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。除已转为农业的草地外，大部分草地用于放牧。NSF CAREER项目将首次研究放牧哺乳动物和土壤微生物之间的相互作用，这些生物共同控制草原氮（N）循环和土壤肥力。有待检验的假设包括：1）大型食草动物是否促进土壤微生物的扩散，以及2）这是否影响土壤氮循环的不同步骤，基于控制每个步骤的微生物的多样性。为此，项目人员，包括学生和公民科学家，将共同努力，测量土壤微生物生物多样性和氮循环活动在野牛和牛放牧和未放牧地区的高草草原。 这些实验将在10厘米（当地土壤微生物栖息地）至1000公里（弗林特山，堪萨斯州地区）的距离范围内进行。这项工作的结果将促进一般知识的调节草地土壤肥力的因素，包括那些支持生态系统的氮保持在当地的区域尺度。了解氮截留对保护公共饮用水质量具有重要意义。 成果还将包括向学生和公民广泛和及时地传播这一知识，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和放牧动物在这些生态系统中的关键作用，有没有一致的观点对草原N循环过程中的大有蹄类动物放牧的广义影响，超越了“放牧草坪”的现象，其中一个较高比例的N是在植物可用的形式，由于消费者驱动的养分循环。这项工作的总体假设是，草原土壤氮循环微生物的分布是更强烈的影响比当地的因素，更大的功能后果较低的功能冗余的公会规模。换句话说，在景观尺度上，大型食草动物的存在对微生物多样性的影响比土壤核心尺度上的土壤因素更强烈，这将与土壤硝化潜力（更专门的N-循环功能）的差异有关，而不是反硝化或分解潜力（顺序不太专门的功能）的差异。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渠道的沟通进行传播。除了这种区域规模的模式评估，实验工作将解析微生物群落组成和土壤pH值，有机质和氮的有效性对氮循环过程的独立影响。该奖项反映了NSF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.