Contrasting Roles of DOP as a Source of Phosphorus and Energy for Marine Diazotrophs

The oceanic dissolved organic phosphorus (DOP) pool is mainly composed of P-esters and, to a lesser extent, equally abundant phosphonate and P-anhydride molecules. In phosphate-limited ocean regions, diazotrophs are thought rely on DOP compounds as an alternative source (P). While both phosphonates effectively promote dinitrogen (N 2 ) fixation, the role P-anhydrides for unknown. Here we explore effect N fixation at two stations with contrasting biogeochemical conditions: one located in Tonga trench volcanic arc region (“volcano,” low phosphate high iron concentrations), other South Pacific Gyre (“gyre,” moderate iron). We incubated surface seawater AMP (P-ester), ATP (P-ester P-anhydride), or 3polyP (P-anhydride) determined cell-specific rates, nifH gene abundance, transcription Crocosphaera Trichodesmium . did not respond any added, suggesting that they were P-limited volcano station outcompeted by conditions gyre station. Conversely, numerous their specific rates stimulated slightly stations. Heterotrophic bacteria responded additions similarly stations, despite availability. use heterotrophic concentrations suggests this compound, addition being P, can be used acquire energy which groups compete. may thus leverage restrictions future stratified nutrient-impoverished ocean.