Biomolecule-induced carbonate genesis in abiotic formation of humic substances in nature

Abstract

Hardie, A. G., Dynes, J. J., Kozak, L. M. and Huang, P. M. 2009. Biomolecule-induced carbonate genesis in abiotic formation of humic substances in nature. Can. J. Soil Sci. 89: 445Á453. Most soil C sequestration research has focused on organic C stabilization, while carbonate precipitation has received little attention. Mineral colloids can accelerate abiotic humification reactions of biomolecules such as amino acids, sugars, and polyphenols, derived from the breakdown of biological residues and metabolites. During these reactions CO 2 is produced as a result of the oxidation of biomolecules. However, the biomolecule-induced formation of carbonate during abiotic humification remained to be uncovered. Here we demonstrate using X-ray diffraction, Fourier transform infrared spectroscopy and C K-edge and Mn L-edge near edge X-ray absorption fine structure spectroscopy that the Maillard reaction (glucose and glycine) and the integrated polyphenol-Maillard reaction pathway (catechol, glucose and glycine), in the presence of birnessite (d-MnO 2 ) produce MnCO 3 (rhodochrosite). Increasing the molar ratio of catechol to glucose and glycine dramatically hampered carbonate formation, which is attributed to the enhanced formation of humic polymers, which increased proton generation and perturbed rhodochrosite crystallization through Mn(II)-humic complexation in the reaction systems. Thus, rhodochrosite formation was a competing reaction with humic substance formation. Our findings are of fundamental significance in understanding the vital role of the nature and relative abundance of biomolecules in abiotic carbonate formation, which merits close attention in understanding and regulating C sequestration in natural environments. . Gene`se de carbonates sous l'effet des biomole´cules durant la formation abiotique des substances humiques dans la nature. Can. J. Soil Sci. 89: 445Á453. La majeure partie des recherches sur la se´questration du C dans le sol se concentrent sur la stabilisation du C et on s'est peu attarde´a`la pre´cipitation des carbonates. Or, les colloı¨des mine´raux peuvent acce´le´rer les re´actions d'humification abiotiques des biomole´cules tels les acides amine´s, les sucres et les polyphe´nols, issues de la de´composition des re´sidus biologiques et des me´tabolites. Pendant ces re´actions, l'oxydation des biomole´cules libe`re du CO 2 . Ne´anmoins, on ne sait toujours pas grand-chose de la formation des carbonates induite par les biomole´cules durant l'humification abiotique. Les auteurs ont recouru a`la spectroscopie XRD, FTIR et NEXAFS C au seuil K pour le C et au seuil L pour le Mn afin de montrer que la re´action de Maillard (glucose et glycine) et que la voie inte´grant les polyphe´nols et la re´action de Maillard (cate´chol, glucose et glycine) produisent du MnCO 3 (rhodochrosite) en pre´sence de birnessite (d-MnO 2 ). En augmentant le rapport molaire du cate´chol avec le glucose et la glycine, on entrave conside´rablement la formation de carbonates, ce qu'on attribue a`la synthe`se accrue de polyme...

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