PS 34-253 - Bacterial communities associated with a vulnerable plant species (Baptisia lactea) in four Michigan conservation areas.

Abstract: Restoring former agricultural systems, old fields and marginal lands to native prairie habitat is a valuable way for land managers to improve plant and pollinator diversity and increase soil C storage. Intriguingly, late-successional plants, with deep and complex root structures, may be important keys to achieving long-term soil C accumulation in restored prairies. Yet many late successional plants are threatened due to habitat loss and also struggle to establish in new restorations in reclaimed systems. This is at least partly because important microbial symbionts either do not exist in the soil, or are in low abundance, due to legacy effects of past land use resulting in permanent changes to soil microbial community composition. Much can be learned about promoting the successful restoration of late-successional species by examining rhizosphere microbial communities that associate with healthy populations. In this study, we focused on the late-successional legume Baptisia lactea (white or prairie false indigo); in the state of Michigan, B. lactea is a species of Special Concern, and it is ranked as Vulnerable (S3). We located four sites in southwest Michigan with thriving populations of B. lactea. We collected soil samples along three transects per site to characterize site-level environmental variables and bacterial communities, and also analyzed soils from the rhizospheres of five B. lactea plants per site. Given the likelihood that bacterial communities would vary site-to-site, we hypothesized that: H1) B. lactea rhizosphere communities would converge across all sites, demonstrating that B. lactea provides a strong habitat filter and selects for the same rhizosphere symbionts and accompanying consortia no matter where it is located; or H2) B. lactea rhizosphere communities would converge only within site, but that both symbionts and accompanying bacterial consortia would differ from site to site. Our results provide evidence for both hypotheses. Among our sites were three restored prairies and one remnant. When examining B. lactea rhizosphere communities in the restored prairies only, there is convergence across sites, in support of the first hypothesis. However, when B. lactea rhizosphere communities from the remnant are included in this analysis, they do not converge with those collected from the restorations, providing support for hypothesis 2. Regardless of the community composition, in all sites there is strong evidence of higher soil organic matter content and higher nitrate levels in B. lactea rhizosphere soils than in reference soils, suggesting that this species could disproportionately contribute to accumulation of organic matter.