EFFECTS OF LIGHT INTENSITY AND TEMPERATURE ONCRYPTOMONAS OVATA(CRYPTOPHYCEAE) GROWTH AND NUTRIENT UPTAKE RATES1

Abstract

ABSTRACTSpecific growth rate ofCryptomonas ovatavar.palustrisPringsheim was measured in batch culture at 14 light‐temperature combinations. Both the maximum growth rate (μm) and optimum light intensity(Iopt)fit an empirical function that increases exponentially with temperature up to an optimum(Topt),then declines rapidly as temperature exceedsTopt.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 NO3−‐uptake proceeded at very slow rates in the dark and was stimulated by both increased temperature and irradiance; NH4+‐uptake apparently proceeded at a basal rate at 8 and l4 C and was also stimulated by increased temperature and irradiance. Rates of NH4−‐uptake were much higher than NO3−‐uptake at all light‐temperature combinations. Below 20 C, PO4−3‐uptake was more rapid in dark than in light, but was light enhanced at 26 C.