Underwater Light Climate and the Growth and Pigmentation of Planktonic Blue-Green Algae (Cyanobacteria) II. The Influence of Light Quality

The influence of variation in light quantity on the growth and pigmentation of eight strains of planktonic blue-green algae has been investigated under defined laboratory conditions. In light-limited cultures the relative concentrations of chlorophyll and phycobiliproteins per cell decline at a similar rate with increasing irradiance. Once maximum growth rate is reached, however, exposure to higher photon flux densities results in a further decline in light-harvesting capacity per cell and also in a reduction in the light absorption bandwidth owing to a preferential decrease in phycobiliprotein synthesis. Quantitative and qualitative changes in the net rates of pigment synthesis at high irradiance appear to be part of an overall mechanism that serves to maintain maximum growth rate under conditions that might otherwise favour chlorophyll photooxidation. At irradiances below those required for maximum growth rate, the net rates of chlorophyll and phycobiliprotein synthesis decline as growth becomes progressively light-limited. Such limitations of pigment synthesis appear to be imposed by genotypic constraints on the maximum cell density and on the size of photosynthetic units rather than by either light or nutrient limitation of chlorophyll and phycobiliprotein synthesis.