Divergent impacts of VPD and SWC on ecosystem carbon-water coupling under different dryness conditions

Chen Zheng; Shaoqiang Wang; Jinghua Chen; Ning Xiang; Leigang Sun; Bin Chen; Zheng Fu; Kai Zhu; Xinlei He

doi:10.1016/j.scitotenv.2023.167007

Divergent impacts of VPD and SWC on ecosystem carbon-water coupling under different dryness conditions

Sci Total Environ. 2023 Dec 20:905:167007. doi: 10.1016/j.scitotenv.2023.167007. Epub 2023 Sep 20.

Authors

Chen Zheng¹, Shaoqiang Wang², Jinghua Chen¹, Ning Xiang³, Leigang Sun⁴, Bin Chen¹, Zheng Fu⁵, Kai Zhu¹, Xinlei He⁶

Affiliations

¹ 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.
² 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. Electronic address: sqwang@igsnrr.ac.cn.
³ College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China.
⁴ Institute of Geographical Sciences, Hebei Academy of Sciences, Shijiazhuang 050011, China; Hebei Technology Innovation Center for Geographic Information Application, Shijiazhuang 050011, China. Electronic address: sunleigang3s@163.com.
⁵ Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay, 91191 Gif-sur-Yvette, France.
⁶ State Key Laboratory of Earth Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China.

PMID: 37739082
DOI: 10.1016/j.scitotenv.2023.167007

Abstract

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.

Keywords: Arid sites; Humid sites; Sensitivity of WUE to SWC; Sensitivity of WUE to VPD.