Collaborative Research: Using stable isotope labeling to trace the fate of amino acids and formation of refractory dissolved organic nitrogen (DON) in the ocean

Dissolved organic nitrogen (DON) is a large pool of reduced nitrogen that influences chemical and biological processes. DON plays important roles in primary production, nutrient availability, and carbon storage in the ocean. The compounds and structures in DON influence its role in these processes.

This project uses novel methods to study amino acids, a group of small organic nitrogen compounds that make-up proteins. Specifically, the study will focus on how amino acids are converted to different forms and “refractory DON.” Refractory DON is important because it can resist degradation and persist in the ocean for several thousand years. This study will use stable isotopes to trace the fate of nitrogen in amino acids and address important questions about marine nitrogen cycling.

Findings from this study will be useful for understanding the composition of DON and how marine organisms use this form of nitrogen. In addition, this project will train graduate and undergraduate students, offer education programs to K-12 students, and enhance ocean literacy through public presentations and radio programs.

This project investigates the fate of nitrogen (N) in amino acids and the processes that contribute to forming refractory dissolved organic nitrogen (DON) in the ocean. Using stable isotope probing with 15N-labeled amino acids and controlled incubations, the study will trace the fate of different amino acids with diverse chemical structures in waters from productive coastal zones to oligotrophic open ocean waters.

The proportions of amino acid-derived N that are remineralized into inorganic forms (e.g., ammonium, nitrite and nitrate), converted to labile DON, and transformed to refractory DON, will be traced and quantified. Through the comparison of labeled and unlabeled incubations, advanced high-resolution mass spectrometry techniques will be applied to characterize the molecular composition of amino acid-derived DON and compare it to naturally occurring refractory DON.

The overarching goal of the project is to improve the understanding of N cycling and the processes that influence the marine DON pool. Results from this project will enhance our understanding of marine N dynamics and the molecular-level composition of the oceanic DON pool. This project will also promote STEM education by training graduate and undergraduate students through a semester by the sea program and summer internships.

K-12 students will have educational opportunities through a summer science program at the University of Texas Marine Science Institute. Results will be disseminated through publications, national and international conference presentations, public lectures and radio programs.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.