Mineralization of forest soil carbon: Interactions with metals

Biodegradability of natural dissolved organic compounds was tested in labor atory experiments. Organic matter was extracted from organic and mineral fo rest soil horizons and was isolated from soil solutions collected by suctio n cups. Carbon moieties were fractionated into hydrophobic acids, hydrophil ic acids, and hydrophilic neutral compounds. Degradability of the organic c ompounds ranged from less than 5% (acid compounds) to 15% (neutral compound s). Metals (Ca, Al) and solid Al2O3 were added to assess the effect of comp lexation reactions as well as the adsorption of organic ligands to mineral surfaces on the rate of mineralization. The rate of CO, respiration was use d to measure the degradability. Glucose was used as reference compound and we found that the addition of metals retarded its mineralization. On the co ntrary the degradation of natural soil organic carbon was not affected, or was even enhanced, with Ca or Al added. Adsorption of organic matter to Al2 O3 decreased the respiration rate by one order of magnitude.