Responses of Four Australian Tree Species to Toxic Concentrations of Copper in Solution Culture

ABSTRACT

In Australia, metal-contaminated sites, including those with elevated levels of copper (Cu), are frequently revegetated with endemic plants. Little is known about the responses of Australian plants to excess Cu. Acacia holosericea, Eucalyptus crebra, Eucalyptus camaldulensis, and Melaleuca leucadendra were grown in solution culture with six Cu treatments (0.1 to 40 μ M). While A. holosericea was the most tolerant to excess Cu, all of the species tested were sensitive to excess Cu when compared with exotic tree and agricultural species. The critical external concentrations for toxicity were < 0.7 μM for all species tested. There was little differentiation between shoot-tissue Cu concentrations in normal versus treated plants, thus, the derivation of critical shoot concentrations was possible only for the most tolerant species, A. holosericea. Critical root Cu concentrations were approximately 210 μg g⁻¹ (A. holosericea), 150 μ g g⁻¹ (E. crebra), 25 μ g g⁻¹ (E. camaldulensis), and 165 μ g g⁻¹ (M. leucadendra). These results provide the first comprehensive combination of growth responses, critical concentrations, and toxicity symptoms for three important Australian genera for use in the management of Cu-contaminated sites.

Keywords:

• Acacia holosericea
• copper toxicity
• critical concentration
• Eucalyptus camaldulensis
• Eucalyptus crebra
• Melaleuca leucadendra

ACKNOWLEDGMENTS

Thank you to David Edwards, Pax Blamey, and Jane O'Sullivan for advice and help with the experimental design, and to Nick Graham, Graham Kerven, David Appleton, and Steve Appleton for analytical assistance. The assistance of Rufus Chaney in reading and commenting on an earlier version of the manuscript is much appreciated.