Soil nitrogen: 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年秋季启动。该实验从C地块（Field C）内氮添加（N addition）实验E001的每个对照组与每个处理组的6个重复样地（replicates）中，随机选取3个样地，以鹿围栏进行围封。这些样地仍沿用E001实验方案（protocols）中规定的营养盐处理措施。1982年至2004年间，C地块内所有E001实验样地曾被一道整体围栏围封，用以排除鹿以及小鼠、田鼠、囊鼠等所有小型哺乳动物（small mammals）。该整体围栏于2004年秋季被拆除，其中被指定为E172实验样地的区域被单独以鹿围栏围封。

E001实验的核心目标是量化长期氮添加对植物群落的物种数量、物种组成、年生长量（annual growth）以及各物种生长量年度动态的影响——该植物群落同时免受大、小型哺乳动物的采食干扰。实验设置8个梯度的氮添加处理，同时配施其他营养盐以确保氮始终为限制性营养元素（limiting nutrient），另设一组不施加任何营养盐的对照组。实验样地以6×9的网格布局排布，单块样地面积为4米×4米，样地间设置1米宽的步道。每年于5月初与6月末两次施加硝酸铵（NH4NO3）氮肥。