The Effects Of Environmental Factors On Growth And Microcystins Production Of Two Microcystis Strains In Taihu Lake

In recent years, cyanobacteria bloomed frequently in many areas. It changed ecological stucture and threatened people's health. Phosphorus is the most important factor that leads to eutrophication. While most correlative studies were carried out in rich nutrition conditions, which were far away from natrual environment. In this paper, more attention were paid to the effect of phosphorus on the growth of two dominant species in Taihu lake- Microcystis aeruginosa and Microcystis flos-aquae; and the effect of temperature, light and disturbance on the growth and microcystin production of two Microcystis species under nitrition limitation. The results were as follows:(1) In monoculture systems, Xmax and growth rate (μ) of two species were larger as the rise of phosphorus concentration. When phosphorus concentration was less than 0.015 mg/L and 0.01 mg/L, the growth of Microcystis aeruginosa and Microcystis flos-aquae were limited seriously respectinely according to the Xmax. When the phosphorus concentration ranged from 0 to 0.02 mg/L, theμof Microcystis aeruginosa increased rapidly. Microcystis flos-aquae had the same growth trade when it ranged from 0 to 0.03 mg/L. In multi-culture systems,μincreased rapidly when the phosphorus concentration ranged from 0 to 0.015 mg/L. Xmax,μand chlorophyll a concentrations in both culture systems indicated the growth of two Microcystis could be inhabited effectively when phosphorus concentration was limited under 0.01 mg/L,(2) The enhancements of temperature and nitrogen concentrations could accelerate the growth of both Microcystis strains. Effects of nitrogen concentratins toμwere different under different temperature. Negtive effects of low temperature to Microcystis flos-aquae were weaker than Microcystis aeruginosa. Positive and significant impacts of temperature and nitrogen concentratins on the intracellular chlorophyll a of both strains were observed, but interaction impacts were not so sigificant as main effects. Temperature was found to have a major negative effect on!cellular microcystin concentrations of both strains, while nitrogen concentration was mild positive. However, total microcystins concentrations of the cultures were higher for the enhancements of temperature and nitrogen concentrations.(3) The cell numbers and total microcystins concentrations of two strains obtained the maximum at 50μmol m-2 s-1. And both high and low light were negtive to the growth and microcystins production of two strains. Both intracellular chlorophyll a and microcystins contents decreased with the rise of light, but there was not linear relationship between them for two strains. Low disturbance density (30 r/min) didn't have significant effect on the growth of Microcystis. With disturbance density largen, Microcystis were inhabitted more seviously. Disturbance density also affected the microcystins production. When disturbance density was high (90 r/min), total microcystins concentrations decreased.