Effects Of Soil Microbial Community And Nitrogen Cycle Under The Role Of Rare Earth Elements

The soil in and around the Bayan Obo rare earth mining area in Baotou,Inner Mongolia is heavily polluted and the ecosystem is relatively homogeneous and fragile.With the effect of rare earth elements on the microbial community structure and functional metabolism in the soil as the main research target,we use metagenomic technology as the research tool to determine the microbial diversity,community structure and functional abundance,which is important for understanding the effect of extreme environmental conditions on the microbial community structure,rare earth elements pollution.It is of great ecological importance to understand the influence of extreme environmental conditions on microbial community structure,the existence pattern of microbial communities in soil environment and the functional response of microorganisms to rare earth elements.Among the key biogeochemical cycles that ecosystems rely on for maintenance,the global nitrogen cycle has been greatly changed by human activities,and most of the nitrogen conversion processes are involved by microorganisms.It is also the focus of this paper to explore the genes involved in rare earth resistance of microorganisms under the action of rare earth elements and to decode the response gene groups of in-situ microbes to the action of rare earth elements.We measured the physicochemical properties and rare earth elements content of soil in the mine area of Bayan Obo,and analyzed the changes of microbial community structure and functional response in soil and its role in the process of nitrogen cycling using macro-genomic techniques,and the following conclusions were obtained.(1)According to the measurement of rare earth elements,the total amount of rare earth from high to low was: mining area >residential area >control area;The measured soils are all alkaline,Oxidation-reduction potential and the contents of total nitrogen and organic matter are very low in the sample sites.(2)The soil microorganisms in the mine area of Bayan Obo were mainly bacteria,and the dominant phyla are Actinobacteria,Proteobacteria,Chloroflexi,Acidobacteria,Firmicutes,Gemmatimonadetes,Bacteroidetes.The dominant genera are Solirubrobacter,Streptomyces,Conexibacter,Rubrobacter,Nocardioides,Mycobacterium.(3)Rare earth elements had a significant effect on the distribution of microorganisms,with higher relative abundance of Solirubrobacter,Streptomyces,Conexibacter,Mycobacterium,Gaiella,and Patulibacter in areas of high rare earth concentration and Microvirga,Geodermatophilus,and Pyrinomonas in areas of low rare earth concentration.(4)High concentrations of rare earth elements affected the phosphopentose acid pathway,starch and sucrose metabolism,and arginine and proline metabolism in microorganisms and might have an inhibitory effect on them.In contrast,total nitrogen and organic matter in the environment may have a facilitative effect on the metabolism of oxidative phosphorylation,two-component system,pyruvate metabolism,amino acid biosynthesis,and carbon fixation pathway in prokaryotes in the community.(5)The analysis of nitrogen metabolic pathways showed that high rare earth content could reduce the abundance of enzymes and genes related to nitrate allotropic reduction,denitrification and nitrogen fixation processes and increase the abundance of functional genes and enzymes related to nitrification processes.(6)The results of the sequencing experiments were further verified by fluorescence quantitative PCR experiments,which revealed that the abundance of nitrification genes(amoA-AOA/B)was higher in the high rare earth region(Y3),while the abundance of denitrification genes(nosZ)genes was higher in the low rare earth region,which was consistent with the sequencing results.