Nitrogen and phosphorus required for the growth of phytoplankton

A method is described for obtaining growths of phytoplankton in samples of crude sea water, similar in composition but several hundred times more dense than phytoplankton communities occurring in the sea. The ratio of nitrogen to phosphorus utilized by such communities has been determined. They use ammonium in preference to nitrate, although the latter may be many times more concentrated than the former. They use urea and uric acid as sources of nitrogen. Certain amino-acids when added as sources of nitrogen were attacked by the bacteria in the community and either the ammonium set free or both the ammonium and the amino-acid were used by the phytoplankton. Others, as d -leucine, were not utilized, or, as l -leucine, only slowly utilized. Sodium nucleinate and caseinate were rapidly broken down when added to crude sea water by bacterial action, and the phosphate produced utilized by phytoplankton. There was no significant utilization of glycerophosphate.