The remineralization and fate of labile organic nitrogen in marine environments

The production of algal biomass and its subsequent remineralization essentially drives elemental cycling and the preservation of a small fraction of organic matter in the ocean. Since proteins account for a major fraction of the algal biomass and half of the algal production is processed by heterotrophic bacteria, understanding bacteria-mediated protein degradation, from extracellular enzymatic hydrolysis, nutrient regeneration to the formation of refractory organic matter, may be one of the key deciphering ocean carbon and nitrogen cycling. While the degradation of organic carbon has been extensively studied, studies on the degradation of organic nitrogen are relatively sporadic. In this study we systemically examined the degradation and fate of small peptides and free amino acids through the ¹⁵N labelling technique. Our laboatory incubation results showed that the fraction of refractory organic nitrogen formed is dependent on specific amino acids. For example, our results showed that as much as 45% of valine N was transformed to refractory dissolved organic nitrogen (DON) as compared to 6% for alanine after 3 weeks of incubation. The DON derived from amino acids was further characterized using high resolution liquid chromatography mass spectrometry and the results will be presented. Overall, our results suggested that the formation of refractory DON in the ocean may be related to specific amino acids, and this formation seems to be rapid, in a time scale of weeks.  

Presentation Preference: Oral

Primary Presenter: Zhanfei Liu, The University of Texas at Austin (zhanfei.liu@utexas.edu)

Authors:

Kaijun Lu, Coastal Carolina University  (Kaijun.lu@utexas.edu)