Arbuscular mycorrhizal fungi (AMF) form a symbiosis within roots of a majority of land plants and provide nutrients such as phosphorus, and services like pathogen protection and drought tolerance, to plant hosts in exchange for photosynthate. We sought to address how patterns of plant performance, mycorrhizal abundance and formation, and AMF community composition might vary with spatial variability of abiotic factors that should influence the importance of the symbiosis to the plant. We measured plant biomass, plant and soil nutrients, hyphal length in the soil and root colonization by AMF for Gaillardia aristata, a native prairie forb, at each of 12 sites from Montana to Minnesota that ranged in mean soil phosphorus availability from 2 to 38 ppm. We also grew G. aristata in the greenhouse with and without mycorrhizas and fertilized with or without phosphorus to determine mycorrhizal responsiveness. Each plant in the mycorrhizal treatment was inoculated with field soil from one of the 12 sites, to test the hypothesis that AMF from sites varying in soil phosphorus availability would vary in their effectiveness at provisioning phosphorus to their host. We identified AMF species present in the roots in the field and greenhouse using next-generation DNA sequencing.
Results/Conclusions
In the field, plants from soils with higher phosphorus availability were larger and had greater phosphorus content in their aboveground tissues. Greater plant phosphorus was associated with greater hyphal length in the soil. Bioinformatics analyses for AMF communities are currently underway. In the greenhouse, plants fertilized with phosphorus grew larger than those fertilized without phosphorus, indicating that plants were phosphorus limited. However, inoculated plants that were fertilized without phosphorus did not differ in size from plants that were fertilized with phosphorus, indicating that mycorrhiza formation alleviated phosphorus limitation. Non-mycorrhizal plants that were not fertilized with phosphorus were more than six times smaller than the plants in the other treatments. AMF from sites low in phosphorus were no more effective than AMF from sites high in phosphorus at provisioning phosphorus to G. aristata in the greenhouse. These results suggest that AMF are crucial for phosphorus uptake in and growth of G. aristata, a species of special concern in Minnesota and in decline regionally, but that the site of origin does not shape subsequent effectiveness of phosphorus provisioning by AMF communities.