The Ocean Nitrogen Imbalance Paradox: Environmental Controls on the Denitrification Isotope Effect

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Intellectual Merit: This study will test the sensitivity of the amplitude of the denitrification isotope effect to culture conditions pertinent to the ocean environment. The isotope effect amplitude will be explored with respect to electron donor, trace oxygenation, and temperature, in both batch and continuous culture experiments of denitrifiers. The proposed work will also involve measurements of the enzymatic isotope effect of the respiratory nitrate reductase of denitrifiers, measurements of its enzymatic activity among cultures, and examination of cellular nitrate transport kinetics of denitrifying strains. The experiments are designed to reveal the physiological basis of the modulation of the isotope effect amplitude, which will further resolve this manifestation in the environment. Broader Impacts: In regards to the broader significance and importance of this study, these new experimental data will provide a basis for integration of nitrogen isotope dynamics in ocean models to test how key environmental parameters can affect the global ocean distribution of nitrogen isotopes. Moreover, the proposal will provide support for a graduate student, who will be introduced to a broad range of techniques and sub-disciplines, from microbiology and enzymology, to oceanography and stable isotope biogeochemistry. The project involves an early career female PI, who will mentor one graduate student throughout the project.