Soil nitrate and ammonium: Herbivory by Nitrogen Interactive Effects on Community and Ecosystem Processes and Dynamics

E172 is an herbivory experiment established by Dave Tilman in fall 2004 by enclosing in deer fences three randomly selected plots from the six replicates of each control and each treatment in the N addition E001 experiment in field C. These plots still receive the nutrient treatments prescribed in the Experiment 001 protocols. From 1982-2004 a fence containing all of e001 plots in Field C was designed to exclude deer and all small mammals, including mice, voles and pocket gophers. This fence was removed in Fall of 2004 and individual plots designated for e172 were enclosed in deer fences.

The purpose of E001 was to measure how adding nitrogen over a long time would 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. 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. The plots are in a 6 by 9 grid and are 4 by 4 meters in size with 1 meter aisles between plots. Nitrogen fertilizer (NH4NO3) is applied twice per year, once in early May and once in late June.

E172是一项植食性实验（herbivory experiment），由戴夫·蒂尔曼（Dave Tilman）于2004年秋季搭建。该实验依托C地块（Field C）内氮添加E001实验的各对照组与处理组的6次重复样地，从中随机选取3块，以鹿类围栏（deer fences）进行围合。这些样地仍严格遵循E001实验方案中的养分处理规则执行。1982年至2004年间，C地块内所有E001实验样地均被统一围栏环绕，用于排除鹿类以及小鼠、田鼠、囊地鼠等所有小型哺乳动物的干扰。该统一围栏于2004年秋季被拆除，原本分配给E172实验的指定样地则被单独加装鹿类围栏。

E001实验的核心目标为量化长期施加氮肥对植物群落的多重影响，包括物种丰富度、现存物种组成、年生长总量，以及各物种的年际生长动态；该植物群落同时排除了大、小型哺乳动物的放牧干扰。实验设置8个梯度的氮添加水平，同时配套添加其他养分以确保氮始终为限制性养分（limiting nutrient），另设不施加任何养分的空白对照组。样地以6×9的网格形式排布，单块样地面积为4×4米，样地之间预留1米宽的通道。实验每年施用两次硝酸铵（NH4NO3）氮肥，分别于每年5月初与6月末进行。