Study On The Characteristics Of Microbial Community In Slope Ecosystem In Loess Hilly Area

Loess hilly area has been one of the areas with the most serious soil erosion and ecological environment degradation in China and even in the world for a long time.It is the key and difficult area of ecological environment construction.The study on the maintenance and regulation function of slope ecosystem widely distributed in loess hilly area will help to improve the climate conditions and ecological environment of this area and its surrounding areas.Vegetation and soil are important members of the slope ecosystem,which contains a lot of carbon,nitrogen,phosphorus and other nutrients.Vegetation-soil system has a profound impact on the biogeochemical process of the terrestrial ecosystem,and plays an important role in the global element balance,especially the carbon balance,in which microorganisms play an irreplaceable role.Microorganism is the engine of the transformation process from plant residues to soil organic matter,and is an important driving force for regulating the transformation and accumulation of nutrients such as vegetation and soil carbon and nitrogen.It is of great scientific and practical significance to study the microbial driving mechanism in the material cycle and energy flow process of vegetationsoil system.In this study,the Sickle Bay area in the northwest of Yanhe River Basin in the loess hilly area was selected as the research area,and the Natural Grassland Slope ecosystem was selected as the research object.With the help of high-throughput sequencing and other technical means,the composition,structure and metabolic function of bacterial and fungal communities in vegetation and soil on different slope positions were determined,so as to provide a scientific basis for the discussion of the role of microbial community in the typical slope ecosystem in the loess hilly area.The main conclusions are as follows.(1)In the slope ecosystem,The dominant bacteria were Proteobacteria and Actinobacteria,and the dominant fungi was Ascomycota in every single layer(fresh plant,standing litter,litter,surface soil(0-0.5cm),lower soil(0.5-2.Ocm)).Bacteria such as Bacteroidetes,Acidobacteria,Gemmatimonadetes,Chloroflexi and fungi such as Basidiomycota also had high relative abundance in most layers.With the decrease of taxonomic level,the composition of microbial community in different layers became more and more abundant.there were many kinds of microorganisms in the slope ecosystem that did not belong to the community of bacteria and fungi,but could be detected by highthroughput sequencing analysis,with high content in fresh plants and other layers.(2)There are some differences in community richness and diversity level of bacteria and fungi in slope ecosystem:In terms of bacteria,litter and soil had similar bacterial community richness and diversity level,and were obviously superior to fresh plants.In the aspect of fungi,except that the richness and diversity of fungal community in fresh plant on the top of slope were significantly lower than that of other layers,the difference between phyllospheric fungi and soil fungi on other slope positions was small,and the richness and diversity of litter fungal community on the bottom of slope is often better than that of soil fungal community.In the aspect of the differences among the slope positions,the diversity level of fresh plant bacterial community on the slope was significantly lower than that of other slope positions,while the differences among the other four levels were relatively small.The distribution patterns of different layers of fungal community were different.(3)There were also some differences in the characteristics of bacterial and fungal community structure:In terms of bacteria,the three analysis methods(PCA principal component analysis,UPGMA clustering analysis based on unweighted UniFrac or weighted UniFrac distance matrix)all showed that the similarity of bacterial community structure between the two layers of soil on each slope position was high,and the similarity between bacterial community structure of fresh plants and that of litter and soil was poor.From the top to the bottom of slope,the difference of bacterial community structure between standing litter and litter was increasing,while the similarity between fresh plants and standing litter gradually exceeded the similarity between standing litter and litter.In terms of fungi,Considering only the differences among different layers caused by the existence of community members,the fungal community structure of the slope ecosystem is relatively stable,on each slop position,The community structure difference between soil and phyllospheric fungi was great,and the similarity between two layers of soil and between standing litter and litter was high.Considering the change of relative abundance of each species,the community structure of fungi in fresh plants and litter was more and more similar,and the differences between standing litter and litter,as well as between two layers of soil were larger and larger.(4)There are a variety of microbial metabolism functional groups closely related to material circulation and energy flow in the terrestrial ecosystem,including Amino Acid Metabolism and Carbohydrate Metabolism functional groups with the highest relative abundance(abOTU 10%)followed by Energy Metabolism(more than 5%),then followed by Metabolism of Cofactors and Vitamins,Nucleotide Metabolism,Lipid Metabolism,Xenobiotics Biodegradation and Metabolism(3-5%).There were obvious differences in the layer distribution of various microbial metabolizing functional groups on the top of slope,from the top to the bottom of slop,the relative abundances of each functional group tend to be the same at all layers.There were obvious differences between slop positions in the relative abundances of many groups in fresh plants,from fresh plant to lower soil,the relative abundance of each functional group tended to be the same at all slop positions.In conclusion,the composition,structure and function of the microbial community in the slope ecosystem show some obvious changes with the changes of the environmental factors represented by the slope position and layer,among which there are obvious differences in the response of bacterial and fungal communities to environmental changes,and there are also some differences between the phyllospheric microbial and soil microbial communities.