Biochar mitigates the effect of nitrogen deposition on soil bacterial community composition and enzyme activities in a Torreya grandis orchard

•N deposition and biochar decreased soil MBC and altered soil microbial community.•Biochar increased Proteobacteria abundance under different levels of N deposition.•Both N deposition and biochar decreased soil enzyme activities significantly.•Biochar amendment can mitigate effect of N deposition through increasing AP content.