The relationship between species richness and community stability to invasion changes under drought stress

While plant diversity enhances community stability against invasions, its interplay with environmental stressors remains unclear. We tested how drought modulates diversity-stability relationships by establishing 300 experimental plots across a richness gradient (1-16 species), introducing invader Symphyotrichum subulatum to half, and applying three drought treatments (none, moderate and extreme). Results revealed a drought-dependent shift: species richness stabilized communities under no drought by intensifying light competition (via selection effects of Patrinia scabiosaefolia/Artemisia migoana), but this effect disappeared under drought stress. Instead, reduced root-shoot-ratio (RSR) emerged as the key driver of stability under drought stress, which was unaffected by species richness. The divergent roles of species richness in mediating light competition (no drought) versus RSR (drought stress) explain this context-dependent stability pattern. These findings provide crucial insights for predicting and managing invasion dynamics in the context of increasing drought extremes.