DISCUSSION
We experimentally assessed the effects of high and low aridity soil
legacies on the growth of the keystone grass species, Themeda
triandra , under drought conditions. We show that microbiota from high
aridity soils supported increased growth of this grass species under
both drought-like, water stress and control treatments, highlighting the
powerful impact of soil legacies and supporting our first hypothesis. We
also show that bacterial alpha diversity was positively correlated withT. triandra biomass, and that each of our treatments (i.e., soil
aridity, sterilisation, and water stress) led to distinct bacterial
assemblages in soils, rhizospheres and endospheres. This supports our
second hypothesis by highlighting the conditional relationships thatT. triandra forms with its bacterial communities that is
dependent on its environment. Finally, we did not see meaningful
differences across the bacterial communities of our soil-only versus
plant-present pots, which goes against the expectations of our third
hypothesis. Our findings highlight the importance of soil microbiota for
host plant growth and fitness under climate change. Our study
underscores the importance of protecting diverse soil communities to
support grassland health, and highlights the potential of harnessing
these communities to increase grassland restoration that is more
resilient to climate change.