Zheng Chen, Wang Shaoqiang, Chen Jinghua, Xiang Ning, Sun Leigang, Chen Bin, Fu Zheng, Zhu Kai, He Xinlei
Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Beijing 100101, China; College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China.
Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Beijing 100101, China; College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China; Key Laboratory of Regional Ecological Process and Environment Evolution, School of Geography and Information Engineering, Chinese University of Geosciences, Wuhan 430074, China.
Sci Total Environ. 2023 Dec 20;905:167007. doi: 10.1016/j.scitotenv.2023.167007. Epub 2023 Sep 20.
Ecosystem water use efficiency (WUE) is an indicator of carbon-water interactions and is defined as the ratio of gross primary productivity (GPP) to evapotranspiration (ET). However, it is currently unclear how WUE responds to atmospheric and soil drought events in terrestrial ecosystems with different dryness conditions. Additionally, the contributions of GPP and ET to the WUE response remain poorly understood. Based on measurements from 26 flux tower sites distributed worldwide, the binning method and random forest model were employed to separate the sensitivities of daily ecosystem WUE, GPP, and ET to vapor pressure deficit (VPD) and soil water content (SWC) under different dryness conditions (dryness index = potential evapotranspiration/precipitation, DI). Results showed that the sensitivity of WUE to VPD was negative at humid sites (DI < 1), while the sensitivity of WUE to SWC was positive at arid sites (DI > 2). Furthermore, the contribution of GPP to VPD-induced WUE variability was 63 % at humid sites, and the contribution of ET to SWC-induced WUE variability was 68 % when SWC was less than the 60th percentile at arid sites. Consequently, one increasing VPD-induced decrease in GPP was generally linked to a decrease in WUE at humid sites, and one drying soil moisture-caused decrease in ET was linked to a WUE increase under low SWC conditions at arid sites. Finally, VPD had a stronger effect on WUE than SWC when VPD was less than the 90th percentile or SWC was greater than the 50th percentile. Our findings underscore the importance of considering ecosystem dryness when investigating the impacts of VPD and SWC on ecosystem carbon-water coupling.
生态系统水分利用效率（WUE）是碳-水相互作用的一个指标，定义为总初级生产力（GPP）与蒸散量（ET）的比值。然而，目前尚不清楚在不同干旱条件的陆地生态系统中，WUE如何响应大气和土壤干旱事件。此外，GPP和ET对WUE响应的贡献仍知之甚少。基于全球分布的26个通量塔站点的测量数据，采用分箱法和随机森林模型，在不同干旱条件下（干旱指数=潜在蒸散量/降水量，DI），分离每日生态系统WUE、GPP和ET对水汽压亏缺（VPD）和土壤含水量（SWC）的敏感性。结果表明，在湿润站点（DI<1），WUE对VPD的敏感性为负，而在干旱站点（DI>2），WUE对SWC的敏感性为正。此外，在湿润站点，GPP对VPD引起的WUE变化的贡献为63%，在干旱站点，当SWC小于第60百分位数时，ET对SWC引起的WUE变化的贡献为68%。因此，在湿润站点，VPD增加导致的GPP下降通常与WUE下降相关，在干旱站点，土壤水分干燥导致的ET下降与低SWC条件下的WUE增加相关。最后，当VPD小于第90百分位数或SWC大于第50百分位数时，VPD对WUE的影响比SWC更强。我们的研究结果强调了在研究VPD和SWC对生态系统碳-水耦合的影响时考虑生态系统干旱程度的重要性。
