High nitrogen enrichment increases the allocation of new organic carbon to deep soil layers

•Response of C dynamics to N addition was evaluated at the scale of whole-soil profile.•Natural stable isotopes (13C and 15N) and radiocarbon techniques were used.•Vertical transport of soil organic matter was promoted under elevated N input.•High nitrogen addition enhanced the soil carbon-sink strength of deep soil layers.•High nitrogen addition facilitated the allocation of new carbon to deep soil layers.