Effects of Nitrogen and Phosphorus on Growth of Microcystis aeruginosa Strains

Objective To explore the effect of phosphorus (P),nitrogen (N) and N/P ratio on the growth of Microcystis aeruginosa strains. Methods Cultured the microcystis that carried out ampliative culture three times in N and P free culture. Inoculated the microcystis to the cultures in which P concentration was 0, 0.5, 1.0, 5.0, 10.0 mg/L respectively and cultured for 19 days. Inoculated the microcystis to the BG-11 cultures in which P concentration was 0.05 mg/L and 5.0 mg/L, add in NaNO3 according to the mol ratio of N/P was 5∶1, 10∶1, 20∶1, 50∶1, 100∶1, and cultured for 19 days. The changes of the count of the microcystis and the concentration of P were observed. Results At beginning, the microcystis in lower P concentration cultures growed better than the microcystis in the higher P concentration, but there was not much difference. At the late exponential phase, the biomass of the microcystis in the higher P concentration cultures exceeded the microcystis in the lower P concentration cultures. Afterward, the microcystis in the cultures ceased growing. And the exponential phase of the microcystis in higher P concentration cultures was longer than the microcystis in lower P concentration cultures. The difference in maximum biomass among each cultures that initial P concentration was 0.05 mg/L was not significant (P0.05), but that was significant at the cultures in which the concentration of phosphorus was 5 mg/L(P0.05). The results was 20∶110∶15∶150∶1100∶1. The specific growth rate of microcystis and P concentration in different P concentration and different N/P ratio cultures decreased with the culture time. Conclusions The initial P concentration affects the microcystis yield significantly, N/P ratio should be concerned in confirming the limiting factor. To control the P concentration in water through different methods will be the effective way to control water bloom.