Study On Genetic Diversity And Environmental Factors Of Soybean Rhizobia In Red Soil Of Hunan Province

Red soil is an important cultivated land resource in our province.Due to its acidity and low soil fertility,the development of agriculture in red soil area is limited.Soybean is the main food crop and economic crop in our province,the production level has been relatively low,mainly by increasing the application of nitrogen fertilizer to improve soybean yield.The symbiotic nitrogen fixation system of rhizobium-leguminous crop has attracted people's attention because of its low economic cost,no energy consumption,green environmental protection and providing a large amount of nitrogen for crops.It is an important measure to inoculate soybean with high efficiency and excellent rhizobia inoculants to reduce the use of nitrogen fertilizer,protect the environment and improve soybean yield.However,the research on the diversity and ecological adaptation mechanism of soybean rhizobia in our province is still insufficient,which limits the development and utilization of excellent rhizobia inoculants.In this study,the rhizobia of soybean nodules in the red soil planting areas of our province was used as experimental materials and the evolutionary process and population distribution of the rhizobia were revealed by molecular biological methods,which provided a theoretical basis for the subsequent screening of high-efficiency rhizobia strains suitable for the red soil planting areas,reducing nitrogen application and improving soybean yield.The main conclusions are as follows:(1)The phylogenetic analysis of the 16S rRNA gene and the housekeeping gene(SMc00019-thrA-truA)showed that the soybean symbiotic rhizobia samples belonged to the genus of Brachyrhizobium,including Bradyrhizobium japonicum?Bradyrhizobium daqingense?Bradyrhizobium dizaoefficiens?Bradyrhizobium elkanii?Bradyrhizobium pachyrhizi?Bradyrhizobium yuanmingense.The results showed that soybean symbiotic rhizobia in Hunan red soil region had rich genetic diversity and the average nucleotide identity(ANI)analysis results indicated that the sample DD03might be a potential new species.(2)The results of phylogenetic analysis of the symbiotic genes(nodA?nifH)and16S rRNA genes indicated that the same root nodules were clustered together with different model strains on the phylogenetic trees of different genes,which indicated that there might be gene transfer among different populations of soybean symbiotic rhizobia in the red soil region of Hunan Province.The results of phylogenetic analysis of the symbiotic genes(nodA?nifH)were consistent,indicating that the symbiotic genes were basically synchronized in the evolutionary process.(3)There was an obvious biogeographic pattern of soybean rhizobia community in the red soil region of Hunan Province,which was affected by environmental factors and geographical distance.There were significant differences in the composition of the rhizobia community in the three ecological regions,Bradyrhizobium diazoefficiens was the most abundant rhizobial community in soybean rhizosphere.The results of redundancy analysis(RDA)and canonical correspondence analysis(CCA)showed that total potassium,available potassium,soil organic carbon,and available nitrogen were the main factors affecting the?diversity of rhizobia community,soil pH and the exchange of Ca and Mg had great influence on the?diversity of rhizobia community in soybean rhizosphere.(4)The copy number of nifH gene in soybean rhizosphere soil nitrogen-fixing microorganisms ranged from 0.48×10~6 to 2.16×10~6,and the copy number of soil nitrogen-fixing microorganisms collected from Changde region was the highest.The abundance of soil nitrogen-fixing microorganisms in different regions showed significant differences,and the abundance was negatively correlated with soil pH.