Heavy metals and their effects on biological activity in subalpine soils on serpentinite (Western Italian Alps)

Ultramafic soils are colonized by peculiar plant communities and species, adapted to high metal contents, but metal speciation, microbial and arthropodal communities have been scarcely studied, particularly under coniferous forests in boreal or subalpine areas. The high acidity and humidity of these habitats make heavy metals potentially highly mobile and bioavailable. Six subalpine soils, in the ophiolitic area of Mont Avic Natural Park, in the Western Italian Alps, were sampled and analyzed in order to understand the effects of their chemistry on biological (BSQ method, based on microarthropal communities) and microbiological activity (microbial biomass, respiration and the derived stress indexes). Five of these soils show strong signs of podzolization and are developed from till composed of mafic and ultramafic materials in different amounts, while the sixth is developed on polluted mine debris. They all have high metal content, high acidity and high metal bioavailability, shown by the chemical speciation; despite the young age of the soils, up to 50% of metals are localized with pedogenic iron oxides and organic matter. These edaphic characteristics influence deeply the arthropodal communities and microbial activity: on metal rich serpentinite soils, microarthropodal communities are impoverished in biodiversity and in exigent euedaphic forms, while the microbial activity indexes (microbial biomass, respiration, qCO2, TOC/biomass) show the existence of important stress factors. All biological properties are linearly related with available Ni, Co and Mn.