Luana Krebs

All Publications

• Forest under stress: responses and recovery of water relations across scales during the compound drought in summer 2022. The New phytologist Shekhar, A., Gilgen, A. K., Ackermann, A., Scapucci, L., Aranda-Barranco, S., Bolshakova, A., Hörtnagl, L., Wang, Y., Richter, F., Turco, F., Gou, R., Krebs, L., Feigenwinter, I., Werner, R. A., Zweifel, R., Etzold, S., Floriancic, M., Osterwalder, S., Gharun, M., Buchmann, N. 2026

  Abstract

  The summer of 2022 was characterized by compound soil and atmospheric drought (CSAD; low soil water content, SWC, and high vapor pressure deficit, VPD) in Central Europe, threatening forest carbon sequestration and water balance, yet linked ecosystem- and tree-level hydraulic responses remain poorly resolved. We assessed the response and recovery of water relations of a beech-dominated montane mixed deciduous forest in Switzerland (CH-Lae) to the 2022 CSAD through a series of ecosystem-scale (evapotranspiration, ET; canopy conductance, Gs) as well as tree-scale measurements, including leaf-level (leaf water potential, LWP; stomatal conductance, gs), stem-level (nighttime stem rehydration, NSR) and root-level (root water uptake depth, RWU depth) variables. During peak CSAD, ET and Gs declined by up to 50%, driven primarily by low SWC. Midday and predawn LWP declined significantly. Beech and maple accessed deeper water (> 70 cm), maintaining NSR and gs during CSAD and fully recovering thereafter; spruce and fir relied on shallow water (< 30 cm), showing stronger NSR reductions but still full recovery post-CSAD. Our findings demonstrate that species-specific hydraulic traits drive forest-scale water dynamics under CSAD conditions. Integrating these insights into forest adaptation strategies will be critical for sustaining forests under intensifying compound droughts in the future.

  View details for DOI 10.1111/nph.71516

  View details for PubMedID 42698125

• Below- and above-canopy methane and nitrous oxide fluxes in a subalpine spruce forest AGRICULTURAL AND FOREST METEOROLOGY Krebs, L., Hortnagl, L., Meier, P., Feigenwinter, I., Gharun, M., Buchmann, N. 2026; 387

  View details for DOI 10.1016/j.agrformet.2026.111261

  View details for Web of Science ID 001785791300001

• Net Ecosystem CO₂ Exchange of a Subalpine Spruce Forest in Switzerland Over 26 Years: Effects of Phenology and Contributions of Abiotic Drivers at Daily Time Scales GLOBAL CHANGE BIOLOGY Krebs, L., Hortnagl, L., Scapucci, L., Gharun, M., Feigenwinter, I., Buchmann, N. 2025; 31 (7): e70371

  Abstract

  Climate change affects carbon sequestration dynamics and phenology in forests, especially in alpine and subalpine regions. Here, long-term trends in climate, net ecosystem CO2 exchange (NEE), net carbon uptake period (CUPnet) and their drivers were investigated, using 26 years of flux measurements in a subalpine spruce forest (CH-Dav, Switzerland; 1997 to 2022). CUPnet length, start (SOS) and end of season (EOS) were extracted from smoothed daily NEE time series. We used machine learning to determine the importance of environmental drivers on daily NEE and CUPnet. Annual mean and maximum air temperatures (Tair) increased, while soil water content (SWC) decreased significantly between 1997 and 2022. Annual C sinks increased from 1997 to 2012, leveled off between 2012 and 2015, followed by a decline. Annual NEE was strongly related to CUPnet length, SOS, and EOS. No significant trends in CUPnet, SOS, or EOS were detected, most likely indicating ecophysiological acclimation, that is, physiological adjustments to changing environmental conditions over the past 26 years. We identified 48 days with significant negative trends in mean daily NEE over the 26 years, that is, stronger net C uptake or weaker net C loss, particularly in spring and autumn, but no significant positive trends. Daylength, incoming shortwave radiation (Rg), SWC, and minimum Tair were the main drivers of daily NEE. SOS was mainly driven by daylength and Tair, EOS by daylength and Rg. Thus, the spruce forest benefited from higher temperature between autumn and spring, with higher net C uptake during favorable conditions and reduced C loss when winter photosynthesis compensated respiration. However, high summer temperatures increasingly limited NEE, suggesting adverse effects for subalpine Picea abies forests in the future. Our study demonstrated that identifying driver contributions to NEE dynamics at daily time scales allows better understanding of the complexity of climate change impacts on forest C dynamics.

  View details for DOI 10.1111/gcb.70371

  View details for Web of Science ID 001534293800001

  View details for PubMedID 40702862

  View details for PubMedCentralID PMC12287681

• Impact of winter warming on CO₂ fluxes in evergreen needleleaf forests BIOGEOSCIENCES Gharun, M., Shekhar, A., Hortnagl, L., Krebs, L., Arriga, N., Migliavacca, M., Roland, M., Gielen, B., Montagnani, L., Tomelleri, E., Sigut, L., Peichl, M., Zhao, P., Schmidt, M., Gruenwald, T., Korkiakoski, M., Lohila, A., Buchmann, N. 2025; 22 (5): 1393-1411

  View details for DOI 10.5194/bg-22-1393-2025

  View details for Web of Science ID 001442240800001

• Forest-floor respiration, N₂O fluxes, and CH₄ fluxes in a subalpine spruce forest: drivers and annual budgets BIOGEOSCIENCES Krebs, L., Burri, S., Feigenwinter, I., Gharun, M., Meier, P., Buchmann, N. 2024; 21 (8): 2005-2028

  View details for DOI 10.5194/bg-21-2005-2024

  View details for Web of Science ID 001207322000001