The bioavailability of 7 organic and 2 inorganic phosphorus compounds to natural communities of coastal marine bacteria and phytoplankton was evaluated. A bioavailability factor (BF) based on changes in the turnover time of the phosphate pool (measured using 3'P0,) in the absence and presence of selected phosphorus compounds, relative to positive controls receiving PO,, was calculated as an index of the relative microbial metabolic preference for each added compound. There were marked differences in the bioavailabihty factors of various substrates tested with values ranging from 0 to 0.2. The results indicate that nucleotides were the most readily utilizable of the combined phosphorus compounds investigated. By comparison, the addition of selected monophosphate esters, either individually or in mixtures, had only a lirmted effect on orthophosphate (PO,) flux. However, orthophosphate appeared to be the preferred and, apparently, universal substrate. The bacterialennched slze fraction (< 0 8 pm) comprised an average of 75 % of the total phosphorus uptake measured in our samples A large but variable percentage of the added organic and combined inorganic compounds accunlulated outside the cells as soluble reactive phosphorus (SRP), indicating an efficient regeneration of orthophosphate from the various phosphorus compounds tested
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Björkman et al. (1994) studied this question.