| The study on the functional genes,community composition and diversity of soil nitrogen cycle microorganisms in desert steppe will not only help enrich the microbial resource pool in desert areas,but also provide a theoretical basis for further exploring the relationship between the structure and function of microbial communities in desert soil.This study used the rhizosphere soil of typical leguminous shrub communities such as Caragana korshinskii,Ammopiptanthus mongolicus,Oxytropis aciphylla and Caragana spinifera at different growth stages(vegetative stage,flowering stage and fruit stage)in the Baijitan National Nature Reserve of Ningxia as materials.The methods of real-time fluorescent quantitative PCR and high-throughput sequencing of functional genes were used to analyze the abundance of functional genes,the structural composition and diversity characteristics of communities of nitrogen cycle microorganisms in the rhizosphere soil of four shrubs at different growth stages,as well as their correlation with soil environmental factors.And combined with isolation and cultivation methods,screen and study the diversity of cultivable aerobic nitrogen-fixing microorganisms in rhizosphere soil.The main results were as follows:(1)The abundance of nitrogen cycle functional genes varies with shrub type and growth period,and the effect of shrub type is greater than that of growth period.The abundance of each functional gene in the rhizosphere soil of C.korshinskii was significantly higher than that of the other three shrubs,and reached the highest at the flowering stage,indicating that the nitrogen cycle microbial resources in the rhizosphere soil of C.korshinskii were the most abundant.Environmental factor correlation analysis showed that the abundance of nifH gene was significantly positively correlated with available potassium and pH;The abundance of amoA and bamoA genes is significantly positively correlated with soil total nitrogen,total phosphorus,total potassium,available potassium,organic matter,and pH;The abundance of nirK and nirS genes is significantly positively correlated with soil total nitrogen,available potassium,and pH.Soil total nitrogen,available potassium and pH significantly affected the abundance of soil nitrogen cycle functional genes.(2)The diversity and structural composition of microbial community in nitrogen cycle were affected by shrub type and growth period.The diversity of nitrogen-fixing microorganism and ammonia-oxidizing bacteria communities in the soil of the C.korshinskii during different growth stages is the highest.In addition to ammonia-oxidizing archaea,Proteobacteria is the dominant phylum of nitrogen cycle microorganisms,with the highest relative abundance of 97.79%.At the genus level,among the functional microorganisms,the community composition among the samples is similar,but there are significant differences in abundance.The dominant genera of nitrogen-fixing microorganism are Skermanella,Azospirillum and Azohydromonas(except SDQ1),with the sum of relative abundance between 63.51%and 91.73%.There are more unclassified bacteria in ammonia-oxidizing archaea,ammonia-oxidizing bacteria and nirS-type denitrification microorganism.The difference of nirK-type denitrification microorganism among different samples was the largest.Sinorhizobium and Paracoccus were the dominant genera,with relative abundance between 4.26%-65.20%and 0.91%-51.93%,respectively.(3)The effects of soil physicochemical factors on various functional microbial communities also vary.Nitrate nitrogen,available phosphorus,available potassium and pH significantly affect the composition of nitrogen-fixing microorganism community,while total potassium,available potassium and organic matter significantly affect the composition of ammonia-oxidizing bacteria community.pH is the main influencing factor of denitrification microorganism community structure.(4)The nitrogen fixing microorganism isolated from the rhizosphere soil of four shrubs belong to 38 genera and have rich diversity.In addition to the common Rhizobium,Pseudomonas and Klebsiella,other uncommon nitrogen-fixing groups such as Brevundimonas,Leclercia and Variovorax were also isolated.There are the most types of nitrogen-fixing microorganism in the rhizosphere soil of C.korshinskii,distributed in 25 genera;The land of C.spinifera is the lowest,only containing 4 genera;Unique nitrogen-fixing groups are distributed in the rhizosphere soil of each shrub. |
