Honors & Awards
Graduate Research Fellowship, National Science Foundation (2014)
Graduate Opportunities Worldwide (GROW); Brazil, National Science Foundation (2017)
B.A., Occidental College, Biology (2012)
Ph.D., University of California, Berkeley, Environmental Science, Policy, and Management (2019)
Kabir Peay, Postdoctoral Faculty Sponsor
The energy-water limitation threshold explains divergent drought responses in tree growth, needle length, and stable isotope ratios.
Global change biology
Predicted increases in extreme droughts will likely cause major shifts in carbon sequestration and forest composition. Though growth declines during drought are widely documented, an increasing number of studies have reported both positive and negative responses to the same drought. These divergent growth patterns may reflect thresholds (i.e., nonlinear responses) promoted by changes in the dominant climatic constraints on tree growth. Here we tested whether stemwood growth exhibited linear or nonlinear responses to temperature and precipitation and whether stemwood growth thresholds co-occurred with multiple thresholds in source and sink processes that limit tree growth. We extracted 772 tree cores, 1,398 needle length records, and 1,075 stable isotope samples from 27 sites across whitebark pine's (Pinus albicaulis Engelm.) climatic niche in the Sierra Nevada. Our results indicated that a temperature threshold in stemwood growth occurred at 8.4 °C (7.12 - 9.51°C; estimated using fall-spring maximum temperature). This threshold was significantly correlated with thresholds in foliar growth, as well as carbon (δ13 C) and nitrogen (δ15 N) stable isotope ratios, that emerged during drought. Multiple, co-occurring thresholds reflected the transition between energy and water limited tree growth (i.e., the E-W limitation threshold). This transition likely mediated carbon and nutrient cycling, as well as important differences in growth-defense tradeoffs and drought-adaptations. Further, whitebark pine growing in energy limited regions may continue to experience elevated growth in response to climate change. The positive effect of warming, however, may be offset by growth declines in water limited regions, threatening the long-term sustainability of the recently listed whitebark pine species in the Sierra Nevada.
View details for DOI 10.1111/gcb.16740
View details for PubMedID 37089078
Nitrogen fertilization disrupts the temporal dynamics of arbuscular mycorrhizal fungal hyphae but not spore density and community composition in a wheat field.
The New phytologist
Elucidating the temporal dynamics of arbuscular mycorrhizal (AM) fungi is critical for understanding their functions. Furthermore, research investigating the temporal dynamics of AM fungi in response to agricultural practices remain in its infancy. We investigated the effect of nitrogen fertilization and watering reduction on the temporal dynamics of AM fungi, across the lifespan of wheat. Nitrogen fertilization decreased AM fungal spore density, extra-radical hyphal density, and intra-radical colonization rate in both watering conditions. Nitrogen fertilization affected AM fungal community composition in soil but not in roots, regardless of watering conditions. The temporal analysis revealed that AM fungal extra-radical hyphal density and intra-radical colonization rate were higher under conventional watering and lower under reduced watering in March than in other growth stages at low (≤ 70 kg N ha-1 yr-1 ) but not at high (≥ 140) nitrogen fertilization levels. AM fungal spore density was lower in June than in other growth stages and community composition varied with plant development at all nitrogen fertilization levels, regardless of watering conditions. This study demonstrates that high nitrogen fertilization levels disrupt the temporal dynamics of AM fungal hyphal growth but not sporulation and community composition.
View details for DOI 10.1111/nph.18043
View details for PubMedID 35179789
Keep your friends close: Host compartmentalisation of microbial communities facilitates decoupling from effects of habitat fragmentation.
Root-associated fungal communities modify the climatic niches and even the competitive ability of their hosts, yet how the different components of the root microbiome are modified by habitat loss remains a key knowledge gap. Using principles of landscape ecology, we tested how free-living versus host-associated microbes differ in their response to landscape heterogeneity. Further, we explore how compartmentalisation of microbes into specialised root structures filters for key fungal symbionts. Our study demonstrates that free-living fungal community structure correlates with landscape heterogeneity, but that host-associated fungal communities depart from these patterns. Specifically, biotic filtering in roots, especially via compartmentalisation within specialised root structures, decouples the biogeographic patterns of host-associated fungal communities from the soil community. In this way, even as habitat loss and fragmentation threaten fungal diversity in the soils, plant hosts exert biotic controls to ensure associations with critical mutualists, helping to preserve the root mycobiome.
View details for DOI 10.1111/ele.13886
View details for PubMedID 34523223
Author Correction: Nonlinear shifts in infectious rust disease due to climate change.
2021; 12 (1): 5326
View details for DOI 10.1038/s41467-021-25692-3
View details for PubMedID 34475385
Nonlinear shifts in infectious rust disease due to climate change.
2021; 12 (1): 5102
Range shifts of infectious plant disease are expected under climate change. As plant diseases move, emergent abiotic-biotic interactions are predicted to modify their distributions, leading to unexpected changes in disease risk. Evidence of these complex range shifts due to climate change, however, remains largely speculative. Here, we combine a long-term study of the infectious tree disease, white pine blister rust, with a six-year field assessment of drought-disease interactions in the southern Sierra Nevada. We find that climate change between 1996 and 2016 moved the climate optimum of the disease into higher elevations. The nonlinear climate change-disease relationship contributed to an estimated 5.5 (4.4-6.6) percentage points (p.p.) decline in disease prevalence in arid regions and an estimated 6.8 (5.8-7.9) p.p. increase in colder regions. Though climate change likely expanded the suitable area for blister rust by 777.9 (1.0-1392.9) km2 into previously inhospitable regions, the combination of host-pathogen and drought-disease interactions contributed to a substantial decrease (32.79%) in mean diseaseprevalence between surveys. Specifically, declining alternate host abundance suppressed infection probabilities at high elevations, even as climatic conditions became more suitable. Further, drought-disease interactions varied in strength and direction across an aridity gradient-likely decreasing infection risk at low elevations while simultaneously increasing infection risk at high elevations. These results highlight the critical role of aridity in modifying host-pathogen-drought interactions. Variation in aridity across topographic gradients can strongly mediate plant disease range shifts in response to climate change.
View details for DOI 10.1038/s41467-021-25182-6
View details for PubMedID 34429405
The generalizability of water-deficit on bacterial community composition; Site-specific water-availability predicts the bacterial community associated with coast redwood roots
Experimental drought has been shown to delay the development of the root microbiome and increase the relative abundance of Actinobacteria, however, the generalizability of these findings to natural systems or other diverse plant hosts remains unknown. Bacterial cell wall thickness and growth morphology (e.g., filamentous or unicellular) have been proposed as traits that may mediate bacterial responses to environmental drivers. Leveraging a natural gradient of water-availability across the coast redwood (Sequoia sempervirens) range, we tested three hypotheses: (a) that site-specific water-availability is an important predictor of bacterial community composition for redwood roots and rhizosphere soils; (b) that there is relative enrichment of Actinobacteria and other monoderm bacterial groups within the redwood microbiome in response to drier conditions; and (c) that bacterial growth morphology is an important predictor of bacteria response to water-availability, where filamentous taxa will become more dominant at drier sites compared to unicellular bacteria. We find that both α- and β-diversity of redwood bacterial communities is partially explained by water-availability and that Actinobacterial enrichment is a conserved response of land plants to water-deficit. Further, we highlight how the trend of Actinobacterial enrichment in the redwood system is largely driven by the Actinomycetales. We propose bacterial growth morphology (filamentous vs. unicellular) as an additional mechanism behind the increase in Actinomycetales with increasing aridity. A trait-based approach including cell-wall thickness and growth morphology may explain the distribution of bacterial taxa across environmental gradients and help to predict patterns of bacterial community composition for a wide range of host plants.
View details for DOI 10.1111/mec.15666
View details for Web of Science ID 000583198200001
View details for PubMedID 33000868