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International audience; This study aimed at determining, in the laboratory, the effects of poplar litter collected in woody habitats contaminated by heavy metals on growth and metal accumulation in the terrestrial isopod Porcellio scaber. Cd, Pb, and Zn pseudototal and CaCl(2)-extractable concentrations in litter types were determined using AAS. Juveniles were fed ad libitum, individually, for 28 days with four litter types presenting an increasing gradient of metal contamination. Individuals were weighed every week and metal body burdens were determined at the end of the experiment. From the first week until the end of the experiment, a decrease in P. scaber growth related to the increase of metal concentration in litter types was recorded. Significant correlations were observed between metal body burdens and metal concentrations in litter types. However, Cd accumulation in woodlice appeared to be related to the Cd/Zn concentration ratio in litter types. All these results showed the potential of weight gain in P. scaber as a suitable indicator for litter quality assessment with ecological relevance.

International audience; A gradient of agricultural intensification (from permanent meadows to permanent crops, with rotation crops and meadows as intermediary steps) was studied in the course of the RMQS-Biodiv program, covering a regular grid of 109 sites spread over the whole area of French Brittany. Soil biota (earthworms, other macrofauna, microarthropods, nematodes, microorganisms) were sampled according to a standardized procedure, together with visual assessment of a Humus Index. We hypothesized that soil animal and microbial communities were increasingly disturbed along this gradient, resulting in decreasing species richness and decreasing abundance of most sensitive species groups. We also hypothesized that the application of organic matter could compensate for the negative effects of agricultural intensity by increasing the abundance of fauna relying directly on soil organic matter for their food requirements, i.e. saprophagous invertebrates. We show that studied animal and microbial groups, with the exception of epigeic springtails, are negatively affected by the intensity of agriculture, meadows and crops in rotation exhibiting features similar to their permanent counterparts. The latter result was interpreted as a rapid adaptation of soil biotic communities to periodic changes in land use provided the agricultural landscape remains stable. The application of pig and chicken slurry, of current practice in the study region, alone or in complement to mineral fertilization, proves to be favorable to saprophagous macrofauna and bacterivorous nematodes. A composite biotic index is proposed to synthesize our results, based on a selection of animals groups which responded the most to agricultural intensification or organic matter application: anecic earthworms, endogeic earthworms, macrofauna other than earthworms (macroarthropods and mollusks), saprophagous macrofauna other than earthworms (macroarthropods and mollusks), epigeic springtails, phytoparasitic nematodes, bacterivorous nematodes and microbial biomass. This composite index allowed scoring land uses and agricultural practices on the base of simple morphological traits of soil animals without identification at species level.

The bioavailability of trace elements in soils is conditioned by both physico-chemical and biological parameters. In this study, the accumulation kinetics of cadmium (Cd), lead (Pb), arsenic (As) and antimony (Sb) were determined for 3 industrially impacted sites to assess the bioavailability of these contaminants to the garden snail (Cantareus aspersus). Mono and multivariate regressions allowed the identification of cation exchange capacity (CEC), silts and organic carbon content as the soil parameters modulating the in situ bioavailability of Cd and Pb. For all elements, the total concentrations in the soils were not good predictor (not significant correlation) of the bioavailability to snails. The Cd, As and Sb assimilation fluxes were correlated with the calcium chloride (CaCl2) extract concentrations, but this correlation was not observed with Pb. The total soil concentration coupled with soil properties best explained the variation in Pb assimilation, whereas their influences on Cd bioavailability were lower, signifying that other parameters such as contamination sources may modulate Cd bioavailability. Here, the As and Sb in situ accumulation kinetics are described for the first time and highlighted a slight bioavailability to snails at the studied sites. The absence of a correlation between the As or Sb assimilation fluxes and total metals in the soil coupled with the absence of influence of soil properties on their bioavailability may result from the speciation of these metalloids, which are known to modulate their mobility in soils. This study highlights the need to consider both physico-chemical and biological aspects of metal and metalloid bioavailability to assess the risk of metal transfer from soil to organisms.

International audience; Ramie plants (Boehmeria nivea) have been cultivated on ion-adsorption rare earth elements (REEs) mine tailings and showed a low ability to accumulate REEs, especially in the stems (REE= 24±17 mg kg-1) with higher concentration in leaves and roots (REE= 57 to 66 mg kg-1). Ramie individual fibers were isolated using three degumming processes: a traditional alkali treatment (AT), a steam explosion (SE) treatment after a neutral (SEN) or after a basic (SEB) impregnation. Cellulose-rich (> 80%) fine fibers with very low amounts of non-cellulosic sugars (

International audience; Concepts and developments for a new field in ecotoxicology, referred to as "landscape ecotoxicology," were proposed in the 1990s; however, to date, few studies have been developed in this emergent field. In fact, there is a strong interest in developing this area, both for renewing the concepts and tools used in ecotoxicology as well as for responding to practical issues, such as risk assessment. The aim of this study was to investigate the spatial heterogeneity of metal bioaccumulation in animals in order to identify the role of spatially explicit factors, such as landscape as well as total and extractable metal concentrations in soils. Over a smelter-impacted area, we studied the accumulation of trace metals (TMs: Cd, Pb and Zn) in invertebrates (the grove snail Cepaea sp and the glass snail Oxychilus draparnaudi) and vertebrates (the bank vole Myodes glareolus and the greater white-toothed shrew Crocidura russula). Total and CaCl(2)-extractable concentrations of TMs were measured in soils from woody patches where the animals were captured. TM concentrations in animals exhibited a high spatial heterogeneity. They increased with soil pollution and were better explained by total rather than CaCl(2)-extractable TM concentrations, except in Cepaea sp. TM levels in animals and their variations along the pollution gradient were modulated by the landscape, and this influence was species and metal specific. Median soil metal concentrations (predicted by universal kriging) were calculated in buffers of increasing size and were related to bioaccumulation. The spatial scale at which TM concentrations in animals and soils showed the strongest correlations varied between metals, species and landscapes. The potential underlying mechanisms of landscape influence (community functioning, behaviour, etc.) are discussed. Present results highlight the need for the further development of landscape ecotoxicology and multi-scale approaches, which would enhance our understanding of pollutant transfer and effects in ecosystems.

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.

Aims: Dicranopteris linearis is a rare earth element (REE), aluminium (Al) and silicon (Si) hyperaccumulator plant which occurs in southern China. To date, there have been no studies on the variation in elemental accumulation among populations of Dicranopteris linearis occurring on REE-enriched and non-REE enriched soils. Methods: In total 43 Dicranopteris linearis individuals and the corresponding rhizosphere soils from 7 populations in southern China were sampled and the plant material and soil composition were chemically analysed for REE and other elements. Results: Dicranopteris linearis populations from REE-enriched soils and non-REE enriched soils both have the ability to accumulate high concentrations of REE (> 1000 mg kg− 1), Al (> 1000 mg kg− 1) and Si (> 10 000 mg kg− 1). The ratios of light REEs (LREEs) to heavy REEs (HREEs) in Dicranopteris linearis pinnae are consistently > 1, regardless of their ratios in the corresponding soils. Concentrations of REE in Dicranopteris linearis pinnae vary significantly among populations and have positive correlations with total and extractable soil REE concentrations. The plant Al and Si concentrations in Dicranopteris linearis populations are uncoupled from variations in soil Al and Si concentrations. The plant REE concentrations have no obvious relationships with the prevailing Al concentrations, but are positively correlated with plant Si and Mn, and negatively correlated with soil extractable P concentrations. Conclusions: The hyperaccumulation of REEs (LREE > HREE), Al and Si in non-REE enriched soils is a species-wide trait. The accumulation of REEs is highly variable and associated with soil REE concentrations, nutrients status, and other soil properties.

Aims: The Australian native hemi-aquatic herb C. helmsii (Crassulaceae) is a copper (Cu) accumulator, tolerant to a wide range of climatic conditions and able to concentrate >9000 μg Cu g−1 in its living tissues. These characteristics suggest practical potential for decontamination of Cu-polluted mine waste waters using a phyto-extraction approach. The aim of this study was to investigate Cu uptake in C. helmsii at different Cu2+ concentrations in solution and to test for the effect of pH on the concentration of free Cu2+ and Cu accumulation in this species. Methods: Different solutions were tested in acid (pH 4.0) and mildly acidic (pH 5.8) conditions at five different Cu2+ concentrations (ranging from 0 to 5 mg Cu L−1). The concentration of free Cu2+ was evaluated using Geochem-EZ software. The distribution of Cu in C. helmsii tissues was examined with micro-X-ray Fluorescence (μXRF) elemental mapping and with Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS). Results: The highest shoot Cu concentration in C. helmsii was 5870 μg Cu g−1 in the 5 mg Cu L−1 treatment. Copper bioaccumulation was positively correlated with the Cu2+ treatment in the different solutions. The μXRF and SEM-EDS analysis revealed that roots accumulated higher Cu concentrations than the shoots. The concentration of free Cu2+ was shown to be dependent upon the type of Fe-chelator (DTPA, EDDHA, HBED) used in the solution due to the displacement of Fe3+ and complexation of Cu2+. Conclusions: Crassula helmsii is highly tolerant to Cu2+ in solution at acidic and mildly acidic pH, and able to accumulate high Cu concentrations in its tissue. This confirms its potential for applications in Cu phyto-extraction of acidic mine effluent waters high in Cu2+.

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’.

International audience; Juvenile snails were exposed during their growth period to Cd-contaminated field and artificial soils and then transferred to uncontaminated soil to assess the sequels of previous exposure on adult reproduction. Growth modelling highlighted growth inhibitions of 5% and 10% after 70 and 84 days of exposure to 20 and 100 mg Cd kg(-1) in artificial soils, respectively. Growth disruption was accompanied by a decrease in the clutch number and a 4-week delay in the egg-laying cycle. Although it was also contaminated at 20 mg Cd kg(-1), the contaminated field soil did not lead to detectable effects in snails, suggesting a lower Cd bioavailability confirmed by the bioaccumulation analysis. We demonstrated that the 28-day growth test, as advised by the ISO-guideline, may not be sufficient to assess sublethal toxic effects of realistically contaminated soils. For this purpose, a life cycle experimental set-up is proposed, allowing a thorough assessment of toxicity during successive life stages.

The effects of maize expressing the Bacillus thuringiensis Cry1Ab protein (Bt maize) on soil microarthropods were assessed in the field at four European locations (two in Denmark and two in France) that differ in their climatic conditions or soil properties. Each site was considered as a separate experiment, with separate statistical comparison. Effects of farming practices using Bt maize were compared with conventional farming practices using near-isogenic non-Bt maize and also (at some of the sites) other conventional varieties. Furthermore, at one field site (Foulum, Denmark), the effects of Bt crops were studied in both conventional tillage and reduced tillage contexts. At another field site (Askov, Denmark), Bt maize effects were also compared to the effects of the chemical insecticide dimethoate. Moreover, at three of the field sites (all except Narbons, France), the possibility of a localised Bt effect around the rhizosphere compared to the bulk soil was assessed by sampling within and between maize rows. There were some significant negative effects of Bt maize on microarthropods in soils with a high clay content. Significant differences of the same magnitude also occurred between different conventional varieties of maize, but the effect of dimethoate appeared clearly greater than Bt effects. It is thus debatable if the Bt maize effect is an effect of the Bt toxin or just an effect of the maize variety. Based on the results, it can be concluded that the effect of Bt maize on soil microarthropods was small and within the normal variation expected in conventional agricultural systems. (C) 2007 Elsevier GmbH. All rights reserved.

To enlarge the possibilities of using organisms of the soil fauna to assess the bioaccumulative potential of chemicals, the kinetic of soil cadmium (Cd) transfer to the terrestrial gastropod Helix aspersa was investigated under laboratory conditions during a long-term experiment (6 months). During the exposure phase (3 months), juvenile snails were subjected to three different concentrations of Cd spiked in artificial ISO soil (ISO 0, 20 and 100 mg Cd kg−1) and to a field soil (ME4) industrially contaminated by 20 mg Cd kg −1. For both soils, internal steady-state Cd concentrations were reached in the viscera of the snails, the main storage organ for Cd, after 2 weeks of exposure whatever the Cd concentration in soil. The equilibrium concentrations in the viscera were 0.7 (±0.1), 11.3 (±2.4), 73.3 (±4.8) and 6.3 (±1.3) mg Cd kg−1 dry mass for ISO 0, ISO 20, ISO 100 and ME4, respectively. During the depuration phase (3 months), from 0 to 52% of the accumulated Cd in the viscera were removed by excretion or relocation in the foot. However, the snails were not able to depurate down to initial concentrations. Data were modelled by integrating a specific growth rate constant into one-compartment toxicokinetic models. This allowed the calculation of Cd uptake rates that can be used as indicators of metal bioavailability. Since this parameter was found to be lower for snails exposed to the field soil ME4, we concluded that lower Cd bioavailability in this field soil was responsible of the lower transfer to the snails compared to the ISO 20 soil, even though they were polluted to similar extents. Internal validation showed that the toxicokinetic models could be applied for predictive purposes, promising for the development of a bioaccumulation directive for terrestrial environment. Keywords: Accumulation, Depuration, Bioavailability, Modelling, Long-term exposure

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.

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.

AimsMetal hyperaccumulation is a rare phenomenon described for an increasing number of plant taxa. In this study we investigated the root growth responses of the well-known nickel, zinc, cadmium hyperaccumulatorNoccaea caerulescensand of the metal tolerant (non-accumulator)Stellaria media, in order to observe root foraging vs avoidance responses to nickel. MethodsTo allow for observations of root growth and foraging preferences, two accessions ofNoccaea caerulescensand two accessions ofStellaria mediaorginating from high nickel and low nickel habitats were grown in rhizotrons with localized nickel enrichment.ResultsThe root density in the control and nickel-enriched soil areas in the rhizotrons with differentN. caerulescensaccessions had distinct responses: moderate nickel avoidance was recorded for the non-nickel accession, while a clear foraging response was observed inN. caerulescensfrom the nickel accession. In contrast, nickel rooting avoidance was observed for bothS. mediaaccessions and was more pronounced in the non-nickel accession.ConclusionsThis study shows thatN. caerulescensoriginating from different accessions responded differently to soil nickel enrichment, with the nickel accession ofN. caerulescensactively foraging for nickel, suggesting a physiological adaptation and demand for this metal. In contrast, a clear nickel avoidance response by a metal tolerant species, S. media, was observed in this study, a phenomenon which has not been previously described; this suggests that root avoidance responses might play a role in the adaptation of metal tolerant species to Ni-rich soils.

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.

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

Evaluation of various mechanisms of Cd2+ and Zn2+ root uptake through modelling, including interactions with Fe uptake. Four increasingly complex models were developed and tested against measured uptake by the hyperaccumulator Noccaea caerulescens grown on three contaminated soils. Model 1 formalises root uptake of free hydrated ions only, to which the dissociation of soil-borne metal complexes was added in Model 2, together with the root uptake of these complexes through the Fe pathway in Model 3. Model 4 represents Strategy I for Fe uptake, with Cd2+ and Zn2+ complexed by a root organic exudate hijacking the Fe adsorption/reduction pathway. Model 1 enables a good prediction of Cd and Zn uptake in acidic or neutral soils. In contrast, the high Cd uptake in the alkaline soil cannot be reached either by simulating additionnally the dissociation of Cd complexes with soil-borne ligands (Model 2), nor by replicating their uptake through the Fe pathway (Model 3). These results suggest that the plant increases the Cd availability in alkaline soil during the uptake process. Supporting this idea, the uptake of Cd desorbed from iron hydroxide and calcium carbonate by root exuded ligands for Fe acquisition (simulated in Model 4) can explain the high Cd uptake from alkaline soil. In acid soils, Cd and Zn uptake can be predicted from their free hydrated concentrations, while in calcareous soils with very low concentrations of free hydrated ions, root exudation for Fe acquisition could make other soil Cd species phytoavailable.

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

International audience; The terrestrial fern Pityrogramma calomelanos, a cosmopolitan tropical species, is one of the strongest known arsenic (As) hyperaccumulator plants. This study aimed to determine whether P. calomelanos preferentially forages for arsenite (As3+) or arsenate (As5+) in As-contaminated soils, and whether a positive root response to As enhances accumulation in P. calomelanos. Therefore, an experiment using rhizoboxes divided in two halves were constructed with a control soil (C) and As3+ or As5+ dosed soil at either 50 and 100 μg g-1 As. Micro-X-ray Fluorescence elemental mapping (μXRF) was employed to analyze the distribution of As in roots and fronds, and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS) was used to determine As distribution in the reproductive tissues of P. calomelanos. The results showed that Pityrogramma roots do not specifically forage for As-contaminated soil; the area based on pixel counts was similar across all the treatments with no statistical differences. However, frond biomass was slightly higher in the treatments C ǀ As3+ and C ǀ As5+, and the highest accumulation of As in fronds was in the As5+ ǀ As3+ (100 μg g-1) treatment, with 3418 and 2370 μg g-1 in old and young fronds respectively. Arsenic cycling across the roots was observed by the μXRF mapping; in C ǀ As5+ (100) the As was higher and evenly distributed in both sections, whilst in C ǀ As3+ (50), the As was higher in the As3+ side. The μXRF mapping showed a broader As distribution in older fronds, where As was highest in the rachis and extended into the pinnule through the midrib. Pityrogramma calomelanos does not specifically root forage for As-enriched zones in the soil and grows healthily without signs of toxicity at lower (50 μg g-1) and higher (100 μg g-1) concentrations of As3+ and As5+ in the soil.

International audience; Purpose: This work is a quantitative evaluation of current hypotheses of iron acquisition by higher plants. Methods: The outputs of three root uptake models were compared to the iron uptake of a single plant species grown in three different soils. Iron hydroxide dissolution kinetics by organic ligands were formalised in the reactive transport modelling, together with ligand and ferric complex degradation. A global sensitivity analysis was performed. Results: Iron uptake by Noccaea caerulescens does not appear to differ from that of other higher plants. The solubility of soil iron hydroxides alone cannot satisfy the plant iron requirements, even in an acidified rhizosphere. For this reason, all plants growing in aerated soils should suffer extreme iron deficiencies, not only those in alkaline soils. The dissociation rate of an Fe3+ complex (for instance with an aminopolycarboxilate ligand) in solution near the root cell membrane is not sufficient to provide the metal needed by the plant. In contrast, the adsorption of the ferric complex on the root cell membrane, before Fe3+ reduction and the absorption of Fe2+ appears to be a very efficient process. This is also the case for iron acquisition through the root secretion of an iron organic ligand dissolving soil iron hydroxides, the rate of ligand excretion being a key parameter. Conclusions: Mechanistic modelling supports the hypothesis of the reduction at the root cell membrane of a ferric complex resulting of iron hydroxide dissolution by a soil- or root-borne organic ligand.

Hyperaccumulators have exceptional phloem translocation capability for heavy metals. This study aims at quantifying the mobility and accumulation of Ni and Co via the phloem in the model hyperaccumulator Noccaea caerulescens. “Phloem loading capability (PLC),” which is calculated by the “Metal content in phloem sap/Metal content in leaves,” was introduced to evaluate the metal phloem mobility, while “Phloem mobility value (PMV)” was used for the normalization of PLC, which sets the PLC of Sr as PMV 0 and that of Rb as 100. The results showed that the PMVs of Ni and Co were 63 and 47, respectively. And the phloem mobility of Rb, Ni, Co, and Sr could be graded as highly mobile, mobile, intermediate, and immobile accordingly. The phloem stream can supply up to 19.1% and 16.0% of the total Ni and Co accumulated in the young leaves, respectively, while for Rb and Sr, the phloem contributes to 29% and 1.4% of the total Rb or Sr, indicating phloem contribution of certain metal is directly linked with its mobility. The results of this study raise the importance of phloem translocation on metal accumulation in shoots and provide insights on the metal cycling process in hyperaccumulators.

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).

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; Partitioning of metals between the soil solid phase and the solution is an important topic in environmental sciences because it determines the metal transfers to aquifers and biological organisms. Complexation of metals with ligands in the soil solution strongly influences the sorption/desorption (SD) of metals, in particular that of the free ion. Because the latter is the metal species principally absorbed by biological organisms, the bioavail-ability of a metal is better reflected by the soil-solution distribution coefficients of the free ion as compared to that of the total metal (sum of the free ion and of the complexes). The present work proposes a modeling approach to determine the distribution coefficients for the free ion and for the metal complexes from SD experiments. The method does not require estimating the mobile pool of the metal sorbed onto the solid phase by any chemical extraction as the modeling relies on the variation of the sorbed metal, which is experimentally exactly estimated from the variation of the amount of metal in solution during the SD experiment. Tested for cadmium (Cd), the model reproduced very well the SD curves observed for the total metal. For any solution:soil ratio including that at field soil moisture, the model gives estimates of important variables including the distribution coefficient for the free ion, the complex, the ligands and the total metal, the concentration of these species in the soil solution and onto the solid phase. The model can be applied as long as the range of the concentration investigated allows to assume a linear sorption of the metal.

International audience; The efficiency of zero-valent iron (Fe-0)for the degradation of contaminants in water or soil can be highly reduced by side reactions with oxygen or water. This work was conducted to test whether this drawback can be effectively suppressed by the carbonation of Fe-0 with pyrolyzed biomass, which forms a Fe3C composite. The composite Fe3C was characterized and its reactivity and stability were assessed in batch tests with methyl orange (MO) as a model pollutant. The results indicated that the removal rate of MO on Fe3C composite was higher than that of Fe-0 (7.587 mg/(g.min) vs. 4.306 mg/(g.min)) at pH 4, where the degradation mechanism was confirmed by high-performance liquid chromatography-mass spectrometry. More importantly, the produced iron oxide in the Fe3C composite was highly suppressed. Regeneration studies showed that after three times of cycling, the removal efficiency of MO on Fe3C composite was kept to 99.42%, but Fe-0 almost lost its reactivity. In situ chemical reduction of a colorimetric redox probe (indigo-5, 5'-disulfonate, I2S) quantitatively demonstrated that Fe3C composite has the reduction kinetics of I2S obviously slower than Fe-0, indicating that Fe3C composite improved the stability of incorporated Fe-0 to resist the side oxidation.

Aims: Dicranopteris linearis is a fern that accumulates unusually high concentrations (up to 0.3% dry weight) of rare earth elements (REEs) in China. Previously, we reported that D. linearis accumulates high concentrations of aluminium (Al) and silicon (Si) in the fronds, but the interactions between these elements and REEs were unknown. Methods: In this study, a range of analytical techniques, including chemical extractions, Scanning-Electron Microscopy with Energy-Dispersive Spectroscopy (SEM-EDS) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) were used to study the association of REEs with Al and Si. Results: The results show that D. linearis accumulates high concentrations of REEs (up to 3830 mg kg−1), Al (up to 9660 mg kg−1) and Si (up to 20,300 mg kg−1), with concentrations increasing with age and frond order of pinna. The extraction patterns suggest the existence of REEs-Si and Al-Si complexes. The SEM-EDS analysis confirmed the existence of phytoliths (Al) deposits in the protoplast and apoplast of the pinna cells. The upper epidermis of the pinnule and the pericycle of the midvein are more concentrated in phytoliths (Al) particles. The LA-ICP-MS analysis revealed that REEs and Al are preferentially compartmentalized within bio-inactive tissues of the pinnules, e.g. necrotic tissues (REEs) and in the margins (Al). Conclusions: Co-deposition of Si with REEs and Al may be a mechanism for dealing with the high concentrations of REEs and Al in D. linearis fronds.

Light Non-Aqueous Phase Liquids (LNAPLs) are one of the most important sources of soil and groundwater contamination worldwide. When they infiltrate through the unsaturated zone, part of the LNAPLs remains trapped by capillary forces. The others accumulate above the top of the water table, forming a floating ‘free’ phase able to generate a long-term dissolved LNAPL plume that durably alters the quality of the water resource. Seasonal variations in the groundwater level lead to significant vertical spreading of these light petroleum hydrocarbon contaminants at the capillary fringe, favoring their release into the air and groundwater. In the climate change context, the IPCC predicts an intensification of these groundwater level variations over the next century in response to variations in rainfall intensity and frequency, whose effects are increased by the use of water resources. This context may strongly impact the mobilization of these organic contaminants and their release to the environment. To study these phenomena, it is, therefore, essential to better understand the impact of the groundwater level fluctuation patterns on the LNAPLs mobilization processes. To this end, an original experimental system combining indirect geophysical (complex electrical conductivity, permittivity), in-situ physical-chemical (pH, Eh, temperature), and geochemical measurements was developed at the GISFI station (Homécourt, France). This device allows the assessment and the comparison of the amount and nature of LNAPLs release into the atmosphere and water from contaminated soil during two groundwater level fluctuations scenarios: one corresponding to the ‘actual’ rainfall pattern based on regional climate records; the other based on the predictions of the most extreme IPCC scenario. This study will be conducted at different scales (laboratory decametric columns and 2 m3 lysimeters) and on soils of different geological complexity. The remobilized hydrocarbons will be collected via suction cups and gas collection chambers as the groundwater table fluctuates and will be regularly analyzed (GC-MS, FTIR). The complementarity of the monitoring methods aims to provide a better understanding of the fate of these organic pollutants at contaminated sites and the evolution of the associated environmental risks in the coming years, under the expected effect of climate change. Preliminary results concerning the hydrocarbon pollution migration through the unsaturated zone and the distribution of the LNAPL will be presented to illustrate the capacity of this new instrumental system.This work is partly funded by the DEEPSURF project "Lorraine Université d’Excellence", ANR-15-IDEX-04-LUE".

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.

International audience; Purpose Assessments of urban soil organic carbon stock (SOCS) are scant because citywide data are scarce. Moreover, we do not know which factors mostly explain SOCS spatial and temporal variations in urban open soils.Methods To fill these knowledge gaps, the present study focused on Paris (France): two periods (1993-2007 and 2008-2016) were compared to better understand SOCS changes at 0-30 cm depth. The effects of anthropic factors (land use, management intensity, cover type, site age and size, city district, and indirectly, resource material used for the site establishment) and soil properties (e.g., soil nutrient contents) on SOCS were studied over the more recent period (2008-2016) on 810 soil samples.Results The changes in green space management methods between both periods resulted in an additional storage of + 43.5 Gg SOC in Paris open soils in 2008-2016 compared to 1993-2007. During 2008-2016, SOCS was still influenced by city history and particularly by the type of resource material used for landscaping, which has changed since the 1950s. SOCS differed significantly among city districts, which represent a combination of all studied anthropic factors: each district has its own history (i.e., soil resource material, green space age), specific number and size of green spaces, current management methods, and plant cover types. Paris green space SOCS was also influenced by soil nitrogen, sand, and magnesium contents as well as pH.Conclusions Modifications of local landscape management methods are a main driver of SOCS changes. Moreover, citywide SOCS distribution tends to depend on city history.

Biocrust-mediated in situ bioremediation could be an alternative strategy to mitigate metal(loid) pollution in aquatic habitats. To better understand the roles of biocrusts in regulating the fate of metal(loid)s, we examined the morphology, composition and structure of biological aqua crusts (BAC) developed in the mine drainage of a representative Pb/Zn tailing pond, and tested their effectiveness for immobilizing typical metal(loid)s. Unlike terrestrial biocrusts, BAC results from an assembly of compounds produced by the strong microbial activity and mineral compounds present in the aquatic environment. The BAC exhibited a unique flexible, spongy and porous structure with a specific surface area of 12-22 m2 g-1, and was able to effectively concentrate various metal(loid)s (e.g. Cd, 0.26-0.60 g kg-1; Pb, 0.52-0.66 g kg-1; As, 10.4-24.3 g kg-1). The concentrations of metal(loid)s (e.g. Cd and As) in the BAC were even three to seven times higher than those in the source tailings, and more than 98% of immobilized metal(loid)s were present as the highly stable non-EDTA-exchangeable fraction. Adsorption on the well distributed micro-particles of the clay minerals (e.g. kaolinite) and the organic matters (2.0-2.7 wt.%) were found to be the major mechanisms for BAC to bind metal cations, whereas adsorption and coprecipitation on Fe/Mn oxide (e.g. FeOOH), was proposed to be the dominant pathway for accumulating metal(loid)s, especially As. The decrease in aqueous concentrations of the metal(loid)s along the drainage could be attributed in part to the scavenging effects of the BAC. These findings therefore provide new insights into the possible and efficient strategy for metal(loid) removal from water bodies, and highlighted the important role of BAC as a nature-based solution to benefit the bioremediation of mining area.

The aim of this study was to assess the potential of the woody nickel hyperaccumulator species Blepharidium guatemalense (Standl.) Standl. for agromining in southeastern Mexico. Pot trials consisting of nickel dosing (0, 20, 50, 100, and 250 mg Ni kg−1), and synthetic and organic fertilization were conducted. Field trials were also undertaken with different harvesting regimes of B. guatemalense. Foliar nickel concentrations increased significantly with rising nickel additions, with a 300-fold increase at 250 mg Ni kg−1 treatment relative to the control. Synthetic fertilization strongly increased nickel uptake without any change in plant growth or biomass, whereas organic fertilization enhanced plant shoot biomass with a negligible effect on foliar nickel concentrations. A 5-year-old stand which was subsequently harvested twice per year produced the maximum nickel yield tree−1yr−1, with an estimated total nickel yield of 142 kg ha−1yr−1. Blepharidium guatemalense is a prime candidate for nickel agromining on account of its high foliar Ni concentrations, high bioconcentration (180) and translocation factors (3.3), fast growth rate and high shoot biomass production. Future studies are needed to test the outcomes of the pot trials in the field. Extensive geochemical studies are needed to identify potential viable agromining locations. Novelty Statement Our research team is a pioneer in the discovery of metal hyperaccumulator plants in Mesoamerica with at least 13 species discovered in the last 2 years. This study is the first to assess the potential of nickel agromining (phytomining) in Mexico (and in all the American continent), using one of the strongest nickel hyperaccumulators reported so far. The promising results of this study are the basis for optimal agricultural management of Blepharidium guatemalense.

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; Plants that naturally accumulate aluminium (Al) may also inadvertently accumulate rare earth elements (REEs) due to the similar chemical properties of Al and REE trivalent ions, and vice versa. In this study, an Al hyperaccumulator plant species, Melastoma malabathricum, and a species known to have a propensity to hyperaccumulate REEs (in addition to Al), Dicranopteris linearis, were evaluated for potential REE accumulation in a one-year pot dosing trial in Sabah, Malaysia. To test whether the Malaysian accessions of D. linearis and M. malabathricum hyperaccumulate REEs (and Al), both species were grown in pots containing soil treated with solutions containing yttrium (Y), lanthanum (La), neodymium (Nd), and a mixture of these three REEs. The results showed that both M. malabathricum and D. linearis accumulated > 1000 µg g−1 Al in their leaves as expected. The shoots of M. malabathricum contained lower REEs than the roots (50 µg g−1 compared to 905 µg g−1). In D. linearis, the mean foliar REE concentrations ranged from 145 to 315 µg g−1, which is below the hyperaccumulation threshold set for REEs (> 1000 µg g−1 REEs). This study revealed that the Malaysian accessions of both M. malabathricum and D. linearis are Al hyperaccumulators, but their REE hyperaccumulation status requires further testing.

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

Five mesofauna communities varying in both structure and composition were exposed to phenanthrene in mesocosms for up to four months. Effects of phenanthrene were assessed on mesofauna population dynamics, fungal biomass (ergosterol concentrations), and litter decomposition (litter mass loss, nitrogen concentration). The effects of each community on the fate of phenanthrene were also assessed. We hypothesize that phenanthrene affects the population dynamics of mesofauna and soil biological functioning depending on exposure duration, type of community, or both. Results show that phenanthrene exerted an effect on mesofauna and that the effects on some species, like Folsomia fimetaria, were influenced by the species composition in the mesocosms, the soil layer, and the sampling date. However, the effects of phenanthrene on ergosterol content and organic matter decomposition were not significantly influenced by community composition. These results demonstrate that interspecific relationships are needed to assess the toxicity of pollutants and should be taken into account in ecotoxicological risk assessment. Furthermore, this work does not support the hypothesis of a direct link between toxic effects of organic pollutants on mesofauna species and soil biological functioning. Five mesofauna communities varying in both structure and composition were exposed to phenanthrene in mesocosms for up to four months. Effects of phenanthrene were assessed on mesofauna population dynamics, fungal biomass (ergosterol concentrations), and litter decomposition (litter mass loss, nitrogen concentration). The effects of each community on the fate of phenanthrene were also assessed. We hypothesize that phenanthrene affects the population dynamics of mesofauna and soil biological functioning depending on exposure duration, type of community, or both. Results show that phenanthrene exerted an effect on mesofauna and that the effects on some species, like Folsomia fimetaria, were influenced by the species composition in the mesocosms, the soil layer, and the sampling date. However, the effects of phenanthrene on ergosterol content and organic matter decomposition were not significantly influenced by community composition. These results demonstrate that interspecific relationships are needed to assess the toxicity of pollutants and should be taken into account in ecotoxicological risk assessment. Furthermore, this work does not support the hypothesis of a direct link between toxic effects of organic pollutants on mesofauna species and soil biological functioning. Five mesofauna communities varying in both structure and composition were exposed to phenanthrene in mesocosms during up to four months. Effects of phenanthrene were assessed on mesofauna population dynamics, fungal biomass (ergosterol concentrations) and litter decomposition (litter mass loss, nitrogen concentration). The effects of each community on the fate of phenanthrene were also assessed. We hypothesize that phenanthrene affects the population dynamics of mesofauna and soil biological functioning depending on exposure duration and/or type of community. Results show that phenanthrene exerted an effect on mesofauna and that the effects on some species, like Folsomia fimetaria, were influenced by the species composition in the mesocosms, the soil layer and the sampling date. However the effects of phenanthrene on ergosterol contents and organic matter decomposition were not significantly influenced by community composition. These results demonstrate that interspecific relationships are needed to assess the toxicity of pollutants, and should be taken into account in ecotoxicological risk assessment. Furthermore, this work does not support the hypothesis of a direct link between toxic effects of organic pollutants on mesofauna species and soil biological functioning.

International audience; 17 Aims. Rinorea cf. bengalensis is a Ni hyperaccumulator which occurs in Sabah (Malaysia), on Borneo Island, 18 that is able to accumulate considerable amounts of Ni and influences the Ni cycle in surface soil layers, both in 19 terms of Ni concentration and Ni isotopic composition. In this study, the biogeochemical processes underpinning 20 Ni isotopic fractionation in the soil-plant system and the mechanisms regulating Ni homeostasis in R. cf. 21 bengalensis plants were elucidated. 22 Methods. Two specimens of R. cf. bengalensis of different ages and associated surface soils were collected from 23 ultramafic soils in Sabah. Soil mineralogy, Ni concentrations, speciation and isotopic signatures were 24 subsequently determined in plant and soil samples. 25 Results. Nickel in R. cf. bengalensis leaves is mainly complexed with citrate. Soil Ni available fractions have 26 different δ 60 Ni values depending on the Ni bearing phases. Rinorea cf. bengalensis specimens take up lighter Ni 27 isotopes and a pronounced isotopic fractionation within the plant is observed, especially in the young specimen. 28 Conclusions. The results suggest that the observed fractionation in the young plant can be attributable to kinetic 29 effects (lighter isotopes move faster), which become less evident in the older specimen, as Ni is redistributed and 30 homogenized through phloem loading and unloading processes. 31 2

Dicranopteris linearis is a fern that grows naturally on the tailings of former rare earth element (REE) mines in southern China. It accumulates REEs in its aerial parts at concentrations that classify this plant as hyperaccumulator. The main objective of this research is to design a process to recover REEs directly from the dry biomass. This process involves three steps: (i) extraction of REEs from the dry plant by leaching with a solution containing acid and/or complexing agents, (ii) precipitation of REEs with oxalate and (iii) calcination to prepare REE oxide. A methodology based on speciation calculation made it possible to determine operating conditions for precipitation by accounting for the influence of the species present according to the extraction method. Simulations were carried out using Chess software, allowing the calculation of the composition of a multicomponent solution at thermodynamic equilibrium. These operating conditions were then validated experimentally. REE extraction from the dry plant was significantly improved under acid conditions (with H2SO4) or with a strong complexing agent (ethylenediaminetetraacetic acid). After optimization of the precipitation conditions, REE precipitation yields were above 90 %. After calcination, the final solid (REE oxide) contained ca 69 % of the REEs present in the initial biomass. The use of sulphuric acid as an extracting agent resulted in the recovery of a solid composed of 52 wt % of REEs (based on metal content). Thus, this study proposes a new recovery route for these strategic elements with a REE concentration factor from soil to final solid of 2500.

Place: Philadelphia Publisher: Taylor & Francis Inc WOS:000553349100001; International audience; Cadmium is a non-essential trace metal, which is highly toxic to nearly all living organisms. Soil pollution causes Cd contamination of crops, thereby rendering plant products responsible for the chronic low level Cd over-exposure of numerous populations in the world. For this reason, Cd accumulation in plants has been studied for about five decades now. The research first focused on the relationships between plant and soil Cd levels, on the factors of the metal availability in soil, as well as the root uptake processes. Cd distribution in plant organs was also investigated, first using a macroscopic and eco-physiological approach, and then with the help of molecular biology tools, at both tissue and cell scales. Cadmium has no biological function and hijacks the transport pathways of micronutrients such as Fe, Mn, or Zn, in order to enter the plant through the roots and be distributed to all its organs. The study of the genes that control the influx and efflux of the Cd(2+)ion in the cytosol, vacuoles, and vascular tissues has significantly contributed to the understanding of the metal root uptake and of its transfer to the aerial parts. However, the mechanisms responsible for its distribution to the different above-ground tissues and specially to fruits and seeds have yet to be clarified. This review summarizes current knowledge in order to present a detailed overview of Cd transport and storage, from the rhizosphere to the different organs and tissues of the plant.

International audience; Increasing use of emerging per- and polyfluoroalkyl substances (PFASs) has caused extensive concerns around the world. Effective detection methods to trace their pollution characteristics and environmental behaviors in complex soil-crop systems are urgently needed. In this study, a reliable and matrix effect (ME)-free method was developed for simultaneous determination of 14 legacy and emerging PFASs, including perfluorooctanoic acid, perfluorooctane sulfonate, 6 hydrogenous PFASs, 3 chlorinated PFASs, and 3 hexafluoropropylene oxide homologues, in 6 crop (the edible parts) and 5 soil matrices using ultrasonic extraction combined with solid-phase extraction and ultraperformance liquid chromatography-mass spectrometry (MS)/MS. The varieties of extractants and cleanup cartridges, the dosage of ammonia hydroxide, and the ME were studied to obtain an optimal pretreatment procedure. The developed method had high sensitivity and accuracy with satisfactory method detection limits (2.40-83.03 pg/g dry weight) and recoveries (72-117%) of all target analytes in matrices at five concentrations, that is, 0.1, 1, 10, 100, and 1000 ng/g. In addition, the ME of this method (0.82-1.15) was negligible for all PFASs, even considering 11 different matrices. The successful application of the ME-free method to simultaneously determine the legacy and emerging PFASs in crop and soil samples has demonstrated its excellent practicability for monitoring emerging PFASs in soil-crop systems.

Rhizosphere pH is the consequence of numerous, complex processes and is a key factor of biogeochemistry at the soil-root interface. This work aimed at evaluating the impact of nutrient root absorption on rhizosphere pH using a mechanistic model formalizing major nutrient cation and anion transport, under the influence of concentration, electric potential gradients and of convection. The electrical neutrality of the system was maintained through a H+ root efflux or influx (or equivalent opposite OH− fluxes). The model outputs were compared to the rhizosphere pH of maize (Zea mays L.), ryegrass (Lolium perenne L.) and Alpine pennycress (Noccaea caerulescens (J. & C. Presl) F. K. Mey.) grown in three different soils, determined with planar optodes. A global sensitivity analysis was carried out in order to highlight the dominating factors. The composition of 37 soil solutions from the literature was used to predict rhizosphere pH. The model most of the time predicts the alkalinisation of the rhizosphere by up to +3.3 pH units, given that in aerobic soils, nitrate is the most absorbed nutrient and its internalization is equilibrated by H+ root absorption (or equivalent OH− excretion). This alkalinisation is close to that observed in the rhizosphere of ryegrass and Alpine pennycress. The rhizosphere pH predictions are very sensitive to the initial composition of the soil solution and quite insensitive to root absorption kinetics and soil buffer power for the various nutrients. Because it favours nitrate diffusion, water content is positively correlated with rhizosphere alkalinisation. Moreover, the lower the root density, the lower the effect of the root uptake on both ion concentrations and on rhizosphere pH. Convection has little influence on rhizosphere pH. This study confirms the prominent role of mineral nutrition in the determination of rhizosphere pH. The model therefore constitutes a tool for understanding and predicting rhizosphere pH.

International audience; Clay-sized soil minerals are known to protect organic carbon (OC) from mineralisation by formation of organo-mineral associations limiting its availability to microorganisms. The impact of soil fauna on these processes is poorly known. The aim of this study was to investigate the effect of earthworms on organic matter (OM) decomposition and association with minerals during a laboratory experiment. We used a model system consisting of fresh OM incubated with and without epigeic earthworms (Eisenia andrei and foetida) in presence of different types and amounts of phyllosilicates (kaolinite, montmorillonite) and an iron oxide (goethite) and combinations of these minerals. Our experimental setup included a high OM:mineral ratio to represent the soil-litter interphase. We monitored OC mineralisation during 196 days. Additionally, we investigated physicochemical parameters and chemical OM characteristics of decomposition products by determination of water-soluble OC (WSOC) and acquisition of solid-state 13C NMR spectra. We also analysed microscale organisation of the organo-mineral associations produced with and without earthworms by transmission electron microscopy (TEM).Earthworms enhanced OC mineralisation in all treatments. They also led to greater reductions of OC emissions in the presence of minerals as compared to the mineral-free control, depending on the type and amount of minerals added. The presence of earthworms affected microbial biomass, the concentration of WSOC and increased the contribution of aromatic compounds to OM decomposition products. Microscale analyses by TEM showed that earthworms favoured association of minerals with partly degraded OM along with completely degraded material, while in absence of earthworms only completely degraded OM was associated with minerals. We conclude that earthworms impact OM decomposition through (1) their effect on microbial biomass and the physicochemical parameters of microbial habitat and (2) the formation of OM associations by changing the OM types associated to minerals and possibly by creating closer association of partly degraded OM and iron oxides. The stability of these associations remains to be investigated.

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.

This study was conducted to assess the impact of polycyclic aromatic hydrocarbon on the composition of rhizodeposits. Maize was submitted to increasing phenanthrene (PHE) concentrations in the substrate (0, 25, 50, and 100 mg PHE.kg−1 of dry sand). After 6 weeks of cultivation, two types of rhizodeposit solution were collected. The first one, called rhizospheric sand extract, resulted from the extraction of root adhering sand in order to collect mucilage and associated compounds. The second one, the diffusate solution, was collected by the diffusion of exudates from roots soaked in water. The impact of phenanthrene on maize morphology and functioning was measured prior to the analysis of the main components of the rhizodeposit solutions, by measuring total carbon, protein, amino acid, and sugars as well as by determining about 40 compounds using GC-MS and LC-MS. As maize exposure to PHE increased, different trends were observed in the two rhizodeposit solutions. In the diffusate solution, we measured a global increase of metabolites exudation like carbohydrates, amino acids, and proteins except for some monoglycerides and organic acids which exudation decreased in the presence of PHE. In the rhizospheric sand extract, we witnessed a decrease in carbohydrates and amino acids secretion as well as in fatty and organic acids when plants were exposed to PHE. Many of the compounds measured, like organic acids, carbohydrates, amino acids, or fatty acids, could directly or indirectly drive PAHs availability in soils with particular consequences for their degradation.

Mercury (Hg) is a highly toxic metal with no known biological function, and it can be highly bioavailable in terrestrial ecosystems. Although fungi are important contributors to a number of soil processes including plant nutrient uptake and decomposition, little is known about the effect of Hg on fungi. Fungi accumulate the largest amount of Hg and are the organisms capable of the highest bioaccumulation of Hg. While referring to detailed mechanisms in bacteria, this mini-review emphasizes the progress made recently on this topic and represents the first step towards a better understanding of the mechanisms underlying Hg tolerance and accumulation in fungal species and hence on the role of fungi within the Hg cycle at Hg-contaminated sites. KEY POINTS: • The fungal communities are more resilient than bacterial communities to Hg exposure. • The exposure to Hg is a threat to microbial soil functions involved in both C and nutrient cycles. • Fungal (hyper)accumulation of Hg may be important for the Hg cycle in terrestrial environments. • Understanding Hg tolerance and accumulation by fungi may lead to new remediation biotechnologies.

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.

Plant and soil 455, 289 ��� 303 (2020). doi:10.1007/s11104-020-04629-7, $Aims$Knowledge on the ecophysiology of cobalt hyperaccumulator species is limited. The nickel hyperaccumulator Rinorea cf. bengalensis from Borneo can accumulate high concentrations of cobalt in nature. This study investigates the cobalt accumulation potential of Rinorea cf. bengalensis in relation to nickel concentrations in soils and the subsequent tissue and cellular-level distributions of cobalt, nickel and major cations.$Methods$Seedlings of Rinorea cf. bengalensis were grown in mixed treatments on ultramafic soil containing a high concentration of available nickel. Cobalt and nickel salts were then added to the soil to study their interactions. The tissue and cellular-level distributions of cobalt, calcium, nickel, and potassium were investigated using synchrotron-based X-ray fluorescence microscopy.$Results$The maximum foliar cobalt concentration reached 1200 ��g g$^{���1}$. Accumulation of cobalt competed with nickel accumulation although nickel seems to stimulate cobalt phloem translocation. Plants suffered toxicity in the treatment with the highest soil cobalt concentration. Cobalt and nickel have contrasting distribution patterns in the leaves of Rinorea cf. bengalensis, with cobalt mainly excreted on the surface of the leaves, whereas nickel is localised in foliar epidermal cells.$Conclusions$Rinorea cf. bengalensis can accumulate high concentrations of cobalt, but is intrinsically more tolerant to nickel. It does not rely on a similar sequestration mechanism for both metals, which could explain the lesser tolerance for cobalt. Nickel appears to be essential for the plant to tolerate high cobalt concentrations. Further studies intending to develop agronomic practices are needed to determine the viability of Rinorea cf. bengalensis for nickel-cobalt agromining., Published by Springer Science + Business Media B.V, Dordrecht [u.a.]

The fern Dicranopteris linearis (Gleicheniaceae) from China is a hyperaccumulator of rare earth element (REE), but little is known about the ecophysiology of REE in this species. This study aimed to clarify tissue-level and organ-level distribution of REEs via synchrotron-based X-ray fluorescence microscopy (XFM). The results show that REEs (La + Ce) are mainly colocalized with Mn in the pinnae and pinnules, with the highest concentrations in necrotic lesions and lower concentrations in veins. In the cross sections of the pinnules, midveins, rachis, and stolons, La + Ce and Mn are enriched in the epidermis, vascular bundles, and pericycle (midvein). In these tissues, Mn is localized mainly in the cortex and mesophyll. We hypothesize that the movement of REEs in the transpiration flow in the veins is initially restricted in the veins by the pericycle between vascular bundle and cortex, while excess REEs are transported by evaporation and cocompartmentalized with Mn in the necrotic lesions and epidermis in an immobile form, possibly a Si-coprecipitate. The results presented here provide insights on how D. linearis regulates high concentrations of REEs in vivo, and this knowledge is useful for developing phytotechnological applications (such as REE agromining) using this fern in REE-contaminated sites in China.