Impact of temperature acclimation on photosynthesis in the toxic red-tide dinoflagellate Alexandrium fundyense (Ca28)

This study assessed the impact of temperature on the photosynthetic activity in the dinoflagellate Alexandrium fundyense (Ca28) for cultures grown at 75 μmol photons m^-2 s^-1 over a range of temperatures. Increasing light intensity under static temperatures caused a 5-fold decrease in the maximum quantum yield for photosystem II (PSII) (F(v)/F(m)). Carbon fixation rates mirrored high-light depressions in F(v)/F(m). Cells in the presence of streptomycin showed an 83% recovery in F(v)/F(m); therefore, only a minor proportion of the decline in F(v)/F(m) was attributable to PSII damage by bright light. For cells transferred to higher temperatures, F(v)/F(m) was less sensitive to high light, decreasing only 20-40% compared to the 80-90% decrease observed for cells incubated at their ambient growth temperature. For cells shifted to higher temperatures, the rapid recovery phase of F(v)/F(m) was not present; therefore, cells did not initiate downregulation of PSII. Higher capacity to maintain electron transport, as indicated by the quantum yields, was confirmed by enhanced carbon fixation. Shifts to lower temperatures significantly increased PSII sensitivity to high light. Overall, these relationships reflect the synergy between photosynthetic light and dark reactions which are differentially impacted by changes in temperature.