Divergent mechanisms governing aboveground biomass in desert plants across a drought gradient

How plant traits and soil factors jointly regulate aboveground biomass (AGB) along soil moisture gradients is central to arid-land ecology. Along a soil moisture transect in China's Kalamaili Nature Reserve, we integrated soil properties with trait-based community metrics to identify the drivers of AGB. AGB was regulated by soil water content (SWC) through both direct effects and indirect nitrogen-mediated pathways, whereby higher total nitrogen increased community-weighted maximum height. The AGB-SWC relationship was strongly nonlinear, with a clear threshold near 28% SWC: responses were weak below this point but increased sharply above it. Driver importance shifted with aridity, as the positive effect of plant height weakened under extreme drought, and its interaction with SWC shifted from synergistic in dry conditions to antagonistic in wetter conditions. These results reveal soil moisture thresholds and context-dependent trait-resource coupling that inform predictions and management of productivity in arid ecosystems.