Microbial communities are shaped by the environment and broader community in which they are a part. The relationship between plant communities and soil bacteria and fungi remains incompletely understood. This study uses a multi-scale approach to examine the relationship between two dominant perennial plants and the microbial communities in the soil nearby. These two perennial plants, the shrub P. glandulosa and the grass B. eriopoda are known to compete, and changes over the past century have dramatically shifted their relative cover and competitive dynamics – today, P. glandulosa has much higher cover, whereas B. eriopoda is in decline. Through an observational approach, the bacterial community was found to be more strongly associated with the cover and growth of the perennial grass B. eriopoda, though both the fungal and bacterial communities are shaped by the primary producers of this ecosystem. Between sites, dispersal limitation likely impacted observed differences, though these differences were also likely shaped by an underlying abiotic gradient. Overall, this study highlights the complex abiotic and biotic drivers of microbial community composition and shows how subtle differences in the abiotic environment can affect the entire ecosystem and lead to distinct ecological responses to change.