Dissertation Research: Effects of an Atmospheric Nitrogen Deposition Gradient on White Spruce (Picea glauca) Ectomycorrhizae

氮有效性可能是影响外生菌根真菌（ECMF）丰度、多样性和功能的重要因素。了解ECMF对氮的响应至关重要，不仅因为氮有效性的自然时空变化，而且因为人为氮沉积改变了森林土壤的氮有效性。最近的证据表明，欧洲ECMF子实体产量和多样性的下降与多种空气污染物有关，包括大气氮沉降。本文研究的目的是确定氮沉降对阿拉斯加短而陡的氮沉降梯度上白云杉ECMF的影响。假设1)在氮源附近ECMF多样性较低；2)在高氮和低氮条件下，ECMF物种在高氮和低氮条件下对根系的定殖能力以及对树木营养和生长的影响不同。最初取样的重点是真菌种类分布、树木营养和生长以及土壤化学。初步结果表明，高氮沉降点的ECMF多样性和丰度低于低氮沉降点。幼苗实验将检验不同ECMF物种在高氮有效性和低氮有效性条件下根系定植和氮转移的差异。这项研究很重要，因为真菌，特别是菌根真菌，是生态系统中分解和养分循环的主要媒介。鉴于慢性人为氮沉降正在世界各地发生，了解这种污染的影响对于理解人类对自然系统影响的未来后果至关重要。

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.