| Bloom is the phenomenon that phytoplankton proliferate and gather unusually in eutrophic lakes, which will lead to problems of water environment, such as water quality declining. The algae bloom is one of the most common blooms. As to the eutrophic lakes at home and abroad, algae bloom is the most common problem of water environment.And the Microcystis aeruginosa is one of the most harmful among cyanobacteria blooms. In order toprovide a theoretical foundation for the effective control of the cyanobacterial bloom, this experiment selected M. aeruginosa, which is the representative algae, as the research object. This paper researched the environmental factors influence on the growth and group formation of M. aeruginosa by single factor and orthogonal experiments, and preliminary revealed the forming mechanism of algae blooms. The environmental factors included initial concentration of N, P and Ca2+, light intensity and temperature.In this experiment, the groups of M. aeruginosa were observed by inverted fluorescent microscope, scanning electron microscope and laser confocal microscope respectively. And the biological reasons of M. aeruginosa groups forming were explained from the micro perspective. Under phosphorus stress, a comparative analysis about activity of alkaline phosphatase(AKP) and antioxidant enzyme(SOD, CAT) was conducted between two phenotypes of M. aeruginosa, single cell and group. The paper explained the reason that M. aeruginosa groups become the dominant algae. In addition, the biological significance of groups forming to Microcystis bloom was summarized.1) In the single factor experiments, the main conclusions are summarized as follows:M. aeruginosaare able to form more intensive groups with maintaining normal growth, high concentration of Ca2+, high light intensity and appropriate temperature are conducive to the formation of M. aeruginosa community. And the advantageous concentration of N, P and Ca2+ is N=10mg/L, P=0.5mg/L, N=50mg/L, P=2.5mg/L, N=100mg/L, P=5mg/L, Ca2+ =130mg/L, Ca2+ =260mg/L, Ca2+ =520mg/L. It is favorable to keep the light intensity4000 lux, 8000 lux and 12000 lux. The appropriate temperatures are 15℃, 20℃, 25℃.2) In the orthogonal experiments, the paper arrived at the following conclusions: Compared with the condition of single environmental factor, many environmental factors working together is more conducive to promote the formation of M. aeruginosagroup. The best combination of the environmental factors for groups formation is N=100mg/L, P=5mg/L, Ca2+=260mg/L, 4000 lux light intensity and 25℃.3) After the comparison of two phenotypes of M. aeruginosa, single cell and group, it could be inferred that M. aeruginosa form groups in two ways. One is that single cell concentrates and gathers into groups. And the other one is proliferation accumulation of M. aeruginosa cell. There is a progressive relationship between these two approaches. In other words, single cell gathers together to form small groups and the proliferation of cells division are to form large groups. However, it is not absolute. In the complex ecosystems, these two approaches are often coexisting as for the growth of M. aeruginosa. In the process of group formation, polysaccharide(EPS) rubber sheath plays a role of cohering cells, protecting cells, providing nutrients, auxiliary adjusting the fbuoyancy and so on. Besides, the Ca2+ can strengthen the stability of cell aggregating.4) Under phosphorus stress, after the comparison of activity of AKP, SOD, CAT between two phenotypes of M. aeruginosa, single cell and group, it could be known that the AKP activity of single cell rose significantly, while that of group kept low level. It could be proved that in the nutrition fluctuating environment, group can keep preponderant in the nutrients(such as phosphorus) competition. As for group, the higher level activity of SOD and CAT can ensure that the excess reactive oxygen was removed in a time, and enhance the ability of resisting adversity stress damage. |
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