JOHNSON, NANCY COLLINS1, DIANE ROWLAND1, LEA CORKIDI2, EDITH ALLEN2.
1Environmental and Biological Sciences, Northern Arizona University, Flagstaff AZ 86011, USA. 2Department of Botany and Plant Sciences, University of California, Riverside, CA 92521, USA.
Atmospheric deposition of anthropogenic nitrogen (N) is enriching many ecosystems, but impacts of this landscape scale N eutrophication on arbuscular mycorrhizae (AM) is unknown. We are studying AM in long-term N fertilization experiments at five grassland sites in North America. These sites vary in soil fertility and management history ranging from abandoned agricultural fields in Michigan and Minnesota to native tall-grass and short-grass prairies in Kansas, Colorado and New Mexico. Analysis of populations of soil-borne spores indicates that N fertilization changes the species composition of AM fungal communities in the field, e.g., Gigasporaceae seem to be particularly sensitive to N eutrophication. We conducted greenhouse experiments to assess how these changes impact performance of native grasses. These experiments show that AM fungal communities from fertilized and unfertilized soils differ in their effects on aboveground and belowground biomass, root/shoot ratio, and chlorophyll content. Furthermore, nitrophilous and nitrophobic grass species differ in the direction and amplitude of their responses to these distinct fungal communities. If N enrichment alters the functioning of AM along the mutualism-parasitism continuum, then AM may play a role in structuring plant communities during N eutrophication.
Key words: nitrogen eutrophication, grassland mycorrhizae, mycorrhizal responsiveness, spore communities.