Data from: Mimicking a rainfall gradient to test the role of soil microbiota for mediating plant species responses to drier conditions

Plant interactions with soil microbiota are important drivers of
biodiversity and ecosystem function, but climate change can modify these
interactions by directly altering the soil community, which can affect the
direction and magnitude of such interactions. We manipulated water
quantity and soil microbiota of two populations of three plant species
that differ in their interactions with soil microbiota and assessed
germination and biomass production under conditions that mimicked a
rainfall gradient in SE Spain. We assessed the importance of soil
microbiota from home and away (drier) sites for alleviating or
exacerbating the effects of drier conditions. Our results suggest that
home soil microbiota enhanced germination of the legume Trifolium
stellatum. Conversely, we found that the grass, Lagurus ovatus, and the
forb, Sisymbrium erysimoides, produced more biomass under moderate drying
with soil microbiota from a drier site than with home soil microbiota,
suggesting that dry-adapted soil microbiota alleviated the negative
effects of drier conditions for these species. This maintenance of
productivity with dry-adapted soil microbiota under drier conditions was
found despite simultaneous reductions in leaf dry matter content and
root-to-shoot ratio that would typically be less optimal trait responses
under reduced water availability. Severe water limitation resulted in
decreased plant biomass regardless of the plant species and soil inoculum,
indicating a threshold effect whereby severe water limitation on growth
supersedes the beneficial effects of soil microbiota. Overall, our results
show that species identity, the severity of water limitation and soil
microbiota interact to determine the response of plants to drier
conditions.