Inoculation with old-growth microbes improves restoration quality and reduces non-native encroachment after seven...

Understanding the mechanisms that promote native seedling establishment in disturbed ecosystems is key to improving the biodiversity and function of landscape restorations. Over seven growing seasons, we examined the effects of site preparation technique, soil microbial inoculations, and their interactions on native plant establishment in the restoration of an invaded grassland. Prior to restoration, field plots were either (a) solarized to clear the non-native grass Bromus inermis or (b) mowed, and one of three soil microbial treatments was introduced into each plot using native tallgrass prairie seedlings as "nurse" plants, inoculated with (1) arbuscular mycorrhizal (AM) fungi isolated from old-growth prairie remnants, (2) remnant prairie soil, or (3) autoclaved inocula. Uninoculated phytometer seedlings were planted at different distances from the nurse plant row to test for plant-soil feedbacks and spread of microbes into the restoration site. A diverse native seed mix was applied to test whether site preparation technique and/or microbial inoculations impacted the composition of the plant community. We found that site preparation technique and microbial inoculation were strong drivers of plant community composition, and saw evidence of plant-soil feedbacks in the first year of the study. By the seventh growing season, there was greater cover of late successional native plant species and increased floristic quality index scores in solarized plots and inoculated plots compared to mowed and uninoculated plots. Overseeding without solarization was mostly effective for establishing native grasses, which comprised 66% of plot abundance after three overseeding attempts. By considering belowground communities at the same time as revegetation efforts, this study demonstrates how soil microbial inoculations can be used in conjunction with site preparation technique as a nature-based tool to accelerate the recovery of invaded grasslands.