Dissertation Research: Quorum Sensing Influences Soil Nitrogen Mineralization and Plant Nitrogen Availability.

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ABSTRACTDissertation Research: Quorum sensing influences soil nitrogen mineralization and plant nitrogen availabilityRhizosphere microbial N mineralization provides plants the majority of their N nutrition, but most soil N is organic (chitin, proteins, lignoprotiens and nucleotides). The rate-limiting step in N mineralization may be digestion of these large molecules by microbial extracellular enzymes. Plants exert some control over bacterial function, and new evidence shows that root exudates can disrupt the dominant mechanism of bacterial-bacterial communication (quorum sensing (QS)) and QS-controlled behaviors, such as extracellular enzyme production. Our first hypothesis is that QS affects rhizosphere N mineralization, and plant health, by increasing soil enzyme activity due to increased signal in the rhizosphere. The second hypothesis is that cross-kingdom interactions in the rhizosphere between mycorrhizae, bacteria and plants affect N mineralization via QS. Microcosms allow easy access to the rhizosphere for manipulation of QS through signal addition, measurement of inorganic N pools and N mineralization. A combination of whole-cell biosensors, process rate measurements, decomposing population and community analyses will reveal the degree to which plants control rhizosphere N mineralization and how important this mode of control is for plant N accumulation. To establish this would be to rewrite the current paradigm that plants and microbes are the passive recipients of each other's excess, and set a new precedent for inter-species chemical communication and competition.