The photosynthesis and growth efficiency of a planktonic blue-green alga,Oscillatoria redekei

Growth rate data of Oscillatoria redekei van Goor grown under a range of irradiances and light:dark cycles were used to examine the relationship between growth rate and light dose (irradiance × duration), the growth efficiency. When growth efficiency was greatest, growth rate responded directly to light dose and similar values for growth efficiency could be obtained at a range of temperatures. This suggests that under these conditions, respiration losses throughout the light:dark cycle were controlled by the photosynthetic carbon input. The maximum growth efficiency observed was 1·7 E m-2 (400–700 nm) per population doubling. Under continuous light, photosynthesis saturated at higher than incident irradiances so that photosynthesis proceeded at a fraction of the maximum rate; under light:dark cycling, photosynthesis was saturated below the highest growth irradiance and therefore proceeded at the saturation value.