EFFECTS OF URBAN HEAVY-METAL POLLUTION ON ORGANIC-MATTER DECOMPOSITION IN QUERCUS-ILEX L WOODS

Decomposition of oak (Quercus ilex) leaves containing different concen trations of Fe, Zn, Cu, Cr, Ni and Pb was measured in laboratory micro cosms. The leaves were collected from a polluted site inside the city of Naples and from a control site away from the city. Soil was sampled from the upper A horizon (0-5 cm) at both sites and analyzed for resp iration, microbial biomass and abundance of fungal mycelia. The soils from the two sites differed significantly in heavy metals concentratio ns. The accumulated mass loss reached an asymptotic value after four m onths both for the control and polluted litters. However, control and polluted litters significantly differed in accumulated mass loss, that was respectively 40 % and 29 % of the initial weight, after 10 months . Moreover decomposition rates appeared to be strongly influenced by m etal contamination in the early stages, while in later stages, they di d not differ significantly. Litter respiration appeared to be inhibite d by metal contamination and showed pattern and rates consistent with those found for litter decomposition. Fungal mycelia were significantl y less abundant both in litter and soil from the polluted site than fr om the control site. Metabolic activity (both as soil respiration and degree of mineralization) was lower in the polluted soil. Soil respira tion and amount of soil mycelia correlated negatively with soil Pb, Zn and Cr concentration.