Nitrogen is often a limiting resource in marine ecosystems, and its availability is heavily influenced by human activities, sometimes causing eutrophication. The study of phytoplankton metabolism under nitrogen-limited and replete conditions is of interest due to eutrophication's ecological and economic implications and the prevalence of nitrogen limitation on marine primary productivity. To investigate the metabolic effects of rapid nitrogen addition on phytoplankton metabolism, 15N-nitrate was traced into polymerized and free amino acids in two treatments of the microalgae Tisochrysis lutea with either initially limiting or replete nitrate concentrations. Using acid digestion, derivatization, and GCMS analysis we found that the culture with a lower initial nitrate concentration incorporated more 15N into alanine, valine, serine, and threonine. This suggests that phytoplankton under nitrogen-limited conditions exhibit greater increases in metabolism than those under replete conditions following rapid nitrogen influxes. Heavy nitrogen incorporation into other metabolites was also detected. This work provides a foundational method for future studies into phytoplankton metabolism under varying environmental conditions.

We explore the Earth in order to discover and understand the ecosystems present on it. Representing 70% of the surface of the globe, the oceans are arguably the place we struggle the most to explore due to their size and depth (we know more about space than we do about our oceans). Dissolved organic compounds, produced by diverse marine organisms for a wide variety of reasons, are present in very low concentration in the oceans. This research was done in order to develop, design, and ameliorate existing techniques to detect and analyze dissolved organic compounds (amino acid in this case) present in seawater. Cation exchange chromatography, derivatization and gas chromatography mass spectrometry were used. The results were not as expected but the methodology is very promising. With some ameliorations, that methodology will be able to help us detect and analyze known and unknown particles at very low concentration in our vast oceans.