Investigation of the Effect of Soil Mineral Composition on Soil Organic Matter Stability

摘要

The soil organic matter (SOM) pools with different stability play different roles in the agricultural and environmental processes, e.g. in the global carbon cycle. In this work Rock-Eval (RE) pyrolysis measurements and mathematical deconvolution of RE pyrograms were used for determining the abundance, quality, and main biological sources of SOM, as well as for evaluating the relative proportion of the labile (fresh plant and litter) and resistant (lignin and cellulose) bio-macromolecules, immature (humic substances) and mature refractory (naturally stable biological compounds, organic matter stabilized by physico-chemical processes and black carbon) geo-macromolecules. The samples were taken from the A-horizons of Leptosol, Luvisol, and Acrisol formed under different soil conditions (mineral composition, pH, and leaching). In agreement with the present vegetation, bulk RE data together with the results from the mathematical deconvolution of pyrograms display terrigeneous plant remnants as precursors of SOM for all the three samples. The presence of the more stable components, indicated by our results in the A-horizon only of Luvisol and Acrisol, could be a consequence of the intense leaching. In contrast, due to the limited leaching, the soluble components also remained in the A horizon of Leptosol, for this reason SOM seems to be relatively well preserved. The comparison of the results measured and calculated on whole soil samples and their mineral-free hydrolysis-resistant macromolecular fractions (ROM) reveals that the stabilization of SOM is mainly controlled by organo-mineral association in Leptosol and Luvisol. These results suggest the importance of iron-oxides and -hydroxides and clay minerals in the stabilization of SOM for Leptosol and Luvisol, respectively, whereas in Acrisol the stability of SOM is due to the high relative contribution of naturally stable organic compounds.