CAPABILITY OF DYNAMIC PHOTOINHIBITION IN ARCTIC MACROALGAE IS RELATEDTO THEIR DEPTH DISTRIBUTION

The capability of several macroalgal species to protect photosynthesis from excessive irradiance by dynamic photoinhibition was investigated relative to their depth distribution ill summer 1995 in the Kongsfjor d (79 degrees N; 12 degrees E, Ny Alesund, Spitsbergen, Norway). Photo inhibition of photosynthesis was induced by exposure of algae from dif ferent water depths to a high photon fluence rate of 500 mu mol m(-2) s(-1) for 2h. Changes in optimal quantum yield (F-v/F-m) were measured during the inhibition phase, Recovery of photosynthesis was subsequen tly induced by dim white light (10 mu mol m(-2) s(-1)) and observed as changes in the variable fluorescence. With a newly developed mathemat ical model different parameters of the response Kinetics of inhibition and recovery were calculated and related to the depth distribution of each algal species. It is shown that two components with slow and fas t reaction kinetics, respectively, are involved in photoinhibition and recovery of photosynthesis. Their possible molecular bases are discus sed. The half-life time (tau) of the inhibition and recovery phases, i .e. the time necessary to reach half maximal response, is clearly I:el ated to the depth distribution of the investigated species. Algae coll ected close to the water surface show a fast reaction of both photoinh ibition and recovery and, hence, have a low tau. With increasing depth the reactions become slower and tau increases, tau was highest in dee p water algae. Further analysis of the reaction kinetics in Laminaria saccharina shows that the relative proportion of the two kinetics invo lved change with the collection depth. In contrast, a significant diff erence in the reaction rates of both kinetics was not observed.