The Formation of Refractory Dissolved Organic Nitrogen From Free Amino Acids in the Ocean

Dissolved organic nitrogen (DON) is actively involved in N cycling and transformation processes the ocean, yet how this large pool formed remains elusive. Here we incubated 15N-labeled individual amino acids (Ala, Val, Phe) seawater monitored their fates over 21 days. About 25%–45% of Phe-N Val-N were transformed to “uncharacterizable DON,” as compared only about 6% for Ala-N, indicating formation refractory DON related specific acids. Through a stable isotope probing approach, 5 Phe-derived molecules from incubations found be present natural waters, possible structures proposed. These results shed new lights on mechanisms DON, including roles particular chemical that may resist decomposition millennial time scales.