Studies On The Physiological And Biochemical Characteristics Of Marine Microalgae In Response To Eutrophication

The effects of eutrophication on the phosphatase activity, three biochemical compositions and photosynthesis of two dominant bloom-forming species (Skeletonema costatum and Prorocentrum donghaiense) isolated from the Changjiang (Yangtze) River were studied. The relationship between the nutrient concentrations and the physiological and biochemical responses were analyzed in order to provide some biological indicators for further exactly evaluating the eutrophication. The main results are as follows:Both S. costatum and P. donghaiense could induce alkaline phosphatase (AP) and acid phosphatase (AcP) under the same nutrient conditions, and both AP and AcP activity had a similar changing trend which meant that they increased with the decreasing of both environmental and intracellular phosphate concentration. The Pearson correlation between the two phosphatses activity and the phosphate concentrations (including environmental and intracellular P) found that the phospahtase activity had a significantly negative relationship with the intracellular phosphate while no significant relationship with the environmental P. In addition, two species could utilize dissolved organic phosphate (including ATP, G-6-P and G-P) and the biomass was significantly increased. For three DOP treatment groups, the highest cell abundance was for ATP treatment, then for G-6-P, and the last for G-P treatment. From the different alkaline phosphatase activity among the three DOP treatments, it could be concluded that the two species may directly absorb and utilize ATP and G-6-P, while for G-P, it may be firstly hydrolyzed to inorganic compounds by alkaline phosphatase and then be absorbed by two species. The induction of acid phosphatase activity indicated that two species could utilize the intracellular accumulated phosphate for growth under the P limited condition. The batch culture experiment showed that during the exponential stage, the cellular total lipid and carbohydrate content were decreased with the depletion of the N and P, but at the end of the experiment when the nutrient was limited, the cellular total lipid and carbohydrate was accumulated. The cellular total proteins were also decreased at the exponential stage, but there was no accumulation at the end of the experiment and the change was much smaller than either total lipid or total carbohydrate. The Pearson correlation between the nutrient concentration and the three biochemical compositions showed that there had a significant positive relationship between the phosphate concentrations and the three biochemical compositions. Additionally, the two species had lower cellular Chl a, Chl c and TCC content under three low nutrient treatment than under the corresponding high low nutrient treatments respectively. For two species cultured under N-limited treatments, the photosynthetic rate of low N treatment was higher than that of high N treatment. While for P-limited treatments, low P treatment group had lower photosynthetic rate than that of high P treatment group. When N/P ratio was 16/1, the low nutrient treatments had lower photosynthetic rate for S. costatum, but the contrary was for P. donghaiense. The Pearson correlation analysis showed that the photosynthetic rates of two species were significantly correlated with the intracellular phosphate, while no significant correlation was between the nitrate concentration and the photosynthetic rate..The innovative aspects mainly include that a comparatively thorough study on the relationship between the physiological and biochemical responses of marine microalgae and the eutrophication were conducted and tried to provide some biological indicators for evaluation of the eutrophication. Another is that a comparative research on the physiological and biochemical responses of two dominant bloom-forming species under the same nutrient condition was done and we tried to explain the mechanism of the blooms and the temporal characteristic of the blooms caused by two species from the physiological aspect.