Phosphate Uptake by Eukaryotic Algae in Cultures and by a Mixed Phytoplankton Population in a Lake: Analysis by a Force‐Flow Relationship*

The phosphate uptake behaviour of monospecific cultures of green algae in the laboratory and of mixed phytoplankton populations in a mesotrophic lake has been analyzed with the aid of a force‐flow relationship. This analysis yields two parameters: A conductivity coefficient, that characterizes the activity of the phosphate uptake system. An external threshold phosphate concentration, below which uptake of phosphate is excluded on energetic grounds. When the phosphate concentration lies below the threshold value, the algae show an activation of the uptake system, reflected in an increase in the conductivity coefficient. Correspondingly, excess phosphate above the threshold value leads to a diminuation of the conductivity. Using this simple analysis, phosphate discharge into lake water may be readily monitored.