Study On The Ecological Mechanism Of Biological Community In Response To Soil Salinity In Bt Cotton Field

Saline-alkali land is potentially exploitable reserve cultivated land resources,but it severely restricted the sustainable development of agricultural production.Due to some factors such as the low degree of cotton mechanization,increasing input of labor cost and production goods,declining of comparative benefits and implementing the strategy of food security,cotton area in the Yangtze River and Yellow River decline sharply,and the planting area is transferring to Binhai saline-alkali land.Since the study of ecological security of planting Bt cotton in saline-alkali land is rare,it became a focus and hotspot in the research of the scholars at home and abroad.Study on the effects and mechanisms of soil salinity on the biological community in transgenic Bt cotton can provide the basis for establishing Bt cottonpests comprehensive prevention and control technology system,environmental safety evaluation and safety management in soil salinity in Bt cotton field.The research object was Bt cotton cultivar GK19,and its parental conventional cotton Simian 3 was used as control.Three salt level treatments(1.15 dSm-1?6.00 dS m-1 and 11.46 dS m-1))were set in rice and wheat seed testing farm of the Dafeng city,Jiangsu.The research were aiming to investigate(1)Effect of salinity on Bt cotton insect community parameters and cotton growth condition,(2)Ecological mechanism of insect resistance of transgenic Bt cotton and the target pest population dynamic in response to soil salinity,(3)The non-target pest and natural enemy population dynamic of transgenic Bt cotton fields in response to soil salinity,(4)Effect of salinity on Bt cotton rhizosphere microbial biomass and activity,and its relationship with exogenous insecticidal protein.The main results were as follows:1.Bt cotton does not affect the structure,composition and biodiversity of arthropod community under soil salinity stress conditions.Under 6.00 dS m-1 and 11.46 dS m-1 salinity leve,no significant differences were detected in the diversity index of insect community,natural enemy sub-community between Bt cotton GK19 and conventional cotton Simian 3.Dominant concentration and uniformity between Bt cotton and conventional cotton were not significantly different.With the increase of salinity levels in Bt cotton field,dominance index of bollworm increased,number of beet armyworm and lacewings decreased obviously,the change of dominant degree of sap-sucking insects and other predators is not obvious.The performance trend of growth,insect structure and composition,biodiversity in the conventional cotton Simian 3 field were consistent with the Bt cotton,but the main cotton pests and their natural enemies insect dominance did not change significantly.2.Soil salinity can inhibit Bt protein expression of Bt cotton significantly,and it led to the declining of resistance of Bt cotton to bollworm in different tissues and organs of different growth period,and the increasing of cotton bollworm populations in field.Correlation analysis showed that,salt content and the Bt protein expression was significantly negative correlated,the Bt protein expression and insect resistance was significantly positive correlated.3.The salt stress of soil can inhibit nitrogen absorption of Bt cotton,it also significantly decreased the content of protein and amino acid,increased the content of soluble sugar,proline and the content of phenol,tannin and other secondary insect-resistent content in Bt cotton leaf.The activity of SOD,CAT,POD and APX enzyme in Bt cotton leaf also increased,and it led to the change of population of beet armyworm,aphid and green lacewing in cotton field.The increased soil salinity and the content of secondary metabolites in the cotton are the main cause of decline of beet armyworm cotton,cotton aphid and lacewings,but the change of other insects was not obvious.The biochemical content changes of conventional cotton Simian 3 were the same as transgenic Bt cotton,but the populations of beet armyworm,cotton aphid and lacewings are higher than that of Bt cotton,no significant differences were found in other insects.4.Under soil salt stress,the content of Bt protein in transgenic Bt cotton rhizosphere soil is very low;with the increase of soil salinity levels,the number ofhalophilic bacteria,phosphatesolubilizing bacteria,ammonifying bacteria,nitrifying bacteria and denitrifying bacteria of rhizosphere soil in Bt cotton reduced significantly,soil microbial biomass carbon and microbial respiration reduced as well;the catalase,urease and alkaline phosphatase in soil were restrained,but neutral phosphatase in soil were not changed;the rise of soil salinity inhibited the amount and activity of Bt cotton rhizosphere soil microorganism,leading to the degradation rale of exogenous insecticidal protein in soil decreasedandBt protein content in soil increased;the rhizosphere soil microbial activity and related enzyme activity between transgenic and conventional cotton were not significantly different.In summary,the soil salinity significantly inhibited the growth of transgenic Bt cotton in cotton field,declining food resources,causing the total number of insects significantly decreased;the expression of Bt protein was reduced,the resistance to Bollworm was decreased significantly,which is conducive to the population of cotton bollworm field rise up;under salt stress,biochemical matter contents in cotton increased,the population of beet armyworm,cotton aphid and lacewings in Bt cotton field were inhibited;trace Bt protein were detected in transgenic Bt cotton rhizospheresoil,and salt significantly inhibited the cotton rhizosphere microbial activity and soil enzyme activity,which is not conducive to the degradation of Bt protein.