PHOTOSYSTEM-II QUANTUM YIELDS, OFF-LINE MEASURED P I PARAMETERS AND CARBOHYDRATE DYNAMICS IN CHLORELLA-VULGARIS GROWN UNDER A FLUCTUATING LIGHT REGIME AND ITS APPLICATION FOR OPTIMIZING MASS-CULTURES/

The influence of hourly fluctuating irradiance on a continuous culture of Chlorella vulgaris on the quantum yield for stable charge separati on at photosystem II (phi(II,E)) was examined. Linear regression analy sis between phi(II,E) and Ft or Fm' showed that Ft or Fm' explained 86 and 54% of the variability in phi(II,E) respectively. The total amoun t of reducible Q(A) remained constant during the light period. Only pi gments that are known to operate in the xanthophyll cycle were variabl e. Violaxanthine reversibly decreased during the day, while an opposit e pattern was observed for antheraxanthine. The changes in violaxanthi ne significantly (P much less than 0.001) explained 87% of Fm' and 90% of the estimated values for the rate constant for energy dissipation by non-photochemical pathways. The magnitude of the variability in phi (II,E) was well within range of regulation by the photosynthetic proce sses itself. The results suggest that phi(II,E) alone can not be used as an index for the optimal cultivation of microalgae. Guidelines are proposed to translate fluorescence-derived parameters into general str ategies to optimize productivity. Estimates of in situ rates of primar y photosynthesis derived from phi(II,E) or from P/I derived estimates were significantly different, while predicted concentrations of carboh ydrate concentrations were similar.