LTER Cross-site: Collaborative Research: Effects of Different-sized Grazers on Nitrogen Cycling across a Grassland Productivity Gradient.

0087201Ritchie 草食哺乳动物可以通过其对养分循环的影响对草原的可持续性和生产力产生深远的影响。最近的研究表明，食草动物可以通过将尿液和粪便中的矿物质氮返回土壤来加速氮的循环，并有利于营养丰富和可分解的植物。或者，它们可以通过改变植物群落的物种组成、降低凋落物质量和减缓分解来减缓养分循环。然而，一个重要的问题仍然存在：什么控制着食草动物会产生哪些影响？这个 LTER 跨站点研究项目提出了关于控制哺乳动物食草动物对温带草原氮循环影响的六大假设。这些假设表明，食草动物的影响可能会因生产力、植物群落中豆科植物的流行程度以及土壤对板结的敏感性而有所不同。此外，不同大小食草动物的密度及其迁徙与季节性使用草地可能会影响氮循环。在现有的不同规模食草动物对草原生物多样性和生态系统功能影响的跨地点研究中，将通过测量食草动物对氮循环的影响来检验假设。这些地点涵盖了广泛的生产力、豆类丰富度、土壤类型和食草动物的季节性利用模式。 通过比较特定的地点对来测试特定的假设并检查所有地点的食草动物效应的广泛模式，这项研究将提供单个地点的研究不可能提供的独特见解。该研究将有助于了解不同草食动物物种如何影响具有不同生产力、植物物种组成和土壤类型的地点的草地可持续生产。这些信息对于评估哺乳动物食草动物（包括家畜）在草原可持续利用和保护中的作用至关重要。

0087201RitchieHerbivorous mammals can have profound effects on the sustainability and productivity of grasslands through their effects on nutrient cycling. Recent studies suggest that herbivores can accelerate the cycling of nitrogen by returning mineral nitrogen in urine and feces to the soil and favoring more nutrient-rich and decomposable plants. Alternatively, they can slow down nutrient cycling by modifying the species composition of plant communities, reducing litter quality, and slowing decomposition. However, an important question remains: what controls which of these effects herbivores will have? This LTER cross-site research project addresses six major hypotheses about what controls mammalian herbivore effects on nitrogen cycling in temperate grasslands. These hypotheses suggest that herbivore effects may vary in response to productivity, the prevalence of legumes in the plant community, and the susceptibility of soil to compaction. In addition, the density of different sized herbivores and their migratory versus seasonal use of grasslands may influence nitrogen cycling. Hypotheses will be tested by measuring herbivore impacts on nitrogen cycling within an existing cross-site study of the effects of different sized herbivores on grassland biodiversity and ecosystem function. These sites encompass a wide range of productivity, legume abundance, soil types, and patterns of seasonal use by herbivores. By comparing particular pairs of sites to test specific hypotheses and examining broad patterns in herbivore effects across all sites, this study will provide unique insights that are not possible with studies at a single site. The research will allow understanding of how different herbivore species affect the sustainable production of grasslands at sites with different productivity, plant species composition and soil types. Such information is critical to evaluating the role of mammalian herbivores, including domestic livestock, in the sustainable use and conservation of grasslands.