Effects Of Mixed Tree Species On The Composition And Functional Characteristics Of Soil Microbial Communities In The Yellow River

Mixed forest has the functions of improving site conditions,increasing the quantity and quality of forest trees,and enhancing the ability of tree species to resist disasters.At the end of the 20th century,the Yellow River Delta region began to strengthen the construction of mixed forests,but the tree species selection,management and other aspects of the mixed forests were still not mature enough,and the technology needed to be further improved.Previous studies have been conducted on the growth of mixed forests and soil environment in this area,but there is no systematic analysis of the effects of mixed types on soil microorganisms.With the emergence of Metagenomics technology,effective methods have been provided for more accurate understanding of the status of microbial habitat,the relationship between structure and function,and the relationship between microorganisms and the environment.Therefore,this article takes the common tree species pure forest and mixed forest in the Yellow River Delta as the research object,and uses Metagenomics technology to analyze the differences in soil microbial composition and functional genes between the mixed forest and the control pure forest,and combines the physical and chemical properties of the soil and soil enzyme activities,to explore the relationship between soil environment and microbial diversity in mixed forests,the results show:1.The content of total sulfur,total phosphorus,nitrate nitrogen,available potassium,available phosphorus,organic carbon,and biomass carbon in the mixed forest of Fraxinus chinensis×Robinia pseudoacaciat and elm and Ulmus pumila×Robinia pseudoacacia mixed forest are significantly higher than the corresponding pure forest.The difference between the mixed forest of Fraxinus chinensis×Robinia pseudoacacia and Fraxinus chinensis forest is the most significant.;the difference between Ailanthus altissima × Robinia pseudoacacia mixed forest and Ailanthus altissima forest is not obvious.The soil nutrient status of the mixed forests of different models is from high to low: Ulmus pumila×Robinia pseudoacacia mixed forest? Fraxinus chinensis×Robinia pseudoacaciat mixed forest? Ailanthus altissima×Robinia pseudoacacia mixed forest.2.The soil urease and invertase activities of mixed forests were significantly higher than the corresponding pure forests.Phosphatase and catalase activities were significantly different among different forest types.In different mixed forests,in addition to catalase,the activities of other enzymes were from large to small: Ulmus pumila × Robinia pseudoacacia mixed forest? Fraxinus chinensis × Robinia pseudoacaciat mixed forest? Ailanthus altissima ×Robinia pseudoacacia mixed forest.3.There are significant differences in the composition of soil microbial communities between different mixed forests and corresponding pure forests.The soil microorganisms in this area are dominated by bacteria(84%-85%);the main dominant phyla are Anhydride(31.60%-33.04%),Proteobacteria(20.81%-21.09%),Proteobacteria,Proteobacteria in mixed forests,The abundance of aerobic bacteria such as Actinomycota was significantly higher than those of control pure forest.There are obviously different bacterial communities between mixed forests.Ammonia nitrogen and available potassium in soil nutrients are the main influencing factors of soil bacteria in this area.4.The annotation results based on the eggNOG and KEGG databases show that the sugar metabolism of soil microorganisms in different forest stands is active.Compared with pure forests,the abundance of soil microbial metabolic function genes in mixed forests increased significantly.The effects are different,and the annotated microbial functional genes in the mixed forest of Ulmus pumila×Robinia pseudoacacia have the highest abundance.5.Specific analysis of the role of soil microorganisms in the C and N cycles by KEGG showed that: in the C cycle process,compared with the control pure forest,the C metabolism is the most active in the mixed forest of Ulmus pumila×Robinia pseudoacacia,glycolysis,tricarboxylic acid cycle.The glycolysis,tricarboxylic acid cycle,and methane metabolism processes in the soil are all promoted.The soil Candidatus?Rokubacteria,Chloroflexi,Verrucomicrobia was significantly related to the fixation and release of CO2.In the process of N metabolism,the abundance of Acidobacteria,Verrucomicrobia,Chloroflexi and Bacteroidetes annotated nitrous oxide reductase,Planctomycetes annotated nitrite reductase,Acidobacteria,Chloroflexi annotated nitrate reductase and Chloroflexi-annotated glutamate synthase in the soil microorganisms of the Ulmus pumila × Robinia pseudoacacia mixed forest and Fraxinus chinensis×Robinia pseudoacacia mixed forest were significantly higher than that of the respective pure forests.Among the different mixed types,the N metabolism of Ulmus pumila×Robinia pseudoacacia mixed forest was the most active.6.The results of carbohydrate annotation from CAZy database indicate that glycosyltransferases and glycoside hydrolases are dominant in the abundance of microbial gene sequences in this region.Among the different mixed types,the relative abundances of glycoside hydrolase,polysaccharide lyase and auxiliary oxidase in the Fraxinus chinensis×Robinia pseudoacaciat mixed forest and Ulmus pumila×Robinia pseudoacacia mixed forest were significantly higher than those of pure forests.In general,mixed forests can improve soil quality to a certain extent,promote different soil microbial communities by affecting the soil environment,and promote the functional metabolism of soil microbes.Among the mixed forests of different tree species,the Ulmus pumila×Robinia pseudoacacia mixed forest has the highest comprehensive benefit.