Influence of light period length on photosynthesis and synchronous growth of the green algaScenedesmus protuberans

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Abstract
Scenedesmus protuberans was grown in turbidostat cultures with various light/dark cycles. Cultures with a light period length of 4–16 h showed a spontaneous partial synchronization of the population. The maximal growth rate was related to the maximal rate of cell division when growing with a L/D cycle. The same μmax was found with continuous illumination. Photosynthetic activities showed daily variations, that were largely influenced by partial synchronization. For cultures with a light period length of 4–8 h photosynthetic activities showed high variations but no daily patterns. These variations were due to changes in population composition. Cultures with a light period length of 12–16 h showed photosynthetic activities with little variation, but with distinct daily patterns related to the phase of the life cycle of the synchronized part of the population. “Young” cells exhibited high photosynthetic activities, while for “old” cells photosynthesis was low, thus reflecting the metabolic needs of the cells. S. protuberans did not adapt to shorter light periods by increasing its photosynthetic potential. This was used to explain the linear decrease in growth rate observed with light periods shorter than 16 h. Ecological implications of synchronized growth of algae are discussed in relation to the determination of μ in field populations.