A systematic assessment of the metallome of selected plant families in the Queensland (Australia) flora by using X-ray fluorescence spectroscopy

Context: Fewer than 10 plant species from Australia were known to hyperaccumulate metal(loid)s, despite metal-rich soils being widespread in Australia. By measuring herbarium specimens with non-destructive portable X-ray fluorescence spectroscopy (XRF) instrumentation their metal(loid)s concentrations can be determined, providing information that could be used to probe the evolution, biogeography, ecology, and physiology of plant species.

Aims: This study aimed to systematically measure herbarium specimens to obtain information on the prevailing concentrations of metal(loid)s in nearly 7000 plant specimens across seven plant families, and to link this data to an assessment of their spatial distribution.

Methods: The raw XRF spectrum of each herbarium specimen was processed using a new data-analysis pipeline recently validated for XRF data of herbarium specimens, to determine the concentrations of the first-row metal transition elements, and other detected elements. The collection localities of each of the herbarium specimens were plotted against rainfall and soil types to assess possible distributional patterns.

Key results: The results showed several newly discovered hyperaccumulator plant species, including 15 for manganese, two for nickel, three for cobalt, three for zinc, two for rare earth elements and one for selenium.

Conclusions and implications: Australia has more hyperaccumulator plant species than previously known and the XRF analysis of herbarium specimens is a powerful tool for their discovery. This research presents a new value proposition for the continued funding of herbarium collections in Australia and could initiate a range of research opportunities to use these data for future studies of plant evolution and adaptation.