Cross-Site: Collaborative Research: Mycorrhizal Responses to Nitrogen Eutrophication at Five Mesic to Semiarid Sites

虽然氮通常是生态系统中最具限制性的营养物质，但持续增加的氮输入可能会导致显著的生态系统应激。人为氮的沉积与最近整个欧洲植物和真菌多样性的损失有关。大气氮沉降对北美草原和灌丛的结构和功能的影响知之甚少，尽管南加州每年每公顷的氮沉降量高达30公斤，美国其他地方的氮沉降量较少。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度至半干旱草原氮富营养化过程中真菌的物种组成变化；(2)评估氮富营养化过程中菌根真菌的种类，以表明真菌的共生或寄生效应；(3)进行生物测定，以确定氮富营养化后低等共生菌是否占主导地位。本研究将在长期生态研究网络内的四个实验草地和南加州的一个灌木草原上研究氮富营养化对菌根的影响。这些位于密歇根州、明尼苏达州、堪萨斯州、新墨西哥州和加利福尼亚州的草原形成了降水和肥力梯度。氮富营养化对植物、菌根真菌和土壤的影响将在以前建立的实验和在这些地点的新样地进行研究。本研究旨在评估菌根对氮的响应在三个尺度上的范围和差异：在单个植物-根界面，在草地群落内，以及在气候和土壤梯度上。这是评估氮富营养化对美国草原菌根-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，因为草原是北美牧场资源和牛肉生产的基础。

9526564 Allen 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 range re sources and beef production in North America.