Adaptation of Biscutella laevigata L, a metal hyperaccumulator, to growth on a zinc-lead waste heap in southern Poland. I: Differences between waste-heap and mountain populations.

Biscutella laevigata is an herbal member of the Brasicacae family and a typical mountain species. It has recently been identified as a hyperaccumulator of lead, cadmium and thallium. Its northern reach runs through Poland, where it is found only in the west Tatra Mountains and on calamine waste heaps in the vicinity of Olkusz (Cracow--Silesian Highland). The peculiar distribution of this species in Poland prompted us to undertake studies to identify the traits that allow this typically mountain species to grow so robustly on industrial waste heaps near zinc and lead smelters in the vicinity of Olkusz. Populations of B. laevigata from waste heaps and the Tatra Mountains were compared both under field (natural) conditions and during cultivation of successive generations under laboratory conditions. It was found that the mountain and waste-heap populations of B. laevigata differed significantly. The plants in the mountain population had thicker leaves covered with cutin and a small number of hairs, whereas the plants from the waste-heap population had thin leaves covered with numerous hairs. The difference in leaf thickness between the two populations (0.15 mm on average) was due to increased dimensions of palisade mesophyl cells whereas the number of cells in their leaves remained similar. These traits were hereditary. This indicates that two geographically distant populations of plants followed two different evolutionary paths to adapt to xerothermic conditions. Moreover, it was shown that the waste-heap population of B. laevigata is more tolerant to heavy metals (lead, zinc and cadmium). In the presence of both zinc and lead, growth of the waste-heap plants was stimulated, while under the same conditions, growth of the mountain population was inhibited lower than 50%. This adaptation facilitates the growth of this population on industrial waste heaps. Our studies show that B. laevigata is a valuable species very well-suited for use in the recultivation of areas containing high levels of heavy metals--the waste-heap population of this species is particularly valuable.