Study On The Host Mortality Rates And Lysogenic Induction Rates Mediated By Virioplankton In Xiangxi Bay

High concentration of nitrogen and phosphorus in the Xiangxi Bay resulted in servious eutrophication.Different types of blooms break out every year.The dominant bloom are dinoflagellate,diatom and green algae in spring,dinoflagellate,diatom,green algae and cyanobacteria in summer,diatom and green algae in autumn.Virioplankton is an important regulator of algae growth.In aquatic ecosystems,Virioplankton can cause 10% to 20%decrease of algae and bacterial production.In this study,the virioplankton abundance and the mortality rates and lysogenic induction rates of the host were explored during the spring bloom period in Xiangxi Bay.Based on this,the effects of hydraulic disturbance on viral infection process were investigated with the original water from Xiangxi Bay under in situ conditions.The results show that:(1)In Xiangxi Bay,the virioplankton abundance during the spring blooms is mainly affected by the abundance of bacterioplankton and phytoplankton,chlorophyll-a,total nitrogen,water temperature,orthophosphate,soluble silicate,transparency.The water temperature increase stimulates the bloom,which in turn affects the permanganate index,total nitrogen,orthophosphate,soluble silicate and transparency,and facilitates the growth of bacterioplankton,thereby promotes the virioplankton abundance.(2)The factors affecting viral-induced host mortality rates and lysogenic induction rates are mainly water temperature,phytoplankton abundance,orthophosphate,soluble silicate and transparency.The main factor affecting the mortality rate of bacterioplankton is the abundance of virioplankton.(3)The results of simulated hydraulic disturbance experiments showed that the disturbance intensity under 13 rpm and 23 rpm condition had a significant promotion on the growth of phytoplankton in sping and autumn.The disturbance effects on the growth of bacterioplankton was quite different between spring and autumn,and which was surpposed to depend on the nutrient surpply.The spring bloom surpplied organic carbon promoted the bacterial growth,while the phosphorus competition between autumn bloom and bacterioplankton inhibited the bacterial growth.The disturbance had no significant effect on the virioplankton abundance.The disturbance under13 rpm and 23 rpm conditioncould promote the increase of the lytic rates of phytoplankton and bacterioplankton,and the maximum mortality rate was observed at the disturbance intensity of 13 rpm.There was no significant difference in the lysogenic induction rates of phytoplankton andbacterioplankton in the autumn culture(P>0.05),while a significant difference in the lysogenic induction rates of phytoplankton and bacterioplankton was detected in the spring culture(P<0.05).The influence of disturbance on the lysogenic induction rates of phytoplankton and bacterioplankton is surpposed greatly affected by the initial conditions of the water,such as the composition of plankton community and nutrient concentration.