ADAPTATION OF UNICELLULAR ALGAE TO IRRADIANCE: AN ANALYSIS OF STRATEGIES

SUMMARY 157INTRODUCTION 158AN.^LYTICAL METHODS 159LIGHT HARVESTING BY MICROALGAE 160RANGE OF PHOTON FLUX DENSITIES ALLOWING GROWTH AND PHOTOSYNTHESIS INPHOTOTHOPHIC MICROALGAE (GENOTYPIC ADAPTATION) 163 Growth 163Photosynthesis 165Photoinhibition 165 PHENOTYPIC ADAPTATION 168 Changes in amounts of pigments 168Interpretation of the effects of pigment changes: models 169Observed changes in P vs I curves 170 ENERGETIC CONSIDERATIONS 174 General 174Reduction of capital costs 175Reduction of maintenance costs 175Energetic costs of changing the photosyothetic apparatus 177S2-S3 decay 177Proton leakage due to passive uniport 178 PHYLOGENETIC ASPECTS OF DIFFERENCES IN LIGHT RESPONSES OF MICROALGALPHOTOSYNTHESIS AND PHOTOLITHOTROPHIC GROWTH 178 Phylogenetic diflerences in photosynthetic structures 178Comparison of tbe photosynthetic characteristics of green algae and otherpbototrophs 180 ECOLOGICAL CONSIDERATIONS 182ACKNOWLEDGEMENTS 185REFERENCES 185 SUMMARY Analysis of data in the literature relating to micrcalgal adaptations to different photon fluxdensities indicates that different algal classes have significantly different ligbt requirennents forgrowth and photosynthesis. Although there is some variability within each class, dinoflagellatesand blue-green algae generally photosynthesize and grow best at low photon flux densities.Diatoms also tend to be able to grow at very low photon flux densities (growth for some specieshas been reported at less than 1 fi.E m"' s~'). Comparison of the photon flux densities at whichphotoinhibition occurs in dinoflagellates and diatoms suggests that the former often experiencephotoinhibition at comparatively low irradiances. In contrast, diatoms often can toleraterelatively high light environments. This tolerance of a large absolute range of photon fluxdensities may, in part, explain why diatoms are often associated with spring blooms. Green algae* New address; Department of Botany, La Trobe University, Bundoora, Victoria, 3083 Australia.0028-646X/83/020157 + 35 S03.00/0 © 1983 The New Phytologist