbon in CO2 enrichment experiments Hungate, B. A., Jackson, R. B., Field, C. B., Chapin, F. S. SPRINGER. 1996: 135-145
  • Photosynthesis, growth and density for the dominant species in a CO2-enriched grassland Jackson, R. B., Luo, Y., Cardon, Z. G., Sala, O. E., Field, C. B., Mooney, H. A. WILEY-BLACKWELL PUBLISHING, INC. 1995: 221-225