Nickel hyperaccumulation by the species of Alyssum and Thlaspi (Brassicaceae) from the ultramafic soils of the Balkans

Hyperaccumulation of nickel to concentrations above 1000 mg kg-1 on a dry matter basis has become recognized as an unusual response by some plant species to the elevated nickel concentrations generally found in soils derived from ultramafi c rocks (oft en referred to as serpentine soils). Such soils are widespread in the Balkans. Th ese soils host some widespread species and a smaller number of regional or local endemics. Several serpentine areas in Albania (AL), Bulgaria (BG) and Greece (GR) have been surveyed because of the presence of nickel hyperaccumulating endemics, including some that are common for all three studied countries. Th e objectives of the study were to widen understanding of the distribution of the nickel hyperaccumulators and their uptake behaviour in relation to the characteristics of their native soil environments. Collection and chemical analysis of both plant and soil samples has allowed evaluation of phenotypic effi cacy in hyperaccumulating nickel. In total, eight taxa were studied. In this work the highest Ni concentrations in leaves (1.5- 2.0%) were found in Alyssum murale at Pojska (AL), A. murale at Kazak (BG), A. markgrafi i at Gjegjan (AL) and Th laspi kovatsii at Fotinovo (BG). Th e maximum quotients of plant Ni concentration to soil Ni concentration range from 13.9 for A. markgrafi i to 6-7 for A. murale, T. kovatsii and T. tymphaeum from northern Greece. Eight of the taxa collected in this work show hyperaccumulation of Ni; these include A. murale subsp. pichleri and all of Th laspi species studied from serpentine in Bulgaria. In total, twenty-fi ve Ni hyperaccumulating taxa are now known from the Brassicaceae of Albania, Bulgaria and Greece. Because of its high biomass production, A. murale is likely to be the most suitable species for Ni phytomining in the Balkans.