Humic Compounds in Soils of Taiga Ecosystems in the Republic of Komi
We documented structure and functionality of specific (humic) substances for podzols and peat-podzols in middle taiga in the Republic of Komi. We identified and quantified the functional groups and molecular fragments with nuclear magnetic resonance spectroscopy (13C-NMR), as follows: carboxylic (-COOH), carbonylic (-C=O); CH3-, CH2-, CH- aliphatic, -C-OR of spirits, ethers and carbohydrates; phenolic (Ar-OH), quinone-type (Ar=O), aromatic (Ar-). Molecular structure of humic substances showed that humic acids contain large amount (up to 44.6%) of aromatic fragments, which support their stability. Aliphatic chains and carbohydrate- or aminoacid-like structures prevail in carbon carcass of fulvic acids (up to 77.8%). Humic compounds in peaty podzolic gleyic soil are enriched with aliphatic structures compared to podzols. Cultivation of soils changes the composition of functional groups among humic compounds by raising the share of aromatic molecular fragments and decreasing of carboxylic functional groups. Concentration of free radicals in the structure of humic substances was studied with electronic paramagnetic resonance method. Humic acids contained 1.5…5 times more free radicals than fulvic acids of the soils under study. Agriculture diminishes paramagnetic activity of humic compounds by more than 20%, which supports accumulation of biothermodynamically stable and more humified substances in arable horizon.