Unexpected 13C-enrichment of organic components from wheat crop soils: evidence for the in situ origin of soil organic matter

Eric Lichtfouse (1) , Sen Dou , Cyril Girardin (2) , Micheline Grably , Jérôme Balesdent (3) , Françoise Béhar (4) , Mireille Vandenbroucke (4)

1 ASD - Agronomy for Sustainable Development
2 Bioemco - Biogéochimie et écologie des milieux continentaux
3 LEMIRE - Laboratoire d'Ecologie Microbienne de la Rhizosphère et d'Environnements Extrêmes
4 IFPEN - IFP Energies nouvelles

Various organic constituents extracted from wheat and from soil organic matter have been analyzed for their carbon content, their absolute concentration and their stable carbon isotope ratios. Most organic subfractions from plants, or soil, are 13C-depleted by up to 9.4‰ relative to bulk organic matter, mainly as a result of their higher lipid content. Furthermore, soil organic constituents are unexpectedly 13C-enriched by +1.5‰ to +4.3‰ relative to homologous plant constituents. Indeed, the selective preservation of plant lignin and lipids, following incorporation into the soil biomass, should have led to the accumulation of 13C-depleted compounds. Hence, these results favour the in situ formation of soil organic matter either by recondensation of small molecules or by selective preservation of biopolymers from soil microorganisms.

Mots clés: 13C; humic acids; humin; soil lipids; plant alkanes; soil alkanes; pyrolysis of humic acids; wheat; soil organic matter

Domaines: Science des sols; Chimie analytique; Géochimie

Eric Lichtfouse, Sen Dou, Cyril Girardin, Micheline Grably, Jérôme Balesdent, et al.. Unexpected 13C-enrichment of organic components from wheat crop soils: evidence for the in situ origin of soil organic matter. Organic Geochemistry, 1995, 23 (9), pp.865-868. ⟨10.1016/0146-6380(95)80009-G⟩. ⟨hal-00192948⟩