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Phytoextraction field trials with Noccaea caerulescens were conducted in Brussels (Belgium) to investigate the benefits of nitrogen fertilization and planting density on phytoextraction efficiency. Both metallicolous (Ganges) and non-metallicolous (NMET, Luxembourg) populations were grown for 6 months in an urban wasteland and in a vegetable garden contaminated with trace metals at two planting densities (50 and 100 plants·m−2, D50 and D100), with and without mineral nitrogen fertilizers. Trials showed that N. caerulescens responded positively to nitrogen fertilization through increased biomass production. However due to lower concentrations in Cd and Zn in fertilized plants, the total metal uptake was differently impacted by fertilization: on one site metal uptake was enhanced while on the other it was reduced. Moreover fertilization had collateral effects as enhancing fungal pathogen development. The effect of planting density of N. caerulescens assessed in this work for the first time highlighted a clear competition between individuals at higher density – proved by lower individual biomass – but the highest metal uptake was nevertheless achieved at the highest density of 100 plants·m−2 because of higher total biomass. Six months after harvest soil exchangeable concentrations were reduced by about 25% for Cd with Ganges population and by 9% for Zn with the NMET population on the best treatment (N fertilized and D100). The feasibility of using N. caerulescens for bioavailable contaminant stripping of moderately contaminated soils was confirmed for Cd and to a lesser extent for Zn.

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; The French programme Réseau de Mesures de la Qualité des Sols e Biodiversité was carried out at a regional scale (Brittany, west part of France) i) to produce a first statement regarding soil biodiversity, ii) to identify bioindicators of anthropic constraints, and iii) to determine baseline values for several biological groups depending on land uses. In this study, 109 monitoring sites were investigated using a systematic framework (a 16 km 16 km regular grid). Six biological groups were studied within four major categories, i.e., macrofauna (all soil macro-invertebrate taxa and earthworms), mesofauna (Acari and Collembola), microfauna (nematodes), and micro-organisms (microbial biomass and functional genes). The abundances of earthworms, nematodes, Acari and the bacterial community (assessed by their encoded 16S rRNA) as well as microbial biomass and earthworm species richness discriminate land uses (crops from meadows from forests). Macro-invertebrate abundance, Collembola abundance and richness, and nematode richness are only relevant for the discrimination of agricultural practices (e.g., management system or fertilisation intensity). Most of the soil biological groups (except Collembola) exhibit lower values of abundance and community richness in croplands than in meadows. This programme allows us to set up a first reference database for soil biological data for France covering microflora and fauna. This substantial reference database will be used to calibrate future research results and to develop management baseline values for stakeholders to assess the status of soil biodiversity under several policies, e.g., the Common Agricultural Policy, Soil Framework Directive, EU and national biodiversity strategies, and policies related to contaminated land management. Therefore it should assist stakeholders in the choice of good agricultural practices.

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.

International audience; The spatial distribution of total and CaCl(2)-extracted Cd, Pb and Zn concentrations in smelter-impacted soils was investigated over a polluted site (40km(2)) in Northern France. The study was conducted on 262 soils sampled in woody habitats. Total and extracted concentrations of trace metals (TMs) rose up to 2402 and 59.5mgkg(-1) for Cd, 41 960 and 13.7mgkg(-1) for Pb, 38 760 and 143.0mgkg(-1) for Zn, respectively. The spatial dependence of both total and extracted concentrations showed a high spatial auto-correlation and ordinary kriging was used to predict soil concentrations. Investigating which variables influenced metal concentrations and their spatial distribution, we found that total concentrations mostly depended on the distance from the smelter, the wind and the organic carbon, while extracted concentrations were mainly modulated by the pH. Conditionally to those variables, other soil properties and landscape characteristics influenced both total and extracted concentrations. We conclude that total and extracted TM concentrations are governed by different processes which act at various spatial ranges: total concentrations are mainly related to input and retention of metals (large scale) whereas extracted concentrations were mainly explained by factors controlling metal solubility in soils (local scale). Spatial distributions of total and extracted TMs differed over the area, which should be considered for risk assessment. Maps of risk based on the US EPA's Eco-SSLs (for plants, invertebrates and vertebrates) were realized, showing that wildlife may be at risk but that the relevance of Eco-SSL values is questionable.

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; The contamination of the topsoil of 262 woody habitats around a former lead smelter in the North of France was assessed. In this urbanized and industrialized area, these kinds of habitats comprise of hedges, groves, small woods, anthropogenic creations and one large forest. Except for the latter, which is 3km away, these woody habitat soils often present a high anthropization degree (a significant amount of pebbles and stones related to human activities) with a high metal contamination. In the studied woody habitat topsoils, Cd, Pb and Zn concentrations largely exceeded those of agricultural topsoils located in the same environmental context. Therefore, atmospheric emissions from the smelter are not the only cause of the high contamination of the woody habitat soils. This last one is related to the nature and the contamination level of deposit in relation with human activities (rubbles, slag, soils, etc). With regard to the results obtained with chemical extractions, the mobility of Cd, Pb and Zn in these soils is also greater than in agricultural soils. In the forest, pollutant solubility is increased by soil acidic pH. The variability of the physico-chemical parameters and the high metal contamination of the topsoils are the main characteristics of the woody habitats located around the former smelter. Although never taken into account during risk assessment, the disturbance of these environmental components could have important biogeochemical impacts (nutrients and metal cycles). Moreover, any modification of the soils' use could potentially cause mobilization and transfer of the pollutants to the biosphere. Six years after the closure of the smelter, and as social and economic pressures considerably increase in this area, the study of these peculiar ecosystems is necessary to understand and predict the bioavailability, transfer, bioaccumulation and effects of pollutants in food chains.

Udgivelsesdato: 010709 Insect resistant Bt-maize (MON 810) expresses active Cry1Ab endotoxin derived from Bacillus thuringiensis (Bt). Snails constitute non-target soil species potentially exposed to Bt-toxin through consumption of plant material and soil in fields where transgenic plants have been grown. We studied the effect of the Cry1Ab toxin on survival, growth and egg hatchability of the snail Cantareus aspersus. From the age of 4 to 88 weeks, snails were fed either powdered Bt-maize or non-Bt-maize and exposed to soil samples collected after harvesting either the Bt-maize or non-Bt-maize. We applied four treatments: non-Bt soil + non-Bt-maize (MM); Bt soil + Bt-maize (BB), non-Bt soil + Bt-maize (MB), Bt soil + non-Bt-maize (BM). Eggs laid by snails not exposed to Bt-toxin were also exposed to the two types of soils (Bt and non-Bt soil).At the end of growth (47 weeks of exposure), snails exposed to Bt-toxin in food and soil (BB) had a growth coefficient (GC) 25% lower than unexposed snails (MM). After the first period of reproduction (68 weeks) a significant difference remained for body mass GC between the BB and MM treatments. Differences in body mass were not significant at the end of exposure (88 weeks). For snails not previously exposed to Bt material, hatchability of eggs was similar in the soils tested. The outcome of the experiments indicates that, in growing snails, long-term exposure is needed to reveal an effect of Bt-maize. The hazard analysis of Bt-maize which we performed, based on a worst-case scenario, i.e. snails having no food choice, should now be complemented by other simple measurements, e.g. food intake, to understand the underlying mechanisms involved.

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.

Summary Potential differences between Bt-maize (MEB307 expressing the insecticidal Cry1Ab protein) and a near-isogenic non-Bt variety (Monumental) in their influence on the garden snail (Helix aspersa), soil microarthropods (Collembola, Actinedida, Acaridida, Gamasida and Oribatida) and mycorrhizal fungi were studied. Growing snails were caged in microcosms allowing the development of Bt or non-Bt-maize (Zea mays L.) on a sandy loam soil. After 3 months exposure, survival and growth of snails were similar in both treatments. Cry1Ab protein was detected in the Bt-maize leaves (22–42.2 μg Bt protein g−1 dry wt), in the snail tissues (0.04–0.11 μg Bt-protein g−1 dry wt) and in their faeces (0.034–5 μg Bt-protein g−1 dry wt). Total soil microarthropod abundance and diversity were similar between control (non-Bt-maize) and the genetically modified (GM) Bt-maize microcosms. The mycorrhizal colonization of roots did not differ between Bt and non-Bt-maize (frequency of mycorrhizal roots was 88.7% and 83.3% respectively). The mycorrhizal infectivity of soils, expressed as MI50 (minimum soil dry weight required to colonize 50% of plants) was measured using red clover. MI50 was similar for soils where Bt or non-Bt-maize was cultivated for 4 months. The detection of Cry1Ab protein in the viscera and faeces of H. aspersa exposed to Bt-maize indicates that snails contribute to the transfer of the Bt-protein from plant to soil or snail predators. This may constitute an alternative route of exposure for Bt-protein in soil, but this was without a negative influence on mycorrhizal fungi or microarthropods. Results showed that Bt-maize was not toxic for the selected non-target species exposed for 3 or 4 months. The microcosms and analyses used in this study represent new methods for assessing effects of chronic exposure to GM plants of several diverse, yet ecologically and temporally associated species. As the soil organisms we studied can also be used in standardized ecotoxicological tests (XP X31-205-2 for mycorrhizal fungi, ISO 11267 for Collembola and ISO 15952 for snails), microcosm exposures represent a way to link laboratory and field methods for the ecotoxicological evaluation of GM plants.

International audience; We studied the relationships between testate amoeba communities and heavy metal (Pb, Cd, Zn, Ni, Cu, Mn, and Fe) concentrations in the moss Barbula indica sampled at 29 sites in and around the city of Hanoi (Vietnam). Our first approach was to compare the heavy metal concentrations and testate amoeba variables between the city (zone 1) and the surrounding (zone 2). Mean moss concentrations of Pb, Cd, Zn, Ni, and Cu were significantly higher and testate amoeba species richness and abundance were significantly lower in zone 1 and the abundance of eight taxa differed significantly between the two zones. We then studied the correlation between heavy metals and testate amoebae. Species richness and abundance were correlated negatively to Pb concentration. Shannon H′ was negatively correlated to both Pb and Cd. The abundance of several species was negatively correlated with Pb, Cd, Zn, and Ni; however, at the community level, Pb emerged as the only significant variable in a redundancy analysis. Our results suggest that testate amoebae are sensitive to and may be good bioindicators for heavy metal pollution, especially lead. Further research is needed to understand the causal relationships underlying the observed patterns.

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

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; 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.

International audience; AbstractPurposeUrban soil contamination by heavy metals is one of the foremost challenges for urban soil quality, especially in the urban agriculture context. Urban gardening is a common practice in many industrialized and developing countries. How sources of soil contamination relate to inputs and influence the heavy metal content in soils, however, is not established yet.Materials and methodsThis study aims to assess the potential of pesticide applications (such as Bordeaux mixture) on soil quality. A set of 104 allotment gardens was selected in three cities in France, and topsoil was sampled and analyzed.Results and discussionThe four most abundant metals in urban vegetable garden topsoils were Zn, Pb, Cu, and Cr. The past and/or present industrial and urban activities are not the only cause of the metal contamination in urban vegetable garden soils. Gardens, where pesticides such as the Bordeaux mixture are being used showed significantly higher total Cu values in soils (78 mg kg−1 compared with 49 mg kg−1 for untreated gardens).ConclusionsEven though the risk of metal contamination through vegetable consumption is usually considered low, we clearly identified indicators of anthropogenic Cd, Cu, Pb, and Zn pollution due to pesticides inputs. This link was particularly strong between the use of Bordeaux mixture and increases Cu levels.

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.

The flora of Papua New Guinea is amongst the richest in the world with an estimated 25,000 plant species. The extreme levels of biodiversity, climatic ranges and soil types suggest a high possibility of metal hyperaccumulator plants existing in Papua New Guinea. However, no hyperaccumulator plants have been reported from this region yet. The use of handheld X-ray fluorescence instruments is a non-destructive and effective method for the systematic quantitative assessment of hyperaccumulation in vast numbers of herbarium specimens. X-ray fluorescence scanning was undertaken at the Queensland Herbarium (Australia) on all Papua New Guinea specimens from seven major families (Celastraceae, Cunoniaceae, Phyllanthaceae, Proteaceae, Rubiaceae, Salicaceae and Violaceae), covering 3164 plant specimens. This preliminary survey revealed the existence of ten zinc hyperaccumulator species (> 3000 µg g−1 Zn), eight manganese accumulator species (> 5000 µg g−1 Mn) and one nickel hyperaccumulator species (> 1000 µg g−1 Ni). These results highlight the potential for discovery of numerous new metal hyperaccumulator plants from the flora of Papua New Guinea if larger-scale systematic screening efforts were undertaken.

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.

Rhizodegradation is the breakdown of organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) using plants and rhizospheric microorganisms. The influence of two phytoremediating plants, Miscanthus × giganteus (M × G) and Trifolium repens L., was studied on a PAH-contaminated technosol composed of soil and sediments. More specifically, microbial density and diversity were studied along with the density of the population of PAH-degrading bacteria. M × G and white clover were tested in mono- and co-culture on the technosol in a mesocosm over 263 days (life cycle of M × G until its senescence). At the beginning and the end of the phytoremediation experiment, microbial density was measured by real-time PCR, targeting bacteria (16S rDNA), fungi (18S rDNA), and PAH-degrading bacteria (PAH-RHDα GP). Bacterial and fungal diversity were determined by metagenomic analysis. The M × G monoculture appeared to increase bacterial diversity compared to non-planted technosol, in contrast to other planting patterns, while fungal diversity appeared to decrease in the presence of any of the plants. Overall, the plants increased the bacterial density in the technosol, while only white clover and the co-culture increased the fungal density, with the latter having a greater impact. Concerning the degrading bacteria, only the co-culture stimulated the PAH-degrading bacterial population. This is remarkable for the PAH rhizodegradation. Even though the co-culture seemed to decrease the microbial diversity in the technosol, this condition was the most interesting with respect to the increase of the bacterial and fungal density as well as the enhancement of the PAH-degrading bacteria in the technosol.

International audience; Stinging nettle (Urtica dioica L.) raises growing interest in phytomanagement because it commonly grows under poplar Short Rotation Coppices (SRC) set up at trace-metal (TM) contaminated sites and provides high-quality herbaceous fibres. The mycobiome of this non-mycorhizal plant and its capacity to adapt to TM-contaminated environments remains unknown. This study aimed at characterizing the mycobiome associated with nettle and poplar roots co-occurring at a TM-contaminated site. Plant root barcoding using the fungi-specific ITS1F-ITS2 primers and Illumina MiSeq technology revealed that nettle and poplar had distinct root fungal communities. The nettle mycobiome was dominated by Pezizomycetes from known endophytic taxa and from the supposedly saprotrophic genus Kotlabaea (which was the most abundant). Several ectomycorrhizal fungi such as Inocybe (Agaricomycetes) and Tuber (Pezizomycetes) species were associated with the poplar roots. Most of the Pezizomycetes taxa were present in the highly TM-contaminated area whereas Agaricomycetes tended to be reduced. Despite being a known non-mycorrhizal plant, nettle was associated with a significant proportion of ectomycorrhizal OTU (9.7%), suggesting some connexions between the poplar and the nettle root mycobiomes. Finally, our study raised the interest in reconsidering the fungal networking beyond known mycorrhizal interactions.

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.

Phytoextraction using hyperaccumulating plants is a method for the remediation of soils contaminated with trace elements (TEs). As a strategy for improvement, the concept of fungal-assisted phytoextraction has emerged in the last decade. However, the role played by fungal endophytes of hyperaccumulating plants in phytoextraction is poorly studied. Here, fungal endophytes isolated from calamine or non-metalliferous populations of the Cd/Zn hyperaccumulator Noccaea caerulescens were tested for their growth promotion abilities affecting the host plant. Plants were inoculated with seven different isolates and grown for 2 months in trace element (TE)-contaminated soil. The outcomes of the interactions between N. caerulescens and its native strains ranged from neutral to beneficial. Among the strains, Alternaria thlaspis and Metapochonia rubescens, respectively, isolated from the roots of a non-metallicolous and a calamine population of N. caerulescens, respectively, exhibited the most promising abilities to enhance the Zn phytoextraction potential of N. caerulescens related to a significant increase of the plant biomass. These strains significantly increased the root elemental composition, particularly in the case of K, P, and S, suggesting an improvement of the plant nutrition. Results obtained in this study provide new insights into the relevance of microbial-assisted phytoextraction approaches in the case of hyperaccumulating plants.

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; A unified framework for simulating various transport processes in the environment is presented. It consists in a single set of partial differential equations. The main feature of this model framework is its exchange layer, which allows to treat several types of transfer between the soil and the surface water. The model framework equations, termed transfer equations, is shown to reproduce three independently-published models developed for soil erosion, river bedload, and chemical transport respectively. By allowing the different processes to be represented within a single model framework, the transfer equations are therefore unifying the representation of particles and chemical fluxes in the environment. The transfer equations are implemented into the open-source software FullSWOF_1D. The code is verified against the approximation of an exact solution, assuring its proper functioning. A good adequacy is found between our numerical results and those published in the literature, attesting the capability of the transfer equations to unify modeling of soil erosion, river bedload, and chemical transport. Hence, the transfer equations can decrease the number of models to be used for simulating transfer of materials in the environment, and limit the number of computer codes to be developed and maintained. The transfer equations could also help in drawing parallels between different fields of hydrology.

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.

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.

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.

International audience; Technosols are defined by the World Reference Base as soils subjected to a strong human influence and containing at least 20% of artefacts. The construction of Technosol using recycled waste material is considered an appealing sustainable use of both natural and anthropic resources. Constructed Technosol can attract and host a multitude of soil organisms, forming a reserve of biodiversity. In this study, we assessed the early colonization – in successional stages – of a constructed Technosol supporting grassland vegetation by the microarthropod community, in particular Collembola. To do this, the taxonomic and functional characteristics of microarthropod communities in a newly constructed Technosol in northeast France were studied for a period of four years. Collembola communities also increased in density and taxonomic richness, as well as in functional richness and dispersion. However, hemiedaphic Collembola dominated the community, particularly in the fourth year. Findings at the end of the survey indicated that the Collembola community in the studied Technosol remained very different to that of natural grassland, while it shared some characteristics with arable land. However, the present research clearly showed that waste material recycling to construct a Technosol could be an opportunity to support soil microarthropod biodiversity.

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 consumption of vegetables grown on soils polluted by trace elements can cause a serious threat for animal and human health and disturb the functioning of the ecosystem. The aim of this work is to determine the concentrations of As, Cd, Co, Cr, Cu, Ni, Pb, Mn, and Zn in soils and different vegetables from market gardens of urban areas in Marrakech city in order to investigate human health risk through ingestion of contaminated vegetables. Plant transfer factor (TF), daily intake of metals (DIM), and health risk index (HRI) were calculated. The concentrations of all metals studied in the garden top soils were within the threshold values. The Cu, Zn, Co, Mn, and As concentration in the edible parts of vegetables were within the safe limits. However, Cd and Pb in Malva parviflora and Cd in Brassica rapa, and Cr and Ni in Coriandrum sativum exceeded their permissible limits. The TF for these nine metals varied between 0.01 and 1.35. The classification of TEs according to their TF is as follows: Cu > Zn > Cd > Ni > Cr > Pb > Mn > Co > As. The maximum value was recorded in Coriandrum sativum while the minimum value was recorded in Cynara cardunculus. The HRI values were within the safe limit (

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.

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.

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.

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; Millipedes (Diplopoda) and terrestrial isopods (Isopoda) may play a significant role in soil decomposition. The present study aimed to contribute to the general understanding of feeding performances of macrodetritivores consuming grass litter by answering two questions. Q1: Are grass litter traits indicating nutritive value (i.e. chemical) and traits indicating feeding deterrents (i.e. mainly physical but not necessarily) both necessary to explain individual feeding performances of soil invertebrates consuming grass litter? Q2: Do grass physical traits indicating physical deterrents (e.g. WHC for mechanical aspects) provide more than, less than or the same amount of information about invertebrate individual performances as grass chemical traits indicating mainly chemical but also physical deterrents (e.g. lignin content directly for digestibility and indirectly for mechanical aspects)? We thus designed a laboratory experiment to assess individual feeding performances of two common macrodetritivores (Armadillidium vulgare (Latreille, 1804) and Glomeris marginata (Villiers, 1789)) in four monospecific treatments of litter from perennial forage grasses (Brachypodium pinnatum P. Beauv., Bromus erectus Huds., Festuca rubra L. and Holcus lanatus L.). A. vulgare feeding performances were correlated with nutritive values (litter N and P contents) and plant mechanical aspects (LDMC: leaf dry matter content). G. marginata performances were correlated with chemical deterrents (cellulose and lignin contents). Thus, (Q1) for grass litters, both traits indicating nutritive value (e.g. N, P) and feeding deterrents (e.g. LDMC, lignin content) are necessary to explain macroinvertebrates feeding performances. We also demonstrated the results depend on the invertebrate species considered. Also, (Q2) chemical deterrents may influence feeding performances of G. marginata the most, while physical deterrents related to mechanical aspects may influence those of A. vulgare the most. Our study indicates that using grass chemical and physical traits that indicate both nutritive value and feeding deterrents can help explain feeding performances of macrodetritivores consuming grass litter.

Although fires are common disturbances in North American forests, the extent to which soil invertebrate assemblages recover from burning remains unclear. Here, we examine long-term (14- to 101-yr) recoveries of soil invertebrate communities from common cut and burn treatments conducted at 6 to 26-yr intervals since 1911 in a deciduous forest in the upper Great Lakes region (USA). We characterize soil surface macro-invertebrate communities during both fall and spring across a long-term, experimental fire chronosequence to characterize invertebrate community recovery at decadal time-scales and community changes between seasons. We posited that changes in invertebrate community structure might, in turn, impact decomposition process. We sampled active organisms at the soil surface using pitfall traps. We described understory vegetation, measured soil properties, and conducted a 4-year litter bag study with big-toothed aspen leaves (Populus grandidentata). Invertebrate community responses followed a habitat accommodation model of succession showing that invertebrate succession is dependent on the soil surface properties. The fall and spring measures revealed that the densities of active invertebrates were highest 101 years after fire. For a given pair of stands, a pattern of sharing higher percentage of taxa was denoted when stands were of similar age. Some species such as the beetle Stelidota octomaculata appeared to be indicator of the chronosequence succession stage because it tracks the successional increase of Quercus and acorn production at the study site. We also found a significant positive correlation between leaf decomposition of soil macrofaunal accessible leaves and millipedes density across the chronosequence. We show that vegetation cover changes and related shifts in habitat structure occurring during post-fire succession are important in shaping communities assemblages. This finding highlights the importance of simultaneously considering abiotic-biotic factors together with above- and belowground measurements to better characterize controls on successional community dynamics after disturbance.