Data from: Soil microbes alter plant fitness under competition and drought

Plants exist across varying biotic and abiotic environments, including
variation in the composition of soil microbial communities. The ecological
effects of soil microbes on plant communities are well known, whereas less
is known about their importance for plant evolutionary processes. In
particular, the net effects of soil microbes on plant fitness may vary
across environmental contexts and among plant genotypes, setting the stage
for microbially mediated plant evolution. Here we assess the effects of
soil microbes on plant fitness and natural selection on flowering time in
different environments. We performed two experiments in which we grew
Arabidopsis thaliana genotypes replicated in either live or sterilized
soil microbial treatments, and across varying levels of either competition
(isolation, intraspecific competition, or interspecific competition) or
watering (well-watered or drought). We found large effects of competition
and watering on plant fitness as well as the expression and natural
selection of flowering time. Soil microbes increased average plant fitness
under interspecific competition and drought, and shaped the response of
individual plant genotypes to drought. Finally, plant tolerance to either
competition or drought was uncorrelated between soil microbial treatments
suggesting that the plant traits favoured under environmental stress may
depend on the presence of soil microbes. In summary, our experiments
demonstrate that soil microbes can have large effects on plant fitness,
which depend on both the environment and individual plant genotype. Future
work in natural systems is needed for a complete understanding of the
evolutionary importance of interactions between plants and soil
microorganisms.