Submitted to: Clays and Clay Minerals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 30, 2004
Publication Date: August 1, 2004
Citation: Gonzalez, J.M., Laird, D.A. 2004. Role of smectites and a1-substituted goethites on the catalytic condensation of arginine and glucose. Clays and Clay Minerals. 52(4):443-450. Interpretive Summary: Increasing the amount of soil organic matter (SOM) improves the ability of soils to supply air, water, and nutrients to growing plants, and may help mitigate global warming by removing greenhouse gasses from the atmosphere. When added to the soil, plant residues decompose rapidly and most of the carbon in the plant residue is released back to the atmosphere as cabon dioxide. However, a small amount of the plant carbon is transformed into new SOM. The mechanisms by which plant residue are transformed into new SOM are only partially understood. We discovered that smectite, a type of clay mineral found in soils, can catalyze the transformation of glucose and arginine (important components of plant tissue) into new SOM. Our results also show that the type of cation absorbed on the surface of a smectite has a big influence on the reaction. Goethite, another type of soil clay mineral, was not able to catalyze the reaction. The results of this study are important for scientists who are studying how SOM is formed and who are trying to develop management strategies that increase SOM. In the long term, this study may also help identify soils with the greatest potential for building new SOM, which will help action agencies design agricultural programs that help mitigate global warming and enhance the quality of agricultural soils.
Technical Abstract: The polyphenol theory of humic substance formation has been extensively studied; however, an alternative theory, that humic substances are formed through the condensation of amino acids and reducing sugars (Maillard reaction), has not been extensively explored. The general objectives of this study were to determine whether smectites and goethites catalyze the abiotic polymerization of arginine and glucose to form humic-like compounds. The effects of smectite type, saturating cation, and the degree of A1-substitution in goethites on the polymerization reaction were also studied. Four cation-saturated smectites and four A1-substituted goethites were abiotically incubated with solutions containing a mixture of arginine + glucose for 21 days at 37 deg C. After the incubations, total C recovered ranged from 80.6 to 123.8% and from 100.5 to 105.1% for the clay and goethites systems, respectively. At the end of the incubation, 21.4 to 50.3% of the added C and 16.5 to 90% of the added N were sorbed on the various smectites in a form that could not be desorbed by washing with 100 mM CaC12. X-ray diffraction analysis indicated that some of the sorbed C was intercalated in the smectites and FT-IR analysis provided evidence of new absorption bands at 1650 and 1668 cm**-1, which are consistent with Maillard reaction products. Thus, it is concluded that smectites catalyze the condensation of arginine and glucose to form humic-like products.