Serengeti Ecosystem Processes: Water or Nitrogen Control?

设计了一个模拟和实地实验研究的研究计划，以确定含有大量大型食草哺乳动物的热带草原生态系统在多大程度上受水、氮、放牧、火及其相互作用的控制。建模将侧重于受这些因素影响的其他营养循环途径，不同营养物质循环的耦合，推广到广泛的现场条件和时间尺度，并模拟在现场不可能进行的实验。将在四个试验田实施统一的23因子分割设计，这些试验田的降水、土壤肥力、土壤盐度、初级生产、火灾和草食具有广泛的干旱到半湿润生态系统的代表性。基本设计将通过广泛的地块进行扩充，其目的是更好地覆盖诸如气候等物理因素的固有变异性。通过模型模拟和实地数据，对12个控制因素平衡的假设进行了验证，包括地上和地下净初级生产力、草食、植物水分和氮状况、凋落物、分解和矿化。食草动物作为氮循环和水文平衡的控制者将作为建模和实验的一个组成部分进行评估。这个项目继续在国内机构得到良好的支持。此外，东道国的科学机构仍然致力于其过去的接受、援助和参与水平。项目组是优秀的，精通学科生态系统和必要但困难的远程物流。我们有理由期待这项工作将继续产生在基础生态学中具有重大意义的发现。同样，可以预期所得的资料将对肯尼亚和其他地方的牧场管理有用。生态系统研究项目建议支持这一5年持续奖励的第一年。

A research plan of modeling and experimental field studies has been designed to determine the degree to which tropical savanna grassland ecosystems containing abundant populations of large, grazing mammals are controlled by water, nitrogen, grazing, fire, and their interactions. Modeling will focus on alternative nutrient cycling pathways as affected by those factors, coupling of cycles of different nutrients, generalizing for a broad range of site conditions and temporal scales, and simulating experiments impossible in the field. A uniform split- plot 23 factorial design will be implemented at four experimental field sites over substantial ranges of precipitation, soil fertility, soil salinity, primary production, fire, and herbivory representative of a broad span of arid to subhumid ecosystems. The basic design will be augmented by extensive plots whose purpose will be to provide better coverage for inherent variability of physical factors such as climate. Twelve hypotheses about the balances of controlling factors will be tested with model simulation and field data on aboveground and belowground net primary productivity, herbivory, plant water and N status, litterfall, decomposition, and mineralization. Grazers as controllers of nitrogen cycling and hydrologic balances will be evaluated as an integral component of modeling and experiments. This project continues to enjoy excellent support at the home institution. Additionally, the host country science establishment remains committed to its past levels of receptivity, assistance and participation. The project group is excellent and well versed in the subject ecosystem and the necessary, but difficult, remote logistics. It is reasonable to expect that findings of major significance in fundamental ecology will continue to be produced by this work. Similarly, one can expect that the resultant information will be useful in range management, both in Kenya and elsewhere. The Ecosystem Studies Program recommends that the first year of this five-year continuing award be supported.