Effects Of Variety And Soil On Bacterial Community And Nitrogen Cycling Functional Flora Structure In The Rhizosphere Of Soybean

Soybean is an important grain and oil crop,which plays an important role in the development of modern sustainable agriculture because of its high content of protein and fat and its ability to biofilm nitrogen fixation with rhizobia symbiosis.Rhizosphere microorganisms are affected by both soil environment and crop genotype,and are closely related to crop health.By participating in soil nutrient cycle,they affect soybean's utilization of soil nutrients and biological nitrogen fixation ability,thus affecting its growth and development.China has a long history of soybean cultivation and abundant soybean germplasm resources,but the characteristics and differences of rhizosphere microorganisms of different soybean varieties remain to be studied.In this study,9 soybean cultivars were grown in Xuzhou and Shijiazhuang were used as experimental materials.Combined with 16 S rRNA and nifH based amplicon sequencing and fluorescence quantitative PCR technology,to study the characteristics and differences of rhizosphere bacteria and nitrogen-fixing bacteria communities,as well as the abundance of nitrogen cycling functional flora among different soybean cultivars.To explore the effects of soybean breeding on rhizosphere microorganisms and the relationship between them and aboveground traits and clarify the selective recruitment of soil microorganisms by the roots of different soybean varieties and their responses to geographical factors.(1)There were differences in rhizosphere bacterial community and nitrogen cycling flora among different soybean cultivars.The alpha diversity of rhizosphere bacteria of landraces is higher than that of improved varieties,and the relative abundance of Nitrospirae,Gemmatimonadetes and Firmicutes were higher in landraces.Cyanobacteria and Proteobacteria were more dominant among the cultivated varieties.Proteobacteria and Cyanobacteria were relatively more abundant in the upright growing soybean,Anaerolineae was relatively more abundant in the semi-upright growing soybean,and Nitrospirae,Gemmatimonadetes,Firmicutes and Acidimicrobiia were more dominant in the semi-trailing growing soybean.Soil water content and ammonium nitrogen content were the main environmental factors that caused the differences in rhizosphere bacterial community structure among different soybean cultivars,which accounted for 20.5% and 7.8% of the differences,respectively.There were differences in the abundance of functional nitrogen cycling bacteria among soybean cultivars.The? diversity of nitrogen fixing bacteria in the rhizosphere of different soybean cultivars was not significantly different,and all of them were dominated by Sinorhizobium.(2)The non-rhizosphere bacterial community and nitrogen cycling flora were different between the two planting sites,but the soybean rhizosphere showed similar trends in relation to the non-rhizosphere.There was no significant difference in the ? diversity of the non-rhizosphere bacterial community between the two sites,and there was no significant difference between the rhizosphere and non-rhizosphere of different cultivars.Compared with Xuzhou,there were fewer denitrifying bacteria in Shijiazhuang.Compared with the non-rhizosphere,the relative abundance of Actinobacteria,Thaumarchaeota and Chloroflexi increased significantly,while Bacteroidetes and Firmicutes decreased significantly.And selectively recruited functional bacteria with nitrification,ammonia oxidation and other related to the mineralization of nitrogen.In addition,the community structure of bacteria and nitrogen-fixing bacteria were significantly different with different locations.In Xuzhou,the communities of bacteria and nitrogen-fixing bacteria were mainly affected by the root location.In Shijiazhuang,the bacterial community of soybean root was mainly affected by the root position,and the nitrogen-fixing bacteria community was mainly affected by the variety.In conclusion,there were differences in the abundance of rhizosphere bacterial communities and nitrogen cycling functional flora among different soybean cultivars,which were related to the evolutionary status of the cultivars and the growth habits of the aboveground.Geographical factors played a major role in influencing the rhizosphere microorganisms of soybean,but the specific recruitment effects of different cultivars planted in different locations on the functional communities related to the iso-nitrogen assimilation of nitrogen fixing bacteria were similar.The results will help to create a good rhizosphere ecological environment and provide a scientific basis for improving the efficiency of soybean nutrient utilization.