PHOTOACCLIMATION OF SCENEDESMUS-PROTUBERANS (CHLOROPHYCEAE) TO FLUCTUATING IRRADIANCES SIMULATING VERTICAL MIXING

Photoacclimation of Scenedesmus protuberans Fritsch to fluctuating irr adiances, simulating vertical mixing, was studied in light-limited con tinuous cultures. The algae were exposed to a simple sinusoidal light regime simulating diurnal irradiance, and two fluctuating regimes in w hich light fluctuations resulting from four and eight vertical circula tions of the algae through the water column were imposed on the sinuso idal light regime. The total daily light dose (TDLD) was kept constant . Maximum photosynthesis increased, and cellular chlorophyll content a nd photosynthetic unit size decreased in response to light fluctuation s. The efficiency of photosynthesis decreased during the light period in the sinusoidal light regime, whereas it remained at the same level in the fluctuating light regimes. The results suggest that prolonged e xposure to intermediate irradiances lowers the photosynthetic efficien cy of S.protuberans more than short exposure to high irradiances alter nated by low-light periods, and that this species is able to optimize its photosynthesis in fluctuating light.