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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.

International audience; 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’.

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.

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.

International audience; 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.

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.

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.

Aims Agromining aims to improve the fertility of naturally metal-rich soils by extracting metals, such as nickel (Ni), using hyperaccumulator plants. Ultramafic soils are characterized by low fertility levels, limiting hyperaccumulator yields. Here, we characterize the potential benefits for phytoextraction efficiency of cocropping a Ni-hyperaccumulator (Odontarrhena chalcidica) and a legume (Vicia sativa), following a two-year field experiment. Methods A two-year field experiment was set up in an ultramafic zone in North-West Spain. Three treatments were tested: co-cropping, fertilized control with ammonium nitrate and non-fertilized control. Results Over the 2 years, co-cropping increased O. chalcidica’s biomass by 24% and 403% compared to fertilized and non-fertilized controls, respectively. Moreover, co-cropping had higher Ni-yields for both years, while fertilization had a negative effect on soil parameters. A non-metric multidimensional scaling analysis of the operational taxonomic units showed that the soil bacterial diversity changed over time. Soil exchangeable Ni and organic carbon influenced the phyla’s relative abundance. Metabolic genes were dominant and their relative abundances increased over time with co-cropping. Conclus i o n Pluriannua l co-cropping of a hyperaccumulator with a legume improved both hyperaccumulator and Ni yields. In contrast, mineral fertilization was shown to be detrimental to some soil microbial parameters. Thus, ameliorating agromining by replacing mineral fertilizers would combine an eco-efficient strategy with sustainable metal recovery., This work was supported by French National Research Agency through the national “Investissements d’avenir” program, reference ANR-10-LABX- 21 - LABEX RESSOURCES21, through the “Agromine” project, reference ANR-14-CE04-0005, through the European ERA-net FACCE_SURPLUS project “AGRONICKEL: Developing Ni agromining on ultramafic land in Europe”, reference ANR-15- SUSF-0003-05, through the “Application of Nickel hyperaccumulating plants in phytomining processes” program, reference I-LINK0900 and the LIFE Environment and Resource Efficiency Programme (Life Agromine; LIFE15 ENV/FR/ 000512).

The rare phenomenon of plant manganese (Mn) hyperaccumulation within the Australian flora has previously been detected in the field, which suggested that the tree genus Gossia (Myrtaceae) might contain new Mn hyperaccumulators. We conducted the first growth experiment on Gossia using a multi-factorial dosing trial to assess Mn, cobalt (Co), and zinc (Zn) (hyper)accumulation patterns in selected Gossia species (G. fragrantissima and G. punctata) after a systematic assessment of elemental profiles on all holdings of the genus Gossia at the Queensland Herbarium using handheld X-ray fluorescence spectroscopy. We then conducted detailed in situ analyses of the elemental distribution of Mn, Co, Zn and other elements at the macro (organ) and micro (cellular) levels with laboratory- and synchrotron-based X-ray fluorescence microscopy (XFM). Gossia pubiflora and Gossia hillii were newly discovered to be Mn hyperaccumulator plants. In the dosing trial, G. fragrantissima accumulated 17 400 µg g−1 Mn, 545 µg g−1 Co, and 13 000 µg g−1 Zn, without signs of toxicity. The laboratory-based XFM revealed distinct patterns of accumulation of Co, Mn, and Zn in G. fragrantissima, while the synchrotron XFM showed their localization in foliar epidermal cells, and in the cortex and phloem cells of roots. This study combined novel analytical approaches with controlled experimentation to examine metal hyperaccumulation in slow-growing tropical woody species, thereby enabling insight into the phenomenon not possible through field studies.

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.

International audience; The hyperaccumulator Pycnandra acuminata is a New Caledonian rainforest tree known to have the highest concentration of nickel in any living organism with 25 wt% in its latex. All trees (with diameter >10 cm) and soil profiles in a 0.25-hectare permanent plot were sampled to assess the biogeochemical compartmentalisation of nickel in a dense stand of Pycnandra acuminata trees. Nickel stable isotope analysis permitted insights into the cycling of nickel in this ecosystem. The total tree biomass of the plot was ~281 tonnes ha-1, approximately 0.44 kg of cobalt, 49.1 kg of manganese, 257 kg of nickel and 6.76 kg of zinc. Nickel stable isotope analysis identified the biotic origin of the nickel in the soil upper layers with P. acuminata shoots enriched in lighter nickel isotopes. The δ60Ni latex signature suggests that long-distance transport, radial xylem and phloem loading are at play in Pycnandra acuminata.

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.

International audience; 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.

New Caledonia is a global biodiversity hotspot known for its metal hyperaccumulator plants. X-ray fluorescence technology (XRF) has enabled non-destructive and quantitative determination of elemental concentrations in herbarium specimens from the ultramafic flora of the island. Specimens belonging to six major hyperaccumulator families (Cunoniaceae, Phyllanthaceae, Salicaceae, Sapotaceae, Oncothecaceae and Violaceae) and one to four specimens per species of the remaining ultramafic taxa in the herbarium were measured. XRF scanning included a total of c. 11 200 specimens from 35 orders, 96 families, 281 genera and 1484 species (1620 taxa) and covered 88.5% of the ultramafic flora. The study revealed the existence of 99 nickel hyperaccumulator taxa (65 known previously), 74 manganese hyperaccumulator taxa (11 known previously), eight cobalt hyperaccumulator taxa (two known previously) and four zinc hyperaccumulator taxa (none known previously). These results offer new insights into the phylogenetic diversity of hyperaccumulators in New Caledonia. The greatest diversity of nickel hyperaccumulators occur in a few major clades (Malphigiales and Oxalidales) and families (Phyllanthaceae, Salicaceae, Cunoniaceae). In contrast, manganese hyperaccumulation is phylogenetically scattered in the New Caledonian flora.

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 &ldquo, resident&rdquo, species of primary ultramafic habitats promoted expansion of the tetraploid O. chalcidica across anthropogenic sites.

The Island of Borneo is a major biodiversity hotspot, and in the Malaysian state of Sabah, ultramafic soils are extensive and home to more than 31 endemic nickel hyperaccumulator plants. The aim of this study was to characterize the structure and the diversity of the rhizosphere bacterial communities of several of these nickel hyperaccumulator plants and factors that affect these bacterial communities in Sabah. The most abundant phyla were Proteobacteria, Acidobacteria and Actinobacteria. At family level, Burkholderiaceae and Xanthobacteraceae (Proteobacteria phylum) were the most abundant families in the hyperaccumulator rhizospheres. Redundancy analysis based on soil chemical analyses and relative abundances of the major bacterial phyla showed that abiotic factors of the studied sites drove the bacterial diversity. For all R. aff. bengalensis rhizosphere soil samples, irrespective of studied site, the bacterial diversity was similar. Moreover, the Saprospiraceae family showed a high representativeness in the R. aff. bengalensis rhizosphere soils and was linked with the nickel availability in soils. The ability of R. aff. bengalensis to concentrate nickel in its rhizosphere appears to be the major factor driving the rhizobacterial community diversity unlike for other hyperaccumulator species.

International audience; Hyperaccumulator plants have the ability to efficiently concentrate metallic elements, e.g. nickel, from low-grade sources into their living biomass. Although the majority of nickel hyperaccumulator plant species restrict cobalt uptake, some species are able to co-accumulate cobalt when growing in ultramafic soils. The asteraceous perennial herb Berkheya coddii from South Africa is one of the most promising agromining crops known globally. It may accumulate nickel in excess of 30 000 mg g À1 in dry leaves, while co-accumulating up to 600 mg g À1 cobalt. This study aimed to elucidate the interactions between nickel and cobalt for uptake by and translocation into B. coddii through a pot experiment including various cobalt/nickel treatment combinations in soil, after which uptake and localisation were recorded. Cobalt in the substrate limits nickel uptake by B. coddii plants and is mainly retained in the basal leaves in contrast to Ni that is rapidly transferred to the top of the plant. B. coddii was more tolerant to high Ni concentration, whether in the substrate or internally but remains a promising crop which could be used, with suitable agronomic measures and practices, for cobalt agromining in areas with high soil cobalt but low soil nickel. A yield of 77 kg ha À1 nickel and 16.5 kg ha À1 cobalt may be attainable under optimum conditions. Significance to metallomics The hyperaccumulator plant Berkheya coddii from South Africa is one of the most promising 'agromining crops' known globally. This article reports on the interactions between cobalt and nickel for uptake and translocation in this species. Cobalt in the substrate inhibits nickel uptake in plants, and while nickel is rapidly transferred to the top of the plant, cobalt is mainly retained in the basal leaves.

International audience; AimsThis 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).MethodsThree 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.ResultsThe 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.ConclusionsNickel 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.

International audience; Agromining is an emerging technology that utilizes selected ‘metal crops' (= hyperaccumulator plants) to extract valuable target metals from unconventional resources for profit from mineralised soils. Growth characteristics, shoot metal concentrations, and agrominable locations are important considerations in economic agromining. Globally, the greatest potential for nickel (Ni) agromining exists in the tropics. However, the agronomic systems of tropical ‘metal crops' have not been previously tested. Furthermore, it is currently unknown whether nutrient dosing of prospective tropical agromining Ni ‘metal crops’ could possibly cause a shoot Ni‐dilution effect which may ultimately limit economically viable Ni yields. We undertook a pioneering study on Ni uptake and growth responses to nutrient dosing in two promising tropical ‘metal crops' (Phyllanthus rufuschaneyi and Rinorea cf. bengalensis). The experiment consisted of a large randomised block growth trial in large pots over 12 months in Sabah (Malaysia). At 3‐month intervals, the plants were exposed to soluble treatments that altered available concentrations of nitrogen (N), phosphorus (P), and potassium (K). We found strong positive growth responses to N and P additions in P. rufuschaneyi, whereas K additions had negative growth effects. In R. cf. bengalensis, all treatments had positive growth effects. The increases in biomass in response to nutrient dosing did not significantly reduce shoot Ni concentrations in both species, with the exception of N addition in P. rufuschaneyi. This study reveals that Ni uptake and growth responses to nutrient dosing are species‐dependent, primarily influenced by the ecophysiology of the species. Inorganic fertilization could possibly be an important component of the management of local ‘metal crops' to be used in viable commercial agromining in the tropics, but this needs to be tested in the field with different formulations of N, P, and K.

Sabah (Malaysia) on the Island of Borneo has a high plant diversity (>8000 species) occurring on a wide range of soils, including ultramafic soils which are known to host hyperaccumulator plants. In this study a new approach (“Herbarium X-ray Fluorescence Ionomics”) was used to obtain elemental data from herbarium specimens using non-destructive X-ray Fluorescence spectroscopy analysis. In total ~7300 specimens were thus analysed for nickel, cobalt, and manganese concentrations at the Herbarium of the Forest Research Centre (FRC) in Sepilok, Sabah. The measurements led to recording a total of 759 specimens (originating from 17 families in 30 genera and 74 species) as trace element hyperaccumulators, including 28 nickel hyperaccumulator species (in 10 families, 17 genera), 12 cobalt hyperaccumulator species (in 3 families, 7 genera), and 51 manganese hyperaccumulator species (in 12 families, 24 genera). The outcomes of this research demonstrate that X-ray Fluorescence scanning is highly useful approach for hyperaccumulator plant discovery in herbarium collections that has the potential to add vast numbers of hyperaccumulating taxa to the global inventory.

Cette etude s’inscrit dans un projet de recherche portant sur l’evaluation des impacts environnementaux et sanitaires de l’orpaillage dans la zone de Komabangou au Niger. L’objectif est de determiner les niveaux de contamination des elements traces dans les sols et d'analyser leur distribution spatiale. Des echantillons des sols ont ete preleves en 2016 dans 27 localites dont 24 sur differents sites de la zone aurifere de Komabangou et 3 sur sites temoins. Les concentrations en elements traces (As, Cd, Co, Cr, Cu, Ni, Pb et Zn) dans les sols ont ete determinees par spectrometrie de masse avec plasma a couplage inductif (ICP-MS). La pollution des sols a ete evaluee en calculant les index de pollution (IP) des sols. Les resultats montrent que les concentrations en elements traces metalliques (ETM) dans les sols different en fonction du site et du metal considere. Les cartes de repartition spatiale montrent une importante concentration des elements traces tels que As, Cd, Pb et Zn au centre de la zone aurifere. Plusieurs de ces teneurs en ETM sont superieures aux seuils reglementaires. Aussi sur les 27 sites etudies, 12 ont des valeurs d’IP superieures a 1 revelant ainsi une contamination des sols par plusieurs elements. Ces resultats montrent une accumulation des metaux dans les sols qui peuvent persister dans l’environnement. Cela peut poser de serieux risques sanitaires pour l’Homme. Pour prevenir tout risque, un plan de surveillance de la contamination des sols devrait etre mis en place et il faudrait envisager de traiter les sites pollues. © 2019 International Formulae Group. All rights reserved. Mots cles : Orpaillage, sols, contamination, elements traces metalliques, valeurs limites, Komabangou, Niger. English Title : Spatial distribution of metallic trace elements in soils of Komabangou gold zone in Niger This study is part of research project on environmental and health impacts of gold mining in Komabangou area of Niger. The objective is to determine pollution levels of trace elements in soils and to analyze their spatial distribution. Soil samples were collected in 2016 at 27 localities, including 24 at different sites in Komabangou gold zone and 3 at control sites. Concentrations of trace elements (As, Cd, Co, Cr, Cu, Ni, Pb and Zn) in soils were determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Soil pollution was assessed by calculating soil pollution index (PI). The results show that metal trace element concentrations in soils differ depending to the site and the metal. Spatial distribution maps show a high concentration of trace elements such as As, Cd, Pb and Zn in the center of the gold zone. Many concentrations of trace elements in soils are above regulatory thresholds. Also, of the 27 sites studied, 12 have PI values greater than 1, revealing soil contamination by several elements. These results show an accumulation of metals in soils, which can persist in the environment. This can pose serious health risks for humans. To prevent any risk, soil contamination monitoring plan should be put in place and consideration should be given to treating polluted sites. Keywords : Gold panning, soils, contamination, trace elements, limit values, Komabangou, Niger.

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.

Agromining is the chain of processes of phytoextraction of economically valuable elements by selected hyperaccumulator plants, and subsequent processing of biomass to produce targeted metals or commercial compounds of high value. Although substantial unrealized opportunities exist for developing economic nickel (Ni) agromining in the tropics, this technology has remained relatively unexplored. This study investigated the soil chemistry of a newly established tropical ‘metal farm’ and elucidated the performance of a prospective ‘metal crop’ species (Phyllanthus rufuschaneyi) to be used in a large-scale tropical Ni agromining program on ultramafic soils in Sabah (Malaysia). We found that a major portion of the site (>90%) had high total Ni concentrations (>2000 μg g−1) in the soil (shallow Eutric Cambisol Magnesic). This study also recorded high phytoavailable soil Ni concentrations in the field site, which is a desired property of soils intended for Ni agromining. Moreover, the average soil pH of the field (pH 6.4) is ideal for maximum Ni uptake in the local candidate species. We recorded low concentrations of Ca, K and P, suggesting the need for a fertilizer regime in the farm. The extraordinary shoot Ni concentrations (>2 wt%), coupled with the high purity of the ‘bio-ore’ derived from Phyllanthus rufuschaneyi, confirm its high potential for economic Ni agromining. The success of our first field trial is critical to provide ‘real-life’ evidence of the value of large-scale tropical ‘metal farming’. Research priorities include the need to intensify the search for candidate species, determine their agronomy, develop mass propagation methods, and to test technologies to process the biomass to recover valuable products.

International audience; Surface mining or other disturbing operations on ultramafic outcrops degrade soil conditions and decrease major ecosystem functions in those habitats. Human disturbances exacerbate the harsh conditions of some ultramafic soils, making recovery more difficult. Recovery of ecosystem functions of disturbed areas may vary from passive to active reclamation measures, depending on the starting situation, available resources and expected outcomes. In this study, three treatments (topsoil application, topsoil + non-compacted, and topsoil + non-compacted + organic amendment), representing a gradient of increasing reclamation effort, were tested for the reclamation of a tropical ultramafic Spolic Technosol in Sabah (Malaysia). Soil treatments were tested at the mesocosm-scale for 12 months, and drainage water fluxes, evolution of soil physicochemical parameters, soil microbial activities and spontaneous plant colonisation, diversity and growth were monitored along the duration of the experiment. The results show that application of topsoil improved the plant biomass and water filtration functions in the non-reclaimed sites, with no additional benefit from lesser compaction. The most intensive treatment (topsoil + non-compacted + organic amendment) gave the best improvements in nutrient cycling and biomass production functions, but with a reduction of water filtration function, due to an increase in soluble concentrations and cumulative fluxes of nickel. Introduced species were dominant in the vegetation colonising the mesocosms, and therefore planting of selected native species will be necessary to create habitats for native biodiversity. This information will be useful to select a strategy for the recovery of degraded tropical serpentinite quarries and dump sites.

Soils derived from ultramafic bedrock are known for hosting distinct vegetation types as a consequence of atypical soil chemistries consisting of high trace elements concentrations (Ni, Cr, Co) and exchangeable cation imbalances (high Mg:Ca quotients); the high Mg:Ca ratio causes Ca infertility in plant species not adapted to ultramafic soils. Ecological studies use a range of single-stage extraction methods for chemical characterization of such soils in order to be able to interpret plant response, and ultimately to explain plant community composition. Few studies to date have compared different soil extraction methods in relation to tropical ultramafic soils. This study compares eight commonly used extraction methods on a large number of ultramafic soil samples collected from Kinabalu Park (Malaysia). The tested methods were: for trace elements: NH4Ac, DTPA, CaCl2, Sr(NO3)2 and Mehlich-3, for exchangeable cations: NH4Ac and silverthiorea, and for plant-available phosphorus: Mehlich-3 and Olsen-P. These single-stage extraction methods were compared and evaluated for predictive power for chemically characterizing soils, interrelatedness and ecological application. The methods were also contrasted with a sequential extraction scheme. Finally, several operational parameters including molar ratio (0.01 and 0.1 M CaCl2, Sr(NO3)2) and pH buffering (DTPA-TEA) were also evaluated. The majority of single-stage extraction methods are highly inter-correlated and predictive power could be improved by including independent soil parameters (pH, CEC, pseudo-total element concentration) in the multivariate regression equation. Ecological interpretation remains difficult because of lack of experimental studies in relation to plant uptake response and potential phytotoxicity effects on tropical native plants from ultramafic soils.

In Galicia (NW Spain), ultramafic outcrops represent approximately 5% of the land surface and several mining and quarrying activities take place in these areas. Resulting mine-soils present physical, chemical and biological properties which limit plant growth and soil functioning. Nickel phytomining, an eco-friendly strategy for metal recovery, could potentially be applied to these areas. A one-year field experiment was carried out in a serpentine quarry to evaluate the performance of four Ni hyperaccumulating plant species, comparing the Mediterranean spp. Bornmuellera emarginata and Odontarrhena muralis with the native populations of Noccaea caerulescens and Odontarrhena serpyllifolia. Field plots were established and amended with inorganic NPK fertilisers or composted sewage sludge. Three replicate plots (4 m2) were planted for each plant species and fertilisation regime. Amending with compost reduced pH from 7.8 to 6.6, and increased soil cation exchange capacity (CEC), nutrient concentrations and Ni availability. Moreover, compost-amended mine-soil presented higher microbial density and activity, parameters which were further stimulated by plant growth. Plant biomass production of all plant species was significantly higher in compost-amended soils than that after NPK fertilisation, being most pronounced for O. muralis and B. emarginata. Despite the reduction in shoot Ni concentrations observed in plants (except O. muralis) grown in compost-amended plots, the increased biomass production led to significantly higher Ni yields (in kg ha−1) in B. emarginata (2.9), N. caerulescens (1.9) and O. muralis (2.3). All plant species were able to establish and grow in the mine-soil (with the Mediterranean species showing a higher capacity for adaptation) and to generate moderate Ni yields. Nonetheless, the results highlight the need for further optimisation in order to enhance the Ni phytoextraction efficiency. Finally, the improvement in soil quality after compost amendment and plant growth support the idea that phytomining systems can be effective approaches for the rehabilitation of soils affected by quarrying operations after mine closure.

International audience; Ultramafic derived soils are characterized by low nutrient soils, a low Ca:Mg ratio, and high metal contents such as Ni, Co and Cr. The vegetation growing on these soils is highly adapted and includes both Ni hyperaccumulator and accumulator species. Today, approximately 530 Ni hyperaccumulator species are listed worldwide and the Ni concentration can be extremely high, e.g. up to 25% in latex from Pycnandra acuminata (Sapotaceae), a tree found in New Caledonia. The aim of this study is to identify the potential role of Ni hyperaccumulator plants in the Ni biogeochemical cycle at the soil surface by using Ni isotopes. A set of Ni hyperaccumulator and Ni accumulator plants as well as topsoils were sampled on the Barro Alto and Niquelândia ultramafic complexes (Goiás State, Brazil). Three Ni hyperaccumulator plants were collected: Justicia lanstyakii, Heliotropium aff. salicoides, Cnidoscolus aff. urens, as well as one Ni accumulator plant, Manihot sp. The isotopic compositions of the whole plants were determined and compared to those of the bulk topsoils and DTPA-extractable Ni. The topsoils exhibited δ60Ni values ranging from −0.30 ± 0.06‰ to 0.16 ± 0.05‰. The DTPA-extractable Ni in the topsoils ranged from 94 to 623 mg kg−1, i.e. 0.9–4.9% of the total soil Ni and was found to be isotopically heavier than the corresponding topsoil (from −0.30 ± 0.05‰ to 0.34 ± 0.08‰). The δ60Ni values for the Ni accumulator plants showed an enrichment in heavy Ni isotopes in the aerial parts of the plant compared to the roots, whereas similar δ60Ni values for the roots, stems and aerial parts suggested that no significant fractionation results from Ni uptake and translocation in Ni hyperaccumulator plants. Moreover, the aerial parts (i.e. leaves and flowers) from all of the plants analyzed showed the highest Ni concentrations and the heaviest δ60Ni values up to 1.21 ± 0.05‰. The enrichment in heavy Ni isotopes in the leaves (0.09 ± 0.06‰

International audience; Lateritic topsoils, which are usually removed and stored apart before mining operations take place, play an essential role in the success of post-mining restoration. They contain elements to recover chemical (organic matter, nutrients) and biological (seed and bud banks, microorganisms) fertility of the soil. Conserving topsoil fertility during storage time is essential for a successful use of topsoil during restoration. In this study, different chemico-mineralogical properties of a lateritic topsoil from the Goro nickel mine (New Caledonia) were monitored from its original in situ emplacement on the soil profile, immediately after its stockpiling and after 24 months of storage. Our analyses show that topsoil experienced noticeable changes immediately after storage, mostly produced by mixing of different soil profiles. Cation Exchange Capacities and concentrations of most elements did not vary even after 24 months of storage. However, a slight reduction of Ni, Cr, K, Na and of the C:N ratio, and an increase of Ca have been observed. Stockpiling has not affected negatively the chemical fertility of the topsoil, although biological parameters should be considered to have a complete view of stockpiling sustainability.

International audience; Ultramafic soils are typically enriched in nickel (Ni), chromium (Cr), and cobalt (Co) and deficient in essential nutrients, making them unattractive for traditional agriculture. Implementing agromining systems in ultramafic agricultural soils represent an ecological option for the sustainable management and re-valorisation of these low-productivity landscapes. These novel agroecosystems cultivate Ni-hyperaccumulating plants which are able to bioaccumulate this metal in their aerial plant parts; harvested biomass can be incinerated to produce Ni-enriched ash or “bio-ore” from which Ni metal, Ni ecocatalysts or pure Ni salts can be recovered. Nickel hyperaccumulation has been documented in ∼450 species, and in temperate latitudes these mainly belong to the family Brassicaceae and particularly to the genus Odontarrhena (syn. Alyssum pro parte). Agromining allows for sustainable metal recovery without causing the environmental impacts associated with conventional mining activities, and at the same time, can improve soil fertility and quality and provide essential ecosystem services. Parallel reductions in Ni phytotoxicity over time would also permit cultivation of conventional agricultural crops. Field studies in Europe have been restricted to Mediterranean areas and these only evaluated the Ni-hyperaccumulator Odontarrhena muralis s.l. Two recent EU projects (Agronickel and LIFE-Agromine) have established a network of agromining field sites in ultramafic regions with different edapho-climatic characteristics across Albania, Austria, Greece and Spain. Soil and crop management practices are being developed so as to Kidd et al. Sustainable Agromining Systems for Nickel Recovery optimize the Ni agromining process; field studies are evaluating the potential benefits of fertilization regimes, crop selection and cropping patterns, and bioaugmentation with plant-associated microorganisms. Hydrometallurgical processes are being up-scaled to produce nickel compounds and energy from hyperaccumulator biomass. Exploratory techno-economic assessment of Ni metal recovery by pyrometallurgical conversion of O. muralis s.l. shows promising results under the condition that heat released during incineration can be valorized in the vicinity of the processing facility.

International audience; The quantification of Ni isotopic fractionation induced by Ni binding to organic acids is a preliminary step to better constrain the mechanisms determining Ni isotopic fingerprint observed in surface soils, waters and plants, as well as the contribution of metal recycling during plant litter degradation. In this study, Ni isotopic fraction induced by reaction with small organic acids, e.g. citric and oxalic acids, and with soil purified humic acids (PHA) was investigated at different Ni-L ratio and pH conditions. The Donnan Membrane Technique was used to separate Ni bound to organic ligands from the free metal. Obtained results highlighted that Ni binding with carboxylic groups produces, in the adopted experimental conditions, a Δ60Nibond-free

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.

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.

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.

International audience; Ultramafic outcrops represent less than 1% of the terrestrial surface but their unusual geochemistry makes them a global hotspot for biodiversity. Ultramafic soils are a peculiarity for soil scientists in all climatic zones of the world. These soils lack essential pedogenetic elements: Al, Ca, K, and P. Whereas serpentinites will most likely give birth to Eutric Cambisols with little influence by climate, peridotites will induce an acceleration of weathering processes; this over-expressed weathering is due to their deficiency in Si and Al and lack of secondary clay formation. Soils evolve towards Ferralsols in tropical conditions. Results from isotopic dilution techniques show that Ni borne by primary minerals is unavailable. Secondary 2:1 clay minerals (e.g. Fe-rich smectite) and amorphous Fe oxyhydroxides are the most important phases that bear available Ni. Therefore, smectite-rich soils developed on serpentinite and poorly weathered Cambisols on peridotite (only in temperate conditions) are the soils with highest availability of Ni. Although soil pH conditions are amajor factor in controlling available Ni, the chemical bounds of Ni to containing phases are even more important to consider. Plants take up significant amounts of Ni, and its biogeochemical recycling seems an essential factor that explains Ni availability in the surface horizons of ultramafic soils.

Most of the research dedicated to agromining has focused on cultivating a single hyperaccumulator plant, although plant diversity has been shown to positively modify soil characteristics. Hence, we compared the effect of cropping a nickel-hyperaccumulator Alyssum murale with a legume (Vicia sativa) to A. murale's mono-culture, on the bacterial diversity and physico-chemical characteristics of an ultramafic soil. A pot experiment with 5 replicates was conducted in controlled conditions for 11 months. The treatments studied were: co-cropping and rotation vs. mineral fertilization controls and bare soil. The introduction of legumes induced a clearly positive effect on the soil's microbial biomass carbon and nitrogen. Arylsulfatase and urease activities tended to be enhanced in the co-cropping and rotation treatments and to be lessened in the mineral fertilization treatments. However, β-glucosidase and phosphatase activities were seen to decrease when legumes were used. Our results showed that the rotation treatment induced a higher organic matter content than the fertilized control did. Actinobacteria was the most-represented bacterial phyla and had lower relative abundance in treatments associating legumes. Conversely, the relative abundance of Acidobacteria and Gemmatimonadetes phyla increased but not significantly in treatments with legumes. The relative abundance of Chloroflexi phylum was shown to be significantly higher for the fertilized rotation control. The relative abundance of β-Proteobacteria subphylum increased but not significantly in treatments with legumes. NMDS analysis showed a clear separation between planted treatments and bare soil and between co-cropping and rotation and fertilized controls. Shannon index showed reduction in microbial diversity that was mainly due to chemical inputs in the soil. This study showed that these new cropping systems influenced both the bacterial diversity and the physico-chemical characteristics of an ultramafic soil. In addition, this study provides evidence that mineral fertilization can negatively impact bacterial communities and some of their functions linked to biogeochemical cycles.

International audience; The largest serpentine outcrops in Europe occur in the Balkan Peninsula. Kosovo, as a part of this region, hosts an ultramafic area of 487 km(2) within its territory. This work reports the first systematic biogeochemical survey on the significant and most representative ultramafic massifs of Kosovo. The aim of this study was (i) to detail the geochemical composition of 12 ultramafic pedons obtained from 10 selected sites chosen as representative for Kosovo, (ii) to inventoriate the flora occurring on these sites and (iii) to identify plant species with potential for use in phytostabilization or phytoextraction purposes. Twelve representative pedons from 10 different sites across the country were excavated and 27 horizon samples were collected. Regarding the serpentine flora, a total of 162 plant taxa located at the ultramafic sites were collected. Soils samples were characterized for basic physico-chemical characteristics and both plant and soil samples were analyzed for chemical composition. The serpentine soils samples displayed a vast array of physico-chemical characteristics which reflected the geochemistry of the bedrock, the degree of weathering and the horizon characteristics. However there appeared to be a relationship between edaphic properties and the occurrence of several plant species. Although most of the plants' species did not show metal concentrations above 1000 mg kg(-1), Odontarrhena muralis (syn. Alyssum murale Waldst. and Kit). and Noccaea ochroleuca (Boiss and Heldr.) F.K.Mey. (syn.Thlaspi ochroleucum), did, thus meeting the criterion of Ni hyperaccumulating plants. Given the aforementioned, the resilience of these plants to both tolerate and accumulate heavy metals may prove useful for phytostabilization.

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. 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. 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. 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.

Metal hyperaccumulator plants represent a unique biological resource for scientific research and practical applications. Though essential, however, an adequate knowledge of the systematics of these plants is often missing. This is the case of Odontarrhena, a large but taxonomically critical group of nickel hyperaccumulators from Eurasia. We present a study on this genus in Albania, to fill a gap in our knowledge of this group from a major centre of diversity of metallicolous flora, and to contribute updated information to the Global Hyperaccumulator Database. Morphological and karyological analyses of material from field collections across all major serpentine outcrops in the country, in different years and seasons, allowed to delimit seven taxa: O. albiflora, O. chalcidica, O. moravensis, O. sibirica, O. decipiens, O. smolikana subsp. glabra and O. rigida. The three latter taxa have been long neglected and were resurrected in view of their clear distinctness, while commonly accepted taxa such as O. bertolonii subsp. scutarina and O. markgrafii were reduced to synonymy of O. chalcidica due to the lack of consistent differentiation. Polyploidy was prevalent, while diploid complements were typical of the two vicariant endemics O. rigida and O. moravensis. Types are indicated or newly designated for each entity, and nomenclatural issues are addressed based on in-depth studies of literature and herbarium material. Revised descriptions, phenology, habitat and distribution data are given for each taxon, as well as original iconographies and chromosome counts. A revised identification key is provided. Shoot nickel concentrations were determined to assess accumulation levels of taxa and populations in natural conditions and their potential for phytoextraction of this metal from the soil. With ca. 23000 and 17000 µg of Ni g-1 of shoot dry weight, respectively, the tetraploids O. chalcidica and O. decipiens were the most promising candidates, especially the latter for its robust habit.

International audience; The majority of nickel hyperaccumulator plant species have been discovered by screening using a field spot test based on dimethylglyoxime. Recently, the use of a portable X-ray fluorescence spectroscopy instruments has enabled non-destructive analyses of existing herbarium collections. Given that the family Phyllanthaceae globally has the greatest numbers of hyperaccumulators, all available specimens from this family, including the speciose genus Antidesma, at the Forest Research Centre Herbarium in Sabah, Malaysia, were analysed. The results reveal 9 new manganese hyperaccumulators in the genus Antidesma, including Antidesma puncticulatum, with manganese concentrations reaching up to 46,400 A mu g g(-1). Prior to this study, only one manganese hyperaccumulator had been recorded in Sabah. The present study is the first to discover nickel hyperaccumulator plant species (four species) in the genus Antidesma, including Antidesma montis-silam with concentrations reaching up to 32,700 A mu g g(-1). Further collection and analyses of plant material of Antidesma montis-silam in the native habitat confirmed the high foliar nickel concentrations. The high nickel hyperaccumulating characteristic and ostensibly fast growth rate of Antidesma montis-silam infer potential for use in agromining technology. Some species in the genus Antidesma exhibit co-accumulation of manganese and nickel. This case-study shows how herbarium XRF screening can lead to discovery of taxa with unique properties.

International audience; Noccaea caerulescens is a pseudo-metallophyte known to hyperaccumulate Zn, Cd and Ni, and a model species for the study of the hyperaccumulation of trace metals. However, information about its ecology is rather scarce. The aim of this work was thus to determine if soil metal content was the main factor responsible for the distribution of N. caerulescens. During 4 years, the Vosges Mountains (north eastern France) were explored during the flowering season. Plants and their rooting soil were analyzed for their trace element content (Cd, Mn, Ni and Zn). The ecological amplitude of N. caerulescens was analyzed using Maximum Entropy Modelling (MaxEnt). Only five populations of the 67 recorded were found on metalliferous soils. All the recorded populations presented a Zn-hyperaccumulator phenotype, whereas only two presented a Cd and/or Ni-hyperaccumulator phenotype. The spatial distribution of mineralized areas did not explain the spatial distribution of the species. The MaxEnt distribution model suggested that the principle explanatory factors were the annual precipitation, soil use and underlying geology. Trace metal concentrations in soils are not the main drivers of N. caerulescens distribution in the Vosges Mountains. Instead, pedological and climatic factors along with recent human activity are the main factors of the colonization of the massif.

Agromining aims to rehabilitate contaminated or natural metal-rich soils (ultramafic soils) by extracting metals of high economic importance, such as nickel (Ni), using hyperaccumulator plants and then to recover these metals for industrial purposes. Ultramafic soils are characterized by low fertility levels and this can limit yields of hyperaccumulators and metal phytoextraction. Here, we characterized the potential benefits for phytoextraction efficiency of co-cropping two plants: a Ni-hyperaccumulator (Alyssum murale; Brassicaceae) and a legume (Vicia sativa; Fabaceae). A field experiment with 3 replicates was set up in an ultramafic zone in North West Spain. Four treatments were tested: co-cropping (“Co”), fertilized mono-culture (“FMo”), non-fertilized mono-culture (“NFMo”) and bulk soil (“BS”). “FMo” and “Co” treatments increased the biomass yields of A. murale by 453% and 417% respectively, compared to “NFMo”. “Co” treatment generated 35% and 493% higher Ni-yields than “FMo” and “NFMo”, respectively. Most of the microbial analyses showed that introducing V. sativa (“Co” treatment) into the cropping system had beneficial effects. “Co” treatment significantly modified the phenotypical structure of bacterial communities and raise the relative abundance of the phylum Bacteroidetes and reduced that of Actinobacteria. In addition, non-metric multidimensional scaling analysis of the operational taxonomic units (OTUs) showed that “Co” was clearly separate from all other treatments. Thus, this study showed that co-cropping a hyperaccumulator with a legume in Ni-agromining systems not only improves plant biomass and Ni-yields, but also enhanced some soil microbial enzymatic activities. Ameliorating agromining by replacing fertilizers would combine eco-efficient or sustainable metal recovery with soil fertility/quality improvement.

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 natural Ni-rich soils. Ultramafic soils in the Balkans display a great variability in Ni concentrations and available Ni levels, both in Albania and the Pindus Mountains of Greece. In Albania, Vertisols are currently being used for low-productivity agriculture (pasture or arable land) on which phytomining could be included in cropping practices. Alyssum murale occurs widely on these ultramafic Vertisols and is a spontaneous weed that grows among other crops. This review chapter presents the different steps that were investigated during the study of soil suitability, and selection of plants up to optimization of agronomic practices, at field scale, as recently developed to reach the implementation stage of Ni agromining in Albania. During a 7-year study we addressed the following questions: (i) what are the optimal soils for Ni agromining in terms of fertility and Ni availability? (ii) what is the phytoextraction potential of local populations of Ni hyperaccumulator species? (iii) what should be the agronomical practices used to optimize the cropping of A. murale for extensive phytomining adapted to a Balkan agricultural setting?

Phytoextraction represents an innovative approach in the management of nickel (Ni) rich soils whether natural (ultramafic) or anthropogenic (contaminated sites). However, its success depends both on the production of a high plant biomass and the ability of plants to accumulate metals. The application of nitrogen (N) fertilizer can improve the biological and chemical soil fertility and thus agricultural yields. Moreover, soil microorganisms play a key role by influencing nutrient flows, which are the main limiting factors of plant growth in degraded soils. In this work, we investigated the effects of two levels of both Ni and mineral N soil applications on the microbial activities and Ni phytoextraction efficiency by Alyssum murale growing in a pot experiment during 5 months. Plant growth, nutrients and Ni uptake, soil microbial populations and their enzymatic activities involved in the biogeochemical cycles of nitrogen, phosphorus, carbon and sulfur (urease, alkaline phosphatase, beta-glucosidase and arylsulfatase, respectively) were determined. The results showed that plant dry mass was unsurprisingly not affected when the soil Ni concentration was increased. However, it led to an increase of the amount of Ni extracted per pot. A negative effect of Ni addition was observed on both total bacteria and urease activity, without any effect on other enzymes. On the contrary, N fertilizer played a significant positive role by promoting both plant growth and Ni phytoextraction, partly as a result of the stimulation and flourishing of bacterial populations.

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.

Ultramafic soils display high concentrations of nickel and a number of nutrient deficiencies. Nickel-hyperaccumulator plants, such as Alyssum murale , have evolved in these environments and developed specific metal homeostasis, showing concentrations of nickel (Ni) sometimes exceeding 1% in their aerial biomass. Rhizosphere bacterial communities associated with Ni-hyperaccumulator plants can differ from those of non-accumulating plants growing on the same site. Among the edaphic factors that could influence the phylogenetic structure of the bacterial communities, altitude and metal-bioavailability such as Ni in particular, could be significant. Our objectives were to understand the specific changes in the structure of the A. murale rhizosphere bacterial community that occurred across two gradients: elevation and Ni geochemistry, using a high-throughput sequencing technique (454-pyrosequencing). In this study, Chloroflexi was the major phylum present, with 53–77% of relative abundance. Moreover, we found that the higher the soil's chemically-available Ni contents, the higher was the relative abundance of Proteobacteria (particularly Alphaproteobacteria ) and Actinobacteria . In contrast, the abundance of Chloroflexi decreased with increasing levels of available Ni. Our results demonstrate that the chemical-availability of Ni in the studied soil drives the bacterial community diversity in the rhizosphere of A. murale, regardless of elevation gradient and other soil physicochemical parameters.

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; In Mexico, ultramafic complexes are present in different regions from the northwest (Baja California Norte) to the southeast (Chiapas). In this paper, we present the results of the exploration of three ultramafic (serpentine) habitats in central and southern Mexico: Cuicatlan-Concepcin Papalo (Oaxaca), Tehuitzingo-Tecomatlan (Puebla), and San Juan de Otates (Guanajuato). Previous geology studies showed that these complexes are mainly made up of serpentinized peridotites. Soil analyses demonstrated typical ultramafic characteristics such as high content of Mg in relation to Ca, and high concentrations of Fe, Cr, Co, and Ni. Soil samples from Oaxaca and Puebla had similar Ni contents around 2300 mg kg(-1), while samples of Guanajuato showed the lowest Ni levels with an average of 200 mg kg(-1) as well as for other metals such as Co, Cr, Mn, and Zn. During this study, 83 plant specimens were collected, of which 52 were identified at genus level and 40 at species level. The collected plants belong to 19 different families such as Anacardiaceae, Fabaceae, Acanthaceae, Asteraceae, Sterculiaceae, and Verbenaceae which are also widely present in other ultramafic areas in Iran, Brazil, Sri Lanka, and Costa Rica. Only two Mexican endemic species are included in the collection. Ni hyperaccumulators were not detected at any of the studied sites. Therefore, hyperaccumulation, as a tolerance mechanism of the flora in response to ultramafic geochemical stress, does not seem to be developed in Central Mexico, as observed in the close Costa Rican site of Santa Elena.