The potential for evolution of heavy metal tolerance in plants

Abstract

The effects of increase in copper contamination in potting compost/copper mine waste mixtures on the germination and growth of the following species has been examined: Agrostis tenuis, Poa trivialis, Lolium perenne, Dactylis glomerata, Cynosurus cristatus, Anthoxanthum odoratum, Arrhenatherum elatius, Plantago lanceolata and Trifolium repens. Copper tolerant A. tenuis from Parys Mountain was used as control. Plant dry weight and plant height decreased with increase in proportion of copper contaminated soil in the mixtures, a conspicuous characteristic was the continued survival and growth of some individuals and the death of others at 1-4, 1-8 and mine soil levels. Agrostis tenuis and Dactylis glomerata produced fully copper tolerant survivors at a frequency of 0·08 per cent. By contrast Poa trivialis, Lolium perenne, Arrhenatherum elatius and Cynosurus cristatus produced survivors having indices of tolerance ranging from 7 to 20 per cent, tolerance, values too low to be considered as fully copper tolerant. Plantago lanceolata, Anthoxanthum odoratum, and Trifolium repens, failed to produce any survivors at all. The heritability of copper tolerance in the selected material: Agrostis tenuis, Lolium perenne, Dactylis glomerata, Arrhenatherum elatius, and copper tolerant A. tenuis was determined. Heritability is discussed in terms of breeding value. The results suggested that while the evolution of tolerance would be easy in A. tenuis it would be difficult in species such as Lolium perenne. The data presented are interpreted as evidence that the exclusion of some species from mine areas is because of their inability to evolve metal tolerance.