HUMIC SUBSTANCES DISTRIBUTION AND TRANSFORMATION IN FOREST SOILS

The distribution and transformation of humic substances in forest soils is investigated by CPMAS C-13 NMR spectroscopy and chemical analyses. Studies on bulk soil samples and humic acid fractions indicate that different forest humus types result from different rates but similar pathways of litter decomposition. The main features of humification in the investigated forest humus profiles are preferential mineralization of carbohydrates, strong alteration of lignin leading to increasing proportions of carbon-substituted aromatic rings and loss of phenolic groups, increase in carboxyl group contents and accumulation of refractory alkyl components. The action of earthworms promotes transformation of plant residues to humic substances and incorporation of organic matter into stable organo-mineral complexes.