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 ( 13 C and 15 N) 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. The response of soil organic carbon (SOC) dynamics to nitrogen enrichment in the scale of whole-soil profiles, especially in deeper soil layers containing approximately half of SOC, remains unclear. Here, the incorporation of new vegetation-derived carbon into whole-soil profiles is estimated by combining natural stable isotopes ( 13 C and 15 N) with radiocarbon analyses under elevated nitrogen inputs with field experiments. The new mechanism responsible for nitrogen-induced carbon sinking in soils is the increased allocation of new carbon to deep soil layers at high nitrogen enrichment resulting from enhanced vertical transport of SOC. Our work provides an unprecedented representation of deep carbon dynamics under elevated nitrogen input and thus supports the development of policies on soil carbon management.