Stabilization Mechanisms of Decomposition Products of Plant Residues by Density Fractions of Loam
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CHEMISTRY
Stabilization Mechanisms of Decomposition Products of Plant Residues by Density Fractions of Loam A. N. Maltsevaa, * and D. L. Pinskiya aInstitute
of Physicochemical and Biological Problems of Soil Science, Russian Academy of Sciences, Pushchino, Moscow oblast, 142290 Russia *e-mail: [email protected] Received March 11, 2020; revised March 31, 2020; accepted April 30, 2020
Abstract—The distribution of decomposition products of corn and clover residues by density fractions of noncalcareous mantle loam was studied under controlled conditions. Two light (2.2 g/cm3 (HF)) fractions were isolated using sodium polytungstate. The LF-1 mainly consisted of incompletely decomposed plant residues; the LF-2, of their decomposition products bound with clay minerals (kaolinite, illite, smectites); and the HF, of the organic matter discretely sorbed on the surface of large grains of quartz and feldspars. It was demonstrated that during stabilization of newly formed organic matter (OM) by different density fractions, they are separated as a result of selective specific adsorption. In this case, the LF-2 is enriched in compounds that do not contain nitrogen, whereas the HF is enriched in nitrogen-containing compounds, including those of microbial nature. As a result, the C/N ratio decreases in the series: LF-1 > LF-2 > HF. The sizes of free and bound to mineral particles organic matter pools were calculated, and a scheme describing the mechanisms of stabilization of decomposition products of plant residues by organo-mineral fractions of different densities was suggested. Keywords: density fractionation, organic matter, organo-mineral associations DOI: 10.1134/S1064229320100129
INTRODUCTION Soil organic matter (OM) is a complex component of the soil heterogeneous in its composition and properties that plays an exceptionally important role in the soil formation and functioning. Physical methods of fractionation make it possible to divide soil OM into more or less homogeneous pools according to their morphological characteristics, density, accessibility to decomposition by microorganisms, and other properties [3, 23, 46, 55]. The study of processes that affect the capacity of soils to decompose incoming organic residues and preserve the newly formed OM in the form of humic substances is important in the regulation of soil OM dynamics. In accordance with the laws of thermodynamics, the processes of transformation of plant residues (PRs) entering the soil lead to the formation of the most stable compounds; the mechanisms of their stabilization in soils include, in particular, the formation of organo-mineral associations [1, 9, 12, 14]. In this case, redistribution of OM between soil mineral components of various densities occurs. The processes leading to an increase in the OM resistance to abiotic and biotic exposure are the processes of OM stabilization in soil, including humification [12]. One of the efficient methods for studying the transformation and stabilization of soil OM is sequential
density fractionation. This meth
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