“…The use of stable isotope techniques (e.g., 13 C) to assess the contribution of different vegetative sources of SOM (Epron, Mouanda, Mareschal, & Lydie‐Stella, ; Hernández et al, ; Souza et al, ), alterations in SOM due to land‐use changes (Vilas Boas, Almeida, Teixeira, Souza, & Silva, ), and to discern the origins of soil C–CO 2 (Millard, Midwood, Hunt, Barbour, & Whitehead, ; Oliveira et al, ) has been reported widely in the literature. In these studies, for the 13 C isotope technique to be useful, there must either be differences in the natural 13 C abundances between soils (soils cultivated with C 3 or C 4 plants) and plants (C 3 or C 4 plants) or a 13 C enrichment in the plant material ( 13 C labelling).…”