Clonal differences in copper and zinc tolerance of birch in metal-supplemented soils

Metal tolerance of a range of birch clones (Betula pendula and Betula pubes cens) originating from metal-contaminated sites in England, Wales, Belgium and Finland were tested in soils supplemented with several concentrations o f copper (Cu) or zinc (Zn) (500, 2000, 5000 mg kg(-1) dry wt. soil of CuSO4 . 5H(2)O or ZnSO4. 7H(2)O) for 4 months and with sub-toxic metal supplement s (500 mg CuSO4, 2000 mg ZnSO4) for 6 months. When grown at high concentrat ions of metals, severe toxicity symptoms (growth inhibition, chlorosis, nec rosis) and clear evidence for differences in tolerance to this toxicity wer e found in a subset of the clones. When all clones were grown at a much low er, sub-toxic level of metal, again significant differences could be found between some of the clones. Clones derived from the same population varied greatly in their tolerance. However, the overall pattern of metal specifici ty varied in agree ment with the type of soil contamination at the site of origin. The growth of the clones from Harjavalta Cu/nickel smelter area was 19% better in Cu than in Zn-supplemented soil, on average. The growth of c lones from Maatheide Zn smelter are was 19% poorer in Cu- than in Zn-supple mented soil. Sensitive clones accumulated more Cu and Zn to the above-groun d parts. Some birch clones were able to survive at about 20-fold higher tha n typical total background Cu or Zn concentrations, whereas most clones wer e able to grow without serious toxic symptoms at about 10-fold concentratio ns. (C) 2001 Elsevier Science Ltd. All rights reserved.