Effects Of UV-B Radiation On The Interaction Of Macro-Algae And Micro-Algae

Enhanced UV-B (280nm~320nrn) radiation resulting from ozone depletion is one of global environmental problems. Not only marine organisms but also marine ecosystem can be affected by enhanced UV-B radiation.The effects of UV-B radiation on interaction of macro-algae and micro-algae were studied using Ulva pertusaje Kllm, Platymonas gelgolandica and Alexandrium tamarense as the materials in this thesis. The result showed as follows:UV-B radiation could inhibit the growth of Ulva pertusaje , Platymonas gelgolandica and Alexandrium tamarense when they were cultured alone, and the growth inhibition of algae was more significant with the increasing dose of UV-B radiation treatment.The two species of micro-algae could inhibit the growth of Ulva pertusaje in mixing culture, and the growth inhibition was more significant with the increasing original inoculating density. However, Ulva pertusaje could inhibit the growth of the two species of micro-algae in early phase and stimulate the growth in later phase when they were in mixing culture.Under UV-B radiation treatment, the Platymonas gelgolandica exhibited inhibition that was more significant to the growth of Ulva pertusaje with increasing original inoculating density. Lower original inoculate density of Alexandrium tamarense could inhibit the growth of Ulva pertusaje under the UV-B radiation treatment, however, with the increasing originalinoculating density, the growth of Ulva pertusaje was stimulated under lower dose of UV-B radiation treatment and inhibited under higher dose of UV-B radiation treatment by Alexandrium tamarense. Compared with that in mixing culture, two species of microalgae showed that the inhibition was more positive to the growth of Ulva pertusaje under UV-B radiation treatment.Activity of antioxidant system in macor-alage and micro-alage could be affected under UV-B radiation. The soluble protein content and Chl-a content showed decreasing trend, but ROS content, HaOa content, MDA content and SOD activity showed increasing trend in culture alone under UV-B radiation treatment. The Chl-a content and ROS content decreased and MDA content increased, while soluble protein content, HaOa content and SOD activity changed irregularly in mixing culture. Under UV-B radiation treatment, the changes of antioxidant system in mixing culture were less obviously than that in culture alone.Furthermore, the vertical polyacrylamide gel electrophoresis (PAGE) was used to identify the isozymes differentiation of PRX and PPO under different treatment conditions. It showed that isozymes of PRX and PPO presented differences respectively in forms of numbers of bands and staining intensity. Therefore, UV-B radiation treatment and the interaction between macro-algae and micro-algae could result in changes of PRX and PPO isozymes.Finally, researching the Ulva pertusaje and the two species of micro-algae filtrates using mirror test showed: the filtrates of the two species of micro-algae that were dealt with different temperatures were notable in the effects of growth of Ulva pertusaje. The filtrates of Ulva pertusaje that were dealt withdifferent temperatures showed significant effects of growth in Platymonas gelgolandica, but showed unapparent effects of growth in Alexandrium tamarense. Therefore, It is possible that the way of growth inhibition in Alexandrium tamarense by Ulva pertusaje was directly cell contacting, while the growth inhibition in Platymonas gelgolandica by Ulva pertusaje and Ulva pertusaje by the two species of micro-algae mainly came from ECP, and other ways and functions of interaction between macro-algae and micro-algae need forward study.