Native Plant Diversity Generates Microbial Legacies That Either Promote or Suppress Non‐Natives, Depending on Drought History

Diverse native plant communities resist non‐native plants more than species‐poor communities, in part through resource competition. The role of soil biota in diversity–invasibility relationships is poorly understood, although non‐native plants interact with soil biota during invasions. We tested the responses of non‐native plants to soil biota generated by different native plant diversities. We applied well‐watered and drought treatments in both conditioning and response phases to explore the effects of ‘historical’ and ‘contemporary’ environmental stresses. When generated in well‐watered soils, the microbial legacies from higher native diversity inhibited non‐native growth in well‐watered conditions. In contrast, when generated in drought‐treated soils, the microbial legacies from higher native diversity facilitated non‐native growth in well‐watered conditions. Contemporary drought eliminated microbial legacy effects on non‐native growth. We provide a new understanding of mechanisms behind diversity–invasibility relationships and demonstrate that temporal variation in environmental stress shapes relationships among native plant diversity, soil biota and non‐native plants.