We determined phosphorus (P) limitation effect on the quantity and quality of dissolved organic matter (DOM) released by heterotrophic prokaryotes (HP). We grew 2 single bacterial strains, Photobacterium angustum and Sphingopyxis alaskensis, and natural HP communities collected in fall and spring from the Mediterranean Sea, on glucose under 2 treatments: P-replete vs. 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 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.

The data are collected in laboratory experiments testing phosphorus (P) limitation effect on the quantity and the quality of dissolved organic matter released by heterotrophic prokaryotes (HP-DOM). Two single bacterial strains and natural HP communities collected in fall and spring from the Mediterranean Sea, were grown on glucose under 2 treatments: P-replete vs. P-limiting. Cell abundance was followed by flow cytometry. Inorganic nutrient, dissolved organic carbon, glucose and fluorescent DOM were measured at the onset (T0) and end of incubation (Tf). Samples at T0 were directly measured and Tf samples were filtered twice onto 0.2 polycarbonate filters.