STUDIES ON RECRUITMENT AND GROWTH CHARACTERISTIC OF MICROCYSTIS IN SEDIMENT

Effect of different environmental factors, such as temperature, light and N/P, on the recruitment of Microcystis colony has been studied. The growth characteristics of Microcystis colony samples from the sediment and pelagic zone were also compared. Meanwhile, the influence of temperature on the chlorophyll a fluorescence of both dormant and vegetative cells of Microcytis sp. 940 was investigated too. The results suggested that the recruitment of Microcystis colony out of the sediment was affected significantly by temperature and light, but not N/P. Microcystis colony in the sediment initiated growth at 15℃ and 30μEm-2s-1, then buoyed to the surface after 15 days. Cultured at 10℃ and 30μEm-2s-1,Microcystis colony in sediment couldn’t recruit during experiment. At 20℃ and 30μEm-2s-1,Microcystis colony grew actively in sediment, then moved into water after 5 days. The recruitment wasn’t affected by different N/P. Microcystis colony initiating growth could obtain enough N/P in sediment. After Microcystis colony moved into water, its growth was restrained by N/P in water. The growth characteristic of Microcystis colony in sediment and pelagic zone was researched. Incubated at 10℃ and 15℃, The growth of Microcystis colony in sediment and pelagic zone was laggard. In contrast to low temperature, its growth at 20℃ and 25℃ was active. The growth of Microcystis colony depended on light. With increasing of light intensity, its growth rate enhanced gradually. In darkness, it couldn’t grow normally and was decomposed gradually by bacteria. However, the Mcrocystis colony that were illuminated at 15℃ and 30μEm-2s-1 grew actively . N/P had no effect on the initiating growth of Microcystis colony in sediment, because the colony could absorb N/P from sediment. But Microcystis colony that had already come into pelagic zone would be constrained by N/P. It was found that the optimal condition for recruitment occurred at 20℃ And 30μEm-2s-1, and the optimal condition for its growth was also 20℃ and 30μ Em-2s-1, which was similar to the growth Microcystis colony in the pelagic zone. Incubated at 10℃ and 15μEm-2s-1, the F 0 fluorescence of the vegetative cells of Microcystis reduced, but that of the dormant cells of Microcystis sp. 940 increased similarly at 20℃ and 25℃, respectively. Microcystis colony that could survive in low temperature might have a mechanism to protect photosystem from damage. Our result illustrated that there is a close relationship between recruitment of Microsystis out of the sediment and the outbreak of Microcystis blooms.