The Combined Effects Of Elevated CO₂and Elevated Temperature On Proliferation Of Cyanophage PP

In this study, Plectonema boryanum IU597was grown under four different conditions:(1)25℃+400ppm CO2(control);(2)29℃+400ppm CO2(elevated temperature);(3)25℃+800ppm CO2(elevated CO2);(4)29℃+800ppm CO2(greenhouse effect). The cultures were incubated for one week, one month, three months, three six months, nine months or a year before analysis. After incubation, the biomass of each culture was measured by the Chl a labeling method and by direct counting of cell numbers. The cell size was determined by microscopy measuring, the adsorption rate of cyanophage PP was determined using the centrifugation method, and the burst size and lytic cycle were affirmed by measuring the one-step growth curve. Results indicated that different culture conditions had no significant influence on the cell size of P. boryanum. However both the elevated CO2and the greenhouse effect conditions could significantly promote the cell number and total Chi a concentration of P. boryanum. The elevated CO2condition also decreased the Chl a content per cell by-31.35-42.42%compared with the control condition. The latent period of cyanophage PP was about260minutes under control conditions, while under the elevated CO2, elevated temperature, and greenhouse effect conditions, the time was brought forward to200,170-200, and140minutes, respectively. The lytic cycle of cyanophage PP was about380minutes under the control conditions, while in the elevated CO2, elevated temperature, and greenhouse effect conditions, the time was brought forward to320-380,320, and260-320minutes, respectively. This indicated that elevated temperature and elevated CO2conditions had a synergistic effect on the latent period and lytic cycle of cyanophage PP. The first hour’s adsorption rate of cyanophage PP was an average of2.7%in the control conditions, while under the elevated CO2, elevated temperature, and greenhouse effect conditions, adsorption rates were an average of1.7%,4.8%, and7.3%, respectively. This indicates that the elevated temperature and elevated CO2conditions had a synergistic effect on absorption rates of cyanophage PP. The burst size of cyanophage PP was an average of32PFLU·cell-1in the control conditions, while in the elevated CO2, elevated temperature, and greenhouse effect conditions, the average burst size was24,51, and32PFU·cell-1respectively. This indicates that the combined effect of elevated temperature and elevated CO2on burst size of cyanophage PP could be counteracted. These results not only suggest that the infectivity of cyanophage PP could be significantly promoted under the greenhouse effect conditions, but also imply that the combined effect of elevated CO2and elevated temperature on the infectivity of algal viruses was complex and caution is needed when studying the overall responses of freshwater virus-mediated processes to global change.P. boryanum that had been cultured under different conditions were restored to controlled conditions and cultured for a month, then we found adsorption burst size of cyanophage PP were significantly lower than the CK conditions, but the lytic cycle is slightly earlyier than CK. The resis-plectonema that had been cultured under different conditions were restored to controlled conditions and cultured for six and ten months, we found that recovery group adsorption rate and lytic rate of cyanophage PP were between elevated CO2conditions and controlled conditions, and they are more likely to controlled conditions.