Molecular Ecological Network Structure And Potential Function Of Bacterial Community In Soil Profile Under Native Tree Plantations In South Subtropical China

Soil profile is a strong and complex physical and chemical gradient.The gradient changes of various soil physical and chemical properties on the profile greatly affect the structure and function of soil interlayer microbial community.As an important component of forest soil ecosystem,soil bacteria play an indis-pensable role in the process of energy flow,nutrient cycle and biogeochemical cycle of forest ecosystem.They play an important role in maintaining the com-munity structure and functional stability of forest ecosystem,and their functions are not limited to the surface of soil,but also play an important role in the deep layer of soil.Exploring the construction and maintenance mechanism of forest soil bacterial community has always been the focus of soil microbial ecology.China’s plantation area ranks first in the world,but as the forest management idea changes from the single goal of pursuing wood yield to the multi-objective of improving ecosystem service quality and efficiency,the construction of high-value native broad-leaved tree plantation has become the development trend of plantation management in subtropical areas of China,resulting in the gradual expansion of the area of native tree plantation.At present,there is little research on the molecular ecological network structure and function of bacterial commu-nity in soil profile of vernacular tree plantations in subtropical area.Therefore,taking the plantations of four typical native tree species（Pinus massoniana,Castanopsis hicklii,Mytilaria laosensis and Michelia macclurei）in the south subtropical region as the research object,this paper uses bacterial 16Sr RNA gene high-throughput sequencing technology,molecular ecological network analysis and FAPROTAX function prediction,To explore the molecular ecolog-ical network structure and potential function of soil bacterial community in dif-ferent soil layers（0～20,20～40 and 40～60 cm）of vernacular tree plantations.The results can enrich the research content of the structure and function of bacte-rial community in forest soil profile,and provide a theoretical basis for the op-timization of biogeochemical cycle of plantation soil ecosystem and the stable exertion of ecological service function.The main conclusions of the study are as follows:（1）The construction of molecular ecological network structure of bacte-rial communities in three soil layers of vernacular tree plantations is non random,and its distribution mode is mainly controlled by deterministic process.（2）There are differences in the structure of bacterial molecular ecologi-cal network in the three soil layers.Compared with the surface layer（0-20 cm）,the middle layer（20-40 cm）and bottom layer（40-60 cm）,the soil bacterial mo-lecular ecological network has larger scale,more complex structure and stronger interaction between species.（3）The bacterial communities in the three soil layers were mainly posi-tively correlated,but the proportion of negative correlation increased with the increase of soil depth.The contents of soil SOC,NH₄⁺-N,NO₃^--N,TP and AP were the dominant factors affecting the differences of molecular ecological net-work structure of bacterial community between soil layers.（4）The key bacterial groups in the bacterial molecular ecological net-works of the three soil layers are module hubs and connectors.The number of modules decreases with the increase of soil depth,while the module hub and connector increase with the increase of soil depth.Actinobacteria and Firmicutes are the key bacteria in the surface layer（0-20 cm）,Proteobacteria,Planctomy-cetes,Acidobacteria and Chloroflexi are the key bacteria in the middle layer（20-40 cm）,and Proteobacteria,Acidobacteria and Actinobacteria are the key bacte-ria in the bottom layer（40-60 cm）Planctomycetes,Firmicutes and Verrucomi-crobia.（5）The comparison of dominant bacterial functional groups of bacterial communities in three soil layers of Native Tree Species Plantation shows that the surface layer（0-20 cm）of urea hydrolysis type is significantly higher than the middle layer（20-40 cm）and the bottom layer（40-60 cm）（P<0.05）,but there is no significant difference between the middle layer and the bottom layer（P>0.05）,and there is no significant difference in other dominant bacterial functional groups（P>0.05）.Chemical heterotrophic,aerobic chemical hetero-trophic,cellulose hydrolytic,Urea Hydrolytic,nitrogen fixation and nitrate re-duction are the groups with the largest proportion in each soil layer.Soil p H,SOC,NH₄⁺-N,NO₃^--N,TP and AP are the main factors affecting the dominant functional groups of bacterial community in soil profile.（6）The potential function of soil bacterial community in vernacular tree plantations is affected by the molecular ecological network structure of soil bac-terial community.The dominant bacterial functional groups involved in soil car-bon and nitrogen cycle were significantly correlated with the key bacterial groups in each soil layer.In conclusion,in terms of the molecular ecological network structure and potential function of soil bacterial community in the plantation area of native tree species in the south subtropical zone,the molecular ecological network of bacteria in the middle and bottom soil is larger,the structure is more complex,and there are more potential functional bacteria.The dominant soil factors af-fecting the molecular ecological network structure and potential function of soil bacterial community in subtropical vernacular tree plantations are consistent.