INFLUENCES OF NITROGEN AND PHOSPHORUS CONCENTRATION ON INTERACTIONS AMONG CHLORELLA VUGARIS, DAPHNIA MAGNA AND CERATOPHYLLUM DEMERSUM

In order to know the influence of nitrogen and phosphorus concentration on the effect of biomanipulation, Chlorella vugaris, Daphnia magna and Ceratophyllum demersum were selected respectively as the representative of phytoplankton, zooplankton and submerged macrophyte, to establish the model of aquatic microcosm to research the influences of nitrogen and phosphorus concentration on the interactions among them, which cultured in the same temperature (25 ) and illumination (200℃ 0—3000 lx) conditions. The result indicated that when both of the three organisms cultured together in high concentration nitrogen (10.5 mg/L) condition, when phosphorus concentration was less than 0.1 mg/L, it was advantageous to D. magna reproduction and C. demersum growth. C. vugaris was keeping multiplication fast, but C. demersum biomass decreased obviously when phosphorus concentration was 0.1 mg/L to 2.0 mg/L. In the low concentration nitrogen (0.5 mg/L) culture solution, when phosphorus concentration was not more than 0.5 mg/L, D. magna could inhibit the C. vugaris multiplication, and the inhibition was not obvious between C. demersum and C. vugaris. When phosphorus concentration rose to 2.0 mg/L, C. vugaris could inhibit obviously the growth of C. demersum. When all of the three kinds of creatures were cultured together in the solution that phosphorus concentration scope was 0.05 mg/L to 2.0 mg/L and nitrogen concentration was high (10.5 mg/L) or low (0.5 mg/L), both of D. magna density and C. demersum biomass increased, but C. vugaris density decreased markedly, and the effect was best when phosphorus concentration scope was 0.1 mg/L to 0.5 mg/L. The ratio of N/P could effect obviously the interaction among Chlorella vugaris, Daphnia magna and Ceratophyllum demersum. In the system of Chlorella vugaris and Daphnia magna adding submerged macrophyte could improve the effect to control alage, and lower the negative effect that was triggered by the wave of N/P ratio. The high concentration nitrogen condition showed inhibitory effect on the growth of C. demersum's, D. magna's and C. vugaris compared with the low concentration nitrogen condition. When phosphorus concentration was 0.5 mg/L, there were better elimination effect on the nitrogen and phosphorus of nutrient solution than the other phosphorus concentration gradient.