PHYSIOLOGICAL RESPONSES OF <i>ANABAENA VARIABILIS</i> (CYANOPHYCEAE) TO INSTANTANEOUS EXPOSURE TO VARIOUS COMBINATIONS OF LIGHT INTENSITY AND TEMPERATURE¹

Abstract

ABSTRACT Light intensity and temperature interactions have a complex effect on the physiological process rates of the filamentous bluegreen alga Anabaena variabilis Kütz. The optimum temperature for photosynthesis increased with increasing light intensity from 10°C at 42 μE·m −2 ·s −1 to 35°C at 562 μE·m −2 ·s −1 . The light saturation parameter, I K , increased with increasing temperatures. The maximum photosynthetic rate (2.0 g C·g dry wt. −1 ·d −1 ) occurred at 35°C and 564 μE·m −2 ·s −1 . At 15°C, the maximum rate was 1.25 g C·g dry wt. −1 ·d −1 at 332 μE·m −2 ·s −1 . The dark respiration rate increased exponentially with temperature. Under favorable conditions of light intensity and temperature the percent of extracellular release of dissolved organic carbon was less than 5% of the total C fixed. This release increased to nearly 40% under combinations of low light intensity and high temperature. A mathematical model was developed to simulate the interaction of light intensity and temperature on photosynthetic rate. The interactive effects were represented by making the light‐saturation parameters a function of temperature.