Erratic hyperaccumulation of nickel, with particular reference to the Queensland serpentine endemic Pimelea leptospermoides

Many hyperaccumulators of nickel (Ni) are endemic to ultramafic soils and always show very high Ni concentrations. Others occur on a variety of substrates but accumulate high Ni from the ultramafic ones. Pimelea leptospermoides is unusual in being an ultramafic endemic that shows a very wide range of Ni concentrations. The present work sought to establish the factors governing the wide variation in Ni uptake by P. leptospermoides, and aimed to investigate the likelihood of this variation originating from plant differences or soil differences. Multiple paired plant and soil samples were taken over the geographic range of occurrence of P. leptospermoides. Plant and soil metal concentrations and soil pH were measured. No evidence was found to suggest that the plants belong to populations with inherent ‘high-Ni’ and ‘low-Ni’ accumulation capability. Instead, the soil pH (covering a range from 6.0 to 8.3) and the total soil Ni concentrations of the ultramafic soils were found to be the major influences on the level of Ni accumulation. The wide variation observed in Ni accumulation by P. leptospermoides from ultramafic soils can be explained by a combination of variations in soil pH and total soil Ni concentrations.