Can Commercial Soil Microbial Treatments Remediate Plant–soil Feedbacks to Improve Restoration Seedling Performance?

Seedling performance is often a limiting factor in ecological restoration. Changes in the soil microbial community generated by invasive plants contribute to seedling failure. A method to remediate invasive species-induced changes to the soil microbial community that results in increased native species seedling performance and decreased invasive species seedling performance could have a large impact on the success of many restoration efforts. In a greenhouse experiment, we first examined the changes in the soil microbial community created by invasive compared to native grasses. Then, we investigated four microbial treatments (bacterial inoculant, fungal inoculant, fungicide, and bactericide/fungicide) to remediate microbial plant–soil feedbacks (PSFs) created by invasive species Bromus inermis and Poa pratensis and increase the performance of natives Andropogon gerardii, Elymus canadensis, Pascopyrum smithii, and Schizachyrium scoparium. We found that the PSF mitigation treatments had some context-dependent utility for restoration. For example, all of the treatments decreased the performance of B. inermis and fungal inoculant decreased the performance of P. pratensis. However, no single treatment increased the performance of all natives. Fungicide increased the performance of A. gerardii and E. canadensis in soil previously occupied by B. inermis and the performance of S. scoparium in soil previously occupied by P. pratensis. If validated in the field, PSF mitigation treatments may have utility for restoration practitioners