Seedling planting information: Interactive Effects of Fertility and Distribution on Plant Community Diversity and Structure

There are four levels of nitrogen, corresponding to treatments A, C, F and G in E001, applied at the same time as in that experiment. For a description of fertilizer added to E052, see file fertilization details. There are four levels of soil disturbance designated 1, 2, 3 and 4.

Level 1: undisturbed
Level 2: 1 pass with a 7 HP Honda rear-tined rototiller with the elevator set to till to a depth of 9 inches
Level 3: 2 passes or however many required to produce about 50% bare ground
Level 4: 3 passes or however many required to produce 100% bare ground. This requires 3 passes in some plots but 5 or 6 in others. In addition, all woody vegetation not destroyed by tilling is cut at the base.

Rototilling is applied in late April.

Each fertilization treatment receives each disturbance treatment, for a total of sixteen treatments. There are four replicates of each of the sixteen treatments. In addition, the four extreme ends (lowest N, lowest disturbance; highest N, lowest disturbance, etc. ) are replicated an additional ten times. Treatments are applied in a completely randomized design. Each of the 104 plots is 5m x 5m.

Measurements taken at E052 will include: 1) species abundances, 2) community biomass allocation to leaves/roots/stems/flowers, 3) above and below ground net primary production and 4) rates of nitrogen mineralization. For a list of treatments, see the treatment layouts in file trmte52.

The plots in E052 are enclosed by a fence to exclude mammalian herbivores. Galvanized welded-wire hardware cloth with 6mm x 6mm openings was buried to a depth of 50cm. Additional hardware cloth extends 60cm above the ground and poultry netting extends to 2m above the ground.

In 1990, ten plots of each of four treatments (N1D1, N1D4, N4D1, N4D4, where N is the level of nitrogen added and D is the disturbance treatment) were randomly selected for the competition experiment. The above and belowground effects of neighbors on transplanted grass seedlings were measured using three competition treatments: transplants were grown in 50cm diameter subplots 1) with no neighbors, 2) with the roots but not shoots of neighbors, 3) with all above and belowground parts of neighbors present. One transplant was grown in the center of each subplot. Competition treatments were applied to subplots within the main plots during 14-18 May, 1990. Competition treatments were replicated three times in each of the ten replicate plots for each of the four combinations of nitrogen supply rate and disturbance. Thus, the 40 plots of the nitrogen and disturbance combinations (2 nitrogen levels x 2 disturbance levels x 10 replicates) each contained 9 subplots (3 competition treatments x 3 replicates), each subplot comprising one transplant in one competition treatment. A total of 360 seedlings were transplanted. Competition treatments were assigned randomly to subplots within each plot.

In 1991, three species of contrasting sizes, life histories, growth rates and positions along gradients of nitrogen and disturbance in the experiment were used: Schizachyrium scoparium, Agropyron repens, and Setaria viridis. Transplants were grown individually in subplots, with 1) all neighbors and 2) no neighbors. The experiment was conducted in high and low nutrient environments to test for the interaction between the environment, the size and the species. There were ten replicate plots of each of the two environments, one receiving no additional nitrogen and the second receiving nitrogen at 17g/m2/yr. In total, there were 32 transplants (3 species x 3 size classes x 2 competition treatments x 1, 2 or 3 replicates) in each plot, and 20 plots (2 environments x 10 replicates), or 640 transplants. Seedlings were transplanted into the field during 3-6 June, 1991.

本实验设置4个氮素水平，对应E001实验中的A、C、F、G组，施肥时机与E001实验一致。如需了解E052的施肥方案详情，请参阅`fertilization details`文件。
本实验设置4个土壤扰动等级，分别标记为1、2、3、4：
等级1：未扰动（undisturbed）
等级2：使用7 HP本田后旋式旋耕机作业1次，旋耕机升降装置调至9英寸耕深
等级3：作业2次，或直至约50%地表裸露所需的作业次数
等级4：作业3次，或直至100%地表裸露所需的作业次数。部分样地仅需3次作业，部分样地则需5至6次。此外，所有经旋耕未被清除的木本植物需从基部砍除。
旋耕作业于四月下旬开展。
每种施肥处理与每种土壤扰动处理均进行组合，共计16种处理组合。每种处理组合设置4次重复。此外，4组极端处理（最低氮素水平+最低扰动、最高氮素水平+最低扰动等）额外增设10次重复。所有处理采用完全随机设计。104个样地的规格均为5m×5m。
E052实验的测定指标包括：1）物种多度；2）群落生物量在叶、根、茎、花中的分配比例；3）地上与地下净初级生产力；4）氮矿化速率。如需查看处理组合列表，请参阅`trmte52`文件中的处理布局图。
E052的样地四周设有围栏，以排除哺乳动物食草动物的干扰。围栏底部埋入孔径为6mm×6mm的镀锌电焊网（hardware cloth），埋深达50cm。额外的镀锌电焊网向上延伸至地面以上60cm，上方再铺设家禽防护网（poultry netting），高度达地面以上2m。
1990年，本实验从4组处理（N1D1、N1D4、N4D1、N4D4，其中N代表氮素添加水平，D代表土壤扰动处理）中每组随机选取10个样地开展竞争实验。实验通过3种竞争处理测定邻体对移栽禾本科幼苗的地上与地下影响：将幼苗种植于直径50cm的小样地中，1）无邻体；2）仅有邻体根系，无地上部分；3）保留邻体的全部地上与地下部分。每个小样地中央种植1株幼苗。竞争处理于1990年5月14日至18日施加于主样地内的小样地中。针对氮素供应水平与土壤扰动的4种组合，每种组合的10个重复样地中，竞争处理均设置3次重复。因此，40个氮素与扰动组合样地（2个氮素水平×2个扰动水平×10次重复）中每个样地均包含9个小样地（3种竞争处理×3次重复），每个小样地对应1种竞争处理下的1株移栽幼苗。本次实验共计移栽360株幼苗，竞争处理在每个样地内的小样地中随机分配。
1991年，实验选取3个在植株大小、生活史、生长速率以及在氮素和扰动梯度上的生态位均存在显著差异的物种：须芒草（Schizachyrium scoparium）、匍匐冰草（Agropyron repens）和狗尾草（Setaria viridis）。幼苗单独种植于小样地中，设置2种竞争处理：1）保留全部邻体；2）无邻体。实验设置高、低两种养分环境，以探究环境、植株大小与物种间的交互效应。两种养分环境各设置10次重复样地：一组不额外添加氮素，另一组氮素添加量为17g/m²/年。每个样地共计种植32株移栽幼苗（3个物种×3个大小等级×2种竞争处理×1/2/3次重复），共计20个样地（2种环境×10次重复），总移栽幼苗数为640株。幼苗于1991年6月3日至6日移栽至野外样地。