Phosphate Exchange and Organic Phosphorus Excretion by Freshwater Algae

Rates of uptake and release of phosphorus compounds by four species of freshwater algae grown in axenic culture at phosphorus concentrations similar to lake water showed that an exchange of phosphate between the cells and the medium was the principal phosphorus flux. Algal-P showed turnover times as short as 69 min but no regular growth phase–turnover time relationship was found. During growth of the cultures, phosphate in the medium became depleted and turnover times as short as 2.7 min were measured. Significant amounts of dissolved organic phosphorus (DOP) were excreted. Some appeared to be of colloidal size.