The Advantages in Competition Based on the Photosynthetic Characteristics of Microcystis aeruginosa

The effects of temperature,light and pH on photosynthesis of Microcystis aeruginosa and Chloromonas rosae were studied by measuring their net photosynthetic O₂ evolutions.The net photosynthesis of both algae increase with the temperature.The net photosynthetic O₂ evolution of M.aeruginosa increased linearly in the range of 10-35℃,indicating that its optimal temperature might be higher than 35℃,while the net photosynthetic O₂ evolution of Ch.rosae decreased dramatically when the temperature was over 30℃.The photosynthesis-light response curves of these two algae are different.The light saturation point(LSP) of M.aeruginosa was around 500 μmol·m^-2·s^-1 and photoinhibition did not occur when the light intensity was as high as 900 μmol·m^-2·s^-1,much different from M.aeruginosa,photosynthesis of Ch.rosae was inhibited when the light intensity exceeded its LSP of 630 μmol·m^-2·s^-1.The photosynthesis of M.aeruginosa,with an optimal pH of 10.0,was very active and stable in the range of pH 6.5-11.5.The optimal pH of Ch.rosae was 7.0,and any slight departure from the optimal pH would significantly reduce its photosynthesis.When the value of pH exceeded 10.0,its net photosynthe-tic O₂ evolution was negative.M.aeruginosa has three important characteristics that are different from Ch.rosae:(1) a wider tolerable temperature range,adaptation to high temperature;(2) lower LSP,higher photosynthesis activity,and more efficient photosynthesis under low light environment;(3) significant pH tolerance,and high photosynthesis activity in neutral and alkaline environment.All these biological characteristics give M.aeruginosa great competition advantages to survive,grow and dominate other phytoplankton in polluted aquatic environment.