Percent light penetration: Long-Term Nitrogen Deposition: Epopilation, 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某植物群落的物种种数、现有物种类群、年生长量，以及各物种种群的年际生长动态的影响，并对该群落实施禁牧，排除大、小型哺乳动物的啃食干扰。本实验在初始土壤养分水平较低的A、B、C、D四块样地中开展。实验共设置8个氮添加梯度，同时配套施加其他养分以确保氮始终为限制性营养因子，另设一个不施加任何养分的对照组。A、B、C三块样地中，9种实验处理各设置6个重复；D样地中，各处理设置5个重复。实验处理被随机分配至各样方。A、B、C样地的样方采用6×9的网格布局，单样方面积为4×4米，样方间设置1米宽的间隔通道。D样地的样方面积为1.5×4米，采用3×17的网格布局。所有样方均围有围栏，以阻挡哺乳动物食草动物；囊鼠（Gophers）一旦被发现即会被诱捕移除。每年施加两次硝酸铵（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。