EFFECTS OF SOLAR ULTRAVIOLET RADIATION ON GROWTH AND PHOTOSYNTHESIS OF HIZIKIA FUSIFORMIS

Effects of solar ultraviolet radiation(UVR) on the growth and photosynthesis of the economic brown alga Hizikia fusiformis were investigated while exposed to full spectrum solar radiation(280-700 nm),solar radiation depleted of UV-B(320-700 nm) and solar radiation deprived of total UVR(400-700 nm) in order to understand its responses to changes in solar UVR.The growth of H.fusiformis was determined by weighting the fresh algae every two days and the photosynthetic oxygen evolution was assayed by a Clark-type oxygen electrode.To determine the contents of chlorophyll a and UV-absorbing compounds(UVAC),methanol extracts from H.fusiformis were scanned from 250 to 750 nm.The concentration of chlorophyll a was calculated using the equation of Porra and the contents of UVAC per fresh mass were estimated by determining the ratio of UVAC to chlorophyll a according to Dunlap et al and multiplying the ratio of chlorophyll a content to fresh weight of the sample used.It was found that the relative growth rate was higher when algae received more daily doses and higher levels of solar irradiances depleted of UVR also led to higher photosynthetic oxygen evolution.However,solar UVR could inhibit the photosynthetic oxygen evolution and growth rate and decrease the content of chlorophyll a of H.fusiformis and higher levels of solar UVR irradiances or doses led to higher inhibitory effects.Although ultraviolet-absorbing compounds were induced by solar ultraviolet radiation,they could not fully counteract the damage to H.fusiformis induced by UVR