Soil carbon: 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.

本实验旨在明确：在排除大、小型哺乳动物放牧干扰的植物群落中，初始生境扰动与长期氮肥施加，会对群落的物种丰富度、现存物种组成、年生长总量，以及各物种的年际生长动态产生何种影响。本实验设置于初始土壤养分水平较低的三块样地（A、B、C）中。实验开展前，通过全面圆盘耙翻耕对样地进行初始土壤扰动。实验共设置8个氮肥施加梯度，同时添加其余养分以确保氮为唯一限制因子，另设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。每块样地中，各处理均设置6次重复。处理组被随机分配至面积为4米×4米的样方中。样方以6行×9列的网格布局排布，样方间设置1米宽的通道。样方网格外围设有围栏，以阻挡哺乳动物食草动物进入。一旦发现囊鼠，立即诱捕移除。1992年春季，本实验增设两个子实验E097与E098：其中E097设置于样地A与C中，各处理组内随机选取的样方将不再施加氮肥；E098设置于样地B中，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，唯一区别为E002在实验开展前进行了全面翻耕扰动。