Cross-Site: Collaborative Research: Mycorrhizal Responses to Nitrogen Eutrophication at Five Mesic and Semi-Arid Sites

9527317约翰逊虽然氮通常是生态系统中最具限制性的营养素，但持续、高水平的氮输入可能会导致显著的生态系统压力。 人为氮的沉积与最近整个欧洲植物和真菌多样性的丧失有关。 尽管加州南部每年每公顷沉积30 kg氮，而美国其他地方沉积量较少，但关于大气氮沉积对北美草原和灌木丛结构和功能的影响知之甚少。 本研究的三个主要目标是：（1）利用显微镜和免疫荧光技术评估中干旱至半干旱草原氮营养化过程中真菌物种组成的变化;（2）评估氮营养化下的菌根真菌种类，以表明真菌的互利或寄生效应;（3）进行生物测定，以确定氮营养化后劣势互利者是否占优势。 本研究将探讨氮富营养化对真菌的影响，在四个实验草地内的长期生态研究网络和在南部加州的灌木草原。 密歇根州、明尼苏达州、堪萨斯州、新墨西哥州和加州的这些草原形成了降水和肥力梯度。 氮富营养化的影响将在植物，菌根真菌和土壤在以前建立的实验和新的地块在这些网站上进行研究。 本研究的目的是评估菌根反应的范围和方差氮在三个尺度：在个别植物根界面，草原社区内，并在整个气候和土壤梯度。 这是评估美国草原中氮富营养化对菌根-植物相互作用的结构和功能的潜在影响的第一步。 这项研究很重要，因为草地是北美牧场资源和牛肉生产的基础。

9527317 Johnson Although nitrogen is frequently the most limiting nutrient in ecosystems, continuous, elevated inputs of nitrogen may cause significant ecosystem stress. Deposition of anthropogenic nitrogen has been associated with recent losses of plant as well as fungal diversity throughout Europe. Little is known about the effects of atmospheric nitrogen deposition on the structure and function of North American grasslands and shrublands, although as much as 30 kg nitrogen per hectare per year is deposited in southern California, with lesser amounts elsewhere in the US. The three principal objectives of this research will be to (1) assess species composition changes of fungi during nitrogen eutrophication in mesic to semiarid grasslands using microscopy and immunoflourescence, (2) assess the kinds of mycorrhizal fungi under nitrogen eutrophication to indicate the mutualistic or parasitic effects of fungi, and (3) conduct bioassays to determine whether inferior mutualists predominate after nitrogen eutrophication. This study will examine the effects of nitrogen eutrophication on mycorrhizae at four experimental grasslands within the Long-term Ecological Research network and at a shrub-grasslands in southern California. These grasslands in Michigan, Minnesota, Kansas, New Mexico, and California form a precipitation and fertility gradient. The effects of nitrogen euthrophication will be studied on plants, mycorrhizal fungi and soils in experiments that have previously been established and in new plots at these sites. This research is designed to assess the ranges and variances of mycorrhizal responses to nitrogen at three scales: at individual plant-root interfaces, within grasslands communities, and across a climatic and soil gradient. This is a first step toward assessing the potential effects of nitrogen eutrophication on the structure and functioning of mycorrhizae-plant interactions in grasslands in the US. This research is important because grasslands are the basis for rang e resources and beef production in North America.