Landscape fire and grazing management history affects soil microbial biogeography

Microbes matter to environmental health - both ecosystem and animal host environments. Animals are an integral part of ecosystems, especially at a landscape scale. Human animals manage ecosystems for agriculture and conservation, and in both agricultural and "wild" ecosystems, non-human animals are often the most charismatic fauna. In addition to microbes supporting soil, animal and ecosystem health, animals may affect microbes in ecosystems. Animals move cells around landscapes, and themselves act as selective filters within the landscape. Non-human and human animals also influence ecosystem attributes like soil pH, soil organic matter, soil nitrogen availability, and soil water content, which in turn can promote the growth of certain types of microbes. Biogeography and metacommunity concepts offer a framework through which to consider the relative influence of microbial movement/dispersal and environmental filtering on soil microbial diversity and microbial community composition. An experimental context in which animal presence and ecosystem attributes are manipulated in factorial is also particularly powerful. Patterns in microbial biogeography are often analogous to patterns in plant biogeography, so there is reason to predict animal-mediated dispersal and environmental filtering may affect soil microbial diversity and community composition in our experimental landscape, similar to plant patterns of diversity. We measured soil microbial community composition in a log-space design across watersheds with a long-term history of annual fire (or infrequent fire) and bison grazing (or no grazing). These watershed-scale treatments affected soil microbial diversity in a way that supports the hypothesis that fire and grazing affect microbial dispersal patterns and thus soil microbial biodiversity.

微生物对生态系统与宿主动物两类环境的健康至关重要。动物是生态系统不可或缺的组成部分，尤其在景观尺度上尤为显著。人类通过农业生产与生态保护活动对生态系统进行管理；无论在农业还是‘野生’生态系统中，非人类动物往往是最具吸引力的魅力型动物类群。除微生物可维系土壤、动物及生态系统健康外，动物也会对生态系统中的微生物产生影响。动物会携带着微生物细胞在景观范围内移动，自身亦可作为景观内的选择性过滤单元。人类与非人类动物还会改变土壤pH值、土壤有机质、土壤有效氮含量与土壤含水量等生态系统属性，进而促进特定类群微生物的生长。生物地理学（biogeography）与集合群落（metacommunity）理论为我们解析微生物运动/扩散（dispersal）与环境过滤作用对土壤微生物多样性及微生物群落组成的相对影响提供了分析框架。设置动物存在与否与生态系统属性调控的析因实验（factorial）设计，亦是极具研究价值的实验范式。微生物生物地理学的分布模式通常与植物生物地理学模式相似，因此我们有理由推测，在本实验的景观系统中，动物介导的扩散与环境过滤作用同样会像调控植物多样性那样，对土壤微生物多样性与群落组成产生调控效应。本研究采用对数空间采样设计，对具备长期年度火烧（或低频率火烧）与野牛放牧（或无放牧）处理历史的流域内土壤微生物群落组成进行了测定。流域尺度的火烧与放牧处理对土壤微生物多样性产生了显著影响，该结果支持‘火烧与放牧可通过调控微生物扩散模式进而影响土壤微生物生物多样性’的研究假说。