Plant aboveground biomass data: Long-Term Nitrogen Deposition: Population, Community, and Ecosystem Consequences

The purpose of this experiment is to measure how adding nitrogen over a long time will affect the number of species, the type of species present, the amount of annual growth, and the change from year to year in the growth of each species in a plant community which is also relieved of grazing by large and small mammals. The experiment is being conducted within fields (A, B, C, and D) which were initially low in soil nutrients. There are 8 different levels of nitrogen addition with other nutrients added to ensure that nitrogen remains the limiting nutrient, and a control which receives no nutrients. There are 6 replicates of the 9 treatments in fields A, B, and C and 5 replicates in field D. The treatments were randomly assigned to the plots. In fields A, B, and C the plots are in 6 by 9 grids and are 4 by 4 meters in size with 1 meter aisles between plots. In field D the plots are 1.5 by 4 meters and are placed in a 3 by 17 grid. The plots are enclosed by a fence to keep out mammalian herbivores. Gophers are trapped and removed as they appear. Nitrogenfertilizer (NH4NO3) is applied twice per year, once in early May and once in late June. This experiment was begun in 1982 by David Tilman.本实验旨在探究长期施加氮肥对植物群落的物种数量、现存物种组成、年生长总量以及各物种生长的年际变化的影响，同时该植物群落已排除大、小型哺乳动物的啃食干扰。实验在初始土壤养分水平较低的地块（A、B、C、D）中开展。设置8种不同的氮肥施加梯度，并额外补充其他营养元素以确保氮成为限制性营养因子，另设不施加任何养分的对照组。A、B、C地块内的9种处理各设置6个重复，D地块内的处理设置5个重复，处理组随机分配至各实验样地。A、B、C地块内的样地采用6×9网格布局，单块样地面积为4×4米，样地间预留1米宽的通道。D地块内的样地面积为1.5×4米，采用3×17网格布局。所有样地均设有围栏以阻挡哺乳动物植食动物，同时会对出现的囊地鼠进行诱捕并移除。实验每年分两次施加硝酸铵（NH4NO3）氮肥，分别于5月初和6月末进行。本实验由David Tilman于1982年启动。