Dissertation Research: The biotic environment and the context-dependent nature of plant-microbial symbiosis

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Plants often harbor a wide variety of microbial organisms within their bodies. Interactions between plants and these microbial symbionts influence the diversity, structure, and function of terrestrial plant communities. In many such interactions the microbe provides host plants with nutrients in exchange for carbon from the plant. Arbuscular mycorrhizal fungi, a soil fungus that specializes in the acquisition of phosphorus, and rhizobia, a nitrogen-fixing soil bacterium are two common nutritional plant symbionts of legume plants. The manner in which each of these symbionts benefits or antagonizes their plant partner varies and is partially determined by soil nutrient levels. Moreover, plants can allocate resources to multiple partners, allowing for the presence of simultaneous interactions to influence the costs and benefits of the interaction. This project evaluates the relative importance of biotic (i.e. co-occurring symbionts) and abiotic (i.e. soil nutrient levels) factors on the consequences of plant-microbial interactions.The majority of investigations on plant-microbial interactions have focused a single host and a single symbiont. Yet in nature plants simultaneously interact with many symbionts. This project experimentally examines the importance of this feature of natural plant-microbe interactions. Results of this project are applicable to many goals of ecological restoration. Because of their ability to fix nitrogen, legumes are important members of plant communities, and are often priority species in restoration management. Many restoration projects begin in post-agricultural fields. While the soils of natural areas are often nutrient limited, disturbed environments are often subjected to high levels of anthropological nutrient deposition. Thus this project aids the success of restoration efforts by shedding light onto the consequences of both unnatural nutrient levels and the soil community the legume-rhizobia interactions. We will incorporate work from this project into a special program at a local children's science museum that elucidates below-ground biological process and organisms.