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Hyperaccumulator plants are able to tolerate extremely high concentrations of metals/metalloids in the soil in which they grow and to accumulate high concentrations in their shoots. To date, a total of 31 hyperaccumulator plant species have been identified in the Balkans, the centre of diversity and speciation in the European flora which is particularly rich in ultramafic areas. A further 8 species have yet to be confirmed through additional studies. Most of the 31 hyperaccumulator taxa (13 taxa or 41.9%) are species of the genus Odontarrhena, all hyperaccumulating Ni, but concentrations of this element above the hyperaccumulation threshold were also found in the genera Bornmuellera and Noccaea (all Brassicaceae), Orobanche (Orobanchaceae), Centaurea (Asteraceae) and Viola (Violaceae). The existence of hyperaccumulators of Tl and Zn is of particular interest because very few species worldwide hyperaccumulate these elements. Multiple metal hyperaccumulation was found in Noccaea kovatsii, as the hyperaccumulation of Zn was found in this species in addition to Ni, the primary accumulated element. Metal hyperaccumulation is discussed in terms of phylogenetic relationships and species distributions, with special attention to their systematics, the detection and recognition of new hyperaccumulating species and the possibilities for their future practical applications in phytotechnologies.

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.

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.

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.

Glass manufacturing operations lead to an increasing number of abandoned slag heaps contaminated with metallic trace elements (MTE). However, the relative influence of edaphic factors on the biodiversity of glasswork wastelands is still poorly understood although closely related to sustainable land management practices. Therefore, the objectives of this research were to provide new insights into glasswork wastelands through the investigation of (i) Orthoptera, diurnal Lepidoptera, plant communities, and (ii) abiotic parameters in the topsoils. To that end, biodiversity indices were computed from ecological inventories performed on the herbaceous layer. In addition, soil samples were taken from the topsoil layer (0-10 cm) to assess agronomic properties, actually (CEC-exchangeable) and potentially bioavailable MTE fractions (DTPA-extractable) and pseudo-total MTE contents. On the one hand, the studied site was able to support a substantially higher than excepted biodiversity with orthopteran assemblages similar to grasslands and a diurnal Lepidoptera diversity comparable to urban parks. We also noted a positive influence of plant richness on the diurnal Lepidoptera community structure. On the other hand, topsoil analysis revealed a severe Pb contamination (1800-3100 mg kg

Background and Aims The aim of this study was to test the frequency distributions of foliar elements from a large dataset from Kinabalu Park (Sabah, Malaysia) for departure from unimodality, indicative of a distinct ecophysiological response associated with hyperaccumulation. Methods We collected foliar samples (n = 1533) comprising 90 families, 198 genera and 495 plant species from ultramafic soils, further foliar samples (n = 177) comprising 45 families, 80 genera and 120 species from non-ultramafic soils and corresponding soil samples (n = 393 from ultramafic soils and n = 66 from non-ultramafic soils) from Kinabalu Park (Sabah, Malaysia). The data were geographically (Kinabalu Park) and edaphically (ultramafic soils) constrained. The inclusion of a relatively high proportion (approx. 14 %) of samples from hyperaccumulator species [with foliar concentrations of aluminium and nickel (Ni) >1000 μg g–1, cobalt, copper, chromium and zinc >300 μg g–1 or manganese (Mn) >10 mg g–1] allowed for hypothesis testing. Key Results Frequency distribution graphs for most elements [calcium (Ca), magnesium (Mg) and phosphorus (P)] were unimodal, although some were skewed left (Mg and Mn). The Ni frequency distribution was bimodal and the separation point for the two modes was between 250 and 850 μg g–1. Conclusions Accounting for statistical probability, the established empirical threshold value (>1000 μg g–1) remains appropriate. The two discrete modes for Ni indicate ecophysiologically distinct behaviour in plants growing in similar soils. This response is in contrast to Mn, which forms the tail of a continuous (approximately log-normal) distribution, suggestive of an extension of normal physiological processes.

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.

Globally, there is a major shift to electric vehicles to combat climate change and these vehicles are currently powered by lithium-ion batteries that contain nickel cobalt manganese oxide materials. This technological change from internal combustion engines means that demand for battery minerals will need to increase by factors of >20 for the critical metals required for batteries in the next three decades. If this scenario plays out, it will require a dramatic increase in the worldwide capacity to produce nickel, manganese, cobalt, and lithium raw materials of sufficient purity. This demand could partly be met by agromining technology, which is a ‘green technology’ that extracts valuable products, including high-purity metal salts useful for the battery industry, from selected plants known as ‘metal crops’. Farming for nickel, cobalt, and manganese is currently within reach, whereas lithium agromining has not yet been developed but has potential. Synopsis: Agromining offers a sustainable approach to economically produce battery-grade raw materials from unconventional sources, thus, producing ‘green technologies’ from ‘green sources’.

International audience; Ultramafic soils are usually marginal in macronutrients (nitrogen (N), phosphorus (P), potassium (K) and calcium (Ca)) for growth of crop plants. Commercial nickel (Ni) agromining is dependent on attaining high yield and high Ni concentration in harvestable biomass of Ni hyperaccumulator species. We previously reported on the biomass responses of two promising tropical ‘metal crops’ (Phyllanthus rufuschaneyi and Rinorea cf. bengalensis) to rates of N, P, and K fertilisers. Calcium, sulphur (S) and organic matter amendments have varied effects on the biomass production and Ni uptake in temperate Ni hyperaccumulator species used in agromining, but the trends in tropical ‘metal crops’ are not reported to-date. We investigated the effects of these amendments on the growth performance and the Ni (and other elements) uptake in P. rufuschaneyi and R. cf. bengalensis The experiments consisted of a large 12-month randomised growth trial in large pots in Sabah (Malaysia) using ultramafic soils under different treatment levels of soluble Ca and S, and organic matter amendments. We found that Ca and S additions had no significant effects on the growth of P. rufuschaneyi and R. cf. bengalensis. Organic matter amendments had strong positive effect on the growth of R. cf. bengalensis (p

International audience; 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.

Ultramafic (i.e. serpentine) soils are widespread in the Balkans and particularly in Albania. They account for a large part of plant endemism in that region and host several hyperaccumulator species, which are characterized by leaf nickel concentrations frequently above 1%. This rich nickel hyperaccumulating flora could serve as candidate to be used in phytoextraction and agromining. Despite recent interest in metal hyperaccumulating plants and agromining, very few studies have investigated the bacterial diversity and the influence of environmental factors on microbial gene profiles in the rhizosphere of hyperaccumulator plants growing on ultramafic soils. Because rhizospheric bacteria could be crucial to the success of phytoremediation, we studied a total of 48 nickel-hyperaccumulating plants which were sampled from four species that are widespread in Albania: Noccaea ochroleuca, Odontarrhena smolikana, O. rigida and O. chalcidica. All samples were taken from the ultramafic regions of Librazhd and Pogradec in eastern Albania in October 2015. Our study shows that Proteobacteria, Actinobacteria and Acidobacteria dominated the soil bacterial communities. Of these three phyla, only Proteobacteria was relatively abundant. This study underlines the influence of soil Cation Exchange Capacity on the bacterial community's diversity and structure. Based on the predicted metagenomes, the genes belonging to amino acid, lipid and carbohydrate metabolisms were identified as major gene families. Our study sheds some light on our understanding of how bacterial communities are structured within and affect the rhizosphere of hyperaccumulator plants from ultramafic soils in Albania.

Purposes To analyze the main edaphic factors that differentiate ultramafic from typical Cerrado environments and act as agents of the development of biochemical and morphological mechanisms of species adaptation to these harsh environments; and to determine the genetic diversity of three Cerrado’s shrubland native species (Justicia lanstyakii, Euploca salicoides, and Oxalis hirsutissima). Methods We conducted chemical analysis of metal contents in soils, as well as on elemental composition, and analysis of DNA extracted from leaf tissues of the three species found in both environments. In leaves of E. salicoides grown in both environments we evaluated the changes in the levels of non-structural carbohydrates (NSC), and total proteins. Results The accessions obtained in ultramafic soils were closer with each other, indicating genetic similarity and major differences in relation to the accessions collected in the Cerrado area. These differentiations probably are related with higher adaptation to soils rich in metals, mainly Ni in ultramafic, and Al in the Cerrado environments. The highest levels of NSC were observed in plants grown in ultramafic soils, including raffinose, which is related to responses to metal detoxification and drought. The allocation of Ni in the trichomes, which does not affect important processes of plant metabolism, is another mechanism developed by E. salicoides to overcome the hyperaccumulation of Ni in their tissues. Conclusions These findings can help select seed collection sites representative of the genetic diversity of native plant species for restoring degraded areas or for phytoremediation of metals.

This article has been accepted for publication in Metalomics Published by Oxford University Press. DOI: 10.1093/mtomcs/mfab045; International audience; Plants have developed a diversity of strategies to take up and store essential metals in order to colonize various types of soils including mineralized soils. Yet, our knowledge of the capacity of plant species to accumulate metals is still fragmentary across the plant kingdom. In this study, we have used the X-Ray Fluorescence technology to analyze metal concentration in a wide diversity of species of the Neotropical flora that was not extensively investigated so far. In total, we screened more than 11 000 specimens representing about 5000 species from herbaria in Paris and Cuba. Our study provides a large overview of the accumulation of metals such as manganese, zinc and nickel in the Neotropical flora. We report 30 new nickel hyperaccumulating species from Cuba, including the first records in the families Connaraceae, Melastomataceae, Polygonaceae, Santalaceae and Urticaceae. We also identified the first species from this region of the world that can be considered as manganese hyperaccumulators in the genera Lomatia (Proteaceae), Calycogonium (Melastomataceae), Ilex (Aquifoliaceae), Morella (Myricaceae) and Pimenta (Myrtaceae). Finally, we report the first zinc hyperaccumulator, Rinorea multivenosa (Violaceae), from the Amazonas region. The identification of species able to accumulate high amounts of metals will become instrumental to support the development of phytotechnologies in order to limit the impact of soil metal pollution in this region of the world.

The aim of this study was to assess the potential of the woody nickel hyperaccumulator species

Initial experiments using Mediterranean Ni-hyperaccumulator plants for the purpose of phytomining were carried out in the 1990s. In order to meet commercial phytoextraction requirements, a technology has been developed using hyperaccumulator species with adapted intensive agronomic practices on naturally Ni-rich soils. Ultramafic soils in the Balkans and other parts of Europe display a great variability in Ni concentrations and available Ni levels. In Albania, Vertisols are currently being used for low-productivity agriculture (pasture or arable land) on which phytomining could be included in cropping practices. In northwestern Greece (Pindus and Vourinos mountain regions), agricultural soils may occur on ultramafic Cambisols. In Spain and Austria, these soils are much more erratically distributed and are seldom used for crops and pastures. In the Balkans, Odontarrhena chalcidica (synonym Alyssum murale) occurs widely on these ultramafic soils and is a spontaneous weed that grows among other crops. Field studies across Europe have now been carried out outside Mediterranean areas and have evaluated the Ni-hyperaccumulator O. chalcidica, as well as two other species native to northwestern Greece (Bornmuellera emarginata and B. tymphaea). At each site, local hyperaccumulator plants were tested for comparison (Noccaea goesingense in Austria and Odontarrhena serpyllifolia s.l. in Spain), in the context of two recent EUfunded projects (by Agronickel and LIFEAgromine). Soil and crop management practices are being developed in order to optimize the Ni agromining process. Field studies have evaluated the potential benefits of fertilization regimes, crop selection, and cropping patterns (introducing agroecological practices), and bioaugmentation using plant-associated microorganisms.

Albanian taxa and populations of the genus Odontarrhena are most promising candidates for research on metal tolerance and Ni-agromining, but their genetic structure remains unknown. We investigated phylogenetic relationships and genetic differentiation in relation to distribution and ploidy of the taxa, anthropic site disturbance, elevation, soil type, and trace metals at each population site. After performing DNA sequencing of selected accessions, we applied DNA-fingerprinting to analyze the genetic structure of 32 populations from ultramafic and non-ultramafic outcrops across Albania. Low sequence divergence resulted in poorly resolved phylograms, but supported affinity between the two diploid serpentine endemics O. moravensis and O. rigida. Analysis of molecular variance (AMOVA) revealed significant population differentiation, but no isolation by distance. Among-population variation was higher in polyploids than in diploids, in which genetic distances were lower. Genetic admixing at population and individual level occurred especially in the polyploids O. chalcidica, O. decipiens, and O. smolikana. Admixing increased with site disturbance. Outlier loci were higher in serpentine populations but decreased along altitude with lower drought and heat stress. Genetic variability gained by gene flow and hybridization at contact zones with “resident” species of primary ultramafic habitats promoted expansion of the tetraploid O. chalcidica across anthropogenic sites.

The discovery of nickel hyperaccumulation, in

International audience; In Albania, ultramafic outcrops cover 11% of the surface and have the potential to support nickel phytomining. In a large-scale in-situ experiment on an ultramafic Vertisols in Pojske we are studying the influence of agronomical practices on Ni phytoextraction yield of Odontarrhena chalcidica (syn. Alyssum murale). Three cropping systems were compared in three plots in 2016-2017; POJ-1 Plot (0.3 ha) was established with plants that had germinated spontaneously without any treatments; POJ-2 plot (0.3 ha) was covered by plants that had germinated spontaneously and was treated with mineral fertilizer (N50P50K50 kg ha(-1)); and POJ-3 Plot (400 m(2)) was divided in four sub plots, where O. chalcidica was planted at a density of 4 plants m(-2) on which, we neither applied fertilizer, nor NPK fertilizer (N65P65K65), pig (FPM; N260:P105:K260 + 15 kg ha(-1)N, P, K) or chicken manure (FCHM; N260:P390:K260 +15 kg ha(-1) N, P, K. Irrigation and mechanical control of weeds was done on POJ-3. After 8 months, shoot Ni concentration, biomass, and Ni yields were higher in O. chalcidica treated with manure and the cost of biomass production was smaller. Nickel yield was more promising (145 kg ha(-1)) than in previous field trials. This study highlights that, using manure, the Ni yield increases Ni phytomining net values, thus agromining can become an economically justifiable agricultural cropping system.

Selenium (Se), a trace element essential for human and animal biological processes, is deficient in many agricultural soils. Some extremely rare plants can naturally accumulate extraordinarily high concentrations of Se. The native legume Neptunia amplexicaulis, endemic to a small area near Richmond and Hughenden in Central Queensland, Australia, is one of the strongest Se hyperaccumulators known on Earth, with foliar concentrations in excess of 4000 μg Se g−1 previously recorded. Here, we report on the Se distribution at a whole plant level using laboratory micro X-ray Fluorescence Microscopy (μXRF) and scanning electron microscopy (SEM-EDS), as well as on chemical forms of Se in various tissues using liquid chromatography-mass spectrometry (LC-MS) and synchrotron X-ray absorption spectroscopy (XAS). The results show that Se occurs in the forms of methyl-selenocysteine and seleno-methionine in the foliar tissues, with up to 13 600 μg Se g−1 total in young leaves. Selenium was found to accumulate primarily in the young leaves, flowers, pods and taproot, with lower concentrations present in the fine-roots and stem and the lowest present in the oldest leaves. Trichomes were not found to accumulate Se. We postulate that Se is (re)distributed in this plant via the phloem from older leaves to newer leaves, using the taproot as the main storage organ. High concentrations of Se in the nodes (pulvini) indicate this structure may play an important a role in Se (re)distribution. The overall pattern of Se distribution was similar in a non-Se tolerant closely related species (Neptunia gracilis), although the prevailing Se concentrations were substantially lower than in N. amplexicaulis.

Background and Aims Hybanthus austrocaledonicus (Violaceae) is a nickel (Ni) hyperaccumulator endemic to New Caledonia. One of the specimens stored at the local herbarium had a strip of bark with a remarkably green phloem tissue attached to the sheet containing over 4 wt% Ni. This study aimed to collect field samples from the original H. austrocaledonicus locality to confirm the nature of the green ‘nickel-rich phloem’ in this taxon and to systematically assess the occurrence of Ni hyperaccumulation in H. austrocaledonicus and Hybanthus caledonicus populations. Methods X-ray fluorescence spectroscopy scanning of all collections of the genus Hybanthus (236 specimens) was undertaken at the Herbarium of New Caledonia to reveal incidences of Ni accumulation in populations of H. austrocaledonicus and H. caledonicus. In parallel, micro-analytical investigations were performed via synchrotron X-ray fluorescence microscopy (XFM) and scanning electron microscopy with X-ray microanalysis (SEM-EDS). Key Results The extensive scanning demonstrated that Ni hyperaccumulation is not a characteristic common to all populations in the endemic Hybanthus species. Synchrotron XFM revealed that Ni was exclusively concentrated in the epidermal cells of the leaf blade and petiole, conforming with the majority of (tropical) Ni hyperaccumulator plants studied to date. SEM-EDS of freeze-dried and frozen-hydrated samples revealed the presence of dense solid deposits in the phloem bundles that contained >8 wt% nickel. Conclusions The occurrence of extremely Ni-rich green phloem tissues appears to be a characteristic feature of tropical Ni hyperaccumulator plants.

The fern

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.

The fern

Low soil fertility in ultramafic soils limits the efficiency of nickel phytoextraction. Developing more efficient cropping systems for agromining can be achieved by the association of a hyperaccumulator with a legume by enhancing soil fertility. However, legume crops can result sensitive to ultramafic soil conditions, including nickel Ni availability. We assessed here whether Lens culinaris is adapted to ultramafic environments by growing on soils displaying a wide range of Ni concentrations and consequently producing functional nodules. The soil was enriched with different Ni concentrations ([Ni]) (0–90 mg Ni kg 1). Natural 15N abundance was used to assess N2 fixation (%Ndfa). Biotic parameters were investigated (nodule number, Ni, carbon and nitrogen concentrations, plant biomass . . . ). Soil parameters were investigated (total [Ni], DTPA-extractable Ni, C and N concentrations . . . ). Most of the physicochemical and biological parameters were significantly affected by the increased soil [Ni]. Nodule numbers per plant was lower under high [Ni] than control (soil without Ni). Nodules lost their capacities to fix N2 under high Ni addition (90 mg Ni kg 1). For many parameters, there were no significant differences between control and treatments up to 60 mg of Ni kg 1 added to the soil. Lentil is able to grow on a soil containing amounts of Ni-DTPA similar to those generally found in serpentine soils. It could be used in association with a hyperaccumulator plant as a nitrogen provider in order to optimize Ni agromining.

On the basis of our previous field survey, we postulate that the pattern and degree of zinc (Zn) isotope fractionation in the Zn hyperaccumulator Noccaea caerulescens (J. & C. Presl) F. K. Mey may reflect a relationship between Zn bioavailability and plant uptake strategies. Here, we investigated Zn isotope discrimination during Zn uptake and translocation in N. caerulescens and in a nonaccumulator Thlaspi arvense L. with a contrasting Zn accumulation ability in response to low (Zn-L) and high (Zn-H) Zn supplies. The average isotope fractionations of the N. caerulescens plant as a whole, relative to solution (Δ(66)Znplant-solution), were -0.06 and -0.12‰ at Zn-L-C and Zn-H-C, respectively, indicative of the predominance of a high-affinity (e.g., ZIP transporter proteins) transport across the root cell membrane. For T. arvense, plants were more enriched in light isotopes under Zn-H-A (Δ(66)Znplant-solution = -0.26‰) than under Zn-L-A and N. caerulescens plants, implying that a low-affinity (e.g., ion channel) transport might begin to function in the nonaccumulating plants when external Zn supply increases. Within the root tissues of both species, the apoplast fractions retained up to 30% of Zn mass under Zn-H. Moreover, the highest δ(66)Zn (0.75‰-0.86‰) was found in tightly bound apoplastic Zn, pointing to the strong sequestration in roots (e.g., binding to high-affinity ligands/precipitation with phosphate) when plants suffer from high Zn stress. During translocation, the magnitude of isotope fractionation was significantly greater at Zn-H (Δ(66)Znroot-shoot = 0.79‰) than at Zn-L, indicating that fractionation mechanisms associated with root-shoot translocation might be identical to the two plant species. Hence, we clearly demonstrated that Zn isotope fractionation could provide insight into the internal sequestration mechanisms of roots when plants respond to low and high Zn supplies.

Phytomining, now called agromining, consists of growing hyperaccumulator plants in orderto farm metals and recover them from the biomass. This technology enables us to extractmetals from secondary resources (e.g. metal containing-soils, mineral wastes, polluted soils)and manufacture high-value products. It has proved feasible for nickel, since more than 400hyperaccumulators have been identified worldwide, able to accumulate at least 1% Ni intheir tissues. Moreover, Ni is a target metal with a relatively high economic value.We have recently designed and patented a method for the synthesis of a nickel salt,ammonium nickel sulfate hexahydrate (ANSH: Ni(NH4)2(SO4)2·6H2O), from the biomass ofthe hyperaccumulator plant Alyssum murale, grown in the Balkans. In this contribution, theprocess has been improved in order to save water, energy and chemicals, while producinga high purity salt. The biomass is dried and ashed, potassium is removed by washing ashwith pure water following a cross-current pathway, nickel is extracted by acid leaching (2 MH2SO4, 95◦C, 2 h, mass fraction of 10%). The leachate is neutralized by Ca(OH)2to reach a pHof 4–5 and magnesium is removed by precipitating MgF2after addition of NaF. Then volumeis reduced by evaporation and ANSH crystallization is run at 2◦C for 4 h. The crystals are dis-solved and a second crystallization is run. The final ANSH was characterized by combinedtechniques (ICP-AES, XRD and gravimetric analysis), and the purity was 99.1 ± 0.2%.

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.

International audience; Nickel (Ni) agromining of ultramafic soils has been proposed as an eco-friendly option for metal recovery, which can also improve the fertility and quality of these low productive soils. The selection of adequate plant species and the analysis of their performance under the different climatic conditions are of interest for optimising the process and evaluating its full viability. A one-year field experiment was carried out to evaluate the viability of the two Ni-hyperaccumulating Mediterranean species, Alyssum murale and Leptoplax emarginata, for agromining purposes in ultramafic soils under a humid-temperate climate. Field plots of 50 m(2) were established and the soil was fertilised with gypsum and inorganic NPK fertilisers prior to cropping. Alyssum murale produced a slightly higher Ni yield than L. emarginata, but Ni bioaccumulation was dependent on the plant phenological stage for both species, being maximal at mid-flowering (4.2 and 3.0 kg Ni ha(-1), respectively). In both species, Ni was mainly stored in the leaves, especially in leaves of vegetative stems, but also in flowers and fruits in the case of L. emarginata. The main contributors to Ni yield of A. murale were flowering stems and their leaves, while for L. emarginata they were flowering stems and fruits. Implementing the agromining system increased soil nutrient availability, and modified microbial community structure and metabolic activity (due to fertilisation and plant root activity). The soil bacterial communities were dominated by Proteobacteria, Actinobacteria, Acidobacteria and Chloroflexi, and the agromining crops modified the relative abundance of some phyla (increasing Proteobacteria, Bacteroidetes and Nitrospirae and reducing Acidobacteria and Planctomycetes). Cultivating A. murale increased the densities of total culturable bacteria, while L. emarginata selected Ni-tolerant bacteria in its rhizosphere. In summary, both species showed great potential for their use in Ni agromining systems, although optimising soil and crop management practices could improve the phytoextraction efficiency. (C) 2018 Elsevier B.V. All rights reserved.

Hyperaccumulator plants have the unique ability to concentrate specific elements in their shoot in concentrations that can be thousands of times greater than in normal plants. Whereas all known zinc hyperaccumulator plants are facultative hyperaccumulators with only populations on metalliferous soils hyperaccumulating zinc (except for Arabidopsis halleri and Noccaea species that hyperaccumulate zinc irrespective of the substrate), the present study discovered that Dichapetalum gelonioides is the only (zinc) hyperaccumulator known to occur exclusively on ‘normal’ soils, while hyperaccumulating zinc. We recorded remarkable foliar zinc concentrations (10 730 µg g−1, dry weight) in Dichapetalum gelonioides subsp. sumatranum growing on ‘normal’ soils with total soil zinc concentrations of only 20 µg g−1. The discovery of zinc hyperaccumulation in this tropical woody plant, especially the extreme zinc concentrations in phloem and phloem-fed tissues (reaching up to 8465 µg g−1), has possible implications for advancing zinc biofortification in Southeast Asia. Furthermore, we report exceptionally high foliar nickel concentrations in D. subsp. tuberculatum (30 260 µg g−1) and >10 wt% nickel in the ash, which can be exploited for agromining. The unusual nickel and zinc accumulation behaviour suggest that Dichapetalum-species may be an attractive model to study hyperaccumulation and hypertolerance of these elements in tropical hyperaccumulator plants.

The technology of agromining has created a new era in the recovery of strategic metals from natural or secondary resources, including industrial wastes. During the last decades, hyperaccumulator plants have changed recognition from merely a botanical curiosity to a prospect having tangible socio-economic and environmental applications. The knowledge base for this group of plant species, with unique properties capable of surviving and thriving in toxic and stressful environments, has increased greatly during the last 20 years, thanks to thorough investigations at various scales involving several disciplines, including botany, ecology, ecophysiology, microbiology, soil science and agronomy. The processes and mechanisms that preside over the hyperaccumulation of toxic metals and metalloids in plants are now better understood. For example, the fate and biopathways of elements in plants is actively being investigated using powerful new explanatory techniques, such as synchrotron and microprobe analysis. In addition, new species having exceptional ability to accumulate metals have been discovered, thereby considerably increasing the number of known hyperaccumulators. In parallel, work conducted by agronomists and soil scientists has allowed the domestication of selected hyperaccumulator species and hence an enabling large-scale implementation of agromining. This approach promotes a new form of agriculture, which could generate income for peoples in developing countries that live on agriculturally mediocre lands, such as those derived from ultramafic bedrock. Finally, the implication of scientific knowledge in the chain, such as chemistry and chemical engineering, and the stimulation of pluri-disciplinary research programs, bring hope to the feasibility of manufacturing specialist products of high industrial interest from agromined bio-ore.

International audience; Globally the discovery of hyperaccumulator plants has been hindered by systematic screening of plant species, and is highly biased towards Ni hyperaccumulators. This is mainly due to the existence of a reagent paper test that is only specific to nickel (based on dimethylglyoxime) such that more than 400 of the approximately 500 known hyperaccumulators species are for Ni. New technical advances now permit massive screening of herbarium specimens using non-destructive, portable X-Ray Fluorescence Spectroscopy (XRF), an approach that has already led to the discovery of numerous hyperaccumulator species new to science. The elemental distribution in selected hyperaccumulator plant tissues can then be further studied using techniques such as desktop or synchrotron micro-XRF, nuclear microprobe (PIXE), scanning/transmission electron microscopy with energy-dispersive spectroscopy (SEM/TEM-EDS), secondary ion mass spectrometry (SIMS) or laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS). The use of histochemical dyes combined with light microscopy further aids in the identification of anatomical and structural features of the studied plant tissues.

International audience; Stable Zn isotope signatures offer a potential tool for tracing Zn uptake and transfer mechanisms within plant-soil systems. Zinc isotopic compositions were determined in the Zn hyperaccumulator Noccaea caerulescens collected at a Zn-contaminated site (Viviez), a serpentine site (Vosges), and a noncontaminated site (Sainte Eulalie) in France. Meanwhile, a Zn-tolerant plant ( Silene vulgaris ) was also collected at Viviez for comparison. While δ(66)Zn was substantially differentiated among N. caerulescens from the three localities, they all exhibited an enrichment in heavy Zn isotopes of 0.40-0.72‰ from soil to root, followed by a depletion in heavy Zn from root to shoot (-0.10 to -0.50‰). The enrichment of heavy Zn in roots is ascribed to the transport systems responsible for Zn absorption into root symplast and root-to-shoot translocation, while the depletion in heavy Zn in shoots is likely to be mediated by a diffusive process and an efficient translocation driven by energy-required transporters (e.g., NcHMA4). The mass balance yielded a bulk Zn isotopic composition between plant and soil (Δ(66)Zn(plant-soil)) of -0.01‰ to 0.63‰ in N. caerulescens , indicative of high- and/or low-affinity transport systems operating in the three ecotypes. In S. vulgaris , however, there was no significant isotope fractionation between whole plant and rhizosphere soil and between root and shoot, suggesting that this species appears to have a particular Zn homeostasis. We confirm that quantifying stable Zn isotopes is useful for understanding Zn accumulation mechanisms in plants.

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(Ni) and IPTSCF(Cd) 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(Ni) = 5.2 +/- 0.9 and IPTSCF(Cd) = 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(Ni) and IPTSCF(Cd) 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.

We investigated the pattern of aluminum (Al) accumulation in leaf tissues of native hyperaccumulator Vochysiaceae species Qualea grandiflora, Callisthene major, and Vochysia pyramidalis, from the Brazilian Cerrado. Non-accumulator Sclerolobium paniculatum was used as a control species. We expected a strong compartmentalization of Al in non-active leaf cell compartments such as cell walls and vacuoles in Al-accumulating species and the absence of Al in critical metabolic sites such as the chloroplasts. Plant leaves were harvested in the field and cut in small segments for histological analysis; hematoxylin dye was used for Al localization in tissues. Results of soil analysis of the three sites and the concentration of Al in leaves indicated that there is no direct relationship between Al availability in soils and Al hyperaccumulation among the Vochysiaceae species evaluated. The cross-sections of leaf tissues showed hematoxylin color in the palisade and spongy parenchyma cells (chloroplast) of Q. grandiflora and C. major. The vascular system of Q grandiflora was not colored, but some cells from the xylem region of C. major were stained. In contrast, the adaxial and abaxial epidermal cells of V. pyramidalis were colored by hematoxylin, as were some cells from the vascular bundle, but color formation was not observed in the cells of palisade parenchyma. Al was not detected in leaves of S. paniculatum. We concluded that, although hyperaccumulation of Al is a common trait in the Vochysiaceae family, the processes of storage and detoxification in leaf tissues differ among the species. Two of the three hyperaccumulator species use chloroplasts as a sink for Al, with no apparent signs of toxicity. Therefore, the physiological role of Al in plant tissues remains to be elucidated. (C) 2010 Elsevier B.V. All rights reserved.

The article Nickel hyperaccumulation in Antidesma montis-silam: from herbarium discovery to collection in the native habitat, written by Philip Nti Nkrumah, Guillaume Echevarria, Peter Damian Erskine, Antony van der Ent, was originally published electronically on the publisher's internet portal (currently SpringerLink) on 08 December 2017 without open access.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; Ultramafic soils are widespread in the Balkans. Albania and Greece are the richest in the number of endemics, including several hyperaccumulator species, growing on serpentine. The objectives of this study were to understand the potential of Ni hyperaccumulation of these species in close relation with the characteristics of their native soil environments. Collection of both plant samples (analysis of element concentrations in aerial parts) and soil samples (analysis of total elements, DTPA-extractable Ni, Fe, and Ni distribution in mineral phases) allowed evaluation of phenotypic efficacy in hyperaccumulating Ni. Nickel availability in soils is controlled by soil weathering and mineral-bearing phases. Unsurprisingly, the highest levels of Ni availability were associated with amorphous Fe-oxides in moderately weathered Cambisols or with high-exchange capacity clays in well-evolved Vertisols. The highest Ni concentrations in leaves were found in Alyssum murale in Pojska (Albania; 2.0%), Alyssum markgrafii in Gjegjan (Albania; 1.9%), Bornmuellera baldacii subsp. markgrafii in Gramsh (Albania; 1.4%), and Leptoplax emarginata in Trigona (Greece; 1.4%). We identified a new member in the Albanian Ni-hyperaccumulator flora: Thlaspi ochroleucum in Pojska (Albania: 0.13% Ni) and in Pishkash (0.14% Ni). With regard to Ni availability in soils, A. markgrafii (Albania) is the most efficient Ni-hyperaccumulator among all species. Alyssum murale, which is widespread in the serpentines of the Balkans, accumulates Ni, with leaf concentration being negatively correlated to total Ca content of soils regardless of Ni availability (DTPA extractable Ni). If this relationship is confirmed, it would mean that genetic variability is not the main factor that explains the hyperaccumulation performance of this species.

We have investigated the accumulation of nickel in a hyperaccumulating plant from the Brassicacae family Leptoplax emarginata (Boiss.) O.E. Schulz. Two supplementary hyperaccumulating plants, which have been the subject of a high number of publications, Alyssum murale Waldst. & Kit and Thlaspi caerulescens J.&C. Presl, and a nonaccumulating species Aurinia saxatilis were also studied for reference. The plants were grown during 4 months in specific rhizoboxes with Ni-bearing minerals as a source of nickel. Nickel speciation was analyzed through X-ray absorption spectroscopy at Ni K-edge (X-ray absorption near edge spectroscopy and extended X-ray absorption fine structure spectroscopy) in the different parts of the plants (leaves, stems and roots) and compared with aqueous solutions containing different organo-Ni(II) complexes. Carboxylic acids (citrate, malate) appeared as the main ligands responsible of nickel transfer within those plants. Citrate was found as the predominant ligand for Ni in stems of Leptoplax and Alyssum, whereas in leaves of the three plants, malate appeared as the chelating organic acid of accumulated metal. Histidine could not be detected either in leaves, stems nor roots of any studied plant sample.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; Knowledge of radionuclide or trace element retention and translocation to plants following an aerial contamination event, for example, sprinkling with contaminated water, is necessary for the evaluation of human exposure through consumption of contaminated vegetables. The fate of 63Ni and 109Cd in all plant parts of three different vegetables after wet deposition on leaves or on fruits was studied. Lettuce (Lactuca sativa L.), radish (Raphanus sativus L.), and bean (Phaseolus vulgaris L.) grown under controlled conditions in a growth chamber were contaminated with 63Ni and 109Cd either on leaves, by means of two different contamination methods (a single early contamination and a repetitive one), or on bean husks (third contamination method: a single contamination at a late stage). Spiked and nonspiked organs were harvested at maturity and radionuclide contents were measured. The fraction retained was on average 56% of the initially administered doses of 63Ni and 87% of 109Cd. The leaf-to-other organ translocation factor was considerably higher for 63Ni (on average 43% of retained radioactivity) than for 109Cd (8%). Nickel-63 migrated throughout the whole plant following foliar contamination, and mainly toward young leaves, seeds in formation, and sink organs, whereas 109Cd migrated to a much lesser extent and only to the organs that were closest to the spiked one, and not at all into fruit. After a fruit contamination event, both radionuclides were translocated into the seeds of spiked fruits. Radionuclide retention and translocation were not affected by plant species, but principally by the type of organ contaminated.

Iodine-129 is a radionuclide of major concern in the international safety assessments for deep geological storage and disposal of nuclear waste because it migrates quickly through the geosphere to the biosphere and then from the soil to humans through the food-chain. However, in organic soils the 129 I may be immobilized over a long time period, and so these soils represent a potential accumulation point in the biosphere. Effects of long residence times of iodine in soils are scarce. The present paper gives some insight on the aging of stable iodine under natural conditions. Stable iodine was introduced as KI in 1987 at the base of a sphagnum bog to simulate arrival of iodine via a groundwater discharge from the geosphere. Fifteen years later, the groundwater, the soil and the vegetation have been sampled and analysed for iodine. The results we present give insight on the mobility of "aged" iodine, the retention properties of the peat, and provide iodine transfer factors for native boreal plant species. This study demonstrates bogs present good sinks for iodine and limit the transfer of iodine to some of the "wildlife" food-chains.

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.

International audience; Until now, there has been little data on the isotope fractionation of nickel (Ni) in higher plants and how this can be affected by plant Ni and zinc (Zn) homeostasis. A hydroponic cultivation was conducted to investigate the isotope fractionation of Ni and Zn during plant uptake and translocation processes. The nonaccumulator Thlaspi arvense, the Ni hyperaccumulator Alyssum murale and the Ni and Zn hyperaccumulator Noccaea caerulescens were grown in low (2 μM) and high (50 μM) Ni and Zn solutions. Results showed that plants were inclined to absorb light Ni isotopes, presumably due to the functioning of low-affinity transport systems across root cell membrane. The Ni isotope fractionation between plant and solution was greater in the hyperaccumulators grown in low Zn treatments (Δ(60)Ni(plant-solution) = -0.90 to -0.63‰) than that in the nonaccumulator T. arvense (Δ(60)Ni(plant-solution) = -0.21‰), thus indicating a greater permeability of the low-affinity transport system in hyperaccumulators. Light isotope enrichment of Zn was observed in most of the plants (Δ(66)Zn(plant-solution) = -0.23 to -0.10‰), but to a lesser extent than for Ni. The rapid uptake of Zn on the root surfaces caused concentration gradients, which induced ion diffusion in the rhizosphere and could result in light Zn isotope enrichment in the hyperaccumulator N. caerulescens. In high Zn treatment, Zn could compete with Ni during the uptake process, which reduced Ni concentration in plants and decreased the extent of Ni isotope fractionation (Δ(60)Ni(plant-solution) = -0.11 to -0.07‰), indicating that plants might take up Ni through a low-affinity transport system of Zn. We propose that isotope composition analysis for transition elements could become an empirical tool to study plant physiological processes.

Ni recovery from serpentine soils by phytomining has proved feasible. Phytomining involves the crop of hyperaccumulating plants with high Ni contents and the valorization of Ni by pyro or hydrometallurgical process. In order to evaluate the Ni content of different plants, we analyzed the organs of 14 hyperaccumulators from three genera: Alyssum, Leptoplax and Bornmuellera. The highest concentration was recorded in the leaves of Leptoplax (34.3 ± 0.7 mg g−1DM). Additionally, we investigated biomass combustion which is the first step of the process we designed to obtain a nickel salt. We showed that temperature and duration were important parameters to ensure a good quality of ashes. At the bench scale, the best conditions were 550°C and 3 h. In this way, we obtained ashes in which Ni could reach 20 wt%. Biomass ashes can be considered as a bio-ore for recovering metal value.

Solute active transport or exclusion by plants can be identified by the values of the Transpiration Stream Concentration Factor (TSCF=xylem:solution solute concentration ratio). The aim of this study was to estimate this parameter for Ni uptake by the Ni-hyperaccumulator Leptoplax emarginata or the Ni-excluder Triticum aestivum cultivar 'Fidel'. The Intact Plant TSCF for nickel (IPTSCF(Ni)) was calculated as the ratio between the nickel mass accumulation in the leaves and the nickel concentration in solution per volume of water transpired. Predominantly, Ni active transport occurred for L. emarginata, with IPTSCF(Ni) values of 4.7-7.2 and convective component proportions of the root Ni uptake flow of only 15-20% for a range of Ni concentrations in solutions of 2-16 µmol Ni l(-1), regardless of the growth period and the time of Ni uptake. Hyperaccumulator roots were permeable to both water and nickel (mean reflection coefficient for Ni, σ(Ni), of 0.06), which was mainly attributed to an absence of exodermis. Results provide a new view of the mechanisms of Ni hyperaccumulation. By contrast, the wheat excluder was characterized by an extremely low mean IPTSCF(Ni) value of 0.006, characterizing a predominantly Ni sequestration in roots. From a methodological viewpoint, the 'microscopic' TSCF(Ni), measured directly on excised plants was 2.4 times larger than its recommended 'macroscopic' IPTSCF(Ni) counterpart. Overall, IPTSCF and σ determined on intact transpiring plants appeared to be very useful biophysical parameters in the study of the mechanisms involved in metal uptake and accumulation by plants, and in their modelling.

Leaves of plants have the ability to accumulate the long-lived fission product (99)Tc. In the present work, an attempt was made to separate and characterize technetium species formed in maize grown on soil contaminated with Tc(VII)O(4)(-) solution. Data obtained from selective extraction, a Phosphorimager and liquid scintillation were employed.

International audience; Isotopic dilution techniques were initially used to evaluate the bioavailability of trace metals contained in soils to plants, i.e., the phytoavailability. Here, we use for the first time an isotopic technique to evaluate the zooavailability of cadmium (Cd), i.e., the bioavailability to an animal organism. A terrestrial invertebrate, the snail Helix aspersa, was exposed for 14 days to a polluted soil that was spiked with 109Cd. Isotopic composition of snail tissues was then determined, allowing the computing of the L value, which can be considered as a biological estimate of the bioavailable Cd pool in the soil. It showed that the bioavailable pool of Cd to H. aspersa represented 58% of the total soil Cd. The Evalue, a chemical estimate of the soil Cd labile pool, was calculated with short-term isotopic exchange kinetics experiments and a time-dependent model describing the isotopic exchange over time. The E(14 days) value indicated that the labile soil Cd pool represented 49.6% of the total soil Cd. The L value was significantly higher than the E value, showing that snails accessed the nonlabile soil Cd pool, generally considered as nonbioavailable. The nonlabile pool contributed for 16% to the total Cd accumulated by snails. These results showed that the uptake of Cd in the nonlabile pool by soil organisms could be important and should be considered in risk assessment procedures for metal polluted soils.

Since 1991, researchers from approximately 45 nations have participated in eight International Conferences on Serpentine Ecology (ICSE). The Conferences are coordinated by the International Serpentine Ecology Society (ISES), a formal research society whose members study geological, pedological, biological and applied aspects of ultramafic (serpentine) ecosystems worldwide. These conferences have provided an international forum to discuss and synthesise multidisciplinary research, and have provided opportunities for scientists in distinct fields and from different regions of the world to conduct collaborative and interdisciplinary research. The 8th ICSE was hosted by Sabah Parks in Malaysia, on the island of Borneo, and attracted the largest delegation to date, 174 participants from 31 countries. This was the first time an ICSE was held in Asia, a region that hosts some of the world’s most biodiverse ultramafic ecosystems. The presentations provided a cross-section of the current status of research in all aspects of ultramafic-biota relations. In this Special Issue of Australian Journal of Botany (Issues 1–2 combined and 3–4 combined), we have compiled a selection of papers from among the oral and poster presentations to provide insights into recent advances in geoecological and applied studies of ultramafic habitats worldwide. Here we provide a preview of select papers found in this Special Issue and summarise some of the contributions made during the 8th ICSE and describe some of the exciting challenges awaiting future research.

International audience; The efficiency of nickel (Ni) phytoextraction by hyperaccumulating Brassicaceae was compared in two types of covers, namely, monoculture or mixed culture. The selected species were from the Pindus Mountains (Greece), including Alyssum murale, Noccaea tymphaea, Leptoplax emarginata and Bornmuellera tymphaea. After 4 months of culture in mesocosms using ultramafic soil (Ni=1480mgkg(-1)), plant biomass yield and Ni concentrations in shoots and roots were recorded for each of six treatments (mixed-culture cover, four monoculture covers and unplanted soil). Microbial biomass carbon, the size of the cultivable rhizosphere bacterial community and its phenotypic structure (Biolog EcoPlates), bacterial and fungal genetic structure (SSCP), as well as the potential production of auxin compounds, were also evaluated. Moreover, measurements of various microbial enzymes were performed. The biomass and shoot Ni concentration (albeit not significant) of B. tymphaea increased in co-cropping system. A slight acidification of the soil occurred and a strong correlation between pH and the size of the bacterial community was also observed. No significant change in enzyme activity was observed among the cover types, except in the case of arylsulfatase. The phenotypic structure of the bacterial communities and the bacterial and fungal genetic structures appeared to be specific to the type of cover, although the size of the culturable bacterial community did not show variation among treatments. Therefore, on the basis of the bioaccumulation coefficient and the translocation factor, our results showed that B. tympheae, and to a lesser extent N. tympheae, were the two species with the greatest Ni phytoextraction potential in co-culture systems.