EFFECTS OF SOLAR-RADIATION AND SOLAR-RADIATION DEPRIVED OF UV-B AND TOTAL UV ON PHOTOSYNTHETIC OXYGEN PRODUCTION AND PULSE AMPLITUDE-MODULATED FLUORESCENCE IN THE BROWN ALGA PADINA-PAVONIA

The effects of solar radiation on photosynthetic oxygen production and pulse amplitude modulated (PAM) fluorescence were measured in the mar ine brown macroalga Padina paronia harvested from different depths fro m the Greek coast near Korinth. In fluence rate-response curves the li ght compensation point for photosynthetic oxygen production increased and the saturation level decreased with increasing exposure rime to so lar radiation. Cutting off the UV-B wavelength range (280-315 nm) from solar radiation reduced the inhibition of photosynthesis, and the org anisms were less affected when all of the UV radiation was filtered ou t, Algae collected from 7 m depth were much more prone to photoinhibit ion than those harvested from rock pools exposed to unfiltered solar r adiation. During continuous exposure to solar radiation, rock pool alg ae showed photoinhibition after longer periods of time than specimens from 7 m or from dark adapted habitats. When subjected to unfiltered s olar radiation the ratio of the variable fluorescence to the maximal f luorescence F-v/F-m (F-v = F-m - F-o) rapidly declined with increasing exposure time. However, again algae from 7 m depth were more pr one t o photoinhibition than rock pool algae. The differences between the tw o ecological strains were less obvious when UV-B or total UV was remov ed from solar radiation. Only in the latter case a complete recovery w as observed after 2 h while, when exposed to unfiltered sunlight, only the rock pool algae recovered completely within that time.