Heavy metals and biological properties of Subalpine soils on ophiolites in the Italian Western Alps

Soils on ultramafic rocks are usually colonized by plant species and communities adapted to high heavy-metal content and low Ca/Mg ratio. However, the effects of metal speciation on microbial activity and arthropodal communities have scarcely been studied, especially under coniferous forests in boreal or subalpine areas. Six typical subalpine soils, in the ophiolitic area of Mont Avic Natural Park, located in the Western Italian Alps, were studied in order to verify the chemical speciation of Ni, Co, Mn, and Cr and their effects on soil biological properties and microbial activity. Five soils, developed from till composed of mafic and ultramafic materials, showed strong signs of podzolization, while the sixth was polluted by mine spoil. All the samples had high metal content, high acidity, and high metal mobility and bioavailability. These edaphic properties deeply influenced both arthropodal communities and microbial activity, all of which were strictly correlated with parent material and bioavailable Ni, Co, and Mn.