Metagenomics reveals divergent functional profiles of soil carbon and nitrogen cycling under long-term addition of chemical and organic fertilizers in the black soil region

•Biogeographic distance rather than fertilization dominated microbial functional profiles in Mollisols.•Chemical fertilization promoted processes of methane oxidation, soil N degradation, nitrification and anammox.•Manure fertilization shifted C fixation and degradation processes and facilitated nitrate reduction.•Chemical plus manure fertilization could potentially enhance N2O emission via denitrification.•Soil P contents were the most influential factor in controlling microbial functional profiles.