Occurrence of heavy metal tolerance and co-tolerance in Deschampsia cespitosa (L.) Beauv. from European and Canadian populations.

By sampling soils and plants from a variety of metal-contaminated sites in Canada and Europe, heavy metal tolerance and co-tolerance have been investigated in the grass Deschampsia cespitosa L. (Beauv.). Soils were analyzed for water extractable Ca, as well as for their heavy metal content (Cu, Ni, Zn, Pb, Cd, Co), electrical conductivity, pH and organic matter. Canadian plant material was collected from non-contaminated areas, as well as sites contaminated by copper and nickel (Sudbury) and nickel and cobalt (Cobalt). European plants were sampled from reference sites and from zinc and lead contaminated locations (Bleikuhle, Pochsand/Germany). Using cloned material the 'in parallel' root elongation technique was employed to determine tolerance indices to individual metals (Cu, Ni, Zn, Pb). Among the Canadian plants, patterns of tolerances matched patterns of soil contamination. Thus, at the Cobalt sites, Cu was not present in elevated amounts, and the plants did not exhibit Cu tolerance. Also, evidence suggests that the close correlation of Cu and Ni tolerance among the Sudbury plants was not the result of Cu-Ni co-tolerance but occurred because ions of both metals were present in elevated amounts at these sites. In addition to the tolerances expected on soil chemistry, plants taken from metal contaminated sites exhibited enhanced tolerance also to metal ions not elevated in the soils of their origin. This is interpreted as general, non-specific, low level co-tolerance. Thus, most Cobalt and Sudbury plants exhibited incidental tolerance at a higher level to Zn and Pb. Correlation analysis revealed very close relations both between Zn and Pb, and especially between Ni and Zn, supporting findings from previous studies. It was concluded that among the Canadian populations tested in this study, Ni tolerance conferred Zn tolerance. Among the European plants examined, the expected tolerances to Zn and Pb were found. However, whereas some control plants from non-contaminated sites exhibited relatively high tolerances to these metal ions, the tolerance of plants from mines was lower than expected. The Zn and Pb tolerant mine populations had no tolerance to Cu and only very low tolerance to Ni, suggesting that the enhanced Zn tolerance associated with Ni tolerance in the Canadian plants is not necessarily reversible, i.e. Zn tolerance does not necessarily confer Ni tolerance.