Structure And Function Of Soil Bacterial Communities Of Mixed Plantation Of Conifer And Broadleaf Tree Species And Their Monoculture Plantations In Southern Subtropical China

Soil bacterial communities play an important role in biogeochemical processes such as mineralization of plant organic matter;nutrient acquisition,and regulation of soil C and N cycle.Establishing pure plantation of native broadleaved tree species and mixed coniferous broadleaved plantations is the developing tendency of forest management in subtropical China,however,the combined mechanism between the structure and function of the soil bacterial community of monoculture and mixed tree plantations has not been clear.The effects of three planted forests,broadleaved Castanopsis hystrix,coniferous Pinus massoniana,and their mixed plantation,on soil bacterial community structure and function under different soil layers(0-20,20-40 and 40-60 cm)in south subtropical China were studied by 16 S r RNA gene high-throughput sequencing and PICRUSt prediction.The results can provide a theoretical basis based on soil bacterial community for tree species selection and the allocation mode of plantation in this area.The main conclusions are as follows:(1)A total of 27 phyla,38 classes,56 orders,104 families,187 genera,and136 species were defined for bacterial groups in the soils of the three study stands,have six dominant phyla and eight dominant genera,respectively.The relative abundance of Acidobacteria in C.hystrix plantation was lower but Burkholderia was higher than those in P.massoniana plantation and mixed plantation.The relative abundance of Bacteroidetes in C.hystrix plantation was higher than that in P.massoniana plantation(P<0.05).The relative abundance of Candidatus＿Solibacter in the mixed forest is significantly higher than that of the C.hystrix plantation and the P.massoniana plantation(P < 0.05).The influence of soil depth on soil bacterial community composition in the studied stand is less than that of the stand type.(2)The structure of the bacterial community in C.hystrix plantation is significantly different from P.massoniana plantation and mixed forest,and the soil bacterial community diversity is sorted by: C.hystrix plantation < P.massoniana plantation and mixed forest,due to soil nitrate nitrogen content.Soil nitrate nitrogen and C/N was the main soil physical and chemical factors leading to the difference of soil bacterial community structure between C.hystrix plantation,and P.massoniana plantation,and mixed plantation.(3)There are 6 first-level functions,41 second-level functions,and 30 nitrogen cycling function in different forests.Among them,the biological pathways metabolic function and nitrogen cycling function in the C.hystrix plantation are lower than those in P.massoniana plantation,and mixed plantation,and the deep influence of the soil layer is not significant.Soil C/N was the main soil physical and chemical factors leading to the difference of soil bacterial community function between C.hystrix plantation,and P.massoniana plantation,and mixed plantation.So the environmental factor affecting the structure and function of the soil bacterial community has consistency.(4)The function of soil bacterial communities affected by soil bacteria community structure.Among them,The relative abundance of Acidobacteria for the most biological function of metabolic pathways has promoted role;The relative abundance of Burkholderia and Bacteroidetes accelerate Ditrification process,the process of Nitrification was opposed;Meanwhile,the relative abundance of Nitrospirae has a promoting effect on Nitrification process.All in all,we suggested that the mixed plantation of P.massoniana and C.hystrix is better than C.hystrix plantation in this area in terms of soil bacterial community structure and function.