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.