Interaction of the Water-Soluble Organic Substances of Coniferous Litter with Minerals and Horizons of Podzolic Soil and
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CHEMISTRY
Interaction of the Water-Soluble Organic Substances of Coniferous Litter with Minerals and Horizons of Podzolic Soil and Podzols E. I. Karavanovaa, *, D. F. Zolovkinaa, **, and A. A. Stepanova aLomonosov
Moscow State University, Moscow, 119991 Russia *е-mail: [email protected] **е-mail: [email protected]
Received December 24, 2019; revised February 20, 2020; accepted February 26, 2020
Abstract—The water-soluble components originated in coniferous litters desorb into solution the native organic substances from the solid phase of the eluvial horizons of podzols and podzolic soil. In podzols, the water-soluble organic matter (WSOM) extracted from litter and then passing through the E horizons are sorbed by the BFH horizons if their concentration in solution exceeds 35 mg C/L. The sorption ranges from tens to hundreds of milligrams of carbon per kilogram of the BFH horizon. The WSOM can be sorbed by the BT horizons of podzolic soil when the concentration of organic substances in the liquid phase is higher than in podzols. The model experiments with minerals show that kaolinite and illite interact with the soluble substances percolating from the litter and selectively extract more hydrophilic and less aromatic components with relatively low molecular weights. On the contrary, goethite interacts with the WSOM prevalently sorbing hydrophobic components, substances of phenolic nature, components enriched in aromatic carbon, and substances with molecular weights less than 7 kDa. The spectral characteristics of WSOM change after the sorption interaction with minerals: the fluorescence associated with the humus substances with the longest conjugation chain decreases or disappears, while new fluorophores containing fragments of phenolic and/or protein structures emerge. The presence of kaolinite and illite in the eluvial horizons and their interaction with WSOM most likely contribute to the transformation of WSOM composition and appearance of the properties maximally favorable for their sorption on iron hydroxides in the lower horizons. Keywords: hydrophilic and hydrophobic compounds, sorption, organomineral interactions, goethite, kaolinite, illite DOI: 10.1134/S1064229320090070
INTRODUCTION The research into the role of soils in the global carbon cycle has been relevant for many years because of both the putative contribution of soil organic matter to the atmospheric carbon dioxide emission and the opposite part of the process, namely, a decrease in the humus stock and the loss in soil fertility. Soils can act as the accumulators of carbon as well as its source for the hydrosphere and atmosphere; moreover, the balance between these two functions depends on climate, soil properties (particle size distribution, pH, etc.), type of land use, and other factors. Preservation of organic carbon in the mineral horizons of forest soils in temperate climate is one of the ways to resolve the problem of stabilization of soil humus. The current conceptual models [17] propose several ways how biochemically stable org
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