Plant diversity has been studied extensively for its impact on a few basic measures, such as biomass production. However, relatively little is understood about interactions between plant diversity and microbial communities. Through removal of natural enemies with pesticide treatments, we found that foliar fungi have a significant impact on plant productivity, and that the impact is greater at higher than at lower plant diversity. We also compared soil bacterial communities associated with Andropogon gerardii (Ag) and Lespedeza capitata (Lc), and focused intensively on streptomycete communities associated with Ag, Schizachyrium scoparium, Lc, and Lupinus perennis from plant assemblages at each of five different diversity levels (monoculture, 4 spp., 8 spp., 16 spp., or 32 spp.). Pyrosequencing of the 16S rDNA gene from soil community DNA revealed significant differences between bacterial communities in the rhizosphere of Ag and Lc. Preliminary analyses also suggest that the frequency and intensity of pathogen inhibitory activity by soil microbes varies among plant species and as a function of plant community diversity. Further work will address streptomycete community diversity and composition by pyrosequencing and will assess disease pressure in home and away soils for each plant and diversity level. Finally, we characterized the inhibitory interactions within and among soil streptomycete communities. Antibiotics are important to species interactions, as evidenced by local selection for antibiotic resistance and intensity of inhibition. However, niche differentiation may represent an alternative to an antibiotic arms race. Plant-microbe and microbial interactions have significant impacts on the evolutionary trajectory of microbial communities, and microbes in turn may have strong impacts on plant productivity and community dynamics.