Changes in Soil Bacterial Community Structure and Diversity of Pinus Tabuliformis Plantation after 65 Years of near-naturalization in North China

Our study investigates the effect of near-naturalization of plantations on soil physicochemical and bacterial features and the difference between soil layers in Baxianshan National Nature Reserve. Four stands were involved, including two forest types: near-naturalized and natural secondary forests, with the former classified into three stages. Soil physicochemical and bacterial properties were determined and analyzed. TC, TN contents and C/N ratio of the surface soil were higher than the corresponding lower layer. TC, TN contents decreased first and then increased with near-naturalization, lower than the natural secondary forests, while the C/N ratio was the opposite; total and endemic OTUs quantity was more in the surface layer than the lower and both increased with near-naturalization; the dominant phyla were Proteobacteria, Acidobacteria, Gemmatimonadetes, and verrucomicrobia, the relative abundance of Proteobacteria increased with near-naturalization while that of other dominant phyla decreased; the α-diversity increased on the whole during near-naturalization and was lower than the natural secondary forests except for Simpson and Shannon index; environmental factors significantly explained the bacterial α-diversity and community structure of natural secondary forests but not near-naturalized forests. This study helps fully understand the change characteristics and response mechanisms of soil bacterial community structure to the restoration of the plantation.