Plant community richness and microbial interactions structure bacterial communities in soil.

Plant species, plant community diversity and microbial interactions can significantly impact soil microbial communities, yet there are few data on the interactive effects of plant species and plant community diversity on soil bacterial communities. We hypothesized that plant species and plant community diversity affect soil bacterial communities by setting the context in which bacterial interactions occur. Specifically, we examined soil bacterial community composition and diversity in relation to plant "host" species, plant community richness, bacterial antagonists, and soil edaphic characteristics. Soil bacterial communities associated with four different prairie plant species (Andropogon gerardii, Schizachyrium scoparium, Lespedeza capitata, and' Lupinus perennis) grown in plant communities of increasing species richness (1, 4, 8, and 16 species) were sequenced. Additionally, soils were evaluated for populations of antagonistic bacteria and edaphic characteristics. Plant species effects on soil bacterial community composition were small and depended on plant community richness. In contrast, increasing plant community richness significantly altered soil bacterial community composition and was negatively correlated with bacterial diversity. Concentrations of soil carbon, organic matter, nitrogen, phosphorus, and potassium were similarly negatively correlated with bacterial diversity, whereas the proportion of antagonistic bacteria was positively correlated with soil bacterial diversity. Results suggest that plant species influences on soil bacterial communities depend on plant community diversity and are mediated through the effects of plant-derived resources on antagonistic soil microbes.