Photosynthesis by Natural Phytoplankton Populations and Its Interrelationship With Light and Temperature

Abstract

<p>Photosynthesis measurements were conducted through the fall, winter and spring of 1974-75 on natural phytoplankton populations from Coote's Paradise (Lake Ontario). Oxygen evolution was measured using oxygen electrodes under a matrix of light and temperature conditions. Respiration was also measured. The P.Q. was determined and averaged 1.13 over the year. The short term oxygen results showed a linear response of net photosynthesis to light. Respiration rates at each temperature were used to calculate gross photosynthesis. The temperature data was converted to Arrhenius plots. The temperature vs. photosynthesis correlations revealed that at least over the time of the oxygen measurement, dark respiration continues in the light. Respiration rates showed a strong seasonal trend. Respiration per mg chl a increased as the water temperature decreased. An excellent relationship was observed between maximum gross assimilation number and temperature. This relationship appears to be independent of species composition and such variables as growth rate, temperature and variations in nutrient conditions. The temperature response revealed indicates no temperature adaptation by the photosynthetic mechanism of phytoplankton and would not be as clearly revealed using cultured algae and in situ¹⁴C techniques.</p>