The role of lignin for the δ13C signature in C4 grassland and C3 forest soils

► Lignin and SOC showed 13C enrichment in C3 forest and 13C depletion in C4 grassland. ► Low influence of lignin on δ13C values of SOC in C4 grassland soils. ► 13C depleted lignin counteracts the prevailing 13C enrichment of SOC in forest soils. ► 13C enriched non-lignin compounds strongly influence δ13C values in C3 forest soils. ► Structural and isotopical degradation of lignin differs between grassland and forest.