Degration Of Bt Protein And Effect On Soil Microbial Activity After Residue Embedded Into Soil From Transgenic Bt Cotton

The environmental security issues had become the focus of debate with transgenic Bt crop acreage increased year by year. Expression exogenous products of transgenic Bt crops could entered into the soil through root exudates or stubble, which may leaded to the variation about the soil microbial number and diversity, and the soil enzyme activities, and affected the soil ecosystem health and stabilizing. So it is important to study the degradation of Bt protein and the effect of on microbial activity after residue embedded into soil from transgenic Bt cottonThe seedling residues and mature straw from transgenic Bt cotton were embedded into soil to study the degradation dynamics of Bt protein and analysis the variety of soil enzyme activities, microbial number and microbial community diversity. The research results were showed as follows:1. The Bt protein of seedling residues from transgenic Bt cotton could degrade quickly in the soil before30d, and then it slowed down steadily. At the end of the sample, Bt protein had only a small amount residues in the soil. The degradation dynamic of Bt protein conformed to the exponential model. According fitting equation, the half-life period of degradation of the thinning seedling and final singling was13.75d,14.76d, respectively.2. There was a small amount Bt protein in the soil after the seedling residues from transgenic Bt cotton embedded into the field at the end period of sampling, but compared with conventional cotton, transgenic Bt cotton had not significantly influence on inverase activities, urease activities, phosphatase activities and protease activities. It concluded that the effects of seedling residues from transgenic Bt cotton on the soil enzyme activity may be the interaction of the Bt protein and the products of residues degradation.3. Compared with conventional cotton straw, different amounts of straw from transgenic Bt cotton embedded into soil had no significant influence on inverase activities, urease activities and protease activities, but could improved significantly phosphatase activities. The highest increase range reached22.13%. It indicated that the effects of different amounts of straw from transgenic Bt cotton embedded into soil on the soil enzyme related to the soil enzyme categories.4. Straw of transgenic Bt cotton could be more beneficial to the growth and reproduction of soil bacteria than the conventional cotton straw, however it had not a remarkable effect on the amount actinomyces and fungi. 5. According to the biolog data, the ability of the transgenic Bt cotton straw take advantage of substrates carbon was0g/kg<5g/kg<10g/kg<20g/kg<30g/kg<40g/kg<50g/kg. Compared with controls, the different amounts of straw from transgenic Bt cotton embedded into soil could improve significantly the microbial species abundance, but could not impact on the species dominance. High-concentrations straw could improve significantly the evenness of soil microbial communities, and increased significantly with the amout of straw. It indicated that the different amounts of straw from transgenic Bt cotton embedded into soil would lead to the changes of microbial diversity index, but the community structure was stable relatively.