Background and aims <p>Cover crops are an important measure for carbon (C) sequestration in agriculture. However, little is known about the potential of cover crops to increase C under Nordic conditions and the efficiency of this measure over time. Here, we quantify the potential contribution of different cover crops to soil organic carbon (SOC) and organic matter fractions, and study how this is affected by the origin of the C input (aboveground or belowground residues).</p> Methods <p>We conducted a ¹³CO₂ pulse-labelling experiment during the growing season of four cover crops adapted to Nordic conditions, representing different plant functional types. The assimilated ¹³C was traced in soil during the following two years. We investigated the fate of cover crop C in two organic matter fractions, Particulate Organic Matter (POM) and Mineral-Associated Organic Matter (MAOM), known to have different persistence in soil.</p> Results <p>Carbon derived from aboveground residues decayed two to three times faster as compared to belowground C. Belowground C inputs were similar among cover crops despite their contrasting root traits and differences in root biomass C. Rhizodeposited-C was consistently the largest belowground C input. Cover crop species affected the quantity of POM-C and MAOM-C, but MAOM-C was preferentially formed from belowground C (ranging from 0.63 ± 0.2 to 0.25 ± 0.1&#xa0;Mg MAOM-C ha⁻¹ across different cover crops), regardless of the species.</p> Conclusions <p>Cover crop species that can combine large belowground biomass production with root traits that promote physical and physico-chemical protection of OM will contribute most effectively to the long-term SOC pool. These aspects need to be balanced with considerations related to agricultural management.</p>