| Soybean (Glycine max), which is closely related to people’s lives, is not only a human major oil crop and vegetable protein source, but also is an important industrial raw material and a potential source of biodiesel. In 1988, the world’s first genetically modified soybean was produced. Since the first generation of Roundup Ready soybean (RRS) was cultivated by Monsanto and authorized commercially in the United States in 1996, RRS have brought huge economic and social benefits. However, with a large area of transgenic crops planting, the potential security issues have caused more and more widespread concern, in which the effect on soil microbial ecosystem has been a hot topic. As an important component in keeping soil biological activity, the soil microorganisms participate in the decomposition of organic matter, nutrient cycling and transformation of soil biochemical process, and any changes in the activity and community structure can sensitively reflect the quality and health of the soil ecosystem. Since the research on the ecological safety of transgenic soybeans started late, the effects on rhizosphere soil nitrogen-fixing bacteria group are rarely reported. Here, we chose the EPSPS transgenic herbicide-resistant soybean in Huang-Huai-Hai region as an example, and studied the effects of the cultivation of genetically modified soybeans on soil nitrogen-fixing bacteria group and made a risk assessment.In this experiment, we chose a genetically modified herbicide-resistant soybean (Zhongzuo J9331) and transgenic control (Zhonghuang 30) as well as a regional test variety of Langfang in Hebei (Zhonghuang 13) as materials, and then the physical and chemical properties of the soil, the N content of the plants and seeds as well as a plurality indices of soil nitrogen-fixing bacteria groups were measured and analyzed. We mainly studied the effects of genetically modified herbicide-resistant soybeans on soil nitrogen-fixing bacteria groups in the field planting conditions, established a relatively complete system of evaluation techniques, and then we established a primary risk assessment model of the effect of genetically modified soybeans on soil nitrogen-fixing bacteria groups using the analytic hierarchy process based on the obtained multiple indices.The results showed that the soil moisture content and pH have no significant changes after the planting of Zhongzuo J9331. We studied some enzymes related with the N cycling in soil, and found that urease and nitrate reductase activity had no significant changes after Zhongzuo J9331 were planted, while the soil nitrite reductase activity were significantly changed at certain growth stage.The N content of the soil varied as the soybean growth, and reached the maximum at the flowering stage, and there were no significant differences between Zhongzuo J9331 and Zhonghuang 30 at four periods. The N content of plants (aerial parts) decreased with the soybean plants growth, which is consistent with the law of nutrient transport and storage from vegetative growth to reproductive growth. There were no significant differences about the N content of plants (aerial parts) between Zhongzuo J9331 and Zhonghuang 30 at the flowering stage. But at the mature stage, the N content of Zhongzuo J9331 was significantly lower than that of Zhonghuang 30. While the study of the N content of soybean seed showed that there was no significant difference between Zhongzuo J9331 and Zhonghuang 30, but both were significantly lower than that of Zhonghuang 13.Results of investigation of nodulation effect of nitrogen-fixing bacteria group showed that the number of nodules increased first and then decreased with the soybean growth, and reached the maximum at the flowering stage. The number of nodules of the three varieties was significantly different at the seedling and mature stages. With regard to the nodule size (nodule surface area) at three periods, there was significant difference between three varieties at the maturity stage, while at the other two periods there were no significant differences. It was suggested that the transgenic soybean had some impact on soil nitrogen-fixing bacteria at some periods, and would further affect the symbiotic nitrogen-fixing process between the soybeans and the soil nitrogen-fixing bacteria groups.The diversity analysis of culturable nitrogen-fixing bacteria in rhizosphere soil showed that the number of nitrogen-fixing bacteria varied with the soybean growth. AT the seedling and flowering stages, the differences of the number of culturable nitrogen-fixing bacteria among three varieties reached significant level, while at the other two periods there were no significant differences. The results showed that the cultivation of Zhongzuo J9331 would lower the diversity of culturable soil nitrogen-fixing bacteria at some periods.Real-time PCR results of nifH-gene expression showed that the abundance of soil nitrogen-fixing bacteria group was gradually increased, and reached the maximum at the maturity stage. The results showed that the abundance of nitrogen-fixing bacteria group of Zhongzuo J9331 was significantly less than that of Zhonghuang 30 at the seedling stage, while at other periods, there were no significant differences. It showed that planting Zhongzuo J9331 would reduce the overall amount of the soil nitrogen-fixing bacteria at certain growth stage.To establish a risk assessment model, we chose indices of the three different varieties to non-dimensionalize and normalize, and then used analytic hierarchy process (AHP) to determine the weight indexes. The results showed that planting transgenic soybean Zhongzuo J9331 in Huang-Huai-Hai region possibly has some impacts on nitrogen-fixing bacteria group, but to obtain an optimal risk assessment model, more experimental replicates, especially more indices should be applied in the future study. |
PDF Full Text Request