Aridity thresholds Reveal transitions in dominant drivers of partitioned Water–Carbon coupling across Central Asian drylands

• Aridity thresholds mark nonlinear shifts in dryland carbon–water coupling. • WUE and WUEc rebound under high aridity, indicating stress-tightened coupling. • Dominant controls shift from vegetation traits to hydroclimatic stressors. • Post-threshold, temperature is positive but VPD negative for WUE and WUEc.