Net Ecosystem CO 2 Exchange of a Subalpine Spruce Forest in Switzerland Over 26 Years: Effects of Phenology and Contributions of Abiotic Drivers at Daily Time Scales

作者：Luana Krebs, Lukas Hörtnagl, Liliana Scapucci, Mana Gharun, Iris Feigenwinter, Nina Buchmann · 发表于：Global Change Biology · 年份：2025 · DOI：10.1111/gcb.70371 · 被引用次数：7 · 研究领域：Plant Water Relations and Carbon Dynamics、Tree-ring climate responses、Fire effects on ecosystems

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 CO 2 exchange (NEE), net carbon uptake period (CUP net ) and their drivers were investigated, using 26 years of flux measurements in a subalpine spruce forest (CH‐Dav, Switzerland; 1997 to 2022). CUP net 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 CUP net . Annual mean and maximum air temperatures (T air ) 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 CUP net length, SOS, and EOS. No significant trends in CUP net , 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 T air were the main drivers of daily NEE. SOS was mainly driven by daylength and T air , EOS by daylength and Rg. Thus...