Uptake of dissolved inorganic and organic bphosphorus compounds by phytoplankton and bacterioplankton

Abstract

Potential sources of dissolved P to phytoplankton and bacterioplankton were examined in a small meso‐eutrophic lake. Kinetic analyses of whole lake water on three dates demonstrated that the maximal rate (Vmax) for phosphate uptake was highest (5.2 nM min‒1) in spring. On all dates, size fractionation of plankton and kinetic analyses of uptake indicated that most (>50%) uptake of phosphate was by phytoplankton at Vmax and by bacteria at ambient concentrations. Isotope dilution assays, with either unlabeled phosphate or various dissolved organic P (DOP) compounds, demonstrated that phosphate was the preferred substrate for uptake into both algae and bacteria. Phytoplankton had greater capacity for uptake of P from both phosphate and DOP than bacterioplankton. We concluded that phytoplankton use both phosphate and DOP, particularly at high substrate concentrations, and that bacterial utilization of P may be limited by the availability of organic C or other nutrients.