氮浓度对铜绿微囊藻、大型溞和金鱼藻三者相互作用的影响

为了解氮浓度对生物操纵和草-藻竞争的影响, 选取铜绿微囊藻、大型溞和金鱼藻分别作为浮游植物、浮游动物和沉水植物的代表, 在温度25℃, 光强2600 lx, 光暗比14h﹕10h, 磷浓度1.5 mg/L时, 研究5种氮浓度(0.5、2、4、8和16 mg/L, 用KNO₃溶液配制)下, 溞-藻, 草-藻和溞-草-藻共培养时各自的增长率和培养液中氮磷削减率的变化。结果表明: 在单独培养铜绿微囊藻时, 氮浓度控制在1.97 mg/L以下, 可有效降低培养液中藻的增长率。在溞-藻共培养时, 大型溞有效控藻的氮浓度范围为0.5—4 mg/L; 在草-藻共培养时, 有效控藻的氮浓度范围为0.5—2 mg/L, 对应氮浓度下(0.5和2 mg/L), 实验末期铜绿微囊藻细胞密度分别是溞-藻共培养的23.89%和21.51%, 控藻效果更好; 在溞-草-藻三者共培养时, 有效控藻的氮浓度范围为0.5—16 mg/L, 且氮浓度为0.5—4 mg/L时, 大型溞和金鱼藻的增长率均显著大于铜绿微囊藻, 铜绿微囊藻的增长率均为负值, 控藻效果最好。大型沉水植物的加入, 可以有效提高生物操纵的控藻效果, 减少水中氮磷含量, 长期有效地改善水质。

IMPACTS OF NITROGEN CONCENTRATION ON THE INTERACTIONS AMONG MICROCYSTIS AERUGINOSA, DAPHNIA MAGNA AND CERATOPHYLLUM DEMERSUM

To evaluate the impacts of nitrogen concentration on both biomanipulation and the competition between algae and water grass, Microcystis aeruginosa, Daphnia magna and Ceratophyllum demersum were selected for experiments to represent phytoplankton, zooplankton and submerged macrophyte, respectively. When two or three of them were cultured together, the changes of growth rate and removal rate of nitrogen and phosphorus were observed with the phosphorous concentration of 1.5 mg/L and 5 different nitrogen concentrations (0.5, 2, 4, 8 and 16 mg/L, prepared with KNO₃ solution), under temperature of 25℃, illumination of 2600 lx, light dark ratio 14h﹕10h. The results indicated that whenM. aeruginosa was cultured separately, its growth rate effectively reduced with a nitrogen concentration less than 1.97 mg/L. When D. magna andM. aeruginosa were co-cultured, the nitrogen concentration which D. magna could effectively control algae was from 0.5 to 4 mg/L. However, the nitrogen concentration which C. demersum could effectively control algae was from 0.5 to 2 mg/L, when C. demersum and M. aeruginosa were co-cultured. When nitrogen concentrations were at 0.5 and 2 mg/L, the cell densities of M. aeruginosa were 23.89% and 21.51%, respectively, of that when D. magna and M. aeruginosa were co-cultured at the last of experiment. So the effect of algae control was better when C. demersum and M. aeruginosa were co-cultured. The algae could be effectively controlled with nitrogen concentration from 0.5 to 16 mg/L, when D. magna, C. demersum and M. aeruginosa were co-cultured, under which the effect of algae control was the best. Especially, the growth rate of M. aeruginosa was all negative and significantly lower than those of D. magna and C. demersum when nitrogen concentration was bewteen 0.5 and 4 mg/L. In the co-culture environment of D. magna and M. aeruginosa, with the addition of large submerged macrophyte, the effect of algae control could effectively enhance, and the nitrogen and phosphorus in the water could be decreased, which can effectively improve the water quality over the long term.