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X-ray fluorescence is a fast, cost-effective, and eco-friendly method for elemental analyses. Portable X-ray fluorescence spectrometers (pXRF) have proven instrumental in detecting metals across diverse matrices, including plants. However, sample preparation and measurement procedures need to be standardized for each instrument. This study examined sample preparation methods and predictive capabilities for nickel (Ni) concentrations in various plants using pXRF, employing empirical calibration based on inductively coupled plasma optical emission spectroscopy (ICP-OES) Ni data. The evaluation involved 300 plant samples of 14 species with variable of Ni accumulation. Various dwell times (30, 60, 90, 120, 300 s) and sample masses (0.5, 1.0, 1.5, 2.0 g) were tested. Calibration models were developed through empirical and correction factor approaches. The results showed that the use of 1.0 g of sample (0.14 g cm−2) and a dwell time of 60 s for the study conditions were appropriate for detection by pXRF. Ni concentrations determined by ICP-OES were highly correlated (R2 = 0.94) with those measured by the pXRF instrument. Therefore, pXRF can provide reliable detection of Ni in plant samples, avoiding the digestion of samples and reducing the decision-making time in environmental management. [ABSTRACT FROM AUTHOR]

Background and aims: The abandoned Allchar Mine in the Republic of North Macedonia is a globally unique deposit with historical tailings from processing ore containing extremely toxic metal(loid)s concentrations, with up to 76.1 g kg−1 and 6.5 g kg−1 of As and Tl, respectively. Methods: Five pseudo-metallophyte species which naturally colonise the Allchar tailings were sampled: Alyssum kavadarcensis, Knautia caroli-rechingeri, Minuartia verna, Plantago lanceolata, and Silene vulgaris. Rhizosphere soils, roots and leaves were collected for each individual. The samples were subjected to elemental analysis to determine macro and micro-elemental concentrations. Results: The results show that the studied species exhibit different strategies in relation to the dominant elements in the substrate, with exclusion being the most common among them. Hyperaccumulation of Tl was found in M. verna and P. lanceolata (with 1770 and 1030 mg kg−1 as the mean concentration, respectively), whereas As was found in concentrations above the threshold for hyperaccumulation and leaf-to-root ratio > 1 in M. verna, S. vulgaris, and A. kavadarcensis (up to 1340, 2870 and 1330 mg kg−1, respectively). Conclusions: The studied plants have great potential for use in phytoremediation of mine wastes contaminated with As and Tl. [ABSTRACT FROM AUTHOR]

Background: The highly diversified flora in the Brazilian Cerrado (savanna) region is attributed to several factors, including the high concentrations of metals in soils, especially Al in widespread Ferralsols and Ni in soils derived from ultramafic rocks. We hypothesized that adaptation mechanisms are responsible for the genetic diversity of the following native plant species that are found in the abovementioned environments: Euploca salicoides (ES), Justicia lanstyakii (JL), and Oxalis hirsutissima (OH). Objectives: We aimed to analyse the main edaphic factors that differentiate ultramafic from Al-rich environments, and act as drivers of the evolution of physiological mechanisms underlying plant adaptation to these harsh environments. Methods: We analysed the chemical attributes of four ultramafic soils (SAP5, SAP7, SAP9, LAT) and an Al-rich soil (CAM), and the elemental composition and DNA of the three species growing in both environments. ES was used as a model species to analyse changes in the levels of non-structural carbohydrates (NSCs) and Ni localization in plant leaves. Results: The soil types presented significant differences in available nutrients and heavy metals. The DNA sampled from the same species from ultramafic sites was genetically closer, but different from that in the Al-rich sites. In ultramafic soils, ES accessions had high levels of NSCs and Ni accumulated in trichomes. Conclusions: The genetic diversity observed in plants growing in both areas is probably related to plant adaptation to the contrasting edaphic conditions of these environments. The raffinose production and Ni allocation to trichomes are mechanisms employed by ES to overcome metal toxification in ultramafic environments. [ABSTRACT FROM AUTHOR]

Purpose: The Cunoniaceae are a major component of the New Caledonian flora with 91 endemic species that are highly unusual in that multiple metals are hyperaccumulated in different species. This makes it an ideal model system for studying the nature of the hyperaccumulation phenomenon. Methods: X-ray fluorescence spectroscopy (XRF) scanning of all herbarium collections of the Cunoniaceae was undertaken at the Herbarium of New Caledonia to reveal incidences of nickel (Ni) and manganese (Mn) accumulation. Following on, the Mn hyperaccumulating P. reticulata and the Ni hyperaccumulating P. xaragurensis were selected for detailed follow-up investigations using synchrotron-based X-ray fluorescence microscopy (XFM). Results: The systematic XRF screening of herbarium specimens showed that numerous species have high foliar Mn and Ni with species either accumulating Ni or Mn, but not both elements simultaneously. Soil 'extractable' Mn and Ni concentrations associated with Pancheria reticulata and P. xaragurensis greatly varies between the species. The XFM data shows that P. reticulata has a distinctive distribution pattern with Mn concentrated in large hypodermal cells. This contrasts with P. xaragurensis where Ni was mainly localized in and around the epidermis, and hypodermal cells were not observed. Conclusions: Manganese and Ni accumulation are differently localized in Pancheria species growing on ultramafic soils, which is not explained by contrasting soils conditions, but represents different ecophysiological adaptations. [ABSTRACT FROM AUTHOR]

The manganese (Mn) hyperaccumulator Gossia bidwillii is a tree species native to subtropical eastern Australia where it occurs on Mn-rich soils. Here, we conducted the first Mn accumulation and tissue-level distribution study on wild and experimentally grown G. bidwillii. Gossia bidwillii plants were subjected to different levels of Mn (250 µg g−1, 500 µg g−1, 1000 µg g−1) soil dosing treatments, whereas the wild G. bidwillii was sampled from growing on highly Mn-enriched natural soils. We used laboratory-based micro-X-ray Fluorescence (µXRF) elemental mapping to elucidate in situ distribution patterns of Mn and other elements in hydrated wild and Mn-dosed G. bidwillii leaves. The data from wild G. bidwillii revealed that it can be strongly Mn-hyperaccumulating with foliar Mn concentrations of 39 000 µg g−1 and 24 000 µg g−1 in old and young leaves, respectively. In the Mn dosing trial, G. bidwillii accumulated 24 400 µg g−1 in old leaves and 17 100 µg g−1 in young leaves in the highest treatment level. The laboratory based µXRF data revealed that Mn is uniformly enriched throughout the laminae and petioles of both young and old leaves in wild G. bidwillii; while in Mn-dosed G. bidwillii, the foliar Mn distribution was primarily concentrated at the leaf-tip and lamina. The approach employed by combining data from the field and controlled experiments was especially meaningful for investigating Mn accumulation in this species and gaining added insight into the phenomenon of Mn hyperaccumulation. [ABSTRACT FROM AUTHOR]

Background and aims: Metallophytes 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 which may have potential to be used in mine site rehabilitation. This study aimed to investigate the soil-plant relationships of metallophytes on the Dugald River gossan. Methods: Plant samples and associated rooting soil samples were collected across the gossan and then analysed for metal concentrations. Soil-plant metal relationships were subsequently explored to characterise the species in relation to metal uptake behaviour. Results: The metallophyte grass, Eriachne mucronata, dominated the gossan, yet there appeared to be no direct relationship between the occurrence of metallophytes and prevailing soil metal concentrations. Using transformation-based redundancy analysis (tb-RDA), two groups of metals, copper (Cu) and Zn-Cadmium (Cd), have been identified to be the primary metals driving species distribution. Crotalaria novae-hollandiae, was able to accumulate high concentrations of each of these metals in its leaves, with up to 16,200 mg Zn kg−1, 545 mg Cu kg−1 and 170 mg Cd kg−1. Conclusions: Soil metal concentrations alone are not suitable indications for metallophyte distribution or composition in a polymetallic environment. Crotalaria novae-hollandiae can tolerate high concentrations of metals and accumulate Zn-Cu-Cd above the respective hyperaccumulation thresholds; the species can be described for the first time as a strong polymetallic indicator-type metallophyte. [ABSTRACT FROM AUTHOR]

The extend of biogeochemical cycling of nickel (Ni) by tropical hyperaccumulator plants in their native habitat is largely unknown, although these unusual plants are suspected to play a major role in the recycling of this element in ultramafic ecosystems. In this study, we have assessed the biogeochemical cycling of Ni (and other elements, including mineral nutrients) by a tropical Ni hyperaccumulator plant, i.e., Phyllanthus rufuschaneyi, which is one of the most promising species for tropical Ni agromining. The study site was a young secondary forest in Sabah (Malaysia) where Phyllanthus rufuschaneyi occurs as the dominant species on an ultramafic Cambisol. For 2 years, we monitored a 100-m2 plot and collected information on weather, biomass increase, soil fertility, water fluxes to the soil and litter fluxes for a wide range of elements, including Ni. The Ni cycle is mainly driven by internal fluxes, notably the degradation and recycling of Ni-rich litter. Over the period of investigation, the Ni litter flux corresponded to the total Ni stock of the litter (5.2 g m−2 year−1). The results further show that Ni turnover varies significantly with the accumulation properties of the plant cover. This points to the major influence of Ni hyperaccumulator plants in building up Ni available stocks in the topsoils, as has also been shown in temperate ultramafic systems. Litterfall and throughfall contribute substantially to the cycling of phosphorus, sulphur and potassium in this ecosystem, with throughfall contributing 2-, 220- and 20-fold higher to the respective nutrient fluxes relative to litterfall. The magnesium:calcium ratio far exceeded 1 in the soil, but was < 1 in the leaves of Phyllanthus rufuschaneyi. The insights from this study should be taken into account when designing tropical agromining operations; as Ni stocks could be more labile than initially thought. The removal of Ni- and nutrients-rich biomass will likely affect available Ni (and major nutrients) for the next cropping seasons, and requires sustainable fertilisation, to be utilized to replenish depleted major nutrients. These findings also have major ecological implications. [ABSTRACT FROM AUTHOR]

Background and aims: Phosphorus is one of the major nutrients that directly or indirectly affects all aspects of plant growth. Tropical nickel hyperaccumulators, including Phyllanthus rufuschaneyi and Rinorea cf. bengalensis from Borneo Island (in the Malaysian state of Sabah), have evolved to grow in extremely P-impoverished ultramafic soils. This study aimed to establish the response of the root and shoot ionome of these two agromining 'metal crops' to soil P availability. Methods: We undertook a soil P dosing trial on P. rufuschaneyi and R. cf. bengalensis in Sabah (Malaysia) over a period of 12 months. We measured the elemental concentrations in the soil solution and roots, as well as in the developed and developing stems and leaves. Results: The results show that root and shoot P accumulation increased markedly as soil P availability increased by 80-fold in P. rufuschaneyi, whereas R. cf. bengalensis did not increase as strongly to P supply, despite a 135-fold increase in soil solution P. The contrasting observations on the root and shoot P accumulation patterns in these species suggests distinct P acquisition strategies in these species. The non-responsiveness of R. cf. bengalensis to increasing soil P availability may be related to its possible association with mycorrhizal fungi. Conclusion: The findings of this study reveal the complexities of phosphate uptake, transport and accumulation in these 'metal crops'. This information is essential to develop appropriate nutrient management in nickel agromining operations. [ABSTRACT FROM AUTHOR]

Background and Aims: In tropical ultramafic soils, potassium (K) is typically the most growth limiting nutrient. However, tropical nickel (Ni) hyperaccumulator plants, including Phyllanthus rufuschaneyi and Rinorea cf. bengalensis (which are 'metal crops' used in agromining) from Malaysia, have unusually high K shoot accumulation compared to other species, despite naturally growing on severely K-impoverished ultramafic soils. This study aimed to establish the response to soil K availability in relation to uptake of K and other elements in the roots and shoots of P. rufuschaneyi and R. cf. bengalensis. Methodology: We undertook an experiment in which soluble K was dosed to ultramafic soil in pots with P. rufuschaneyi and R. cf. bengalensis in Sabah (Malaysia). Results: The results show that root K concentrations increased markedly as the soil K availability increased by 35-fold, whilst the corresponding effect on K accumulation in the shoots of P. rufuschaneyi and R. cf. bengalensis was not significantly different in relation to soil K dosing. Observed divergent responses between root and shoot K accumulation in these species suggests a separate genetic control of K uptake and xylem loading in P. rufuschaneyi and R. cf. bengalensis. Conclusion: The tight control of root-to-shoot K translocation and constrained K accumulation in shoots under a soil K gradient is likely an adaptive mechanism to the evolution of these species to grow in highly nutrient-impoverished ultramafic soils. This study provides information that will be useful for better nutrient management of tropical Ni metal farms that use K-efficient Ni 'metal crops'. [ABSTRACT FROM AUTHOR]

Aims The agronomy of tropical 'metal crops' had not yet been tested until a recent pot trial was undertaken to test the growth and nickel (Ni) yield of two promising Ni 'metal crops' (Phyllanthus rufuschaneyi and Rinorea cf. bengalensis) from Sabah, Malaysia. The present study investigates the growth and Ni yield in P. rufuschaneyi in response to inorganic and organic fertilisation under field conditions. Methods: A two-year field experiment was undertaken on an ultramafic Cambisol in Sabah. Two experiments were set up with different types of fertilisers, either organic or inorganic. Ten 9-m2 plots were amended with either NPK (370 kg ha−1) or N (120 kg ha−1) fertilisation and were monitored during the first year. Another experiment with 25-m2 plots was set up to test three treatments of organic amendment (0, 1 or 2 kg m−2 of shredded P. rufuschaneyi biomass). Results: The results show that despite considerable variability, Ni concentration was generally lower in plant shoots amended with N only (i.e. urea). However, treatments showed no statistical effect on plant biomass and Ni yield in the short-term, even though organic treatments had a strong positive effect on the availability of Ni. Conclusion: The short-term effects of inorganic and organic treatments on Ni yield of the tropical 'metal crop' Phyllanthus rufuschaneyi were not apparent (75 kg Ni ha−1 yr−1). The field trials are ongoing to assess long-term effects. The preliminary results suggest that with appropriate agronomic systems and plant breeding, the Ni yield could be substantially increased. [ABSTRACT FROM AUTHOR]

Background and aims: The nickel hyperaccumulator Bornmuellera emarginata (Brassicaceae) is a species adapted to thrive on naturally nickel-enriched ultramafic soils in the Balkans and a promising candidate for use in nickel agromining. The main aim of this study was to provide insight into the physiological mechanisms of nickel hyperaccumulation in B. emarginata.Bornmuellera emarginata was cultivated under various nickel exposure concentrations (control, 1, 10, and 100 µM nickel in solution), and different pH levels of the hydroponic solution for four weeks. During this period, the plants underwent assessment for various physiological parameters, including photosynthetic pigments, leaf relative water content, tolerance index, and metal accumulation in plant tissues.The results show that the translocation factors and bioconcentration factors were > 1 even at 1 µM nickel in solution. This confirms the ability of B. emarginata to hyperaccumulate nickel (up to 6600 mg kg−1) over a wide range of nickel concentrations in hydroponics. Nickel at 100 µM (a concentration that is an order of magnitude higher than the highest soil solution nickel concentration found in ultramafic soils) induced only mild physiological stress symptoms (e.g. a minor proline response). Alterations in the solution pH did not cause any significant effect on nickel accumulation in the plants.Bornmuellera emarginata is a highly adapted nickel-tolerant and nickel hyperaccumulating species that shows very little stress responses even to extreme nickel exposure concentrations in hydroponics. This species shows interesting trade-off responses between nickel and other metals, including non-competitive uptake of zinc. The potential for this species to accumulate zinc should therefore be further explored.Methods: The nickel hyperaccumulator Bornmuellera emarginata (Brassicaceae) is a species adapted to thrive on naturally nickel-enriched ultramafic soils in the Balkans and a promising candidate for use in nickel agromining. The main aim of this study was to provide insight into the physiological mechanisms of nickel hyperaccumulation in B. emarginata.Bornmuellera emarginata was cultivated under various nickel exposure concentrations (control, 1, 10, and 100 µM nickel in solution), and different pH levels of the hydroponic solution for four weeks. During this period, the plants underwent assessment for various physiological parameters, including photosynthetic pigments, leaf relative water content, tolerance index, and metal accumulation in plant tissues.The results show that the translocation factors and bioconcentration factors were > 1 even at 1 µM nickel in solution. This confirms the ability of B. emarginata to hyperaccumulate nickel (up to 6600 mg kg−1) over a wide range of nickel concentrations in hydroponics. Nickel at 100 µM (a concentration that is an order of magnitude higher than the highest soil solution nickel concentration found in ultramafic soils) induced only mild physiological stress symptoms (e.g. a minor proline response). Alterations in the solution pH did not cause any significant effect on nickel accumulation in the plants.Bornmuellera emarginata is a highly adapted nickel-tolerant and nickel hyperaccumulating species that shows very little stress responses even to extreme nickel exposure concentrations in hydroponics. This species shows interesting trade-off responses between nickel and other metals, including non-competitive uptake of zinc. The potential for this species to accumulate zinc should therefore be further explored.Results: The nickel hyperaccumulator Bornmuellera emarginata (Brassicaceae) is a species adapted to thrive on naturally nickel-enriched ultramafic soils in the Balkans and a promising candidate for use in nickel agromining. The main aim of this study was to provide insight into the physiological mechanisms of nickel hyperaccumulation in B. emarginata.Bornmuellera emarginata was cultivated under various nickel exposure concentrations (control, 1, 10, and 100 µM nickel in solution), and different pH levels of the hydroponic solution for four weeks. During this period, the plants underwent assessment for various physiological parameters, including photosynthetic pigments, leaf relative water content, tolerance index, and metal accumulation in plant tissues.The results show that the translocation factors and bioconcentration factors were > 1 even at 1 µM nickel in solution. This confirms the ability of B. emarginata to hyperaccumulate nickel (up to 6600 mg kg−1) over a wide range of nickel concentrations in hydroponics. Nickel at 100 µM (a concentration that is an order of magnitude higher than the highest soil solution nickel concentration found in ultramafic soils) induced only mild physiological stress symptoms (e.g. a minor proline response). Alterations in the solution pH did not cause any significant effect on nickel accumulation in the plants.Bornmuellera emarginata is a highly adapted nickel-tolerant and nickel hyperaccumulating species that shows very little stress responses even to extreme nickel exposure concentrations in hydroponics. This species shows interesting trade-off responses between nickel and other metals, including non-competitive uptake of zinc. The potential for this species to accumulate zinc should therefore be further explored.Conclusions: The nickel hyperaccumulator Bornmuellera emarginata (Brassicaceae) is a species adapted to thrive on naturally nickel-enriched ultramafic soils in the Balkans and a promising candidate for use in nickel agromining. The main aim of this study was to provide insight into the physiological mechanisms of nickel hyperaccumulation in B. emarginata.Bornmuellera emarginata was cultivated under various nickel exposure concentrations (control, 1, 10, and 100 µM nickel in solution), and different pH levels of the hydroponic solution for four weeks. During this period, the plants underwent assessment for various physiological parameters, including photosynthetic pigments, leaf relative water content, tolerance index, and metal accumulation in plant tissues.The results show that the translocation factors and bioconcentration factors were > 1 even at 1 µM nickel in solution. This confirms the ability of B. emarginata to hyperaccumulate nickel (up to 6600 mg kg−1) over a wide range of nickel concentrations in hydroponics. Nickel at 100 µM (a concentration that is an order of magnitude higher than the highest soil solution nickel concentration found in ultramafic soils) induced only mild physiological stress symptoms (e.g. a minor proline response). Alterations in the solution pH did not cause any significant effect on nickel accumulation in the plants.Bornmuellera emarginata is a highly adapted nickel-tolerant and nickel hyperaccumulating species that shows very little stress responses even to extreme nickel exposure concentrations in hydroponics. This species shows interesting trade-off responses between nickel and other metals, including non-competitive uptake of zinc. The potential for this species to accumulate zinc should therefore be further explored. [ABSTRACT FROM AUTHOR]

Background and aims: The genus Denhamia(Celastraceae) includes fifteen Australian species, many of which have a propensity for manganese (Mn) (hyper)accumulation. Among the key aims of this study were to: i) elucidate Mn accumulation in D. bilocularis, D. celastroides, D. pittosporoides and D. silvestris under controlled conditions; ii) examine the in situ distributions of Mn and other elements in tissues of i) above, and also in two other species growing in their natural habitat, i.e. D. silvestris and D. cunninghamii; iii) test numerous Denhamia herbarium specimens for Mn accumulation using portable X-ray fluorescence spectroscopy (XRF). Methods: Portable XRF and laboratory micro-XRF were used to examine Mn accumulation and foliar distribution patterns in several Australian Denhamia species. These techniques were variously applied to fresh field material and experimentally-raised plants treated with Mn (250 μg g−1, 500 μg g−1 and 1000 μg g−1) and dry herbarium material. Results: The findings revealed D. bilocularis as a new Mn hyperaccumulator, with foliar Mn concentrations of up to 15,300 μg g−1 in herbarium samples, and 13,700 μg g−1 in experimentally grown plants. Laboratory μXRF maps consistently showed that foliar Mn accumulation was localized at the extremities of wild D. cunninghamii and D. silvestris leaves; whereas it was found in the vasculature of experimentally grown D. bilocularis and D. pittosporoides leaves. Conclusions: This study presents evidence that Mn accumulation across the Australian Denhamia species is taxonomically variable, however further work is required. [ABSTRACT FROM AUTHOR]

Nickel hyperaccumulation in Blepharidium guatemalense Standl. (Rubiaceae) was found in the tropical forests of south-eastern Mexico. This study aimed to document the geographic extent of nickel hyperaccumulation in this species, to understand its process of hyperaccumulation and to explore nickel distribution within the tissues of this plant. To accomplish these objectives, a complete non-destructive elemental screening of herbarium specimens was performed with a hand-held X-ray fluorescence spectrometer. Besides, rhizosphere soils and plant tissues were collected in Mexico and analyzed for physical–chemical parameters. Finally, elemental distribution maps of nickel and other elements in plant tissues were obtained by X-ray fluorescence spectroscopy and microscopy. This study revealed that Blepharidium guatemalense is distributed throughout Chiapas, Tabasco and Campeche, reaching the maximum nickel concentration in leaves (4.3 wt%) followed by roots and seeds (2.0 wt%) and bark (1.8 wt%). Simultaneous hyperaccumulation of cobalt and nickel was found in 15% of the herbarium specimens. Blepharidium guatemalense has uncommon re-distribution mechanisms via phloem since this tissue is the highest nickel-enriched from all parts of the plant (from roots to leaves). A high total nickel (mean of 610 µg g−1) was found in rhizosphere soils even though no evidence of ophiolite emplacement in that area has been reported. Blepharidium guatemalense represents the first hypernickelophore (> 1 wt% Ni) to be reported as growing in soils that are neither ultramafic nor enriched by anthropogenic pollutants. [ABSTRACT FROM AUTHOR]

Aims: The tropical nickel (Ni) hyperaccumulator plants, Rinorea cf. bengalensis and Phyllanthus rufuschaneyi, are locally common on ultramafic soils in the Malaysian state of Sabah on the island of Borneo. The aim of this study was to determine whether the structure and diversity of R. cf. bengalensis rhizosphere microbial communities were dependant on the Ni concentrations in the different rhizosphere soils studied. Methods: Rinorea cf. bengalensis and Phyllanthus rufuschaneyi were subjected to a randomized block design experiment in which four Ni dose levels were applied (0, 60, 240, 600 mg Ni kg−1) × 5 replicates per level for 12 months cultivation. At the end of the trial foliar elemental concentrations were measured. In addition, rhizosphere soils were collected for elemental and microbial analyses. The microbial analysis consisted of measuring microbial enzymatic activities and a diversity analysis based on Illumina sequencing. Results: The Illumina sequencing analysis yielded 2,649,138 sequences grouped under 2430 different Operational Taxonomic Units (OTUs) belonging to 25 phyla. No impact of the Ni amendments was shown for the four microbial enzymatic activities tested, even at the highest Ni dose level (600 mg Ni kg−1). Higher microbial enzymatic activities were found in the rhizosphere of R. cf. bengalensis relative to P. rufuschaneyi. Nickel concentrations appeared to have a high impact on the P. rufuschaneyi rhizosphere soils, whereas no effect was found for the rhizosphere bacterial community diversity of R. cf. bengalensis. Conclusions: There may be a significant role of rhizodeposits associated with R. cf. bengalensis that protect and preserve the microbial communities in the rhizosphere, regardless of the prevailing nickel concentrations. [ABSTRACT FROM AUTHOR]

Aims: This study aimed to establish elemental profiles and to spatially resolve the elemental distribution in five New Caledonian woody Ni hyperaccumulator plant species (Geissois pruinosa var. pruinosa, Homalium francii, Hybanthus austrocaledonicus, Psychotria gabriellae, and Pycnandra acuminata) originating from the Cunoniaceae, Salicaceae, Violaceae, Rubiaceae, and Sapotaceae families respectively. Methods: Using synchrotron-based micro-X-ray Fluorescence (μXRF) imaging of different plant tissues, from the roots to the shoots and reproductive organs, this study aimed to clarify how distribution patterns of nickel, and other physiologically relevant elements, differ between these species. Results: The results show that the tissue-level and cellular-level distribution of nickel in P. gabriellae, H. austrocaledonicus, G. pruinosa var. pruinosa, and H. francii conform with the majority of studied Ni hyperaccumulator plant species globally, including (temperate) herbaceous species, with localization mainly in epidermal cells and phloem bundles. However, P. acuminata has nickel-rich laticifers, which constitute an independent network of cells that is parallel to the vascular bundles and are the main sink for nickel. Conclusions: Synchrotron-based micro-X-ray Fluorescence (μXRF) is a powerful method for investigating how metal hyperaccumulation influences acquisition and spatial distribution of a wide range of elements. This non-invasive method enables investigation into the in vivo distribution of multiple elements and the structure and organisation of cells (e.g. laticifers). [ABSTRACT FROM AUTHOR]

Aims: Knowledge on the ecophysiology of cobalt hyperaccumulator species is limited. The nickel hyperaccumulator Rinorea cf. bengalensis from Borneo can accumulate high concentrations of cobalt in nature. This study investigates the cobalt accumulation potential of Rinorea cf. bengalensis in relation to nickel concentrations in soils and the subsequent tissue and cellular-level distributions of cobalt, nickel and major cations. Methods: Seedlings of Rinorea cf. bengalensis were grown in mixed treatments on ultramafic soil containing a high concentration of available nickel. Cobalt and nickel salts were then added to the soil to study their interactions. The tissue and cellular-level distributions of cobalt, calcium, nickel, and potassium were investigated using synchrotron-based X-ray fluorescence microscopy. Results: The maximum foliar cobalt concentration reached 1200 μg g−1. Accumulation of cobalt competed with nickel accumulation although nickel seems to stimulate cobalt phloem translocation. Plants suffered toxicity in the treatment with the highest soil cobalt concentration. Cobalt and nickel have contrasting distribution patterns in the leaves of Rinorea cf. bengalensis, with cobalt mainly excreted on the surface of the leaves, whereas nickel is localised in foliar epidermal cells. Conclusions: Rinorea cf. bengalensis can accumulate high concentrations of cobalt, but is intrinsically more tolerant to nickel. It does not rely on a similar sequestration mechanism for both metals, which could explain the lesser tolerance for cobalt. Nickel appears to be essential for the plant to tolerate high cobalt concentrations. Further studies intending to develop agronomic practices are needed to determine the viability of Rinorea cf. bengalensis for nickel-cobalt agromining. [ABSTRACT FROM AUTHOR]

Aims: Nickel hyperaccumulator plants require highly evolved mechanisms to avoid cellular-level toxicity to cope with the high prevailing concentrations of nickel in their seeds and seedlings. This study aimed to investigate tissue-level distribution and redistribution of Ni and other physiologically relevant elements during the germination of hyperaccumulator plants. Methods : Berkheya coddii Roessler (Asteraceae) and Odontarrhena muralis sensu latu (Waldst. & Kit.) Endl. (O. chalcidica), formerly Alyssum murale (Waldst. & Kit.) (Brassicaceae), were germinated for several days at room temperature before using synchrotron micro X-ray Fluorescence Spectroscopy (µXRF) to obtain high-sensitivity and high-resolution elemental images of live/hydrated plants at various stages of seed germination and seedling growth. Results: The results show that fruits and seeds of both species were highly enriched in nickel. In Berkheya coddii, nickel was located in the cotyledons, the micropylar area, the seed coat, and the point of attachment of the pappus with the cypsela body. In Odontarrhena muralis seeds, nickel occurred in the cotyledons and hypocotyl. The emergence of true leaves initiates nickel and calcium redistribution within seedlings in both species. Conclusions: The diversity in physiological responses to nickel in Berkheya coddii and Odontarrhena muralis does not only occur at the mature stage, but is inherent to both species as seed elemental storage and tolerance mechanisms during seedling development differ. [ABSTRACT FROM AUTHOR]

Background: Phytoextraction is an in situ technique that can be applied to minerals and mining wastes using hyperaccumulator plants to purposely bio-concentrate high levels of metals or metalloids into their shoots in order to remove them from the substrate, while achieving monetary gain. Phytoextraction can be applied to a limited number of elements depending on the existence of hyperaccumulator plants with suitable characteristics. Although phytoextraction has been trialled in experimental settings, it requires testing at field scale to assess commercial broad-scale potential. Scope: The novelty and purported environmental benefits of phytoextraction have attracted substantial scientific inquiry. The main limitation of phytoextraction with hyperaccumulators is the number of suitable plants with a high accumulation capacity for a target element. We outline the main considerations for applying phytoextraction using selected elemental case studies in which key characteristics of the element, hyperaccumulation and economic considerations are evaluated. Conclusions: The metals cobalt, cadmium, thallium and rhenium and the metalloids arsenic and selenium are present in many types of minerals wastes, especially base metal mining tailings, at concentrations amenable for economic phytoextraction. Phytoextraction should focus on the most toxic elements (arsenic, cadmium, and thallium) or especially valuable elements (selenium, cobalt, and rhenium). The value proposition is in the clean-up of contaminated land in the case of toxic elements, whereas it is in the 'bio-ore' generated by the process in the case of valuable elements. [ABSTRACT FROM AUTHOR]

Aims: Data on the variability of hyperaccumulation potential of the facultative serpentinophytes Noccaea kovatsii and N. praecox on different geological substrates are scarce. The aim of this study was to assess the accumulation potential of these two species from ultramafic and non-ultramafic substrates, with special emphasis on the hyperaccumulation of Ni, Zn and Cd. Methods: Samples of plants and corresponding soils were collected from 16 sites covering a wide range of geochemistry. Elemental concentrations were determined in the roots, shoots and the rhizosphere soils. The pH, particle size distribution and content of organic matter were also determined in the soil samples. Results: All ultramafic accessions of both species hyperaccumulated Ni with high intraspecific variability. Only one accession of N. kovatsii from a schist soil hyperaccumulated Zn, with also a high Cd accumulation. Accumulation and translocation of Ni in both species were much higher in the ultramafic accessions, whereas Zn accumulation and translocation was found in both ultramafic and non-ultramafic accessions. Conclusions: Ni accumulation and translocation was restricted to ultramafic populations of both species, whereas it is a species-wide trait for Zn. This study provides new and comprehensive information on the natural variation of hyperaccumulation of Ni, Zn and Cd in N. kovatsii and N. praecox. [ABSTRACT FROM AUTHOR]

Aims: This study investigated the physico-geochemical properties of three types of ultramafic substrates in Sabah (Malaysia) and further characterised their influence on nickel (Ni) accumulation in two selected tropical 'metal crops' (Phyllanthus rufuschaneyi and Rinorea cf. bengalensis). Methods: Three experiments, consisting of a randomised block growth trial in large pots over 12 months in Sabah, were conducted: i) soil ratio experiment (Cambisol:Ferralsol:Leptosol), ii) soluble Ni dosing experiment with added 0, 60, 240, 600 mg Ni kg−1, and iii) soil pH adjustments (pH 5.2, 5.8 and 6.4) experiment. Results: The results show that the low pH status of Ferralsol did not result in increased extractable Ni concentrations, indicating that Ni-bearing phases and mineralogy play a major role in Ni extractability in these substrates. The increasing order of extractable Ni concentrations was Ferralsol < Leptosol < Cambisol. The selected 'metal crops' had remarkable shoot biomass (~40 g pot−1) and foliar Ni concentrations (>15 g kg−1 in P. rufuschaneyi) in the Cambisol, >5-fold higher relative to that recorded in Leptosol and Ferralsol. Mixing the Cambisol with the other substrates significantly improved Ni yield in both species relative to the individual substrates. The effect of Ni addition on the selected 'metal crops' was species-dependent, whereas reduction of soil pH in Cambisol significantly reduced Ni yield in both species. Conclusions: Nickel accumulation patterns in 'metal crops' in response to the diverse ultramafic soils in the tropics are influenced by the physico-geochemical characteristics of the soil types. Soil Ni extractability in these soils is more dependent on the Ni-bearing phases and mineralogy rather than the pH status. This study provides useful information on plant-soil interactions required for identifying suitable substrates for implementing tropical Ni agromining. [ABSTRACT FROM AUTHOR]

Background and aims: Pioneer plants may improve the ecological restoration of degraded ultramafic areas by plant-soil interaction processes. In this study, we assess the effect of the pioneer actinorhizal tree C. terminale (Casuarinaceae) on the recovery of plant communities and soil functions on degraded tropical ultramafic sites. Methods: Soil and plant samples were collected along a tree-age gradient in two degraded ultramafic sites in Sabah (Northern Borneo, Malaysia): a Technosol and a Leptosol. Chemical composition of plants and soils, and biological activity of soils were assessed at both sites. Plant colonisation was assessed by plot vegetation surveys. Results: An improvement in soil fertility parameters (pH reduction from 8.5 to 6.8, an increase in the concentrations of several nutrients and enhanced soil enzyme activities) was observed along the C. terminale age gradient. However, plant cover and diversity was only improved around mature trees at the site that was not impacted by mining. Conclusion: C. terminale promotes the recovery of several soil functions, mainly related to the storage and recycling of N, P, K, S. Besides plant-soil feedback, other environmental factors (i.e. exposition to sunlight, drought) may play an important role on revegetation of ultramafic soils. [ABSTRACT FROM AUTHOR]

Aims: Based on a recent taxonomic revision of the genus Odontarrhena in Albania, our work aimed at comparing the taxa and populations of this genus in terms of nickel accumulation and levels of other metals in relation to their concentrations in the soil at distinct Albanian ultramafic outcrops. Methods: Several populations of different Odontarrhena species were sampled from 20 different outcrops across the entire Albanian territory. Concentrations of Ni, Co, Cr, Mg, Ca, K, Fe and Mn were determined in soil, roots and shoots of all specimens sampled. Results: Ultramafic soils across Albania showed variable metal composition, with significant differences between sites. Large differences in mineral element concentrations were also found between the plants which were not related to species identity or geographical distribution of their populations. Conclusions: Shoot Ni concentrations in Albanian Odontarrhena taxa depend on soil Ni concentrations but not on species identity. For O. chalcidica, the more widely distributed species, the environmental fingerprint for shoot metal composition was found not only for Ni, but also for Ca and Mg, the latter showing a positive linear relationship between soil and plant concentrations. [ABSTRACT FROM AUTHOR]

Aim: The identification and use of hyperaccumulator plants in mining projects has been recognized as an important component of mine planning at several sites around the world. The objective of this research was to provide information on relevant plant tissue chemistry and an indicative assessment of the potential for phytomining at Weda Bay Nickel (WBN), Halmahera.Methods: The first stage was the identification of native nickel hyperaccumulator plants. In total, 280 plant tissue samples from 10 nickel accumulator species and 46 matching rhizosphere soil samples were collected. Chemical analyses of plant tissue samples were performed and physico-chemical parameters of the rhizosphere soils were also measured.Results: A total of three species were considered as metal crops: Rinorea aff. bengalensis (up to 22,200 mg kg−1 dry weight at 2 m above ground level), Ficus trachypison (1060 mg kg−1) and Trichospermum morotaiense (5180 mg kg−1), but only R. aff. bengalensis has sufficiently high Ni concentrations in biomass to warrant field trials.Conclusions: Utilising a successional planting strategy, F. trachypison and T. morotaiense could be used to facilitate site conditions, followed by the metal crop R. aff. bengalensis. Using this design, a nickel yield of 330 kg per hectare would be possible every 4 years. In addition to allowing the recovery of nickel, this approach could be an integrated mine site rehabilitation strategy to mitigate environmental impacts, improve soil quality and facilitate transition to other land-uses such as native forest. [ABSTRACT FROM AUTHOR]

Background: Hyperaccumulator plants are unusual plants that accumulate particular metals or metalloids, such as nickel, zinc, cadmium and arsenic, in their living tissues to concentrations that are hundreds to thousands of times greater than what is normal for most plants. The hyperaccumulation phenomenon is rare (exhibited by less than 0.2% of all angiosperms), with most of the ~500 hyperaccumulator species known globally for nickel.Scope: This review highlights the contemporary understanding of nickel hyperaccumulation processes, which include root uptake and sequestration, xylem loading and transport, leaf compartmentation and phloem translocation processes.Conclusions: Hyperaccumulator plants have evolved highly efficient physiological mechanisms for taking up nickel in their roots followed by rapid translocation and sequestration into the aerial shoots. The uptake of nickel is mainly involved with low affinity transport systems, presumably from the ZIP family. The presence of high concentrations of histidine prevents nickel sequestration in roots. Nickel is efficiently loaded into the xylem, where it mainly presents as Ni2+. The leaf is the main storage organ, which sequestrates nickel in non-active sites, e.g. vacuoles and apoplast. Recent studies show that phloem translocates high levels of nickel, which has a strong impact on nickel accumulation in young growing tissues. [ABSTRACT FROM AUTHOR]

Purpose: Soils provide a variety of ecosystem services (ESs) that are crucial to food security, water security, energy security, climate change abatement, and biodiversity, especially in densely populated countries such as China. At present, China is facing great challenges from serious soil heavy metal (HM) contamination which has damaged soil ESs and soil security. In this paper, we evaluate the ESs that contaminated soils can potentially provide before and after remediation, and we explore the connections between these ESs and the achievement of soil security in China. Materials and methods: After an introduction to the concepts of ESs and soil security and a review of the current status of soil HM contamination in China, the ESs that can potentially be provided by HM-contaminated soils are discussed. Finally, we discuss the current remediation status of HM-contaminated soils from the standpoint of optimizing the ability of these soils to provide ESs. Results and discussion: The status of the provision of ESs by HM-contaminated soils of croplands, brownfields, and mining wastelands is described in detail. Contaminated cropland soils fail to provide provisioning (e.g. , food production), cultural, and regulating services, while the regulating and supporting services of brownfield soils are greatly reduced. The ESs of mining wasteland soils have been severely damaged, resulting in a high potential for contamination of surrounding ecosystems. Recent soil remediation projects have demonstrated that the damaged ESs of HM-contaminated soils can be restored, which would enhance Chinese soil security. However, it has often been the case that only visible ESs (e.g. , food production and vegetation cover) are addressed, while other less noticeable but important services (e.g. , water quality and biodiversity) are neglected. Therefore, we propose a framework for the evaluation of ESs provided by HM-contaminated soils. Conclusions: The ESs that could potentially be provided by HM-contaminated soils would help to achieve soil security in China, not only by improving food security, water security, and energy security but also by helping to protect soil biodiversity and abate global climate change. The ESs provided by HM-contaminated soils should be taken into account in soil policy and management systems as well as by the remediation industry. [ABSTRACT FROM AUTHOR]

Background: Nickel (Ni) phytomining operations cultivate hyperaccumulator plants ('metal crops') on Ni-rich (ultramafic) soils, followed by harvesting and incineration of the biomass to produce a high-grade 'bio-ore' from which Ni metal or pure Ni salts are recovered. Scope: This review examines the current status, progress and challenges in the development of Ni phytomining agronomy since the first field trial over two decades ago. To date, the agronomy of less than 10 species has been tested, while most research focussed on Alyssum murale and A. corsicum. Nickel phytomining trials have so far been undertaken in Albania, Canada, France, Italy, New Zealand, Spain and USA using ultramafic or Ni-contaminated soils with 0.05-1 % total Ni. Conclusions: N, P and K fertilisation significantly increases the biomass of Ni hyperaccumulator plants, and causes negligible dilution in shoot Ni concentration. Organic matter additions have pronounced positive effects on the biomass of Ni hyperaccumulator plants, but may reduce shoot Ni concentration. Soil pH adjustments, S additions, N fertilisation, and bacterial inoculation generally increase Ni phytoavailability, and consequently, Ni yield in 'metal crops'. Calcium soil amendments are necessary because substantial amounts of Ca are removed through the harvesting of 'bio-ore'. Organic amendments generally improve the physical properties of ultramafic soil, and soil moisture has a pronounced positive effect on Ni yield. Repeated 'metal crop' harvesting depletes soil phytoavailable Ni, but also promotes transfer of non-labile soil Ni to phytoavailable forms. Traditional chemical soil extractants used to estimate phytoavailability of trace elements are of limited use to predict Ni phytoavailability to 'metal crop' species and hence Ni uptake. [ABSTRACT FROM AUTHOR]

Aims: This study evaluated the effect of phloem translocation on Ni accumulation in the hyperaccumulator Noccaea caerulescens. Methods: The first experiment assessed the metal and organic compound concentrations in phloem sap. Leaves were cut from plants grown in nutrient solutions added with 100 μM Ni or Zn, and then used for phloem sap extraction by means of the EDTA-stimulated exudation method. In the second experiment, Ni was applied to old leaves as a foliar spray to assess bidirectional movement of Ni in phloem. Results: In the first experiment, enrichment of Ni or Zn was found in phloem exudates, indicating high Ni and Zn phloem loading and translocation capacity in N. caerulescens. Amino acids, e.g. nicotianamine and histidine, were present at low concentrations in exudates, which are insufficient for Ni and Zn chelation. On the contrary, concentrations of organic acids, especially malate, were high in all treatments, which may be involved in Ni and Zn chelation in phloem. The second experiment showed that 89 % of Ni exported from old leaves was translocated upward to young leaves, whereas only 11 % moved downward to roots. Conclusions: Phloem sap of N. caerulescens is enriched in Ni and malate, the majority of which moves upward to young tissues. Phloem translocation may play an important role for Ni accumulation in young leaves of N. caerulescens. [ABSTRACT FROM AUTHOR]

Nickel hyperaccumulator plants have been the focus of considerable research because of their unique ecophysiological characteristics that can be exploited in phytomining technology. Comparatively little research has focussed on the soil chemistry of tropical nickel hyperaccumulator plants to date. This study aimed to elucidate whether the soil chemistry associated with nickel hyperaccumulator plants has distinctive characteristics that could be indicative of specific edaphic requirements. The soil chemistry associated with 18 different nickel hyperaccumulator plant species occurring in Sabah (Malaysia) was compared with local ultramafic soils where nickel hyperaccumulator plants were absent. The results showed that nickel hyperaccumulators in the study area were restricted to circum-neutral soils with relatively high phytoavailable calcium, magnesium and nickel concentrations. There appeared to be a 'threshold response' for the presence of nickel hyperaccumulator plants at >20 μg g carboxylic-extractable nickel or >630 μg g total nickel, and >pH 6.3 thereby delimiting their edaphic range. Two (not mutually exclusive) hypotheses were proposed to explain nickel hyperaccumulation on these soils: (1) hyperaccumulators excrete large amounts of root exudates thereby increasing nickel phytoavailability through intense rhizosphere mineral weathering; and (2) hyperaccumulators have extremely high nickel uptake efficiency thereby severely depleting nickel and stimulating re-supply of Ni from diffusion from labile Ni pools. It was concluded that since there was an association with soils with highly labile nickel pools, the available evidence primarily supports hypothesis (2). [ABSTRACT FROM AUTHOR]

Purpose: Raw geological materials excavated then piled on large surface areas are submitted to pedogenetic factors. Knowledge of the evolution of this freshly exposed material is required to predict the newly developed Technosol and the corresponding ecosystem. The pedogenetic evolution of a Technosol developed on excavated Callovo-Oxfordian clay minerals (COx) is assessed from the analysis of natural soils developed on analogous materials. Materials and methods: Work was based on the hypothesis that the evolution of raw geological materials could be deduced from that of natural soils on similar outcrops in similar climatic conditions. A comparison was made on the basis of mineralogical and geochemical criteria between the unweathered clays and soil material collected from the horizons of two reference pedons on a COx outcrop in North-Eastern France, used by forest or agriculture, and a 10-year-old Technosol derived from freshly excavated COx material piled under outdoor climatic conditions. Soil profiles were described and each sampled horizon was characterized for mineralogy, and physical and chemical properties. Results and discussion: Soil profiles were classified as Vertic Stagnic Hypereutric Cambisol (Forest) and Vertic Stagnic Calcaric Cambisol (Meadow), and compared to the Calcaric Technosol (no vegetation yet). They clearly showed brunification and decarbonatization as the major processes having governed their evolution. Signs of clay leaching were also visible on the forest soil. A fairly good adequacy was observed between soil material sampled in the soil deep horizons (2.5 m), the Technosol deep horizon (1.7 m), and the freshly excavated material. Slight differences were recorded, however, i.e., salt loss (NaCl), sulfide oxidation, and precipitation of gypsum from sulfate and calcium released by decarbonatization, as earlier observed in leaching experiments. Salt loss is a rapid process almost completed to the same extent in the Technosol after 10 years than in the Calcaric Cambisol after centuries. The soil under forest showed signs of stronger pedogenetic evolution than the soil submitted to agriculture (meadow), probably because the latter has been refreshed by man-induced erosion. Conclusions: COx evolution can be predicted from the analysis of soils developed on similar outcrops. The Technosol developed on these carbonated materials would evolve as a result of extremely rapid leaching of the soluble phases, then surface enrichment of organic matter, surface decarbonatization, and progressive brunification of the whole profile as the major processes, and give rise to a Cambisol. Technosol study is an interesting approach for dating the age of pedogenetic processes. [ABSTRACT FROM AUTHOR]

This study aimed at relating the variability of Ni biogeochemistry along the ultramafic toposequence to pedogenesis and soil mineralogy. Hypereutric Cambisols dominate upslope; Cambic Vertisols and Fluvic Cambisols occur downslope. The soil mineralogy showed abundance of primary serpentine all over the sequence. It is predominant upslope but secondary smectites dominate in the Vertisols. Free Fe-oxides are abundant in all soils but slightly more abundant in the upslope soils. Whereas serpentines hold Ni in a similar and restricted range in every soil (approx. 0.3 %), Ni contents in smectites may vary a lot and Mg-rich and Al-poor smectites in the Vertisol could hold up to 4.9 % Ni. Ni was probably adsorbed onto amorphous Fe-oxides and was also exchangeable in secondary smectites. High availability of Ni in soils was confirmed by DTPA extractions. However, it varied significantly along the toposequence, being higher in upslope soils, where Ni-bearing amorphous Fe-oxides were abundant and total organic carbon higher and sensibly lower downslope on the Vertisols: Ni varied from 285 mg kg in the surface of soil I (upslope) to 95.9 mg kg in the surface of Fluvic Cambisols. Concentration of Ni in Alyssum murale shoots varied from 0.7 % (Hypereutric Cambisols) to 1.4 % (Hypereutric Vertisol). Amazingly, Ni uptake by A. murale was not correlated to Ni, suggesting the existence of specific edaphic conditions that affect the ecophysiology of A. murale upslope. [ABSTRACT FROM AUTHOR]

Aims: The primary aim of this study was to investigate the impact of active nickel and cadmium transport, transpiration and shoot biomass production on Ni and Cd accumulation in the leaves of the Ni-hyperaccumulator Leptoplax emarginata. A secondary objective was to observe the effects of various concentrations of nickel and cadmium in solutions on the plant growth and ecophysiological characteristics of these plants. Finally, the study sought to identify possible nickel and cadmium concentration gradients in solution as a function of the root distance. Methods: The Intact Plant Transpiration Stream Concentration Factor (TSCF=xylem/solution solute concentration ratio) was determined for both Ni and Cd and for the selected intact transpiring Ni-hyperaccumulator Leptoplax emarginata, cultivated on two contrasting fertilized and Ni-Cd-contaminated sandy porous media (rhizotrons with central root compartments, linked to Mariotte tubes operated at −1 kPa). IPTSCF and IPTSCF were calculated as the ratios between the hyperaccumulator plant's nickel or cadmium mass in the leaves and the nickel or cadmium concentration in solution by the volume of water transpired during the period of culture. Plant growth characteristics and gas exchanges were also recorded. Results: IPTSCF values were much greater than 1 (IPTSCF = 5.2 ± 0.9 and IPTSCF = 4.4 ± 0.6) whatever the amount of available Ni and Cd. This characterized a predominantly active plant metal uptake. Moreover, biological regulation was reported: plant growth and transpiration were significantly lower for hyperaccumulator plants cultivated in sand which was rich in available Ni and Cd, than for hyperaccumulator plants cultivated in topsoil, poor in available Ni and Cd. In the soil rhizosphere, capillary flow was related to transpiration and a depletion pattern was developed for Ni and sometimes for Cd. Conclusions: Overall, the Intact Plant Transpiration Stream Concentration Factor appeared to be a relevant metal bioconcentration factor taking into account the predominant type of metal transport from roots to leaves, plant growth and transpiration coupling and metal availability. IPTSCF and IPTSCF values were much greater than 1 and similar whatever the amount of available Ni and Cd. This characterized a predominantly active plant combining Ni and Cd uptake and biological regulations dependent of the Ni and Cd concentrations in solution. [ABSTRACT FROM AUTHOR]

Background, aim, and scope The presence of labile chromate in the soils is an environmental problem because of its high toxicity. The isotopic exchange kinetics (IEK) methods have been shown to be a useful tool to measure the phytoavailability of major (P, K) and trace elements (Cd, Zn, Ni, Pb) in soils. This study focused on the potential of applying IEK for chromate to characterize its availability in two tropical ultramafic Ferralsols. Materials and methods Two Ferralsols (NIQ II and NIQ III) of the ultramafic complex of Niquelândia (Goias, Brazil), known to have a high content of extractable chromate, were investigated. We adapted IEK for chromate in order to distinguish different pools of available chromate according to their rate of exchange kinetic. Results The extractable Cr(III) ranged from 9 to 132 mg kg-1, whereas extractable Cr(VI) ranged from 64 to 1,014 mg kg-1. The intensity factor, i.e., concentration of soluble Cr, ranged from 78 to 231μg L-1 in profile NIQ II and from 6 to 141μg L-1 in profile NIQ III. The highest concentrations were found in both topsoils and in the NIQ II-5 horizon. Most of the Cr(VI) was labile in short (E0-1 min) or medium-term (E1 min-24 h) in both soils. The E0-1 min and E1 min-24 h represented 39 to 83% of labile Cr (VI) in NIQ II and 69 to 80% in NIQ III. A high quantity of Cr(VI) was thus extremely labile and highly available, particularly in NIQ II. Moreover, both soils had a high buffering capacity of soluble Cr(VI) by labile pools. Discussion The Cr(VI) availability is large and varied significantly among the soil profiles. The r1/R parameter has long been considered as an indicator of the soil "fixing capacity" for ions like P. The values of r1/R for Cr(VI) measured on the two studied soils are among the lowest ever reported for any element, especially in the organic matter-poor and iron oxide-rich horizons (r1/R in the 0.001- 0.003 range). But, considering the high proportion of labile CrVI in these soils, it is more appropriate to relate r1/R to the buffer capacity. The latter was extremely high and probably due to labile Cr(VI) retained in its majority by low-energy bonds on the surface of colloids.… [ABSTRACT FROM AUTHOR]

Ultramafic outcrops are widespread in Albania and host several Ni hyperaccumulators (e.g., Alyssum murale Waldst. & Kit.). A field experiment was conducted in Pojske (Eastern Albania), a large ultramafic area in which native A. murale was cultivated. The experiment consisted in testing the phytoextraction potential of already installed natural vegetation (including A. murale) on crop fields with or without suitable fertilisation. The area was divided into six 36-m2 plots, three of which were fertilised in April 2005 with (NPK + S). The soil (Magnesic Hypereutric Vertisol) was fully described as well as the mineralogy of horizons and the localisation of Ni bearing phases (TEM-EDX and XRD). Ni availability was also characterised by Isotopic Exchange Kinetics (IEK). The flora was fully described on both fertilised and unfertilised plots and the plant composition (major and trace elements) and biomass (shoots) harvested individually were recorded. The soil had mainly two Ni-bearing phases: high-Mg smectite (1.3% Ni) and serpentine (0.7% Ni), the first one being the source of available Ni. Ni availability was extremely high according to IEK and confirmed by Ni contents in Trifolium nigriscens Viv. reaching 1,442 mg kg−1 (A new hyperaccumulator?). Total biomass yields were 6.3 t ha−1 in fertilised plots and 3.2 t ha−1 in unfertilised plots with a highly significant effect: fertilisation increased dramatically the proportion of A. murale in the plots (2.6 t ha−1 vs. 0.2 t ha−1). Ni content in the shoots of A. murale reached 9,129 mg kg−1 but metal concentration was not significantly affected by fertilisation. Phytoextracted Ni in total harvest reached 25 kg Ni ha−1 on the fertilised plots. It was significantly lower in unfertilised plots (3 kg Ni ha−1). Extensive phytomining on such sites could be promising in the Albanian context by domesticating already installed natural populations with fertilisation. [ABSTRACT FROM AUTHOR]

The in situ phytoextraction of cadmium from soils can only be achieved using plants that are both tolerant to high Cd concentrations and able to extract sufficient amounts of the metal. However, very few plant species are capable of remediating Cd polluted soils in a reasonable time frame. This paper aims to show that the population of the hyperaccumulator Thlaspi caerulescens J. & C. Presl. from Viviez (south of France), which has a high Cd-accumulating capability, is an efficient tool to remove Cd from contaminated soils. Roots of T. caerulescens Viviez proliferate in hot spots of metals in soils which is particularly advantageous because of heterogeneity of the distribution of metal in polluted soils. Isotopic techniques showed that plants from this population acquire Cd from the same pools as non-accumulating species, but that it was much more efficient than non-hyperaccumulators at removing the metal from the soil labile pool. This is due: to (i) a specific rooting strategy, and (ii) a high uptake rate resulting from the existence in this population of Cd-specific transport channels or carriers in the root membrane. Growth and overall extraction can be improved with appropriate N fertilisation, supplied either as mineral fertilisers or uncontaminated sewage sludge. Selecting bigger plants is possible from within a suitable Cd-accumulating population to improve the phytoextraction process. Growing the Cd-accumulating populations results in a reduction in the availability of Cd and Zn as shown with field and lysimeter experiments conducted for several years. As a result, on a practical aspect, Cd hyperaccumulating populations of T. caerulescens may be used as a tool to efficiently reduce the availability of Cd in soils, providing appropriate populations are used. [ABSTRACT FROM AUTHOR]

This study focused on the influence of ultramafic terrains on soil and surface water environmental chemistry in Peninsular Malaysia and in the State of Sabah also in Malaysia. The sampling included 27 soils from four isolated outcrops at Cheroh, Bentong, Bukit Rokan, and Petasih from Peninsular Malaysia and sites near Ranau in Sabah. Water samples were also collected from rivers and subsurface waters interacting with the ultramafic bodies in these study sites. Physico-chemical parameters (including pH, EC, CEC) as well as the concentration of major and trace elements were measured in these soils and waters. Geochemical indices (geoaccumulation index, enrichment factor, and concentration factor) were calculated. Al2O3 and Fe2O3 had relatively high concentrations in the samples. A depletion in MgO, CaO, and Na2O was observed as a result of leaching in tropical climate, and in relation to weathering and pedogenesis processes. Chromium, Ni, and Co were enriched and confirmed by the significant values obtained for Igeo, EF, and CF, which correspond to the extreme levels of contamination for Cr and high to moderate levels of contamination for Ni and Co. The concentrations of Cr, Ni, and Co in surface waters did not reflect the local geochemistry and were within the permissible ranges according to WHO and INWQS standards. Subsurface waters were strongly enriched by these elements and exceeded these standards. The association between Cr and Ni was confirmed by factor analysis. The unexpected enrichment of Cu in an isolated component can be explained by localized mineralization in Sabah. [ABSTRACT FROM AUTHOR]

Background: Nickel hyperaccumulator plants are of much interest for their evolution and unique ecophysiology, and also for potential applications in agromining—a novel technology that uses plants to extract valuable metals from soil. The majority of nickel hyperaccumulators are known from ultramafic soils in tropical regions (Cuba, New Caledonia and Southeast Asia), and one genus, Phyllanthus (Phyllanthaceae), is globally the most represented taxonomic entity. A number of tropical Phyllanthus-species have the potential to be used as ‘metal crops’ in agromining operations mainly because of their ease in cultivation and their ability to attain high nickel concentrations and biomass yields.Results: One of the most promising species globally for agromining, is the here newly described species Phyllanthus rufuschaneyi. This species can be classified in subgenus Gomphidium on account of its staminate nectar disc and pistillate entire style and represents the most western species of this diverse group. The flower structure indicates that this species is probably pollinated by Epicephala moths.Conclusions: Phyllanthus rufuschaneyi is an extremely rare taxon in the wild, restricted to Lompoyou Hill near Kinabalu Park in Sabah, Malaysia. Its utilization in agromining will be a mechanism for conservation of the taxon, and highlights the importance of habitat and germplasm preservation if rare species are to be used in novel green technologies. [ABSTRACT FROM AUTHOR]