EFFECTS OF SOLAR-RADIATION ON PHOTOINHIBITION AND PIGMENTATION IN THERED ALGA PORPHYRA-LEUCOSTICTA

The effect of solar radiation on photosynthesis, quantum yield of fluo rescence and pigmentation under solar radiation in a laboratory system and in the natural habitat during a daily cycle was investigated in t he red eulittoral alga Porphyra leucosticta. Optimal (F-v/F-m) and eff ective (Delta F/F-m') quantum yield of fluorescence, photosynthetic ef ficiency and maximal photosynthesis were drastically reduced by UV-B ( 280-315 nm) radiation in algae transferred from the laboratory (grown in white light) to solar radiation for 3 h. The absorptance due to cho rophyll and biliproteins (phycoerythrin and phycocyanin) increased aft er 3 h of incubation in photosynthetically active radiation (PAR, 400- 700 nm) and PAR+UV-A (315-400 nm) whereas no changes were observed und er PAR+UV-A+UV-B. In the field, the effective quantum yield and oxygen production decreased at noon during a daily cycle, indicating photoin hibition. When solar UV-A and UV-B radiation was removed by means of s elective filters, the average effective quantum yield increased by 28 +/- 2% SD. Chlorophyll and biliprotein concentration presented a daily pattern which was affected by UV radiation. Both chlorophyll and bili protein contents were reduced at noon, followed by recovery in the aft ernoon, but only when UV radiation was cut off. The difference between the maximal and minimal chl a concentration during the daily cycle wa s greater in the presence of UV radiation, but the difference for phyc oerythrin and phycocyanin was greater under PAR alone. These results s eem to indicate that the accumulation of pigments is affected by solar radiation, with short-term changes induced by UV Light. The ecologica l relevance of the daily variations of photosynthesis and pigmentation under solar radiation is discussed.