Mechanism of chemical root pruning in kangaroo paw (Anigozanthos flavidus) by selected heavy metal carbonates

Abstract

SummaryHeavy metal carbonates/hydroxides of copper (Cu), cobalt (Co) and zinc (Zn) were tested for their ability to induce root pruning in container-grown Anigozanthos flavidus (kangaroo paw). Co (1 and 2 mol eq 1–1) and Cu (2 and 5 mol eq 1–1) were the best heavy metals for root pruning, while Zn was only effective at 5 mol eq 1–1. Successful root pruning was accompanied by 80% of root tips at or near the container wall being morphologically dead, whilst within the media a maximum of 25% of roots were dead. Increase in shoot/root ratios and a decrease in the root branching coefficient were strongly correlated with root pruning ability. The mitotic index was significantly lower in heavy metal pruned root tips, and this was accompanied by an uptake of the respective heavy metal. Heavy metals also significantly reduced the amounts of potassium present in root tips at or near the container wall, demonstrating some nutritional imbalances, and that potassium levels may be a sensitive indicator of heavy metal toxicity. During the eight-week experimental period, heavy metals were slowly released into the media water, the amounts were low and below water quality guidelines. The moderate effects of Co in affecting mitosis and potassium nutrition during root pruning, and its general lower toxicity in the environment suggest that Co may be utilized as a suitable and effective chemical root pruning agent.