EFFECTS OF LIGHT INTENSITY AND TEMPERATURE ON<i>CRYPTOMONAS OVATA</i>(CRYPTOPHYCEAE) GROWTH AND NUTRIENT UPTAKE RATES¹

Abstract

ABSTRACT Specific growth rate of Cryptomonas ovata var. palustris Pringsheim was measured in batch culture at 14 light‐temperature combinations. Both the maximum growth rate (μ m ) and optimum light intensity (I opt ) fit an empirical function that increases exponentially with temperature up to an optimum (T opt ), then declines rapidly as temperature exceeds T opt . Incorporation of these functions into Steele's growth equation gives a good estimate of specific growth rate over a wide range of temperature and light intensity. Rates of phosphate, ammonium and nitrate uptake were measured separately at 16 combinations of irradiance and temperature and following a spike addition of all starved cells initially took up nutrient at a rapid rate. This transitory surge was followed by a period of steady, substrate‐saturated uptake that persisted until external nutrient concentration fell. Substrate‐saturated NO 3 − ‐uptake proceeded at very slow rates in the dark and was stimulated by both increased temperature and irradiance; NH 4 + ‐uptake apparently proceeded at a basal rate at 8 and l4 C and was also stimulated by increased temperature and irradiance. Rates of NH 4 − ‐uptake were much higher than NO 3 − ‐uptake at all light‐temperature combinations. Below 20 C, PO 4 −3 ‐uptake was more rapid in dark than in light, but was light enhanced at 26 C.