Structure And Diversity Of The Soil Bacterial Community In Typical Monoculture Plantations In Subtropical China

Soil bacteria have important ecological functions in the forest ecosystem,yet the composition and diversity of soil bacterial communities in monoculture plantations remain unclear.We combined Illumina MiSeq high-throughput sequencing of the variable region(V4-V5)of the 16SrDNA gene in soil bacteria with bioinformatic analysis to examine the changes in bacterial community composition,relative abundance,and diversity index values in the topsoil(0-20 cm)and subsoil(20-40 cm)of typical monoculture plantations composed of five endemic species for subtropical China(Castanopsis hystrix,Mytilaria laosensis,Michelia macclurei,Paramichelia bailonii,and Pinus massoniana)and one extraneous fast-growing species(Eucalyptus),at the same time,we explored the main soil physical and chemical properties that affect these changes.Our study provides valuable insights into soil fertility regulation and bacterial carbon,nitrogen,and phosphorus cycling in monoculture plantation ecosystems.(1)Six soil layers contained 21 phyla,34 classes,47 orders,82 families,and 131 genera of classified bacteria,andAcidobacteria,Proteobacteria,Chioroflexi,and Actinobacteriawere the dominant bacterial phyla.The relative abundances of Acidobacteria,Proteobacteria,and Actinobacteria in the different soil layers were lower,but the relative abundance of Chioroflexi was higher in the Eucalyptusplantationthan in the five native tree species plantations,But in different soil layers,the relative abundance of dominant fungi was different.The physical and chemical properties of soil were different from those of pure plantation.At the same time,it was found that the influence of soil layer on the bacterial community composition and relative abundance of artificial pure forest was less than that of pure plantation of different species.(2)In the same soil layer,the Alpha diversity of the eucalyptus forest bacterial community is higher than that of 5 native species.The main factors are soil water content,pH,C/N,nitrate nitrogen content and available phosphorus content.(3)In the same stand,the Alpha diversity of the soil bacterial communities in the 6 artificial forests was not identical in the different soil layers,and the main factors were soil water content,C/N,nitrate nitrogen and available phosphorus content.The soil water content had a very significant positive correlation(P<0.05)to soil bacterial richness(P<0.05).Soil C/N is a indicator of soil bacterial diversity.There is a very significant negative correlation(P<0.05).At the same time,it was found that the influence of soil layer on Alpha diversity of artificial pure forest bacterial community was less than that of pure plantation of different species.(4)Beta diversity based on species classification and phylogenetic analysis of Beta diversity,it was found that the soil surface layer of Eucalyptus and the bottom samples were classified as one class,while the soil surface layer and the bottom sample of the 5 species of native tree plantation were classified as one category,indicating the soil bacterial community structure of eucalyptusplantation and the 5 native species plantations are obvious differences.In this study,there are only 1 mixed samples in the soil surface and the bottom layer of each stand,but there is no repetition of the sample.In the future,the number of repeated samples can be increased so that the information of the bacterial community in the forest soil can be fully reflected.