Higher Levels of Soluble Reactive Phosphorus Promote Labile Organic Nitrogen Cycling in Subsurface Coastal Waters

Remineralization of labile organic nitrogen is a key part cycling in seawater, yet factors controlling this process remain poorly understood. The degradation and fate amino acids coastal waters were investigated with incubation experiments using 15N-labeled alanine (Ala). Ala, including the release NH4+ through remineralization, subsequent removal via assimilation nitrification, formation refractory dissolved (DON), was more rapid subsurface (mid-depth 8 m bottom 17 m) than surface (2 northern Gulf Mexico summer. This pattern attributed to different levels soluble reactive phosphorus (SRP) observed at depths water column. addition orthophosphate low SRP (<0.1 μmol L−1) significantly accelerated remineralization acid, DON. acid further nitrification SRP-replete are linked growth heterotrophic bacteria ammonia-oxidizing archaea, respectively. Taken together, these results suggest that enriched pre-primed for N metabolisms, providing mechanistic insights into marine waters.