9520760 Fahey Nitrogen availability may be an important factor influencing the abundance, diversity, and function of ectomycorrhizal fungi (ECMF). Understanding ECMF responses to nitrogen is critical not only because natural spatiotemporal variation in nitrogen availability, but also because anthropogenic nitrogen deposition has altered nitrogen availability in forest soils. Recent evidence suggests that declining production and diversity of ECMF fruitbodies in Europe is correlated with multiple air pollutants, including atmospheric nitrogen deposition. The objective of this dissertation research is to determine the effect of nitrogen deposition on ECMF of white spruce over a short, steep nitrogen deposition gradient in Alaska. Hypotheses are that 1) there is lower ECMF diversity near the nitrogen source, 2) ECMF species dominant at high and low nitrogen sites differ both in their ability to colonize roots, and in their effect on tree nutrition and growth, under high and low soil nitrogen availability. Initial sampling focused on fungal species distribution, tree nutrition and growth, and soil chemistry. Preliminary results indicate that high nitrogen deposition sites have lower diversity and abundance of ECMF than low nitrogen deposition sites. Seedling experiments will examine differences among ECMF species in root colonization and nitrogen transfer under high and low nitrogen availability This research is important because fungi, in general, and mycorrhizal fungi, in particular, are primary agents of decomposition and nutrient cycling in ecosystems. Given that chronic anthropogenic nitrogen deposition is occurring throughout the world, knowledge od the effects of this pollution is essential for understanding the future consequences of humankind's impact on natural systems.
