Ecological Effect In Microcosm Systems After The Lysis Of Cyanobacteria Host By Cyanophage PP

The influence of the lysis of cyanobacteria by cyanophage PP on nutrition cycle was studied, and some nutrition concentrations, such as DOC, TOC, ammonia, nitrate, phosphate, total nitrogen and total phosphorus were monitored after the lysis of cyanobacterium Plectonema boryanum under laboratory conditions. The lysis systems were treated with and without bacteria respectively and the biomass of bacteria was also calculated. After the lysis of the host cyanobacteria, the bacteria biomass increased quickly and the nutrition cycle in different system performed differently. The concentration of DOC in both systems increased right after the lysis, while the DOC concentration of the system without bacteria was significantly higher than that of the system with bacteria. And then, the concentration of DOC and TOC decreased step by step in both systems, but the concentration in system with bacteria decreased more quickly. The ammonia concentration of the bacteria system continued to increase while remained stable in the other system. Phosphate concentration in both systems increased, and the concentration increased more slowly in the system with bacteria at the beginning, but the condition was reversed later. The total phosphorus and nitrogen concentration kept stable through the experiment. In an additional experiment, duckweed was added to the lysis systems to see the influence of lysis on the growth of duckweed. It was found that the duckweed grew more quickly in the lysis system with bacteria than that without bacteria, while the duckweed in both lysis system grew more quickly than that in the Andrews' medium.Based on the experiments in laboratory, an experiment in small cement pond was carried out. The experiment group was composed by duckweed and cyanophage-host system, while the control group was only composed by cyanophage and its host. During the experiment, the concentration of nutrient and chlorophyll a, the biomass of bacteria and duckweed were monitored. In the control group, after the lysis of host cyanobacteria, Microcystis and diatom dominated the pond. While in the experiment group, duckweed grew quickly after the lysis and absorbed the nitrogen and phosphorus so efficiently as to prevent other kinds of phytoplankton from blooming. In both groups, the lysis led to the succession of bacteria and the change of nutrition concentration.All the results mentioned above suggests that cyanophage and bacteriaplankton may play very important roles in the nutritional cycle in water-body, and it also implies that duckweed may be applied in the control of cyanobacteria blooms.