CAREER: How do microorganisms and grazing mammals interact at local to regional scales to regulate grassland nitrogen cycling processes?

草原生态系统覆盖了地球植被表面的三分之一以上。除了改作农业用途的草地外，大多数草地都用来放牧牲畜。该项目将首次研究放牧哺乳动物与土壤微生物之间的相互作用，这些微生物共同控制草地氮循环和土壤肥力。有待验证的假设包括：1)大型食草动物是否会促进土壤微生物的扩散；2)这是否会影响土壤n循环的不同步骤，这取决于控制每个步骤的微生物的多样性。为了做到这一点，包括学生和公民科学家在内的项目人员将共同努力，测量高草草原上野牛和牛放牧和未放牧地区的土壤微生物生物多样性和氮循环活动。这些实验将在10厘米（当地土壤微生物栖息地）到1000公里（堪萨斯州弗林特山地区）的距离范围内进行。本研究的结果将促进对草地土壤肥力调节因子的一般认识，包括那些支持生态系统氮保持在局地和区域尺度上的因子。了解氮潴留对保护公共饮用水质量很重要。成果还将包括向学生和公民广泛和及时地传播这些知识，并使学生和公民参与科学研究过程。尽管全球草地生态系统的重要性以及放牧动物在这些生态系统中的关键作用，但除了“放牧草坪”现象之外，没有关于大型有蹄类放牧对草地N循环过程的普遍影响的一致观点，在“放牧草坪”现象中，由于消费者驱动的养分循环，更高比例的N以植物可利用形式存在。本研究的总体假设是，草地土壤氮循环微生物的分布受景观尺度的影响比局部因素更强烈，对功能冗余度较低的行会产生更大的功能后果。换句话说，大型食草动物在景观尺度上的存在对微生物多样性的影响比对土壤核心尺度上的土壤因子的影响更强烈，这将与土壤硝化势（一种更专业化的n循环功能）的差异相关，而不是与反硝化或分解势（依次较少专业化的功能）的差异相关。评估这一假设的证据将与堪萨斯州弗林特山地区的土地管理者合作收集，并将通过与牧场主、高中班级和大学班级以及传统学术机构的沟通传播。除了区域尺度的模式评价外，实验工作还将分析微生物群落组成、土壤pH、有机质和氮有效性对氮循环过程的独立影响。主要目标是获得更大规模的空间、时间和概念知识，并将这些知识传播给广泛的受众。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Grassland ecosystems cover over a third of Earth's vegetated surface. Except for those converted to agriculture, most grasslands are used for livestock grazing. For the first time, this NSF CAREER project will study interactions between grazing mammals and soil microbes, organisms that together control grassland nitrogen (N) cycling and soil fertility. Hypotheses to be tested include: 1) whether large grazers promote dispersal of soil microbes, and 2) whether this affects different steps of the soil N-cycle based on the diversity of microorganisms that control each step. To do this, project personnel, including students and citizen scientists, will work together to measure soil microbe biodiversity and N-cycling activity in bison- and cattle- grazed and ungrazed areas of tallgrass prairie. These experiments will be conducted across distances ranging from 10-cm (local soil microbial habitat) to 1000-km (Flint Hills, KS region). Results from this work will advance general knowledge of the factors regulating grassland soil fertility, including those supporting ecosystem N retention at local to regional scales. Understanding N retention is important for protecting public drinking water quality. Outcomes will also include broad and timely communication of this knowledge to students and citizens, and engagement of students and citizens in the scientific research process. Despite the importance of grassy ecosystems globally and the key role of grazing animals in these ecosystems, there is no coherent perspective on the generalized effects of large ungulate grazing on grassland N cycling processes, beyond the “grazing lawn” phenomenon, in which a higher proportion of N is in plant-available form due to consumer-driven nutrient recycling. The overarching hypothesis of this work is that the distribution of grassland soil N cycling microbes is more strongly affected by landscape-scale than local factors, with greater functional consequences for guilds with lower functional redundancy. In other words, the presence of large grazers at the landscape scale will affect microbial diversity more strongly than will edaphic factors at the soil core scale, and this will be associated with differences in soil nitrification potential (a more specialized N-cycling function) more than differences in denitrification or decomposition potential (sequentially less specialized functions). Evidence to evaluate this hypothesis will be collected in collaboration with land managers across the Flint Hills, KS, region, and will be disseminated through communication with ranchers, high school classes and college classes, as well as traditional academic outlets. In addition to this regional-scale pattern evaluation, experimental work will parse the independent effects of microbial community composition and soil pH, organic matter and N availability on N cycling processes. Larger-scale spatial, temporal and conceptual knowledge gain, and dissemination of this knowledge to a broad audience, are the main goals.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.