DISSERTATION RESEARCH: Rhizosphere Control of Soil Carbon Protection on Mineral Surfaces

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Storage of carbon in soil is of high interest to ecosystem scientists because it enhances soil fertility and potentially decreases the production of gases like carbon dioxide and methane. Plant roots provide the major input of soil carbon, transferring carbon dioxide captured from the atmosphere into the soil system. Microorganisms in the soil are the primary consumers and decomposers of this carbon, and can transform it back into carbon dioxide, or into methane. It follows that the part of the soil where microorganisms come in contact with plant roots is a hotspot for carbon transformation. This graduate student research research project will follow the fate of root-derived carbon in soil, examining the role of soil microbial communities and associated soil minerals in carbon stabilization. The project will involve collaboration with scientists at national laboratories and promote participation of students from under-represented groups in the research. While carbon (C) association with soil minerals is thought to be a critical step in soil C stabilization, the underlying mechanisms - particularly in the persistence of mineral-carbon associations - are poorly understood. The student will grow the common annual grass, Avena barbata, (wild oat) under a 13CO2 atmosphere in soil microcosms, thus enabling her to follow the fate of the root-derived C. Using a technique called stable isotope probing (SIP), she will trace the 13C derived from the plant into soil microbes and on to soil minerals. In this project, the researchers will investigate how the longer term fate of C, present on minerals or in soil microorganisms is effected by the presence or absence of A. barbata. The research will examine (1) the fate of mineral-associated C, (2) the influence of mineralogy, (3) the influence of the rhizosphere, the zone of plant root influence, and (4) the role of the microbial community. By constraining both the mechanisms of mineral-C association and persistence, the researchers can begin to understand and quantify the importance of these associations in C cycling and environmental change models.