CHEMICAL ROOT PRUNING OF KANGAROO PAW (ANIGOZANTHOS-FLAVIDUS) BY SELECTED HEAVY-METAL CARBONATES

The six heavy metal carbonates of copper (Cu), cobalt (Go), lead (Pb), nickel (Ni), strontium (Sr) and zinc (Zn) were tested for their abili ty to induce root pruning in container plants. The monocotyledon Austr alian native species Anigozanthos flavidus (kangaroo paw) was used as test material because it normally develops a coarse root system, and i s susceptible to constriction and root circling in containers. Of the heavy metals tested, Pb and Ni caused toxicity to plants and markedly decreased shoot and root growth. Therefore, these two metals were unsu itable as root pruning agents, and at all concentrations tested did no t increase shoot/root ratios; perhaps the best indicator of root pruni ng. Sr and Zn were not toxic at concentrations tested, but were ineffe ctive at root pruning plants in containers (except for Zn at the highe st concentrations tested). Cu and Co were the best heavy metals for in ducing root pruning, while at the same time minimally affecting the gr owth of shoots. Cu increased the shoot/root ratios of plants, but conc entrations of 1.0-2.0 mol eq l(-1) were required. Co, however, was mor e effective than Cu, and significantly increased the ratios of shoots/ roots at lower concentrations of 0.5-1.0 mol eq l(-1). This feature of Co in combination with its general lower toxicity in the environment suggests that Co is the better heavy metal to use as a chemical root p runing agent.