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Spatial Variation in the Molecular Composition of Dissolved Organic Matter from the Podzol Soils of a Temperate Pine Forest

Abstract : Spatial Variation in the Molecular Composition of Dissolved OrganicMatter from the Podzol Soils of a Temperate Pine ForestEmmanuelle Maria,†Pierre Crançon,‡Gaëtane Lespes,†and Maxime C. Bridoux*,‡†Universitéde Pau et des Pays de l’Adour (UPPA)/CNRS, Laboratoire de Chimie Analytique Bio-Inorganique et Environnement,UMR IPREM 5254, Technopôle Hélioparc, Av. du Président Angot, 64000 PAU, France‡CEA, DAM, DIF, F-91297 Arpajon, France*SSupporting InformationABSTRACT:In podzols, the production and mobilization ofdissolved organic matter (DOM) account for a considerableloss of carbon from the forestfloor. The dynamics of DOM inthe podzol soils of a pine forest result from complexinteractions between water infiltrations, weathering, biologicaltransformation, and retention-mobilization mechanisms. How-ever, little is known about how the molecular composition ofDOM changes spatially in the podzol soil as it moves from theupper horizons (organic (O) and eluvial (E)) to the illuvialhorizon (B(h/s)) to the groundwater. In this study, DOMsamples were collected in the upper (A1) and accumulation(Bh) horizons of a sandy permeable podzol with a hydrologyoccurring exclusively through drainage of shallow water (no surface runoff), as well as from the groundwater. Samples wereconcentrated on a Strata-X-AW solid-phase extraction cartridge and directly infused using electrospray ionization in the negativemode coupled with an LTQ-Orbitrap mass spectrometer. Over 2300 monoisotopic molecular formulas of CHO and CHONwith molecular weights up to 600 Da, assigned mainly to lignin-like compounds (53%), tannins (22%), condensed aromatics(14%), protein-like compounds, lipids (3%), aminosugars/carbohydrates (1%), and unsaturated hydrocarbons, were identifiedin DOM from the upper podzol horizon (A1), indicating that leaching of plant debris dominates the DOM pool released in thesoil seepage waters. Among all molecular formulas detected, 31% were unique to A1, while only 6.9% were only detected in Bhand 12.9% in Gw. Van Krevelen diagrams of these unique formulas clearly highlighted an evolution of the OM molecularcomposition along the podzol soil profile, from the upper horizon, through the accumulation horizon, to the groundwater with ashift from the high-oxygen, plant-derived compounds (tannins-like and lignin-like) to the low-oxygen classes (unsaturated andcondensed hydrocarbon), suggesting a reduction process either microbially mediated or via preferential adsorption of oxygen-functionalized DOM compounds to mineral surfaces
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Emmanuelle Maria, Pierre Crançon, Gaetane Lespes, Maxime Bridoux. Spatial Variation in the Molecular Composition of Dissolved Organic Matter from the Podzol Soils of a Temperate Pine Forest. ACS Earth and Space Chemistry, ACS, 2019, 3 (8), pp.1685-1696. ⟨10.1021/acsearthspacechem.9b00164⟩. ⟨hal-02282793⟩



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