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Transgenic crops were grown in an increasingly large scale around world, and accompanied by public concern about their potential ecological and environmental impacts. Evaluation of the effect of genetically modified crops on soil enzyme activity and nutrient content is critical for the soil ecosystem. In order to investigate the effects of planting transgenic soybean on enzyme activities and nutrient contents of rhizosphere soil, the changes of the enzyme activities (urease, alkaline phosphatase and hydrogen peroxidase) and nutrient contents (nitrate nitrogen, ammonium nitrogen, available phosphorus) in rhizosphere soil were examined in microcosm experiments. Two varieties of transgenic soybean M88(CP4 epsps), ZB(Bt cry1Ab + CP4 epsps) and a conventional soybean Zhonghuang 13 were selected. Compared with the conventional variety, the soil enzyme activities (alkaline phosphatase and hydrogen peroxidase) and available phosphorus content of transgenic soybean had no significant difference, but the nitrate content decreased significantly. However, remarkable diiferences existed between M88 and ZB in terms of ammonium nitrogen and urease activity in rhizosphere soil. Compared with the conventional variety, the urease activity and ammonium nitrogen content of transgenic soybean M88 had no significant diiference. In transgenic soybean ZB, the urease activity decreased significantly, and the ammonium nitrogen content increased significantly. [ABSTRACT FROM AUTHOR]

Based on the polymerase chain reaction - denaturing gradient gel electrophoresis (PCR- DGGE) and sequence analysis, two herbicide tolerant genetically modified soybeans ( PAT, ALS ) and the corresponding non - transgenic soybeans (PAT1, ALS1 ) and the local main non - transgenic soybean (Zhonghuang 13, CK) were selected to investigate the effects of herbicide tolerant transgenic soybean cultivation on nitrogen - fixing bacteria in rhizosphere under field experiment. The results showed that the community composition similarity of soil nitrogen -fixing bacteria between transgenic soybean ( PAT, ALS ) and the corresponding non - trans genic soybean ( PAT1,ALS1 ) was approximately 60% . Compared to the corresponding non - transgenic soybeans (PAT1, ALS1), the diversity index (H) and evenness index (EH) of nitrogen - fixing bacterial nifH genes in rhizoshpere of herbicide tolerant genetically modified soybeans (PAT, ALS) both showed no significant difference (p >0. 05) . The sequen-cing and phylogenetic analysis indicated that nitrogen - fixing bacterial nifH genes in rhizoshpere of herbicide toler-ant genetically modified soybeans ( PAT, ALS ) and the corresponding non - transgenic soybeans ( PAT1, ALS1 ) mainly belonged to cyanobacteria, Proteobacteria and Firmicutes. Nitrogen - fixing microbial communities were sig-nificantly (p <0. 05) influenced by the levels of the available phosphorus ( AP) and nitrate nitrogen ( N03 - N) when canonical correspondence analysis was used to identify relationship between nifH gene and soil physicochemi-cal factors. This result indicated that herbicide tolerant genetically modified soybeans had no significant effects on the diversity of soil nitrogen - fixing bacterial nifH genes in rhizosphere. [ABSTRACT FROM AUTHOR]