Seven years later: native AMF inoculation improves grassland successional stage, floristic quality index, and diversity, while suppressing weeds.

Abstract

Reintroducing key soil microbes, such as arbuscular mycorrhizal (AM) fungi, can enhance prairie restoration, but the long-term persistence of these effects is unclear. In 2017, a tallgrass prairie restoration experiment was established that applied an inoculation gradient of native AM fungal inoculant ranging from 0 to 8192 kg/ha. Here, we sample the resulting prairie community establishment and spread seven growing seasons later (72 months). We found that AM fungal application increased total diversity, floristic quality index, and average coefficient of conservatism scores-metrics that assess an area's ecological integrity based on plant species. Moreover, high application densities of native AM fungi reduced non-native plant abundance. Furthermore, inoculated prairie plots were more likely to extend 1.5 m into adjacent nonseeded old-field plots, enhancing native diversity and reducing invasion in marginal lands. These findings highlight the lasting benefits of native AM fungal inoculation in prairie restoration and their potential to facilitate long-term ecosystem recovery, aligning with global biodiversity conservation efforts such as the UN Sustainable Development Goal 15 (Life on Land). Given that land managers spend ~25% of their time and considerable economic input managing invasive species, these findings demonstrate that the reintroducing native AM fungi from reference ecosystems during grassland restoration could provide a cost-effective means of enhancing ecological outcomes.