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Multidecadal persistence of organic matter in soils: multiscale investigations down to the submicron scale

Abstract : Minerals, particularly clay-sized minerals, protect soil organic matter (SOM) from decomposition by microorganisms. Here we report the characterization of SOM and the associated minerals over decades of biodegradation, in a French long-term bare fallow (LTBF) experiment started in 1928. The amounts of carbon (C) and nitrogen (N) in the study area declined over time for six fractions (sand, coarse silt, fine silt, coarse clays, intermediate clays, and fine clays). The C : N ratios of SOM associated with silt fractions remained constant, whereas the ratios significantly decreased in clays, reaching very low values in intermediate and fine clays (C : N < 5) after 8 decades of LTBF conditions. Xray absorption spectroscopy revealed the following: (i) bulkscale SOM chemical speciation remained almost constant; (ii) submicron particulate OM was present in coarse clays, even after 79 years of LTBF conditions; and (iii) illite particles became progressively SOM-free with time, whereas mixed-layer illite/smectite and smectites were always associated with OM throughout the bare fallow treatment. In summary, these results suggest that clay-sized minerals preferentially protect N-rich SOM and that smectites and mixedlayer illite/smectite seem to protect associated OM more effectively than pure illites.
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https://hal.archives-ouvertes.fr/hal-03021217
Contributeur : Sylvain Bernard <>
Soumis le : mardi 24 novembre 2020 - 11:14:34
Dernière modification le : mardi 8 décembre 2020 - 03:44:59

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Suzanne Lutfalla, Pierre Barré, Sylvain Bernard, Corentin Le Guillou, Julien Alléon, et al.. Multidecadal persistence of organic matter in soils: multiscale investigations down to the submicron scale. Biogeosciences, European Geosciences Union, 2019, 16, pp.1401-1410. ⟨10.5194/bg-16-1401-2019⟩. ⟨hal-03021217⟩

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