Metal complexing properties of forest floor leachates might promote incipient podzolization in a Cambisol under deciduous forest

The characteristics of both the mineral substrate and the humus layer are of key importance in podzol formation. However, the properties of the forest floor leachates are seldom considered. We measured the complexation capacity by Cu2+ titration (CuCC), the optical density (E4/E6), as well as the concentrations of dissolved organic carbon (DOC) and of major and trace ions in the liquid extracts of forest floors of two Cambisols and two Luvisols on loess under deciduous forest. The vegetation consists of a mixture of beech, oak and maple. The humus type is a fibrimor in one Cambisol and a moder in the three other soils. Both in the solid phase and in the liquid extracts of the forest floors, the Si/(Al+Fe) and C/(Al+Fe) atomic ratios are much larger in the fibrimor than in the moders. In the liquid extracts, the complexation capacity (CuCC) and the density of metal binding sites (CuCC/DOC) are larger in the fibrimor than in the moders. These large CuCC and CuCC/DOC in the fibrimor leachate are linked with relatively small stability constant of the humus–Cu complex and relatively large E4/E6 ratio, i.e. with reactive organic ligands with low molecular weight and weak aromatic character. These characteristics are associated with current incipient podzolization in the Cambisol with a fibrimor, and might be considered as an indicator of a substantial podzolizing potential of the forest floor.