GEL-PERMEATION CHROMATOGRAPHY AND CU-BINDING OF WATER-SOLUBLE ORGANIC-SUBSTANCES FROM LITTER AND HUMUS LAYERS OF FOREST SOILS

Water-soluble organic substances extracted from either litter (Ol) or humus horizon (Ah) of soils under birch, beech, fir, oak, pine and poplar were fractioned by gel permeation on Sephadex G25. Cu-binding by extracts at pH 6.0 was determined with the binding sites of the gel matrix loaded with Cu. Comparisons were made among the two horizons and the forest stands. Soluble organic substances of litter and humus extracts were fractionated into three and two groups, respectively. Compounds apparently of low molecular weight dominated most litter extracts, whereas in aqueous solutions of the humus horizons compounds apparently of high molecular weight were more important. Cu-binding capacities were higher in extracts of the humus horizon (2.6-6.0-mu-mol Cu per mg DOC) than in litter extracts (0.7-0.9-mu-mol Cu per mg DOC). Differences in elution profiles and Cu-binding of sample solutions were found particularly between the two horizons within the soil profiles and less between the different forest stands.