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

JOHNSTON等人。海狸创造的池塘和草地是北美大片地区整体水和养分流动调节的关键组成部分。这些海狸池塘和草甸的景观位置非常适合接收来自上游的地表径流、水流和地下水排放，这使得海狸池塘和草甸的水文控制功能比它们单独的面积所推断的要大得多。湿润的禾本科草甸是海狸池塘在水文环境变化过程中所经过的关键阶段，而水文环境的变化可能决定着这些景观的动态。在以往研究表明氮限制这些草甸植物生长的基础上，这项新的研究将试图量化不同氮源在海狸草甸的相对重要性，以及氮供应对植被组成、结构和生产力的影响。为了验证这些关系，将河狸池塘和草甸的水文和养分预算的空间明确模型与不同营养和水分制度下的植物生长、冠层分配和垂直光梯度模型耦合在一起。该模型将使用在旅行者国家公园收集的水文数据进行参数化，并使用温室和生态环境实验来研究物种对水、光和营养的反应。然后，该模型将在几个不同水文的草甸中，沿着水深梯度和养分有效性的植被空间格局进行测试。该研究将为理解景观通过水和养分输送对植物物种分离和生产力的控制提供重大进展。它还将促进对湿润生态系统中禾草属物种的分离和生产力是如何被控制的理解，在这种生态系统中，短暂的冠层动态，而不是对养分的总响应，可能决定了群落动态。

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.