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.