Photoinhibition of photosynthesis in the marine brown algae Fucus serratus as studied in field experiments

Abstract

ABSTRACT: In field experiments photoinhibition of photosynthesis'inthe intertidal brown alga Fucus serratus was investigated by meansof both fluorescence and oxygen measurements. Samples were takenfrom thalli floating just below the water surface. Dunng fallingtides the ratio variable fluores- FF) cence/maxlrnum fluorescence( J , decreased with increasing photon fluence rates. As during risingtides only samples could be measured that were previously desiccated,F,/F, increased. Plants living in a rock pool and, hence, not emersingduring falling tides showed a considerable decrease of photo- syntheticcapacity due to photoinhibition. Measured algae samples were collectedafter experiments, kept for about 24 h in dim light for recoveryand then measured again. These values were used as references inorder to calculate the extent of photoinhibition. Oxygen measurementssupport results obtained with the fluorescence technique. In themorning photosynthetic capacity decreased with increasing photonfluence rates. Photosynthetic capacity recovered in the late afternoonand early evening when photon fluence rates decreased. However, ifon a sunny day a n algal sample oriented perpendicularly to the sun'srays was continuously irradiated, a strong decrease of photosyntheticcapacity was observed which was not reversible under the dim lightconditions of the afternoon and early evening. This indicates photodamage.