Diagnostics, Treatment, and the Wisdom of Plants
by Guest Writer Robert Wilson
Some species act as bio-indicators, revealing underlying nutrient imbalances or environmental stress through changes in leaf colour, growth form, or flushing behaviour. Others function as bio-accumulators, with remarkable abilities to draw specific elements, like heavy metals, out of the soil, offering us pathways for in-situ remediation.
A recent experience with our Macadamia jansenii collection brought this into sharp focus. This Critically Endangered species, endemic to Central Queensland, is part of a dedicated conservation display here at the gardens. Propagated asexually from wild-collected mother plants, each individual is genetically important, preserving a unique slice of the species’ very limited diversity.
However, we noticed significant variability in performance across the bed. Some plants flourished, while others declined without a clear reason. After consulting with partner institutions and confirming that genetic variability was to be expected (and in fact known to display in certain clones) in such a wild-provenanced group, the pattern still felt inconsistent.
The breakthrough came from one of our Technical Officers, who unearthed historic soil test data from the site, which revealed high Copper levels. Levels that could absolutely affect plant health, especially in sensitive, wild species like Macadamia jansenii.
We faced a dilemma: move the affected plants and risk splitting the collection/losing specimens to transplant shock, or work toward in-situ remediation. Fortunately, nature had already provided an answer, Helianthus annuus, the humble sunflower, is a known bio-accumulator of Copper.
Plants like sunflowers have a remarkable ability to draw up and store or metabolise excess ions and compounds in the soil. By sowing a crop throughout the bed, we began a live remediation experiment. The results? A noticeable improvement in the health of this Macadamia collection.
There’s another facet to the story: indicator plants, species whose physiological responses reveal shifts in environmental conditions, disease pressure or pest populations. Some signal their own stress, prompting timely intervention. Others, when deliberately integrated into planting schemes, serve as early detection tools, providing advance warning of broader issues before more sensitive or high-value plants are affected. In skilled hands, they move beyond passive symptoms to become active sentinels within the landscape. A classic example can be found in vineyards, where roses are traditionally planted at the ends of grape rows. Highly susceptible to Powdery Mildew, they often show symptoms ahead of the vines, giving growers a timely cue to apply preventative treatments.
Whether acting as bio-accumulators to remediate heavy metals or as indicators of pest, disease, or climate stress, plants are constantly offering feedback to those who know how to read it.