Influence of light and three nitrogen sources on growth of Heterosigma carterae (Raphidophyceae)

Abstract

Growth rates of Heterosigma carterae (Hulburt) comb, nov., isolated from the 1989 bloom in Big Glory Bay, New Zealand, were studied in continuous batch cultures, with 48 combinations of light and nitrogen (N) sources: NO₃ ^–, NH₄ ⁺, and urea. Light had more influence on cultures grown with NO₃ ^– than cultures grown with the other N sources. At 160 μmol photons m^–2 s^–1, the growth rate of H. carterae was highest with NO₃ ^–, intermediate with NH⁺ ₄, and lowest with urea. At lower irradiances, growth rates of NO₃ ^–‐grown H. carterae were lower than those of either form of “recycled” N. For NH₄ ⁺‐ and urea‐grown cultures, nutrient concentration contributed to a greater variation of growth than did light. H. carterae exhibited signs of toxicity at high concentrations of NH₄ ⁺ and urea, particularly at low light levels. The implication of the variations in growth rate under different combinations of light and N sources is that maximum growth of H. carterae in the field is probably attained in the well‐illuminated, upper water column with NO₃ ^– as the major N source. When either NH₄ ⁺ or urea is the major N source, a lower maximum growth rate is probably attained over a greater range of illumination deeper in the water column.

Keywords:

• growth rates
• light
• nitrogen sources
• interaction
• Heterosigma carterae