PS 34-239 - How does the inoculation of locally adapted strains of species-specific rhizobia promote the growth of rare legumes across the Midwest?

Abstract: Legacy effects induced by anthropogenic change have displaced soil microbial communities over time. The absence of these soil microbes, despite restoration efforts, may explain why late-successional herbaceous species are commonly missing from prairie restorations. Rhizobia bacteria, for example, are a group of soil microbes that form mutualistic relationships with leguminous plant species. I am interested in whether the dependence legumes have on this relationship varies across geographic locations and species. To investigate this, I established a species-specific rhizobia inoculation experiment including a total of five plant species across four states in the Midwest. Seeds of each plant species and their rhizobia partners were sourced from the same provenance to retain their local genotypic relationship. Each plant species was then germinated and grown for 13 weeks in sterile soil until three days prior to field transplantation when they were either left as control or inoculated with their respective rhizobia treatments. Transplantation of each plant species at each site occurred throughout June of 2022. Year one measurements of stem height were taken in September 2022 and survival measurements will be collected in June 2023. After one growing season, I found a variation in response of each plant species at each site to rhizobia inoculation. Dalea purpurea at the Michigan sites and Lespedeza capitata at the Ohio site, for example, exhibited a strong positive response to inoculation. In contrast, rhizobia appeared to reduce growth of Dalea purpurea at the Indiana sites. We will continue to monitor the growth and survival of our plants during 2023. We found that reintroducing legumes along with their rhizobia symbionts can improve the establishment of rare legumes under some conditions. However, at other sites, inoculation with rhizobia reduced legume growth, indicating that the context dependency of mutualisms can determine the success of rare species reintroductions within restorations.