Effects of ecological and environmental factors on water use efficiency of major terrestrial ecosystem in China

Study region China, based on eddy covariance (EC) measurements from 52 flux sites (176 site-years) covering forest, grassland, and cropland ecosystems. Study focus This study investigates spatial variation in annual water use efficiency ( WUE ) – a key indicator of carbon-water interactions – across Chinese terrestrial ecosystems, previously unanalyzed using EC data. We assessed the distribution of WUE and its responses to physiological, climatic (temperature, precipitation), soil-atmospheric (soil water content, vapor pressure deficit, soil drought stress index), and ecosystem drivers (leaf area index), with emphasis on differences among forest, grassland, and cropland. New hydrological insights for the region Growing season WUE averaged 1.67 ± 0.55 g C kg⁻¹ H₂O across all site-years. Forests exhibited significantly higher WUE (2.13 ± 0.26 g C kg⁻¹ H₂O) compared to croplands (1.61 ± 0.39 g C kg⁻¹ H₂O) and grasslands (1.56 ± 0.47 g C kg⁻¹ H₂O). WUE responded positively to increases in temperature, precipitation, and soil water content, both directly and indirectly via enhanced leaf area index; forests showed the lowest sensitivity. Threshold annual soil drought stress index ( DSI ) values of 0.38 (forest), 0.45 (grassland), and 0.52 (cropland) differentiated wet and drought conditions. Ecosystem carbon-water coupling is primarily governed by surface conductance ( Gs ). These findings reveal fundamental spatial patterns of WUE and provide a novel approach for regional carbon budget assessments.