Ecosystem water use efficiency and carbon use efficiency respond oppositely to vegetation greening in China's Loess Plateau

Yue Wang; Guangyao Gao; Yanzhang Huang; Zhuangzhuang Wang; Bojie Fu

doi:10.1016/j.scitotenv.2025.178575

Ecosystem water use efficiency and carbon use efficiency respond oppositely to vegetation greening in China's Loess Plateau

Sci Total Environ. 2025 Jan 22:964:178575. doi: 10.1016/j.scitotenv.2025.178575. Online ahead of print.

Authors

Yue Wang¹, Guangyao Gao², Yanzhang Huang¹, Zhuangzhuang Wang¹, Bojie Fu³

Affiliations

¹ State Key Laboratory for Ecological Security of Regions and Cities, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China.
² State Key Laboratory for Ecological Security of Regions and Cities, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China; Shaanxi Yan'an Forest Ecosystem Observation and Research Station, Beijing 100085, China; National Observation and Research Station of Earth Critical Zone on the Loess Plateau in Shaanxi, Xi'an 710061, China. Electronic address: gygao@rcees.ac.cn.
³ State Key Laboratory for Ecological Security of Regions and Cities, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China; Shaanxi Yan'an Forest Ecosystem Observation and Research Station, Beijing 100085, China; National Observation and Research Station of Earth Critical Zone on the Loess Plateau in Shaanxi, Xi'an 710061, China.

PMID: 39848146
DOI: 10.1016/j.scitotenv.2025.178575

Abstract

Ecosystem water use efficiency (WUE) and carbon use efficiency (CUE) are critical parameters to determine the trade-off between water consumption and carbon sequestration in drylands. However, the roles of vegetation cover, climate factors and soil moisture in affecting the coupling of WUE and CUE were still poorly understood. This study combined the spatial random forest model and structural equation model to detect the drivers of WUE and CUE variations in China's Loess Plateau during 2001-2020, a typical water-limited region with about 87 % of area experiencing significant vegetation greening. The WUE increased significantly (P < 0.05) in 92.7 % of the greening area (0.024 ± 0.020 gC kg^-1H₂O yr^-1), and CUE decreased (-0.0011 ± 0.0011 yr^-1) and increased (0.0010 ± 0.0012 yr^-1) slightly in half and half of the greening area. The vegetation greening trend was a dominant factor positively influencing the variation of WUE (with 42.0 % explanation), whereas CUE exhibited a negative response to the greening trend (with 25.0 % explanation). However, the regions with dense vegetation cover (NDVI >0.5) were unfavourable for the increase of WUE but favourable for the increase of CUE. Vegetation greening exerted effect on WUE mainly via the path of gross primary productivity and ratio of transpiration to evapotranspiration (path coefficient: 0.83), whereas it had direct effect on CUE (path coefficient: 0.48). An increase in VPD facilitated the enhancement of both WUE and CUE. There was an optimal annual precipitation range (400-600 mm) that maximized WUE enhancement, and annual temperature (∼10 °C) optimized CUE increase. The findings indicate that despite the improvement in WUE, the vegetation greening may not necessarily enhance carbon sequestration potential in drylands. This study enhances the knowledge of the interaction between vegetation dynamics and water‑carbon coupling in drylands, contributing to ecological restoration practices and sustainable ecosystem management.

Keywords: Carbon use efficiency; Curvilinear response; Drylands; Ecosystem water use efficiency; Vegetation greening; Water‑carbon coupling.