Litter carbon and nitrogen: 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与长期氮肥添加，对同时解除大、小型哺乳动物放牧压力的植物群落的物种数量、现存物种组成、年生长量，以及各物种生长的年际变化的影响。本实验设置于初始土壤养分含量较低的地块（A、B、C三区）。实验开展前，通过全面圆盘耙耕对样地进行初始扰动。设置8个氮肥添加梯度，并额外施加其余养分以确保氮为唯一限制性养分，另设不施加任何养分的对照组。氮肥采用硝酸铵（NH4NO3），每年分两次施用，分别于5月初与6月末施加。每个地块内各处理组均设置6次重复。处理组被随机分配至4米×4米的样方中。样方以6行×9列的网格排布，样方间设置1米宽的通道。所有样方网格均以围栏围合，以阻隔哺乳动物草食动物；囊鼠一经发现即诱捕移除。1992年春季，设立子实验E097与E098：其中E097设于A、C两区，将各处理组内随机选取的样方停止施加肥料；E098设于B区，将各处理组内随机选取的样方进行焚烧处理。需注意，E002的实验设计与E001相似，仅E002在实验启动前进行了全面圆盘耙耕处理。