Influence Of Chang-Zhu-Tan Urbanization On Forest-Grass Soil Bacterial Community Structure

During the development of the city,the land use of its surrounding areas will change drastically,forming a heterogeneous environmental gradient,which directly or indirectly affects the composition and diversity of the soil bacterial community,thereby affecting the ecosystem services it carries.However,the dynamic changes of soil bacterial communities under the change of urban development environment have not yet been fully understood,and the changes of soil bacterial communities in different land use types under urban-rural gradients are rarely studied.Therefore,this paper uses Illumina Miseq-16S rRNA sequencing to verify the changes in the bacterial community diversity and structural composition of the surface soil of the Changzhutan urban agglomeration in Hunan Province on the urban-rural gradient,and analyzes the bacterial community diversity in forest and grassland in urban and rural areas.Differences in gradients and structural equation modeling(SEM)were used to quantify the impact of environmental factors on bacterial communities.Through analysis,the main results of this research are as follows:(1)High-throughput sequencing showed that a total of 5,548,698 valid read sequences were generated in forest soil samples,242,617 OTUs,and 47 phylum were obtained;a total of 5,239,946 read sequences were amplified in grassland samples,296924 OTUs were obtained,and 51 phylum were obtained..The relative abundance of bacterial communities shows that Proteobacteria,Acidobacteria,Actinobacteria,Chloroflexi,Bacteroidetes and Verrucomicrobia are all The dominant phylum of soil bacterial community in the sample plot.The change of dominant bacteria phyla on the urban-rural gradient is relatively stable,while the bacterial phyla in forest soil changes more on the urban-rural gradient than grassland soil.(2)The diversity index and richness index of soil bacterial communities showed a decreasing trend on the gradient of urban-suburban-rural.The diversity and abundance of bacterial communities are highest in cities,followed by suburbs,and finally rural areas.In addition,through comparative studies in different land uses,it is found that the abundance and diversity of bacterial communities in grassland sample plots are higher than that in forest land.(3)VPA analysis of variance found that in forest plots,the explanation rate of urbanization intensity to soil bacterial community variation was 6.8%;the explanation rate of soil physical and chemical properties and soil heavy metals to soil bacterial community variation reached 17.8%;spatial variables had an effect on soil The explanation rate of bacterial community variation was 4.4%.In the grassland sample plot,the explanation rate of urbanization intensity to the variation of soil bacterial community was 3.4%;the explanation rate of soil physical and chemical properties and soil heavy metals to the variation of soil bacterial community was 7.3%;the explanation rate of spatial variables to the variation of soil bacterial community Is 6.9%.The results show that urban development can change the composition and diversity of soil bacterial communities to a certain extent,but most of the variation of soil bacterial communities cannot be explained by the above factors.In addition,RDA analysis shows that TOC,TP,C\N,SWC and Mn are the key factors affecting the composition of soil bacterial communities,and pH is the main driving force affecting the composition and diversity of soil bacterial communities.(4)Structural equation modeling(SEM)was used to quantify the impact of environmental factors on bacterial communities.The results showed that the diversity of soil bacterial community in forest land is mainly affected by pH,while the diversity of soil bacterial community in grassland is more affected by urbanization,spatial variables and soil physics and chemistry.In addition,there is a clear correlation between urbanization and soil physical and chemical properties in forest and grassland.In summary,the intensity of urbanization will affect the structure of soil bacterial communities.The diversity and abundance of soil bacterial communities are different on the urban-suburban-rural gradient.Proteobacteria,Acidobacteria and Chloroflexum are the main bacterial phyla in soil.In the process of urban development,the physical and chemical properties of the soil were changed to a certain extent,which indirectly changed the soil bacterial community.In the process of exploring urbanization,the changes and driving forces of the diversity and structure of soil bacterial communities can provide a scientific theoretical basis for the healthy development of urban soil environments.