AME 37:237-245 (2004)  -  doi:10.3354/ame037237

ABSTRACT: Changes in phosphorus (P) pools after the addition of nitrogen + organic carbon to Baltic Sea bacteria, as well as the relationship of this supply to the stimulation of bacterial alkaline phosphatase activity (APA), were investigated. Furthermore, the utilization of dissolved organic phosphorus (DOP) without and after stimulation, and if DOP was sufficient to meet the P demand, was studied. The simultaneous amendment of both substrates provoked a decrease of phosphate in water and an increase of P in the bacterial fraction. During the course of the experiments, the changes occurred in parallel with the stimulation of the APA. The increase in P in the bacterial fraction was predominantly influenced by the phosphate concentration. If the phosphate concentration was below the P demand, then DOP was used. DOP usage by bacteria proved dependent on the DOP concentration in the water. At concentrations of about 0.20 µM, the DOP consisted of material not usable by bacteria. At high concentrations of 0.44 µM, 0.15 µM of DOP was used. The maximum stimulation of bacterial APA correlated inversely with DOP changes, and high APA could not be associated with the amount of DOP degradation. Without exogenous nitrogen and carbon supply, phosphate and the available DOP in Baltic Sea water samples were sufficient to satisfy the bacterial need of P. However, after the addition of nitrogen and carbon, the available P pools were not capable of covering the P demand.

KEY WORDS: Alkaline phosphatase activity · Phosphorus pools · DOP · Bioavailable DOP · Baltic Sea