Diversity of arbuscular mycorrhizal fungi in native prairie, agricultural, and prairie restoration sites in northwestern Minnesota
Predicting the capacity for different land uses to maintain diversity of belowground organisms requires an understanding of how changes in land use affect these belowground communities. Relatively few studies have been conducted to examine how conversion of prairie to agriculture alters the community of arbuscular mycorrhizal (AM) fungi, despite the importance of these fungi for plant host establishment and community composition; fewer have documented how the AM fungal community changes in response to prairie restoration. To gain an understanding of the differences in AM fungal communities across land uses, we have initiated a long-term study comparing community composition of AM fungi in native prairie, current and abandoned agricultural sites, and recently restored prairie in northwestern Minnesota. In addition to differing in plant diversity, these sites also show considerable variation in nutrient availability and the relative abundances of grasses and forbs. To complement our field study, we are also assessing germination, seedling growth and competitive ability of common native and exotic plant species in the greenhouse in soils with and without AM fungi.
Our first two years of sampling soil nutrient availability and species richness of plants and AM fungal spores suggest that sites with an agricultural legacy exhibit reduced richness of AM fungal spores relative to native prairie. AM fungal spore richness was positively correlated with grass species richness and negatively correlated with available phosphorus. Presence of AM fungi early in a plant’s life seems to have little effect on seedling success for exotic and some native plant species, but strong positive effects for other natives, supporting the findings of other studies that AM fungi can be important drivers of plant community composition. Based on our work to date, we predict that sites with the greatest species diversity of native grasses and lowest phosphorus availability should support the highest richness of AM fungi. The relatively high concentrations of phosphorus and low diversity of native grasses in many prairie restorations may limit their ability to maintain diverse AM fungal communities, implying a potential negative feedback to plant diversity.