COS 115-2 - Efficacy of arbuscular mycorrhizal communities from soils of differing phosphorus availability for the grassland forb Gaillardia aristata

Background/Question/Methods

Soils shape both plant and plant-associated fungal communities. Do soils leave functional legacies in the composition of soil fungal communities? A key role of arbuscular mycorrhizal (AM) fungi for plants is the uptake of phosphorus, which can differ by an order of magnitude in its availability across soil types. To test the hypothesis that AM fungal communities are influenced by soil phosphorus availability, we collected rhizosphere soils and roots from 12 sites in Montana, North Dakota, and Minnesota that differed in P availability and characterized their AM fungal communities using high-throughput sequencing of the fungal ITS2 rDNA region. To test whether differences in AM fungal communities associated with soil P availability influenced the subsequent utility of AM for P uptake, we inoculated a mycorrhiza-responsive plant species found at all of our field sites, blanketflower (Gaillardia aristata), with soils from each of our sites, grew the plants in the greenhouse with or without P fertilization, and assessed the resulting AM fungal communities in roots, plant performance, hyphal length in the soil and phosphatase production after 18 months.

Results/Conclusions

In the field, AM fungal communities differed with soil P availability, but soil P availability was also strongly correlated with elevation and summer temperature and rainfall. However, in the greenhouse, AM fungal communities did not change in response to P fertilization. There was also no difference in biomass or P concentration of blanketflower, or hyphal length in the soil, between plants inoculated with AM fungal communities from low P soils and those inoculated with communities from high P soils. With the exception of phosphatase production, which was slightly higher in soils inoculated with AM fungi from low P soils, there appeared to be no legacy of soil P availability for mycorrhizal efficacy in this species. These results suggest that mechanisms other than functional differentiation may be important for diversity of AM fungi in planta.