Consumption of dissolved organic carbon by marine bacteria and demand for inorganic nutrients

Abstract

Seawater cultures were used to study seasonal and diel variations in bacterial growth and nutrient availability.In both the Baltic Sea and the Northeast Mediterranean, the least available component for bacterial growth was phosphorus.In the Baltic Sea, carbon was available in excess for bacterial growth on all sampling occasions.Compared to the controls, additions of nonlimiting concentrations of inorganic nitrogen and phosphorus increased the yield of bacteria compared to the control with 156% and the degradation of dissolved organic carbon (DOC) by 64 % (as determined by high temperature catalytic oxidation).Analogous, bacterial growth yield increased along with an accumulation of inorganic nutrients in diel experiments with an intact foodweb (microcosm).The concentration of uthzable carbon (UC) was determined from bacterial consumption of DOC in seawater cultures during non-limiting nutrient conditions.Utilizable phosphorus (UP) and utilizable nitrogen (UN) were calculated by converting the bacterial biomass in the cultures into phosphorus and nitrogen equivalents.In the Baltic the average concentrations of UC, UN and UP were found to be 23 FM C. 0.6 pM N and 0.03 pM P respectively.Heterotrophic bacteria preferentially utilized inorganic nitrogen and phosphorus to support growth on a short time scale (days).Bacterial carbon content decreased as a result of nutrient additions from 51 k 7 to 32 f 5 fg C cell-' Growth efficiencies varied from 11 to 54 % in untreated cultures compared to 14 to 58% in cultures supplemented with nitrogen and phosphorus.