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

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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.