Soil pH: Long-Term Nitrogen Deposition During Grassland Succession

The purpose of this experiment is to measure how initially disturbing an area and 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. This experiment is conducted within fields (A, B, and C) which were initially low in soil nutrients. The ground was disturbed by thoroughly disking the area prior to establishment of the experiment. 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. Nitrogen fertilizer (NH4NO3) is applied twice per year, once in early May and once in late June. There are six replicates of each treatment per field. The treatments were randomly assigned to plots of size 4 by 4 meters. The plots are in 6 plot by 9 plot grids with 1 meter aisles between plots. The plot grids are enclosed by a fence to keep out mammalian herbivores. Gophers are trapped and removed as they appear. In the spring of 1992, subexperiments E097 and E098 were established. E097 is in fields A and C where randomly selected plots within each treatment no longer receive fertilizer. E098 is in field B where randomly selected plots within each treatment are burned. Note that the design of E002 is similar to E001 except E002 was thoroughly disked prior to establishment.

本实验旨在探究初始生境扰动结合长期氮素添加，以及移除大、小型哺乳动物放牧压力，对植物群落的物种数量、现存物种类型、年生长量，以及各物种年际生长变化的影响。本实验设置于初始土壤养分含量较低的A、B、C三块样地中。实验开展前，通过彻底圆盘犁翻耕该区域以实现生境初始扰动。实验设置8个氮素添加梯度，同时配施其他养分以确保氮为唯一限制性营养因子，并设置不施加任何养分的对照组。氮肥（硝酸铵NH4NO3）每年施加两次，分别于5月初与6月末施用。每个样地内，每种处理设置6个重复样方。处理组随机分配至规格为4米×4米的样方中。样方以6行×9列的网格排布，样方之间设置1米宽的通行通道。整个样方网格设有围栏以阻挡哺乳动物植食动物，同时设置陷阱捕捉并移除出现的囊地鼠。1992年春季，本实验建立了两个子实验E097与E098：其中E097设置于A、C样地中，对应各处理组内随机选取的样方将不再施加肥料；E098设置于B样地中，对应各处理组内随机选取的样方将进行火烧处理。需注意，E002的实验设计与E001近似，仅E002在实验开展前经过了彻底圆盘犁翻耕。