Gm Cotton Effects On Soil Microbial Diversity

Since transgenic Bt cotton was successfully cultivated in early1990s, transgenic cotton has been one of the fastest commercialized transgenic crops around the word. Soil ecosystem is an important part of the entire ecosystem, and soil microbial diversity and activity is the basis of health and stability of agro-ecosystems. So study of transgenic cotton on soil biological community structure and functional group activity is crucial in ecological risk assessment and monitoring of transgenic crops. Aphid damage is serious in China; the control still relies greatly on chemical pestcides. Wild shepherd’s purse agglutinin (WSA) cotton is a new type targeting aphid. Transgenic Cry1Ac+Cry2Ab cotton targets beet armyworm and Spodoptera litura, which makes up for the limitation that transgenic Bt targeting only cotton bollworm and pink bollworm. In this study, transgenic WSA cotton and Cry1Ac+Cry2Ab cotton and their control (conventional cotton) were selected as experimental materials to monitor physical and chemical properties of transgenic cotton and conventional cotton at different cotton-growing seasons. Phospholipid fatty acid (PLFA) analysis, polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis of bacterial16S rRNA gene, carbon substrate utilization diversity (BIOLOG) analysis, enumeration of microbial populations and measurement of soil enzyme activities were employed to assess the potential risk of transgenic cotton on soil enzyme activities and soil microorganism. The result showed that:1. Compared with conventional cotton, transgenic WSA cotton significantly affected soil potassium content at the first and third sampling stage only. Soil dehydrogenase and urease activity of WSA cotton didn’t vary from conventional cotton.2. The number of culturable microorganisms wasn’t significantly affected by transgenic WSA cotton during the whole sampling period. Biolog and PLFA analysis showed that the transgenic WSA cotton did not significantly affect the microbial community structure, while differences in microbial community structure at different sampling times are more obvious.PCA analysis of DGGE profiles showed that soil bacterial community structure of WSA cotton has significant differences from conventional cotton at the second and third sampling time. This result is similar to cluster analysis result. 3. Compared with conventional cotton, no obvious difference was found in physical and chemical indicators of both rhizosphere and bulk soil of transgenic cotton with crylAc+cry2Ab during sampling periods. The number of culturable microorganisms did not change significantly, either.4. Biolog analysis showed that there existed relatively obvious differences in community structure of the bulk soil microorganisms between transgenic cotton with cry1Ac+cry2Ab and conventional cotton during three sampling stages. Transgenic cotton with crylAc+cry2Ab from three sampling times distributed intensively, indicating stable and similar microbial community structure. So were the rhizospheric soil of both transgenic cotton with cry1Ac+cry2Ab and conventional cotton from three sampling times. Distinct differences in bulk soil microbial community structure of PLFA between transgenic cotton with cry1Ac+cry2Ab and conventional cotton occurred at the third and forth sampling stages; obvious differences in rhizosphere soil microbial community structure of PLFA between transgenic cotton and conventional cotton occurred at the first and third sampling stages.5. Position and intensity of detectable DGGE bands didn’t differ significantly between transgenic cotton with cry1Ac+cry2Ab and conventional cotton at all sampling time, either bulk or rhizosphere soil. Cluster analysis based on DGGE profiles showed no persistent significant difference in the rhizosphere soil bacterial community structure during all sampling period. Bacterial community structure in non-rhizosphere soil differed greatly in four sampling times.