Accumulation of Potentially Toxic Elements in Viola L. (Sect. Melanium Ging.) from the Ultramafic and Non-ultramafic Soils of the Balkan Peninsula

The aim of the present study was to assess the metal concentrations in five species of the genus Viola L. (section Melanium) from 12 ultramafic outcrops and two non-ultramafic (prolluvium and dolomite) soils from Serbia and Bosnia and Herzegovina. The concentrations of P2O5, K2O, Ca, Mg, Fe, Mn, Zn, Cu, Cr, Co, Cd and Pb in soils and plant samples, as well as their shoot-to-root ratio, biological concentration and accumulation factors were determined. Five investigated Viola species growing on 14 different localities displayed considerable differences in concentration of potentially toxic elements in their roots and its accumulation in their shoots. Viola kopaonikensis and V. beckiana from ultramafic soils could be classified as strong Ni accumulators, since moderately high level of Ni was measured in their shoots (up to 266 mg kg−1 and 337 mg kg−1, respectively), while in V. tricolor high amount of the same element was accumulated in the roots (up to 395 mg kg−1). Population of V. beckiana from dolomitic site in Bosnia and Herzegovina accumulated high concentrations of Pb in the shoots (67.1 mg kg−1), as well as of Cd in both roots and shoots (81.1 mg kg−1 and 60.5 mg kg−1). The results also suggest that V. kopaonikensis populations from the ultramafic soils of Serbia emerge as Cr accumulators, which is quite rare trait within the genus Viola. It seems that species from Melanium section apply quite different strategies against toxic elements. Future studies should strive to explain what adaptive mechanisms are hidden behind it.