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

Although plant diversity is known to enhance community stability to biological invasions, its interaction with environmental stressors remains poorly understood. We examined how drought stress affects the stability of native communities with different levels of plant diversity to invasion, by establishing experimental plant communities (300 plots) across a species richness gradient (1, 2, 4, 8 and 16 species), introducing the invasive herb Symphyotrichum subulatum to half of the communities, and applying three drought treatments (no, moderate and extreme drought). Results showed that a drought‐dependent shift in community stability to invasion (quantified as the aboveground biomass change ratio between invaded and uninvaded communities): the positive richness–stability relationship observed under control moisture conditions became nonsignificant under drought stress. Plant diversity enhanced community stability under control moisture conditions by intensifying light competition (light interception efficiency) through selection effects (the presence of Patrinia scabiosaefolia and/or Artemisia migoana ). Under drought stress, however, the change in the root–shoot‐ratio (RSR) negatively influenced community stability. The effect of this change on stability was not significantly modulated by species richness. Different influences of species richness on light competition and the change of RSR explain the drought context‐dependent role of species richness in stability. These findings provide crucial insights for predicting and managing invasion dynamics in the context of increasing drought extremes.