Water‐Stressed Canopy Stomatal Behaviors Across Environmental Gradients and Ecosystems Within an Inland River Basin

Stomatal behavior plays a critical role in determining the vegetation water‐carbon cycles under climate change. While research on the response of leaf stomata to environmental stresses has become increasingly prevalent, understanding of the variability of stomatal behavior in climate‐sensitive and ecologically fragile regions remains limited. We selected typical ecosystems of the inland Heihe River Basin in China, compiled data on water‐carbon fluxes, meteorological factors, and soil water content across ecosystems and environmental gradients, quantified thresholds of atmospheric (AS), soil (SS), and compound water stresses (CS) that suppress ecosystem evapotranspiration, then estimated the canopy stomatal conductance ( G c ) by eliminating non‐vegetation information from the surface conductance, finally analyzed differences in water‐stressed G c and quantified the sensitivity of G c to environmental and biological factors using the machine learning approach. We found that water stress thresholds varied along with environmental conditions, and these thresholds were correlated with stomatal parameters in the Medlyn equation ( R 2 ≥ 0.30). The mean G c was minimal under CS, and the mean G c under AS was lower than that under SS. The sensitivity of G c to influencing factors under SS was greater than under other water stresses, and the effects of soil water on G c were uniquely negative in riparian ecosystems. By emphasizing the complexity and variability of canopy stomatal behaviors under water stresses within the basin, our study advances the understanding of plant physiological responses to environmental stresses and informs the enhancement of stomatal conductance parameterizations in Earth system models.