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

Soils on ultramafic parent materials are rich in heavy metals (particularly Ni, Cr, Co, Mn), and thus can show toxicity symptoms on non-adapted organisms, due to heavy metal content. High soil acidity increases metal mobility and bioavailability; the podzolization process increases these effects. Only few studies deal with metal bioavailability and toxicity on arthropodal and microbioal communities in subalpine and boreal ophiolitic pedo-environment. Six pedons were thus analyzed in the ophiolitic area of Mont Avic Natural Park (Valle d’Aosta, Italy), under subalpine forest, in order to assess metal bioavailability and toxicity on arthropodal and microbial communities, using stress indicators and biodiversity indexes. - Total heavy metal content (Co, Mn, Ni, Cr) is always very high, particularly in soils on ultramafic parent materials and even more in the soil polluted by mine debris. Available metals often reach the toxicity value, particularly for Co, Ni, Mn. - Metal mobility and availability are increased by the strong acidity and the podzolization process. - Cr (VI) reaches toxicity values in some Bs horizons. - The composition of microarthropodal communities is influenced by metal content: on serpentinite, and in the polluted soil, exigent taxonomic groups are missing (low BSQ values). - Heavy metal stress is also evidenced by microbial biomass, activity and stress symptoms (metabolic quotient, TOC/biomass). Metal toxicity is verified in polluted and in natural serpentinite soil