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A) Image captured of the Dugald River gossan by Nicolls et al. (1965), North to South facing. B) Image captured using a drone of the same site in 2018, South to North facing. In both images the change in species composition with a treeless assemblage on metalliferous soils is clearly visible
Source publication
Background and aimsMetallophytes are plants that can tolerate extreme metal concentrations in the soil in which they grow. The Dugald River zinc (Zn)-lead (Pb) gossan in Queensland (Australia) is one of the largest metal deposits in the world with a surface gossan formed after weathering over millions of years. It hosts a range of metallophytes whi...
Citations
... The second example pertains to the facultative Zn hyperaccumulator Crotalaria novo-hollandiae (Fabaceae), shown in Fig. 3. Hyperaccumulation of Zn in this taxon is restricted to a few occurrences on Zn-Pb gossans that are naturally enriched in Zn where it can attain up to 16,200 μg g −1 Zn in its leaves (Tang et al. 2022). This herbarium specimen was originally collected in 1976 from the Dugald River Zn-Pb mineralized outcrop near Cloncurry in central Queensland, Australia. ...
Background and aims
An innovative approach “Herbarium Ionomics” used a handheld X-ray fluorescence (XRF) device to non-destructively extract quantitative elemental data (i.e. , the metallome) from herbarium specimens. This has led to the discovery of numerous hyperaccumulator plants. Once a new hyperaccumulator is identified through XRF screening, the next step is to verify whether this is in fact ‘real’ as there are numerous causes for anomalous measurements caused by artefacts.
Methods
Here we report on the use of a scanning μ-XRF for herbarium specimens to answer the question whether the abnormal concentrations of a particular element truly represent hyperaccumulation as well as reveal broad patterns of elemental distribution to provide the first hints at the ecophysiology of the hyperaccumulated element.
Results and conclusions
The use of μ-XRF analysis of herbarium specimens can form the starting point for further studies using specimens properly prepared for micro-analytical investigations.
... Zinc is required by plants to produce enzymes for energy production, electron transport, chlorophyll biosynthesis, the maintenance of membrane integrity, and antioxidant activity (Dalcorso et al. 2014). Only 20 Zn-hyperaccumulator plant species have been reported globally (Reeves et al. 2018a), including two in Australia, namely, Crotalaria novae-hollandiae (16 200 μg Zn g −1 ; Tang et al. 2022) and G. fragrantissima (3900 μg Zn g −1 ); the latter is able to simultaneously co-accumulate up to 13 200 μg Mn g −1 , 480 μg Co g −1 and 834 μg Ni g −1 ; Fernando et al. 2013;Abubakari et al. 2021b). This study found that the Salicaceae had two Zn-hyperaccumulating taxa. ...
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.
... There are only two Zn hyperaccumulator plant species known from Australia, namely, Gomphrena canescens R.Br. (Amaranthaceae) from the Bulman Prospect in the Northern Territory (Farago et al. 1977) and Crotalaria novaehollandiae DC. (Fabaceae) from the Dugald River outcrop in Queensland (Cole et al. 1968;Tang et al. 2022). These species are both widespread on non-metalliferous soils and, hence, facultative hyperaccumulators. ...
... It is widespread in the semi-arid central and northern part of Australia in the states of Queensland and the Northern Territory (Atlas of Living Australia (ALA) 2022). C. novaehollandiae is a facultative hyperaccumulator that hyperaccumulates Zn only when growing on highly Zn-enriched soils, such as the Dugald River Zn-Pb gossan near Cloncurry and can accumulate up to 16 200 μg Zn g −1 in its leaves (Tang et al. 2022). C. novae-hollandiae has desirable traits for Zn phytoextraction on the basis of its high biomass production, nitrogen-fixing ability and high shoot Zn concentrations when occurring on Zn-enriched soils. ...
... Two species were used in the experiments, namely, C. novaehollandiae (metalliferous accession) and C. cunninghamii (non-metalliferous accession). Seeds of C. novae-hollandiae were collected from the Dugald River Lode Zn outcrop in Queensland, Australia (Tang et al. 2022), whereas seeds of C. cunninghamii were obtained from the Nindethana Seed Company (King River, WA, Australia). Seeds were germinated in perlite-vermiculite mix (ratio 1:1). ...
Context Root foraging by hyperaccumulator plants in response to patchily distributed metals has been observed in several obligate hyperaccumulators, but it is not known whether facultative hyperaccumulators respond similarly. Aims This study investigated the root-growth behaviour in the leguminous zinc (Zn) hyperaccumulator Crotalaria novae-hollandiae compared with the non-accumulating Crotalaria cunninghamii in response to localised soil Zn enrichment in the soil to observe foraging versus avoidance responses. Methods We conducted rhizotron experiments in which we exposed the Crotalaria species pair to juxtaposed treatments, which were either homogenous (each half of the treatments containing same Zn concentrations) or heterogenous (different Zn concentrations in each half of the treatments). The Zn concentrations were 0 μg Zn g−1 (control), 2000 μg Zn g−1 and 5000 μg Zn g−1 in the form of zinc carbonate). Key results We found that none of the treatments had significantly different rooting density and root biomass, regardless of the Crotalaria species. This finding contrasts with increased root proliferation in Zn-rich patches found for other obligate hyperaccumulator species. Conclusions and implications The no-preference root response towards Zn in Crotalaria may partly explain the facultative hyperaccumulation mechanism displayed by these species. This root response towards Zn may ultimately affect Zn phytoextraction efficacy when utilising Crotalaria species in a heterogenous Zn soil substrate. These findings highlight the need for rhizosphere investigations prior to field phytoextraction applications.
... HM ions are actively removed from plants by excluders, which make up the majority of plant species capable of living in soils high in dangerous trace elements (Sun et al. 2022;Tang et al. 2021Tang et al. , 2022. An HM ion is only toxic to the roots of an excluder plant, while the aerial parts are mainly unaffected by the toxin. ...
Contamination of agricultural soils with heavy metals present lethal consequences in terms of diverse ecological and environmental problems that entail entry of metal in food chain, soil deterioration, plant growth suppression, yield reduction and alteration in microbial community. Metal polluted soils have become a major concern for scientists around the globe. In more recent times, armed with new knowledge and understanding, removal of heavy metals using different applications has emerged as a solution for waste treatment and contaminant remediation in water and soil. However, the description of metal toxicity to the plants and its removal and degradation from the soil is limited. There are a number of reports in the literature where PGP bacterial inoculation and various chelating agents improves metal accumulation and it's detoxification in different plant parts without influencing plant growth. Therefore, there is a need to select some useful chemicals which possess the potential to improve plant growth as well as expedite the phytoremediation of metals. In this review, we have discussed the mechanisms possessed by different chelating agents to promote plant growth and phytoremediation of metals. We anticipate that this analysis of interconnected systems will lead to the discovery of new research fields.
... A subset of metallophytes are hyperaccumulators which can accumulate metal or metalloid concentrations at orders of magnitude greater levels than non-accumulators (van der Ent et al. 2013). The hyperaccumulation threshold depends on the metal/metalloid, in the case of Zn the hyperaccumulation threshold is 3000 μg Zn g −1 whilst for Cd it is 100 μg Cd g −1 (Krämer 2010;van der Ent et al. 2013). ...
... A subset of metallophytes are hyperaccumulators which can accumulate metal or metalloid concentrations at orders of magnitude greater levels than non-accumulators (van der Ent et al. 2013). The hyperaccumulation threshold depends on the metal/metalloid, in the case of Zn the hyperaccumulation threshold is 3000 μg Zn g −1 whilst for Cd it is 100 μg Cd g −1 (Krämer 2010;van der Ent et al. 2013). Hyperaccumulation is a rare occurrence which occurs in approximately 0.2% of angiosperms (Cappa and Pilon-Smits 2014). ...
... In Australia, C. novaehollandiae was originally discovered to be a Zn hyperaccumulator accumulating up to 8975 μg Zn g −1 from the Dugald River Zn-Pb-Cd gossan in central Queensland (Farago et al. 1977). Recent investigations on the Dugald River site have revealed that C. novae-hollandiae is a polymetallic Zn-Cu-Cd hyperaccumulator that can accumulate up to 16,200 μg Zn g −1 , 545 μg Cu g −1 and 170 μg Cd g −1 (Tang et al. 2021). As a species, C. novaehollandiae occurs across the Northern areas of Australia, and an assessment of over 200 C. novae-hollandiae specimens at the Queensland Herbarium (BRI) using portable X-ray fluorescence (pXRF) for foliar metal concentrations was conducted to identify other instances of metal hyperaccumulation. ...
Purpose Hyperaccumulators are plants with the ability to tolerate and accumulate high concentrations of potentially phytotoxic metals. The Australian legume Crotalaria novae-hollandiae accumulates remarkably high concentrations of zinc (Zn), cadmium (Cd) and copper (Cu) in its shoots when growing on metalliferous (Zn-Cd ‘calamine’) soils. This study aimed to investigate zinc-cadmium tolerance in C. novae-hollandiae and to compare it with the closely related, but non-metalliferous, C. cunninghamii.
Methods Crotalaria cunninghamii and C. novaehollandiae were exposed to Zn (3–1000 μM) and Cd (0–60 μM) treatments in hydroponics culture. At the end of the experiment, harvested plants were segmented into roots, old and young stems, old and young leaves for elemental analysis with Inductively coupled plasma atomic emission spectroscopy (ICP-AES). Laboratory-based micro-X-ray fluorescence (μXRF) analysis was used to elucidate elemental distribution in a shoot and in leaflets.
Results Crotalaria cunninghamii accumulated up to 1210 μg Zn g−1 and 47.6 μg Cd g−1 in its leaves, with a 75% reduction in biomass in the Zn treatment. Crotalaria novae-hollandiae accumulated up to 16,600 μg Zn g−1 and 1250 μg Cd g−1, with a 70% increase in biomass when exposed to Zn. The species both exhibited chlorosis and stunted growth in the Cd treatments, while only C. cunninghamii exhibited toxicity symptoms in Zn treatment.
Conclusions Crotalaria novae-hollandiae has limited tolerance for Cd and based on the accumulation and distribution of foliar Zn and Cd it is suspected that C. novae-hollandiae has different uptake and tolerance mechanisms when compared to other widely studied Zn-Cd hyperaccumulators (such as Noccaea caerulescens and Arabidopsis halleri).
Purpose
The increasing volumes of mine tailings that are being generated globally because of the rise in metal demand, whilst ore-grades continue to decline, call for novel sustainable management options. Phytoextraction using hyperaccumulator plant species may be one of such strategies to deal with these large volumes of contaminated materials. However, base metals (such as zinc, lead, copper) mine tailings are inherently polymetallic that necessitate targeting multiple metal(loid)s simultaneously for effective phytoextraction. The aim of this study was to conduct a proof-of-concept experiment for polymetallic phytoextraction of base metal mine tailings.
Methods
Selected hyperaccumulator plants ( Noccaea caerulescens targeting zinc, Biscutella laevigata and Silene latifolia targeting thallium, Phytolacca octandra targeting manganese, Pityrogramma calomelanos targeting arsenic) were grown in monocultures and mixed cultures for 12 weeks on tailings from the zinc-lead-copper Dugald River and Mt Isa Mines, Queensland, Australia.
Results
Noccaea caerulescens accumulated zinc and manganese (up to ~ 1 wt% and ~ 1.4 wt%, respectively) with zinc-manganese co-localization at the leaf apex and margins. The monocultured B. laevigata exhibited severe toxicity symptoms, which were alleviated when co-cultured with N. caerulescens . Trichomes were important storage sites for zinc and manganese in B. laevigata . Silene latifolia accumulated higher thallium than B. laevigata, whilst P . octandra promoted thallium accumulation in S. latifolia.
Conclusions
This proof-of-concept test of polymetallic phytoextraction provides a real-life demonstration of this innovative technology which could be adapted to further experiments at base metal mines around the world.
