Understanding the mechanisms that enable and promote native seedling establishment in disturbed ecosystems is key to improving the biodiversity and function of landscape restorations. In a field experiment, we examined the efficacy of utilizing arbuscular mycorrhizal fungi (AMF), a key soil microbial functional group, to improve native prairie plant survival and growth in smooth brome (Bromus inermis) dominated grasslands. Inoculated nurse plants were used to re-establish key functional groups of soil microbes in the field site. Nurse plants (Echinacea pallida, Schizachyrium scoparium, Asclepias tuberosa, and Lespedeza capitata) were inoculated with AMF isolated from a nearby remnant prairie, whole soil from a remnant prairie, or autoclaved soil/AMF mix to test the hypothesis that inoculum from prairie remnants will improve native seedling establishment in B. inermis-dominated grasslands. The field site was also seeded with a diverse native prairie seed mix to test the effect of soil microbial treatment on plant community diversity. Over the course of a growing season, data were collected on native plant survival, growth, and plant community diversity in each plot. Differences in treatment effects between plots were used to determine whether there was an additional benefit of using whole prairie soil inocula versus AMF alone.
Native prairie plant survival and growth was higher in plots inoculated with AMF or whole soil from remnant prairies. Four months after planting, seedlings inoculated with whole prairie soil or AMF had survival rates of 70% and 65% respectively, whereas only 50% of the uninoculated seedlings survived. Plants inoculated with whole prairie soil or AMF were also more than 10% larger than uninoculated seedlings. Species richness of native plants was higher in field plots inoculated with native soil microbes compared to the uninoculated controls, with an average of 17 native plant species in plots inoculated with whole prairie soil, 12 native plant species in plots inoculated with native AMF isolated from remnant prairies, versus 10 native plant species in uninoculated plots. Taken together, this study shows that inoculation with native soil microbes is critical for the survival and growth of native prairie plants in grasslands where the microbial community has been disrupted. In addition to informing restoration management strategies, this study will improve our understanding of the different factors that regulate diversity in plant communities, linking microbial diversity to ecosystem function.