Evapotranspiration (ET) returns over 65% of the precipitation in terrestrial ecosystems to the atmosphere, playing an essential role in global water and energy cycles. The shortage of decades-long continuous measurements of ecosystem processes limits our understanding of how changing climate impacts forest ecosystems. Research team of Professor Zha Tianshan from School of Soil and Water Conservation of BFU used continuous eddy-covariance and hydrometeorological data over 2002–2022 from a young Douglas-fir (Pseudotsugamenziesii var. menziesii [Mirb.]), one of the most important and productive temperate timber tree species in western North America, storing more C than other major forested ecosystems in the biome, to assess the long-term trend and interannual variability in evapotranspiration (ET) and transpiration (T). Collectively, annual T displayed a decreasing trend over the 21 years with a rate of 1% yr−1, which is attributed to the stomatal downregulation induced by rising atmospheric CO2 concentration. Similarly, annual ET also showed a decreasing trend since evaporation stayed relatively constant. Variability in detrended annual ET was mostly controlled by the average soil water storage during the growing season (May–October). Though the duration and intensity of the drought did not increase, the drought-induced decreases in T and ET showed an increasing trend. This pattern may reflect the changes in forest structure, related to the decline in the deciduous understory cover during the stand development. These results suggest that the water-saving effect of stomatal regulation and water-related factors mostly determined the trend and variability in ET, respectively. This may also imply an increase in the limitation of water availability on ET in young forests, associated with the structural and compositional changes related to forest growth.

The research results entitled "Long-term trend and interannual variation in evapotranspiration of a young temperate Douglas-fir stand over 2002–2022 reveals the impacts of climate change" were recently published in Plant, Cell & Environment, a prestigious international journal in botany. Dr. Li Xinhao from the School of Soil and Water Conservation serves as the first author, and Professor Zha Tianshan is the corresponding author.

This work was supported by the National Key Research and Development Program of China (2020YFA0608100), the National Natural Science Foundation of China (NSFC: 32101588, 32071842, 32071843, 31901366), funding for Fluxnet Canada (Natural Sciences, Engineering Research Council of Canada [NSERC], BIOCAP Canada Foundation, and the Canadian Foundation for Climate and Atmospheric Sciences [CFCAS]), an NSERC DiscoveryGrant (TAB) of the Natural Sciences, Engineering Research Council of Canada (NSERC), and a China Scholarship Council (No. 202206510021).

Paper link: http://doi.org/10.1111/pce.15000

Written by Li Xinhao and Liu Peng
Translated and edited by Song He
Reviewed by Yu Yangyang