| The planting area of genetically modified(GM)crops continues to increase since its commercial cultivation in 1996.And GM crops made an enormous contribution to feed the world's population,food security,sustainability and climate change.However,the resulting ecological risk and environmental safety also caused wide public concern,especially its influence on soil ecological environment.The interactions between plant roots and soil microorganisms are essential for the function and stability of ecosystems and plant health.Transgenic plants may induce shifts in the enzyme activities of soil and microbial community composition.And they may have potential impacts on processes performed by the soil microorganisms.In this study,experimental materials are a high-methionine soybean line carrying the Arabidopsis cystathionine ?-synthase gene(ZD91)and its non-transgenic soybean counterpart(ZD).Detecting the soil enzyme activity,diversity of microbial community,bacteria numbers related to nitrogen cycle and their community structures.The transgenic soybean ZD91 and its counterpart ZD were provided by the Ministry of Agriculture of the People's Republic of China.This study was performed at Nanchong(30°48'N,106°04'E),Sichuan Province,China,in which a completely randomized block design was set out in two successive growth seasons of soybean(2012 and 2013)in the same field.Each soybean cultivar had four randomly distributed blocks.The samples were collected in both years at four growth stages[seedling stage(SS),flowering stage(FS),pod-setting stage(PS)and maturity-setting stage(MS)],and taking five-point sampling method to assess the safety of the environment in the rhizosphere soil.The main results are as follows:1.Measuring the activity of invertase and alkaline phosphatase in rhizosphere soil to detecting the change of soil enzyme activities,respectively,using 3,5-Dinitrosalicylic acid colorimetric method and the disodium phenyl phosphate colorimetric method.The results showed that:few significant differences were detected in enzyme activities between ZD and ZD91 at all of the growth stages over two consecutive growing seasons.There were no obvious regular differences between growth stages,and we predicted those differences were associated with soil temperature and humidity.2.The Biolog FF microplates were used to evaluate the functional diversity of fungal communities.The results indicate that the substrate utilization,diversity indices and substrate utilization patterns of the fungal communities in rhizospheric soil did not differ between ZD and ZD91.So the high-methionine soybean line ZD91 had no effect to the functional diversity of fungal communities.3.We investigated the soil microbial population during nitrogen fixation and ammonium oxidation by monitoring nitrogen-cycling functional genes(nifH and amoA-AOB)using quantitative real-time PCR.The results showed that transgenic soybean ZD91 may cause a short-term effect on ammonia-oxidizing bacteria during crop growth,but the influence was weakened gradually over time and ultimately vanished.The ANOVA analysis proved that the most important regulator of nitrogen-cycling genes abundance was growth stage,not cultivar.4.Nitrogen-transforming bacterial community structure was examined by constructing clone libraries.The results suggested that the transgenic soybean ZD91 has no apparent impact on nitrogen-fixing and ammonia-oxidizing bacteria in rhizosphere soil and the dominant microflora were similar.The PCA revealed no significant differences in the nitrogen-fixing and ammonia-oxidizing bacteria structure between the two cultivars.Moreover,the phylogeny of nitrogen-cycling genes(nifH and amoA-AOB)was found to match largely to uncultured bacteria in our study,highlighting the importance of further analyzing the nitrogen fixation and ammonification processes of the transgenic soybean ZD91.Overall,the data from this study indicate no adverse effects of the high-methionine soybean line ZD91 on the soil ecosystem and its cultivation is safe and reliable.This study carried out basic data of assessing the biosafety of transgenic soybean to the environment.And these findings will be technically useful for assessing the risk of transgenic plant in the future. |
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