Phosphorus limitation determines the quality of dissolved organic matter released by marine heterotrophic prokaryotes

We determined phosphorus (P) limitation effect on the quantity and quality of dissolved organic matter (DOM) released by heterotrophic prokaryotes (HP). We grew two single‐bacterial strains from different lifestyles, the copiotrophic Photobacterium angustum and the oligotrophic Sphingopyxis alaskensis, and natural HP communities collected in fall and spring from the Mediterranean Sea, on glucose under two treatments: P‐replete versus P‐limiting. DOM release by HP comprised up to 30% of the initial carbon provided for growth. P‐availability influenced carbon allocation to different cellular processes (respiration vs. growth), but did not significantly affect the net quantity of DOM released by HP. However, using fluorescence spectroscopy, we demonstrated an effect of P‐limitation on DOM quality, with a predominance of humic‐like compounds under P‐limitation but protein‐like compounds under P‐repletion. Our results suggest that P‐limitation could determine the fate of HP‐derived DOM in the ocean, thus affecting the microbial carbon pump.