| With the development of genetic engineering technology and the commercial planting of genetically modified(GM)crops on a large scale,it becomes a hot topic about the potential harm from transgenic crops to soil biological characteristics and their effects on soil ecosystem.The rhizosphere is a key zone with respect to the mechanisms of soil nutrient dynamics.Soil microorganisms can maintain the soil biological activity and have an effect on soil physicochemical properties and enzyme activities.We here examined the impact of transgenic high-methionine soybean cultivar ZD91 on soil main physicochemical properties,enzyme activities,and functional diversity of microbial communities in rhizosphere soil.The results showed that transgenic soybean ZD91 has no apparent impact on soil physicochemical properties,enzyme activities,and functional diversity of microbial communities.Moreover,our results suggested that different planting years and crop growth stages affect the these parameters,but not cultivar variances that remain the least explanatory factor.Among the microorganisms,bacterial population was higher in number(>70%)and it play an important role in the natural cycling of materials.Previous studies have shown that methionine from root exudates affects the rhizosphere bacterial population involved in soil nitrogen fixation.A transgenic line of Zigongdongdou soybean cultivar(ZD91)was examined for its influence to the rhizosphere bacterial communities.Using 16S rRNA amplicon sequencing(Illumina Miseq platform)analysis of the V4 region and DNA extracted from bacterial consortia collected from the rhizosphere of soybean plants grown in an agricultural field,we characterized the populational structure of the bacterial community involved.We found that Acidobacteria,Proteobacteria,Actinobacteria,Bacteroidetcs.Verrucomicrobia,Planctomycetes,and Firmicutes constitute the dominant taxonomic groups in either the ZD91 transgenic line or parental cultivar ZD,and that there was no statistically significant difference in the rhizosphere bacterial community structure between the two cultivars.Arbuscular mycorrhizal fungi(AMF)are known to be involved in promotion of plant growth and health.The AMF of the phylum Glomeromycota form mutualistic symbioses with the majority of land plants,including many crops.We here also examined the impact of a transgenic line of the Zigongdongdou soybean cultivar(ZD91)on the arbuscular mycorrhizal(AM)fungal communities in rhizosphere soil.Our investigations based on clone libraries were conducted in field trials at four different crop growth stages over two consecutive years(2012～2013).A total of 155 operational taxonomic units(OTUs)of AM fungi were identified based on the sequences of small subunit(SSU)rRNA genes.In addition,there were no significant differences found in AM fungal diversity in rhizosphere soil during the same crop growth stage between transgenic soybean ZD91 and its parental line Zigongdongdou(ZD).Our results suggested that different planting years and crop growth stages affect the dynamics of the AM fungal communities,but not cultivar variances that remain the least explanatory factor.In conclusion,transgenic high-methionine soybean ZD91 has no apparent impact on the structure and function of rhizospheric microbial communities.And this study thus provides a theoretical basis for monitoring the environmental impact by transgenic soybean ZD91. |
