EFFECTS OF UV-RADIATION ON PHOTOSYNTHESIS OF PHYTOPLANKTON EXPOSED TOSOLAR SIMULATOR LIGHT

A sunlight simulator was used to investigate the effects of short term irradiation on photosynthetic oxygen production and chlorophyll fluor escence in the unicellular algae Dunaliella salina and Ochromonas dani ca. Oxygen evolution was measured with a Clark-type electrode and init ial (F-0) and maximal (F-m) fluorescence were determined by means of a pulse amplitude-modulated (PAM) fluorometer. Using different long-pas s filters, a UV exclusion study was performed comparing the effects of irradiation with full sun simulator light, with sun simulator light w ithout UV-B and short wavelength UV-A radiation and without any UV com ponent. In D. salina, exposure to full sun simulator light caused a ma rked drop in photochemical efficiency indicated by a decline in the in itial slope of the irradiance-response curve for photosynthetic oxygen production and by a decrease in the ratio F-v/F-m, whereas only a sli ght inhibition of photosynthetic activity was observed irradiating wit h PAR and UV-A radiation or with PAR alone. In the case of O. danica, a strong inhibition was observed under all irradiation conditions. The results are consistent with preliminary data obtained with outdoor ex periments.