Impacts Of Transgenic Insect-Resistant Cotton On Community Structure And Functional Diversity Of Soil Microorganism

Transgenic insect-resistant cotton was the first genetically modified crop that allowed commercial production in China. Application of transgenic plants produces great social and economic benefits, simultaneously, it may cause environmental security issues, including the possible risk to soil ecosystems. Soil microbial diversity and the dynamic balance of soil ecosystems contact closely, thus it is an important part of the security assessment for transgenic plant on soil ecosystem(Wei et al.,2011). Transgenic crylAc+cry2Ab cotton targets Spodoptera exigua and Spodoptera litura, which broadens the insect spectrum of transgenic insect-resistant cotton in China. Transgenic JHBPl cotton resists cotton bollworm by RNA interference. The impacts of transgenic crylAc+cry2Ab cotton and transgenic JHBP1 cotton on community structure and functional diversity of soil microorganism are still rarely reported.Enumeration of microbial populations, carbon substrate utilization diversity (Biolog) analysis, polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis were employed to assess the potential risk of transgenic crylAc+cry2Ab cotton and transgenic JHBP1 cotton on soil microbial community structure and functional diversity at different cotton-growing stages. The result showed that:(First)Impacts of transgenic crylAc+cry2Ab cotton on community structure and functional diversity of soil microorganism1. Determination of the population of culturable soil microorganism indicates that the soils in transgenic crylAc+cry2Ab cotton and conventional cotton fields shared a similar trend in variation of the population of culturable bacteria, fungi and actinomycetes throughout the entire cotton growth period, and no significant difference existed between the two in total population of soil microorganism, except bacteria and actinomycetes at the budding stage (p<0.05).2. Biolog analysis showed that the soil bacteria in transgenic crylAc+cry2Ab cotton and conventional cotton fields differed significantly in activity and carbon utilization capacity at the seedling and budding stages(p<0.05). Compared with conventional cotton, three diversity indices (Shannon-Wiener, Simpson and McIntosh) showed significance only at the budding stages (p<0.05).3. DGGE profiles of soil bacteria between transgenic crylAc+cry2Ab cotton and conventional cotton showed high similarity at all sampling stages. PCA analysis of soil bacterial DGGE profiles demonstrated that soil bacteria in both fields varied in community structure with growth stage and differenced sharply only at the flower and boll stage. Compared with soil bacterial DGGE profiles, DGGE profiles of soil fungi of both cottons contained fewer detectable bands, and position and intensity of them differed significantly between each other. PCA analysis of soil fungal DGGE profiles showed that soil fungi in both fields varied in community structure with growth stage and differenced sharply only at the seedling stage.(Second)Impacts of transgenic JHBP1 cotton on community structure and functional diversity of soil microorganism1. Soils in transgenic JHBP1 cotton and conventional cotton fields shared a similar trend in variation of the population of culturable soil microorganism (such as bacteria, fungi and actinomycetes) throughout the entire cotton growth period, and no significant difference existed between the two in total population of soil bacteria, fungi and actinomycetes at different sampling stage.2. Biolog analysis showed no significant difference existed between transgenic JHBP1 cotton and conventional cotton fields in soil bacterial activity at all sampling stages. Compared with conventional cotton, no significant difference existed between the two in three diversity indices, except Shannon-Wiener at the seedling stage (p<0.05). PCA analysis showed that the soil bacteria in the two differed significantly in carbon utilization capacity at the seedling and budding and aging period stages (p<0.05).3. DGGE profiles of soil bacteria between transgenic JHBP1 cotton and conventional cotton showed high similarity at all sampling stages. PCA analysis of soil bacterial DGGE profiles demonstrated that soil bacteria in both fields varied in community structure with growth stage, and no significant difference existed between the two in community structure. The result of soil fungal DGGE analysis was consistent with that of soil bacteria. PCA analysis of soil fungal DGGE profiles demonstrated that soil fungi in both fields varied in community structure with growth stage and differenced sharply only at the budding stage.It is concluded that soil microbial community structure and functional diversity of both transgenic cottons was essentially consistent with their respective control during different growth periods; compared with conventional cotton, soil microbial community structure and functional diversity of transgenic cry1Ac+cry2Ab cotton and transgenic JHBP1 cotton was changed only at some certain stage.