Growth of some strains of Stigeoclonium (Chlorophyta) on nitrate, ammonium, ammonium nitrate and urea

Abstract

Nine unialgal strains of five Stigeoclonium species were cultured in synthetic medium with various concentrations of ammonium, nitrate, ammonium nitrate and urea. Growth responses to 5 mg N1^-1 of the various nitrogen sources varied only a little. All strains grew well in media with concentrations of nitrate and urea between 12·5 and 25 mg N1^-1. Ammonium concentrations beyond 5 and 12·5 mg N1^-1 inhibited the yield of most cultures, while yields obtained with NH₄NO₃ showed intermediate values to NO₃ and NH₄ as sole nitrogen sources. It is most unlikely that nitrate attains saturation levels in the field, but concentrations of ammonium may be high enough to inhibit growth of Stigeoclonium at certain sites. A clear relationship between growth responses of the strains and the nitrogen levels of their original field situation was not found. The justification for comparing bioassay results with the inorganic nitrogen or total nitrogen concentration of the testwater is discussed.