Control of Productivity and Plant Species Segregation by Nitrogen Fluxes to Wetland Beaver Meadows

Johnston等人。DEB-9615326由河狸创造的池塘和草甸是北美大片区域整体水和营养通量调节的关键组成部分。这些河狸池塘和草地位于理想的景观位置，非常适合接收地表径流、溪流和来自上游来源的地下水排放，赋予河狸池塘和草地不成比例的水文控制功能，而不是仅凭它们的面积来推断。潮湿的禾本科草甸是河狸池塘在水文状况变化期间经过的关键阶段，水文状况可能控制着这些景观的动态。在前人研究的基础上，这项新的研究将试图量化不同氮源在河狸草甸中的相对重要性，以及向植被供应氮素对其组成、结构和生产力的影响。为了测试这些关系，在不同营养和水分条件下，一个空间上显式的河狸池塘和草甸的水文和营养收支模型将与一个植物生长、树冠分配和垂直光梯度的模型相耦合。该模型将使用在旅行者国家公园收集的水文数据，并使用温室和中观实验对物种对水、光和营养的反应进行参数化。然后，将根据不同水文条件下几个草地上的植被沿水深和养分有效性梯度的空间格局对该模型进行测试。这项研究将为理解通过水分和养分输送对植物物种隔离和生产力的景观控制提供重要进展。它还将促进对潮湿生态系统中禾本科物种的物种分离和生产力如何控制的理解，在潮湿生态系统中，决定群落动态的可能是瞬时冠层动态，而不是对营养的总体反应。

JOHNSTON et al. DEB-9615326 Ponds and meadows created by beaver are key components of the regulation of overall water and nutrient fluxes over large areas in North America. These beaver ponds and meadows occur in landscape positions ideally suited to receive surface runoff, stream flow, and groundwater discharge from upstream sources, giving beaver ponds and meadows a hydrologic control function disproportionately greater than would be inferred by their area alone. Moist graminoid meadows are a key stage through which beaver ponds pass during changes in hydrologic regimes which may govern the dynamics of these landscapes. Building on previous research that has shown N limitation of plant growth in these meadows, this new research will attempt to quantify the relative importance of different N sources in beaver meadows, and the effect of N supply to vegetation on its composition, structure, and productivity. To test these relationships, a spatially explicit model of hydrology and nutrient budgets within beaver ponds and meadows will be coupled to a model of plant growth, canopy allocation, and the vertical light gradient under different nutrient and water regimes. The model will be parameterized using hydrologic data collected in Voyageurs National Park and using greenhouse and mesocosm experiments on species responses to water, light, and nutrients. The model will then be tested against spatial patterns of vegetation along gradients of water depth and nutrient availability in several meadows of different hydrology. This research will provide significant advances in understanding of landscape controls on plant species segregation and productivity via water and nutrient delivery. It will also advance understanding of how species segregation and productivity of graminoid species are controlled in moist ecosystems, in which transient canopy dynamics, rather than total response to nutrients, may be determining community dynamics.