Plant-microbe interactions can be important drivers of plant community dynamics. It is unclear, however, as to how these interactions change in response to abiotic environmental drivers and how plant-microbe interactions influence plant evolution. Here we manipulated the structure of the belowground microbial community and the soil moisture environment to replicated populations of Brassica rapa to investigate how the biotic and abiotic soil environments independently and interactively influence plant phenotypes and patterns of natural selection on plant traits.  

Results/Conclusions

Microbial community structure influenced plant phenotypes and patterns of natural selection on plant growth and phenological traits.  In soils with experimentally simplified microbial communities, plants were smaller, had reduced chlorophyll content, produced fewer flowers, and were less fecund when compared to complex soil community, whereas selection on plant traits was stronger when plants were grown in simplified, less diverse soil microbial community.  In contrast, the soil moisture treatments had relatively weak effects on plant phenotypes and little impact on patterns of natural selection, despite having strong effects on soil microbial structure. Together, our results suggest that belowground microbial diversity may be a strong agent of natural selection and that microbial diversity may be a key factor influencing plant evolution, just as recent studies have demonstrated that microbial diversity plays key roles influencing plant community diversity, productivity, and ecosystem functions.