Interaction of the Water-Soluble Organic Substances of Coniferous Litter with Minerals and Horizons of Podzolic Soil and Podzols

摘要

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.