Changes In Microbial Flora And Bacterial Physiological Group Diversity In Rhizosphere Soil Of Transgenic Bt Cotton

The environment release of transgenic plants may be accompanied by ecological effects including changes in plant-associated with microflora. Transgenic cotton containing gene to produce the insecticidal toxin from Bacillus thuringiensis (Bt) has been widely planted. Most research on Bt cotton has focus on invasiveness, gene flow to indigenous organisms, development of resistance in target pests, and director indirect effects on non-target organisms and ecosystem. A few studies have been published to evaluate the ecological effects of Bt cotton on microbial flora. A field release of Bt cotton grown under normal agricultural practice was monitored for changes in total bacterial, actinomycetic and fungal populations in 2006 and 2007. The results are as follows:1. There was a positive correlation between the leaf surface microorganisms and cotton development. The total number of bacteria,fungi and actinomyces began to rise at seedling and reached its peak at flower stage,but decreased obviously at boll-opening stage Although there were difference in the colony-forming unites of culturable bacteria, act inomycetes and fungi of rhizosphere soil between Bt cotton and non-Bt cotton in different growing period and different years. The trend of annual differences was basically consistent at the same development stage of cotton. Few significant differences were observed and none of the differences were persistent in microbial population in rhizosphere soil between Bt cotton and non-Bt cotton at seedling and boll-opening stage. Total bacterial populations in rhizosphere soil of Bt cotton were significantly higher than that of non-Bt cotton at flower and boll stage. Total act inomycete populations in rhizosphere soil of Bt cotton differed minimally from that of non-Bt cotton at flower and boll stage. Total fungi populations in rhizosphere soil between Bt cotton and non-Bt cotton in 2006 were not consistent with that in 2007 at flower and boll stage. Total fungi populations in rhizosphere soil of Bt cotton were significantly higher than that of non-Bt cotton in 2006. On the contrary, total fungi populations in rhizosphere soil of Bt cotton were significantly lower in 2007.Diversity, composition and distribution of bacterial physiological groups in rhizosphere soil between Bt cotton and non-Bt cotton was analyzed with Simpson index, Shannon-Wiener index and evenness index at flower, boll and boll-opening stage in 2007. The effect of Bt crop on microbial communities of rhizosphere soil should be carried out before commercial release. How ever, these results should be considered as being preliminary, as only one Bt cotton variety and only total numbers of culturable rhizosphere microbes were evaluated. More studies on other Bt varieties and un-culturable microbes are necessary to confirm the effect of Bt cotton on biodiversity in soil.2. According to amount grade of bacterial physiological groups of phyllosphere of Bt cotton and non-Bt cotton we known that Ammonifying bacteria and Aerobic cellulose-decomposing were rare groups, Nitrite bacteria and Desulfurizing bacteria were subordinate groups associated with Bt cotton and non-Bt cotton at stages of boll opening and flower-boll. There was significant difference in other bacterial physiological groups of phyllosphere of the two varieties.3. In the analysis of diversity changes of bacterial physiological groups, we concluded that total fungi populations in rhizosphere soil of Bt cotton were significantly higher than that of non-Bt cotton at at flower, boll and boll-opening stage. However, D, H ,R and diversity indexes of Bt cotton were all lower than that of non-Bt cotton.