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处理，施肥时机与该实验完全一致。关于施加至E052的肥料添加说明，请参阅《施肥细节》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；
等级2：使用7马力本田（Honda）后置旋耕机（rototiller）作业，配套升运器设定耕深为9英寸；
等级3：作业1次以上，直至约50%的地块变为裸地；
等级4：作业3次以上，直至地块完全变为裸地；部分地块仅需3次作业即可达标，部分地块则需5至6次作业。此外，所有未被旋耕破坏的木本植被（woody vegetation）均需在基部截断。
旋耕作业于四月下旬开展。

所有施肥处理均需搭配各扰动处理，共计16种组合。每种组合设置4个重复样地。此外，4种极端组合（最低氮素+最低扰动、最低氮素+最高扰动、最高氮素+最低扰动、最高氮素+最高扰动）额外设置10个重复样地。实验采用完全随机设计（completely randomized design），每个样地尺寸为5m×5m，共104个样地。

E052实验的测量指标包括：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（net primary production）；4）氮矿化速率（nitrogen mineralization）。处理组列表请参阅trmte52文件中的处理布局图。

E052的样地周围设有围栏以排除哺乳动物食草动物（mammalian herbivores）。具体做法为：将孔径为6mm×6mm的镀锌电焊网（galvanized welded-wire hardware cloth）埋入地下50cm深处，同时将该电焊网延伸至地面以上60cm处，再在上方加装高度达2m的家禽防护网（poultry netting）。

1990年，我们从4种处理组合（N1D1、N1D4、N4D1、N4D4，其中N代表氮素添加水平，D代表扰动处理）中随机选取10个样地开展竞争实验。实验通过3种竞争处理，测定相邻植株对移植禾本科幼苗（transplanted grass seedlings）的地上与地下影响：将幼苗种植于直径50cm的小样方（subplot）中，分别设置1）无相邻植株；2）仅保留相邻植株的根系而去除地上部分；3）保留相邻植株的全部地上与地下部分。每个小样方的中心位置移植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方中。
针对氮素供给与扰动的4种组合，每种组合的10个重复样地中，竞争处理均设置3个重复。因此，40个氮素-扰动组合样地（2个氮素水平×2个扰动水平×10个重复）中各包含9个小样方（3种竞争处理×3个重复），每个小样方对应1种竞争处理下的1株移植幼苗。共计移植幼苗360株。每个样地内的小样方均随机分配竞争处理。

1991年，我们选取了3种在本实验氮素与扰动梯度上具有差异化体型、生活史（life histories）、生长速率及生态位位置的物种：须芒草（Schizachyrium scoparium）、匍匐冰草（Agropyron repens）与狗尾草（Setaria viridis）。实验将幼苗单独种植于小样方中，设置2种竞争处理：1）保留全部相邻植株；2）无相邻植株。本实验设置高、低两种养分环境，以检验环境、植株体型与物种间的交互作用。两种养分环境各设置10个重复样地：一组不额外施加氮肥，另一组按17g/m²/yr的速率施加氮肥。每个样地内共计32株移植幼苗（3个物种×3个体型等级×2种竞争处理×1、2或3个重复），共计20个样地（2种环境×10个重复），总移植幼苗数为640株。幼苗于1991年6月3日至6日移植至田间。