Plants and soil microbes are linked through biotic interactions, but they may also respond to common environmental drivers. Understanding how plant and microbial communities respond to each other and to environmental gradients can contribute to understanding patterns of beta diversity above and belowground. In this study we investigated the relationships between plant and microbial communities, as well as environmental variables across a gradient of vegetation communities: open hill prairie habitat, the woody encroached edges, and the surrounding woodlands. We collected plant species composition and cover of all rooted vascular plants using a modified Daubenmore cover-class scale and did Illumina sequencing for microbial community composition. We also measured environmental variables such as light, distance between plots, and soil edaphic factors. We ran Generalized Dissimilarity Models (GDM) for plant and microbial community response to each other’s communities and all environmental variables.
Based on our GDM, turnover in the soil bacterial community was the strongest driver of plant community beta diversity. However, plants also responded to changes in the fungal community and abiotic factors such as moisture, elevation, light availability, nitrate, and pH. Bacterial and fungal community turnover was driven almost exclusively by pH and ammonium gradients, with plant species composition having little to no impact on changing the microbial communities. Despite this, microbial community composition was broadly different between prairie habitats, shrub-encroached borders, and woodland. Additionally, neither plant nor microbial communities showed evidence of strong autocorrelation when sampled at the scale of our study. Our results suggest that relationships with soil bacteria can be just as important as environmental drivers in determining plant species turnover. However, soil bacterial communities do not respond to plant species composition per se, but they are instead influenced by general habitat characteristics along the grassland to woodland gradient.