DISSERTATION RESEARCH: Linking microbial community assembly and elemental cycles in a natural micro-ecosystem

微生物群落存在于地球上的每一个环境中，并对生物圈的健康发挥着至关重要的多种生态功能。死亡有机物的分解以及随后营养物质的再循环回到食物网，主要是微生物在从人类消化道到海底的栖息地中发挥的作用。像植物和动物一样，这些微生物群落经历了由环境变化和相互作用（如竞争和捕食）引起的时间更替（演替）。此外，由于细菌和古生菌等微生物的繁殖时间非常快，并且可以与不相关的个体交换遗传物质，因此它们可以迅速适应新的环境并在其中茁壮成长。拟议的研究有两个主要目标：第一，调查微生态系统内微生物适应和群落演替的时间尺度，第二，评估这些变化对食物网中营养物质分解和再循环的影响。了解微生物演替如何影响在各种生物尺度上运行的过程与农业生产和土地管理直接相关，拟议的研究将测试一些长期存在的假设，即竞争在驱动生态系统内营养循环中的作用。除了支持研究生的工作，本科生将得到指导。猪笼草将被用作模式生态系统，以研究微生物演替对养分循环的影响。加州的猪笼草，Darlingtonia californica，是一种食肉植物，从专门的充满水的叶子捕获的昆虫猎物中获得营养。消化是由一个水生微生物群落，迅速发展和变化的投手的生命周期。由于微生物生态相互作用和进化往往发生在相似的时间尺度上，因此有可能在一个发育中的猪笼草生态系统中研究各种生物尺度上微生物演替的原因和后果。拟议的研究包括三个主要途径。首先，复制环境基因组和代谢研究将用于评估投手的微生物群落的分解能力如何随时间变化。接下来，实验室竞争分析将测试微生物群落是否随着演替的进行而更善于竞争限制生长的营养物质。最后，利用氮和碳的稳定同位素进行的实地研究将把微生物群落的时间变化与猪笼草微生态系统内营养循环的速率联系起来。

Communities of microorganisms are found in every environment on the planet and perform myriad ecological functions critical to the health of the biosphere. The decomposition of dead organic matter and the subsequent recycling of nutrients back into the food web are roles played primarily by microbes, in habitats ranging from the human digestive tract to the ocean floor. Like plants and animals, these microbial communities experience turnover with time (succession) resulting from both environmental change and interactions such as competition and predation. Furthermore, since microbes such as bacteria and archaea can have very rapid generation times and exchange genetic material with unrelated individuals, they can rapidly adapt to, and thrive in, a novel environment. The proposed research has two main goals: first, to investigate the time-scale of microbial adaptation and community succession within a micro-ecosystem, and second, to evaluate the consequences of these changes for the breakdown and recycling of nutrients in the food web. An understanding of how microbial succession affects processes operating at a variety of biological scales has direct relevance to agricultural production and land management, and the proposed research will test some long-standing assumptions regarding the role of competition in driving nutrient cycling within an ecosystem. In addition to supporting the work of a graduate student, undergraduates will be mentored. Pitcher plants will be used as model ecosystems to examine the effects of microbial succession on nutrient cycling. The California pitcher plant, Darlingtonia californica, is a carnivorous plant that receives nutrients from insect prey captured by specialized water-filled leaves. Digestion is enabled by an aquatic microbial community that rapidly develops and changes over a pitcher's lifespan. Because microbial ecological interactions and evolution often occur on similar time-scales, it is possible to study the causes and consequences of microbial succession at a variety of biological scales within a developing pitcher plant ecosystem. The proposed research includes three main approaches. First, replicated environmental genomic and metabolic studies will be used to assess how the decomposing abilities of a pitcher's microbial community change with time. Next, a laboratory competition assay will test whether microbial communities become better at competing for growth-limiting nutrients as succession proceeds. Finally, a field study utilizing stable isotopes of nitrogen and carbon will link temporal changes in a microbial community to their rates of nutrient cycling within the pitcher micro-ecosystem.