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

0087201里奇草食性哺乳动物可以通过它们对养分循环的影响，对草地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无机氮返回土壤，并有利于营养更丰富和可分解的植物来加速氮的循环。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：什么控制这些影响食草动物将有？这个LTER跨站点研究项目解决了六个主要的假设是什么控制哺乳动物草食动物对温带草原氮循环的影响。这些假设表明，草食动物的影响可能会有所不同的生产力，在植物群落中的豆科植物的患病率，土壤压实的敏感性。此外，不同大小的食草动物的密度和它们的迁移与季节性使用草地可能会影响氮循环。将通过测量草食动物对氮循环的影响来测试假设，该影响是在现有的不同大小的草食动物对草地生物多样性和生态系统功能的影响的跨站点研究中进行的。这些地点包括广泛的生产力，豆类丰富，土壤类型和食草动物的季节性使用模式。 通过比较特定的网站对测试特定的假设，并检查广泛的模式，在所有网站的食草动物的影响，这项研究将提供独特的见解，是不可能与研究在一个单一的网站。这项研究将有助于了解不同的草食动物物种如何影响不同生产力，植物物种组成和土壤类型的草地的可持续生产。这些资料对于评价包括家畜在内的食草哺乳动物在可持续利用和养护草原方面的作用至关重要。

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.