PHOTOSYNTHETIC OXYGEN PRODUCTION AND PAM FLUORESCENCE IN THE BROWN ALGA PADINA-PAVONICA MEASURED IN THE FIELD UNDER SOLAR-RADIATION

The effects of solar radiation on photosynthetic oxygen production, pu lse amplitude-modulated (PAM) fluorescence and pigmentation were measu red in the Mediterranean brown macroalga Padina pavonica (Linnaeus) La mouroux under field conditions and natural sunlight. Exposure of thall i to solar radiation for 1 h caused a dramatic decrease of their photo synthetic quantum yield, which recovered to initial levels after they had been placed in the shade for 3 h. Photoinhibition also occurred at the natural growth site of P. pavonica during the hours of maximal so lar irradiance. Photosynthetic oxygen production was also affected by high levels of solar radiation both in algae harvested from the surfac e and from 6 m depth; oxygen production started to decrease after a fe w minutes of exposure, and negative values were found after Ih of sola r exposure. Chlorophyll a content in P. pavonica also decreased during the hours of maximal solar irradiation. These results suggest that ph otoinhibition of P. pavonica occurs during part of a typical summer da y on Mediterranean coasts.