The Effect Of Enhanced UV-B Radiation On The Growth, Physiological And Biochemical Characteristics Of Two Marine Microalgae Under Different Nitrogen Sources

Decrease of stratospheric ozone has been a significant global environmentalproblem, resulting in more UV radiation,especially UV-B reaching the surface of theearth. The enhanced UV radiation pose an important threat to the ecological systems,including marine ecological system, and marine microalgae is exposed to the potentialharmful UV-B radiation. Platymonas gelgolandica and Isochrysis galbana Parke8701are choosed as experimental materials to study the enhanced UV-B radiation onthe growth, physiological and biochemical characteristics of two marine microalgaeunder different nitrogen sources. The results are as follows:1. Acute toxicity test of UV-B radiation on marine microalgae(1) Low intensity and low dose of UV-B radiation can stimulate the growth of thetwo marine microalgae while high dose of UV-B radiation inhibited the growth of thetwo marine microalgae. Under the same radiation dose, inhabitation effect wasenhanced with the increasing of UV-B intensity for P. gelgolandica while there wasno ignificant different for I.galbana.(2) I. galbana was more sensitive to UV-B radiation than P. gelgolandica.2. Enhanced UV-B radiation on the growth, physiological and biochemicalcharacteristics of two marine microalgae under different nitrogen sources(1) Urea was the best nitrogen source for P. gelgolandica，secondly，ammoniumchloride and sodium nitrate. I. galbana grew well with sodium nitrate and urea andammonium chloride was the worst. The specific growth rate of the two marinemicroalgae increased first then decreased with UV-B radiation. Under UV-B radiationof0.5W/m2,the specific growth of P. gelgolandica with urea was the highest and there was no significant different between different nitrogen sources groups for I.galbana. Under UV-B radiation of0.25W/m~2, there was no significant differentbetween different nitrogen sources groups for P. gelgolandica and the specific growthof I. galban. with sodium nitrate was the highest.(2) The content of chlorophyll a of P. gelgolandica was decreasing with UV-Bradiation while under low intensity UV-B radiation（0.25W/m~2）, the content ofchlorophyll a under urea presented a decreasing first and then increasing gradually.The content of chlorophyll a of I.s galbana presented a decreasing first and thenincreasing gradually with UV-B radiation. Under different nitrogen sources, P.gelgolandica had more unsaturated fatty acids while I. galbana had more saturatedfatty acids. The maximum value of EPA was found under sodium nitrate in P.gelgolandica.and UV-B radiation can stimulated its value.The value of EPA andDHA were very low in I. galbana and the value of PUFA decreased with UV-Bradiation.(3)Nitrate reductase activity(NRA) of P. gelgolandica was found to be no significantdifferent under different nitrogen sources, while NRA of I. galbana was higher undersodium nitrate than that of other source of nitrogen. After UV-B radiation treatment,NRA of the two marine microalgae showed a trend of decreased first and thenincreased. There was no significant different between different nitrogen sourcesgroups for P. gelgolandica and NRA of I. galbana was higher under sodium nitratethan that of other source of nitrogen.