Effect of short-term variations in light intensity on photosynthesis of a marine phytoplankter: A laboratory simulation study

Parameters of photosynthesis and growth were measured for a marine diatom (Lauderia borealis) grown in axenic continuous culture under three different light regimes: constant, simulated diurnal variation, and fluctuating. The light fluctuations were systematic increases and decreases in light intensity superimposed on the diurnal regime. In the first two regimes, a morning maximum and an afternoon depression in photosynthesis were observed. In the fluctuating light regime, the afternoon depression was less pronounced and the morning maximum was enhanced. The results may be explained by postulating a time-dependent value for the light-saturated rate of photosynthesis. Light utilization mmol O₂ cell^-1 (E m^-2)^-1] was the same for the diurnally varying and fluctuating regimes, despite the fact that the peak light intensity in the fluctuating regime was double that of the diurnally varying regime.