The effects of nitrogen addition on soil organic carbon decomposition and microbial C-degradation functional genes abundance in a Pinus tabulaeformis forest

•Low N addition significantly increased the gene abundances for degrading labile C.•High N addition significantly decreased the abundance of all C-cycling genes.•N addition influenced C-cycling genes through altering soil C and N nutrient status.•C-cycling gene abundances play an important role in SOC decomposition.