SOIL MICROBIAL COMMUNITY AS AFFECTED BY HEAVY METAL POLLUTION IN A MEDITERRANEAN AREA OF SOUTHERN ITALY

The relationship between pollution by heavy metals and soil microbial community was investigated in an area of Southern Italy mainly used for agriculture but also affected by industrial and extractive activities as well as vehicular traffic. Soil samples were seasonally collected in permanent crop fields (i.e. citrus and peach orchards, olive groves and vineyard) and uncultivated areas (coniferous and mixed forests, shrublands, grazing lands). Soil samples were analysed for chemical (water content, pH, cation exchange capacity, organic C, Cr, Cu, Zn, Pb and Cd contents) and biological properties (microbial biomass, fungal mycelium, soil respiration, potentially mineralizable nitrogen, metabolic quotient and carbon mineralization rate). The results showed that heavy metal contents in the studied soils generally fell within the limit values after Italian law, with the exception of soil from vineyard that generally exceeded the limit value for Cu, probably because of the large use of copper-containing fungicides. The soil Pb content was always above the values reported for typical unpolluted soils and sometimes the same was also observed for Cd and Cu. The data suggest that Cr, Cu and Zn mainly derive from agricultural activity, whereas Pb and Cd were mainly introduced by cement industry associated with extractive activity. The soil microbial community was negatively affected by increased Cr, Cu and Zn contents, but not by Pb and Cd. Among the heavy metals considered, Cr and Zn had the highest negative effect on soil microbial community.