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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.

Technosol construction through assemblage of treated soil and recycled wastes is an innovative option for the restoration of degraded lands and re-use of industrial wastes. Recent studies have evidenced that Technosols could support soil functions such as primary production but the knowledge about other ecosystemic services, such as nutrient cycling, is limited. We investigated how the total bacterial community and key functional microbial communities involved in nitrogen cycling were influenced by the depth and type of Technosol. We found that despite being artificially constructed, Technosols exhibited a gradual change in microbial activity and abundance along the soil profile. Both nitrification and denitrification rates decreased with increasing depth as previously observed in other soil systems. Potential denitrification and nitrification were correlated with Technosol physico-chemical properties but also with abundances of nirS denitrifiers and bacterial amoA gene, respectively. The correlation between nitrification rates and bacterial ammonia-oxidizers suggests that bacteria are driving nitrification in Technosols. A-RISA fingerprints showed a distinct community structure along different Technosol layers. Technosol properties affected denitrification strongly than nitrification underlining the importance of better understanding the microbial communities in Technosols to maximize their potential for nutrient cycling, an essential ecosystem function.

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; 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.

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.

The early stages of bacterial colonization of a sterilized soil put in contact with the same non-sterile soil were investigated. Soil mesocosms of 269 cm3 composed of sterilized spherical remoulded soil clods of 27 mm diameter surrounded by non-sterilized 2–4 mm soil aggregates of the same soil (considered as a source of bacterial colonizers) were designed. Bacterial colonization was monitored from 0 to 14 days in three concentric portions of the sterilized clods (outer, intermediate and inner) and in the surrounding non-sterile soil, by measuring cell numbers and substrate-induced respiration (SIR). In addition, modifications of genetic diversity of the soil bacterial community associated to colonization were monitored with the ribosomal intergenic spacer analysis (RISA) technique in the intermediate portion of the sterilized soil clod and in the surrounding non-sterile soil aggregates. Assessments of bacterial cell numbers and SIR rates showed that the sterilized soil clod was colonized rapidly during incubation time from its outer to its inner portion. In addition, the bacterial genetic structure of the clod varied during incubation time, suggesting succession of bacteria during recolonization. Comparison of cell numbers, SIR rates and bacterial genetic structure between the soil clod and the surrounding soil aggregates showed that the colonization process in the clod led to the establishment of a bacterial community different from the surrounding soil aggregates.

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.

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.

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; 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: 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.

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.

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; 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; 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.

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; 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.

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; 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.

Purpose: Journal of Soils and Sediments publishes the main outcomes of SUITMA 9 Conference in its Special Issue. SUITMA (Soils of Urban, Industrial, Traffic, Mining and Military Areas) working group organizes conferences biannually all over the world. The ninth conference organized in Moscow in May 2017 involved more than 215 speakers from 25 countries, whose presentations focused on challenges and opportunities of urbanization for soil functions and ecosystem services. Materials and methods: The main outcomes of SUITMA 9 were analyzed in comparison to the previous SUIMTA conferences and the main topics were distinguished. Manuscripts accepted for publishing in the Special Issue were reviewed and presented. Results and discussion: Comparison of the topics highlighted in different special issues highlighted the evolution of the SUITMA studies from fundamental morphological descriptions and classifications to applied studies on soil engineering, assessment of SUITMA functions and ecosystem services. Conclusions: The manuscripts accepted to the Special Issue covered included various case studies of SUITMA ecosystem services (e.g. global and local climate regulation, biodiversity maintenance and improvement, nutrients balance and recreation) and disservices (e.g. pollution by heavy metals, polycyclic aromatic hydrocarbons and sulfur). The increasing role of SUITMA studies for urban management and decision making was concluded.

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

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).

International audience; Aims: Phytoremediation of soil contaminated by trace elements is a technology using plants and microorganisms to sequester, inactivate, or extract contaminants from the soil. The assemblage formed by the partnership between plants and microorganisms is referred to as the plant holobiont concept. Among holobiont microorganisms, endophytes are associated with the plant at its earliest growth stage and are localized inside plant tissues. While plant tissues shelter endophytic microbial communities, mutualistic endophytes have shown a potential for plant growth promotion that will deeply and durably benefit the plant holobiont. In this review, we describe the state-of-the-art knowledge of the endophytes’ role in plant growth promotion and the prospects for phytoremediation technologies.Results: Mutualistic symbionts have been demonstrated to improve plant growth, germination and yield. Indeed, they improve plant nutrition, increase plant resistance to bio-aggressors and stimulate plant metabolite productions. Research has shown that endophytes improve plant performance especially under extreme conditions such as drought, nitrogen deficiency, salinity and exposition to metal phytotoxicity. Endophyte inoculation has shown potential for plant growth promotion and has increased metal translocation in hyperaccumulator shoots by mitigating stresses from contaminated and naturally metal-rich soils.Conclusions: Endophytes have demonstrated their potential to enhance the plant’s physiological status under metallic stress, the growth of both roots and shoots, as well as increasing metal uptake in the shoot biomass of a wide diversity of hyperaccumulating plants. Endophyte-assisted phytoremediation is a promising technology for the remediation of polluted or naturally metal-rich soils.

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

Seed endophytic bacterial (SEB) communities have been little studied to date, although these microorganisms may assist seeds and seedlings to cope with environmental stresses. Hyperaccumulators have become models for studying plant adaptation to extreme environments, such as metalliferous soils. This work aims to characterize the endophytic bacterial communities associated with hyperaccumulating seeds collected from their native ecosystems (nonmetalliferous or calamine soils). Using 16S rRNA metabarcoding, endophytic bacterial communities were characterized for seeds from 14 Noccaea caerulescens populations. Plant genomes and environmental properties of the sites had previously been described. In all plant populations the metabarcoding revealed a large SEB core microbiome composed of the main phyla and sub-phyla: ɣ-Proteobacteria (56.56%) > α-Proteobacteria (32.23%) > Actinobacteria (7.93%) > Firmicutes (3.78%). According to the literature, some operational taxonomic units (OTUs) found in the core microbiome may be related to “plant growth promoting endophytes” (PGPE). The changes in the relative abundance of phyla/subphyla were correlated to altitude, pH, and soil exchangeable elements (Al, Mg, Cd, Mn, Zn), yet the main parameters observed to drive SEB diversity were the plants’ genetics. The distinction between populations based on calamine soils and nonmetalliferous soils failed to explain the SEB communities’ structural dissimilarities. In fact, the factor that best explained these dissimilarities was the plant’s genetic subunit. Future research, based on transcriptomic approaches, should study the ecological roles of the SEB communities and their involvement in the adaptation of hyperaccumulators to metalliferous soils.

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.

International audience; The growing demand for strategic resources such as rare earth elements (REEs) for development of modern technologies has spurred an increase in mining activities and consequently a release of REEs into the environment, posing a potential threat to human health. Phytoextraction or phytomining, regarded as an in situ and low-cost means to use the growth and harvest of hyperaccumulator plants that take up high concentrations of metals in their shoots, allowing metal removal from contaminated soil (phytoextraction) or commercial production of high value metals (phytomining). In this chapter, we review the discovery of REE hyperaccumulators worldwide, focusing on the fern species Dicranopteris linearis (synonym D. dichotoma) that preferentially takes up light REEs and Phytolacca americana that preferentially incorporates heavy REEs. Although less well understood, mechanisms of REE uptake, translocation, and distribution in hyperaccumulator plants are discussed. Finally, we analyze the challenge of improving REE yield by phytomining, and taking D. linearis and P. americana as examples, estimate the phytomining potential for REEs using these species based on their biomass production, REE concentrations in the ash and current market prices for REEs.; La demande croissante de ressources stratégiques telles que les éléments de terres rares (ETR) pour le développement de technologies modernes a entraîné une augmentation des activités minières et, par conséquent, un rejet d'ETR dans l'environnement, ce qui constitue une menace potentielle pour la santé humaine. La phytoextraction ou phytomining, considérée comme un moyen in situ et peu coûteux d'utiliser la croissance et la récolte de plantes hyperaccumulatrices qui absorbent de fortes concentrations de métaux dans leurs pousses, permet d'éliminer les métaux des sols contaminés (phytoextraction) ou de produire commercialement des métaux de grande valeur (phytomining). Dans ce chapitre, nous passons en revue la découverte des hyperaccumulateurs d'ETR dans le monde, en nous concentrant sur les espèces de fougères Dicranopteris linearis (synonyme D. dichotoma) qui absorbe préférentiellement les ETR légers et Phytolacca americana qui incorpore préférentiellement les ETR lourds. Bien que moins bien compris, les mécanismes d'absorption, de translocation et de distribution des ETR dans les plantes hyperaccumulatrices sont discutés. Enfin, nous analysons le défi d'améliorer le rendement des ETR par phytomining, et en prenant D. linearis et P. americana comme exemples, nous estimons le potentiel de phytomining pour les ETR en utilisant ces espèces sur la base de leur production de biomasse, des concentrations en ETR dans les cendres et des prix actuels du marché pour les ETR.

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; The soil, at the interface between geosphere, biosphere, and atmosphere, is a particularly challenging object to study. The ecological and environmental impacts of soil functioning encourage soil scientists to exploit new technologies to generate new data or develop new research protocols. Among these technologies, 3D printing is a promising technology for improving the understanding of soils. The general principle of 3D printing is to build parts by adding materials layer by layer following a three-dimensional solid model. The 3D printing technology makes it possible to produce almost any geometrically complex shape or feature in a wide range of materials. Its interest lies in its ability to produce customized objects easily and rapidly in an endlessly reproducible 3Darrangement. A large number of techniques and materials are available, which differ in their principles, advantages, and shortcomings. In this article, we present the main challenges and opportunities of using 3D printing in soil science. To this end, we present a review of the literature from 2000 to 2019 to identify and understand recent applications of 3D printing in this field. We first describe applications such as the manufacturing of agricultural equipment and laboratory devices in soil science, the development of new construction materials, or the geotechnical characterization of soil as a construction base. However, none of these applications requires replication of the soil functional properties as opposed to applications that would be dedicated to improving the understanding of soil functioning. We detail here the challenges and opportunities of building soil models that reproduce its physical, chemical, biological properties, and its dynamics in contact with living organisms. Despite the remarkable and rapid progress made in the development of 3D printing in recent years, this technology is still underused in the field of soil science. In particular, very few applications focus on the functioning of the soil itself as an ecological compartment. Indeed, several technical limitations have still to be overcome. 3D printed objects must be biocompatible, chemically and mechanically stable, and must be spatially resolved on the microscale. Many efforts are being made by the 3D printing community to push these boundaries. This paves the way for the wider use of 3D printing in soil science. In the near future, the availability of additive manufactured soil models, with strict and controlled composition and structure, will provide researchers with an irreplaceable opportunity to conduct reproducible experiments and better understand soil functioning factors.

With the rise in urban population comes a demand for solutions to offset environmental problems caused by urbanization. Green infrastructure (GI) refers to engineered features that provide multiecological functions in urban spaces. Soils are a fundamental component of GI, playing key roles in supporting plant growth, infiltration, and biological activities that contribute to the maintenance of air and water quality. However, urban soils are often physically, chemically, or biologically unsuitable for use in GI features. Constructed Technosols (CTs), consisting of mixtures of organic and mineral waste, are man-made soils designed to meet specific requirements and have great potential for use in GI. This review covers (1) current methods to create CTs adapted for various GI designs and (2) published examples in which CTs have been used in GI. We address the main steps for building CTs, the materials and which formulae should be used to design functional CTs, and the technical constraints of using CTs for applications in parks and square lawns, tree-lined streets, green buffer for storm water management, urban farming, and reclaimed derelict land. The analysis suggests that the composition and structure of CTs should and can be adapted to available wastes and by-products and to future land use and environmental conditions. CTs have a high potential to provide multiple soil functions in diverse situations and to contribute to greening efforts in cities (and beyond) across the world.

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

Dredged sediments from waterways are often contaminated due to human activities. We tested an original remediation method consisting of mixing dredged contaminated sediments with contaminated soil to create a technosol and establish a phytoremediation technique. The objective was to determine if the Miscanthus x giganteus (MxG) and white clover co-culture could improve the PAH dissipation compared with monoculture. MxG and white clover were tested in mono- and co-culture on a technosol composed of sediments and soil in mesocosm during 263 days (a life cycle of MxG until its senescence). PAHs measurements and ecotoxicity and genotoxicity tests were performed at the beginning (T0) and the end (TF) of the phytoremediation experiment. PAH removal varied according to the planting patterns and the PAHs involved, but overall, the presence of vegetation significantly induced dissipation of total PAHs in the technosol. After 263 days of culture, 26.24% of the total 16 priority PAHs were removed with white clover monoculture, 29.27% with co-culture, and 31.65% with MxG monoculture. Moreover, after 263 days of culture, the index of additive cancer risk (IACR) values were 4.26 for the non-planted technosol, 3.43 for MxG monoculture, 3.31 for white clover monoculture, and 3.43 for co-culture. The different planting patterns improved the decrease of the IACR values in the technosol compared with the non-planted technosol, even if it remained above the reference value. Furthermore, co-culture significantly enhanced the dissipation of pyrene and anthracene and decreased the technosol ecotoxicity in contrary to MxG monoculture. The present study showed the possibility to remediate dredged sediments after mixing them with soil, thus opening a new way to clean up contaminated excavated sediments. The presence of vegetation significantly promoted the dissipation of the total 16 priority PAHs and improved the decrease of the IACR values. Co-culture was more efficient for the dissipation of specific PAH, such as pyrene and anthracene, compared with MxG monoculture. Moreover, the co-culture improved the decrease of the technosol ecotoxicity contrarily to other planting patterns.

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.

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.]

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

Purpose: Anthropogenic activities lead to soil degradation and loss of biodiversity, but also contribute to the creation of novel ecosystems. Pedological engineering aims at constructing Technosols with wastes and by-products to reclaim derelict sites and to restore physico-chemical functions. Materials and methods: The biological (dynamics of soil and epigeic macroinvertebrate assemblages) and physical (chemical and physical fertility) properties have been studied in two constructed Technosols under grassland during four years after their implementation. Results and discussion: The soils exhibited a moderate chemical fertility (high organic matter and calcium carbonate contents, low nitrogen content) and a good physical fertility that only slightly evolved over the monitored period. Macro-invertebrates have colonized these soils. This colonization was characterized by an increasing number of individuals and species over time. The diversity and abundance values fell within those quoted in the literature for similar natural soils. Epigeic invertebrates presented a succession, indirectly linked to changes in soil parameters. No succession was recorded for soil invertebrates. However, the proportion of soil detritivores, an important functional group for soil evolution, grew consistently. Questions about soil invertebrates functional complementarity/redundancy emerge in such artificially created ecosystem. Conclusions: The constructed Technosol, on which a meadow was sown and well-established after 4 years, can host numerous soil invertebrates. In addition, an increase in diversity was monitored throughout the duration of the study.

International audience; In the last decades, anthropogenic disturbances have altered the ability of soils to provide diverse functions. Certain anthropogenic soils, with a low fertility level and often contaminated, ended up underused and derelict. Although derelict for humans, these soils may be refuges for biodiversity, but their biological functioning remains poorly understood. To this end, a trait-based approach of soil invertebrate communities might be an effective predictor of ecosystem state. The present work aims to highlight the in situ links between the abiotic characteristics of derelict soils and the taxonomic and functional structure and composition (through a trait-based approach) of macrofauna and Collembola communities inhabiting these soils. We studied 6 different derelict soils: two soils from coking plants, one soil from a settling pond, two constructed soils, and an inert waste storage soil. We measured fifteen abiotic soil parameters that inform on fertility and contamination. We took into account sixteen traits and ecological preferences to characterize the functional structure and composition of Collembola and macrofauna communities. Soil fertility (organic matter content, C:N ratio, P, Ca and Mg concentrations, cation-exchange capacity, and clay content) and moderate contamination (Pb, Cd, Zn, and PAH concentrations) altered the taxonomic and functional composition of Collembola and macrofauna communities by selecting traits such as body length, pigmentation, vertical distribution, diet type, and habitat preference. Compost-amended constructed soil properties selected taxonomic and functional community composition of slightly disturbed soil. In contrast, metal-contaminated constructed soil harbored a higher proportion of Collembola displaying the traits and ecological preferences of instable ecosystems. The study of functional profiles of Collembola and macrofauna communities in the derelict soils evidenced that they support different communities with more or less wide functional potential. It underlines the interest of multiple biotic component studies to reach a better ecosystem description.

International audience; Soil surface roughness is a key factor for our understanding and modelling of geomorphologic processes related to exchanges of soil, water and gas. It has an impact on soil properties and tillage outcome. Soil surface roughness can be characterized both globally and locally. The interest of clod segmentation is to allow for both characterizations. Segmenting clods on a digital elevation model (DEM) of a soil surface is a complex problem because soil surfaces are complex surfaces of several level of roughness and because considering elevations results in smooth and poorly contrasted images. However, a DEM in 3 dimensions gathers more information than a profile of 1 dimension or an image of 2 dimensions.Multiresolution analysis has shown interest for roughness analysis of complex surfaces. We have used it to introduce a new approach for soil roughness analysis and to lay the foundations for clod segmentation. In this paper, we propose a complete wavelet-based approach for accurate clod contour delineation. It relies on several steps: detecting clods on the surface approximations by a supervised detection of local maxima, validating and merging the detections by shape and overlap tests, delineating the clod contours by intersecting locally the soil surface elevations with the estimated plane of the clod base and validating the contours by detecting and correcting the wrong patterns, with statistical pattern recognition. This segmentation method was evaluated in several roughness conditions, made in the laboratory, by comparison with other segmentation method. An indicator of goodness of agreement was introduced for this purpose.This wavelet-based segmentation method showed robustness to the presence of furrows and to the smoothing by rainfall and showed ability to retrieve clod diameters.