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Hyperaccumulator plants exhibit extreme ecophysiological characteristics, which make them suited for phytoremediation. Understanding their ecological strategies might help identify the species and functions to be favored in phytoremediation, restoration, and conservation projects for metalliferous sites.

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.

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

Odontarrhena serpyllifolia (Desf.) Jord. &amp, Fourr. (=Alyssum serpyllifolium Desf.) occurs in the Iberian Peninsula and adjacent areas on a variety of soils including both limestone and serpentine (ultramafic) substrates. Populations endemic to serpentine are known to hyperaccumulate nickel, and on account of this remarkable phenotype have, at times, been proposed for recognition as taxonomically distinct subspecies or even species. It remains unclear, however, to what extent variation in nickel hyperaccumulation within this taxon merely reflects differences in the substrate, or whether the different populations show local adaptation to their particular habitats. To help clarify the physiological basis of variation in nickel hyperaccumulation among these populations, 3 serpentine accessions and 3 limestone accessions were cultivated hydroponically under common-garden conditions incorporating a range of Ni concentrations, along with 2 closely related non-accumulator species, Clypeola jonthlaspi L. and Alyssum montanum L. As a group, serpentine accessions of O. serpyllifolia were able to tolerate Ni concentrations approximately 10-fold higher than limestone accessions, but a continuous spectrum of Ni tolerance was observed among populations, with the least tolerant serpentine accession not being significantly different from the most tolerant limestone accession. Serpentine accessions maintained relatively constant tissue concentrations of Ca, Mg, K, and Fe across the whole range of Ni exposures, whereas in the limestone accessions, these elements fluctuated widely in response to Ni toxicity. Hyperaccumulation of Ni, defined here as foliar Ni concentrations exceeding 1g kg−1 of dry biomass in plants not showing significant growth reduction, occurred in all accessions of O. serpyllifolia, but the higher Ni tolerance of serpentine accessions allowed them to hyperaccumulate more strongly. Of the reference species, C. jonthlaspi responded similarly to the limestone accessions of O. serpyllifolia, whereas A. montanum displayed by far the lowest degree of Ni tolerance and exhibited low foliar Ni concentrations, which only exceeded 1 g kg−1 in plants showing severe Ni toxicity. The continuous spectrum of physiological responses among these accessions does not lend support to segregation of the serpentine populations of O. serpyllifolia as distinct species. However, the pronounced differences in degrees of Ni tolerance, hyperaccumulation, and elemental homeostasis observed among these accessions under common-garden conditions argues for the existence of population-level adaptation to their local substrates.

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

Cistus ladanifer has a well-defined taxonomic identity. 2,2,6-trimethylcyclohexanone may be an authenticity and taxonomic marker. Its traits and applications make it a possible economic resource fitted for Mediterranean areas. Cistus ladanifer is a dominant shrub species endemic to the western Mediterranean region. Due to its dominant nature and its potential ecological, aromatic or pharmacological applications, C. ladanifer has been the object of numerous studies. In this review current knowledge on different aspects of this species is summarized, from its taxonomy to its chemical characterisation or its competitive traits. There are no doubts about the taxonomic entity of C. ladanifer, although the recognition of infraspecific taxa deserves more attention. Given that the fragrant exudate of C. ladanifer holds a very specific composition, one species specific carotenoid, 2,2,6-trimethylcyclohexanone, derivative is proposed as an authenticity marker for uses of C. ladanifer in pharmacological or aromatic industries. Evidence is also gathered on the extreme adaptation of C. ladanifer to stressful conditions in the Mediterranean region, such as the ability to survive in low hydric and high solar exposition conditions, presistence in poor and contaminated soils, and growth inhibition of several other plants through the release of allelochemicals. Thus, the finding of potential applications for this plant may contribute to enhance the economic dimension of derelict lands, such as mine tailings or poor agricultural Mediterranean areas.

The combination of genotypic selection, targeted and improved cultivation, and processing techniques for specific applications gives C. ladanifer the potential to be used as a valuable resource in Mediterranean areas with poor agronomic advantages. Cistus ladanifer (rockrose) is a perennial shrub, well adapted to the Mediterranean climate and possibly to upcoming environmental changes. As a sequence to a thorough review on taxonomic, morphological, chemical and competitive aspects of C. ladanifer, the research team focuses here on the economic potential of C. ladanifer: from production to applications, highlighting also known biological activities of extracts and their compounds. The use of this natural resource may be a viable solution for poor and contaminated soils with no need for large agricultural techniques, because this species is highly resistant to pests, diseases and extreme environmental factors. In addition, this species reveals interesting aptitudes that can be applied to food, pharmaceutical, phytochemical and biofuel industries. The final synthesis highlights research lines toward the exploitation of this neglected resource, such as selection of plant lines for specific applications and development of agronomic and processing techniques.

Gentle remediation options (GRO), i.e. in situ stabilisation, (aided) phytoextraction and (aided) phytostabilisation, were implemented at ten European sites contaminated with trace elements (TE) from various anthropogenic sources: mining, atmospheric fallout, landfill leachates, wood preservatives, dredged-sediments, and dumped wastes. To assess the performance of the GRO options, topsoil was collected from each field trial, potted, and cultivated with lettuce (Lactuca sativa L.) for 48 days. Shoot dry weight (DW) yield, photosynthesis efficiency and major element and TE concentrations in the soil pore water and lettuce shoots were measured.GRO implementation had a limited effect on TE concentrations in the soil pore water, although use of multivariate Co-inertia Analysis revealed a clear amelioration effect in phytomanaged soils. Phytomanagement increased shoot DW yield at all industrial and mine sites, whereas in agricultural soils improvements were produced in one out of five sites. Photosynthesis efficiency was less sensitive than changes in shoot biomass and did not discriminate changes in soil conditions.Based on lettuce shoot DW yield, compost amendment followed by phytoextraction yielded better results than phytostabilisation; moreover shoot ionome data proved that, depending on initial soil conditions, recurrent compost application may be required to maintain crop production with common shoot nutrient concentrations.

Background and aims Alyssum section Odontarrhena is the largest single clade of Ni-hyperaccumulator plants, most of which are endemic to ultramafic (serpentine) soils. Alyssum serpyllifolium is a facultative hyperaccumulator able to grow both on limestone-derived and ultramafic soils. Analysis of different populations of this species with contrasting phenotypes could allow the identification of genes involved in Ni-hyperaccumulation and serpentine tolerance. Methods A glasshouse pot experiment on compost-amended ultramafic soil was carried out with three ultramafic (U) and two non-ultramafic (NU) populations of A. serpyllifolium. The leaf ionome was determined by elemental analysis and used as a proxy for serpentine adaptation. A Ni-hyperaccumulating phenotype was estimated from leaf Ni concentrations. Cultured plants were genotyped using Amplified Fragment Length Polymorphism (AFLP) markers. Outlier analysis and regressions of leaf ionome over band distribution were applied to detect markers potentially involved in Ni-hyperaccumulation and serpentine tolerance. Results As well as U populations, some plants from NU populations were found to be able to hyperaccumulate Ni in leaves to concentrations exceeding 0.1% (w/w). U populations had a higher Ca/Mg leaf ratio than NU populations, mainly due to Mg exclusion. 374 AFLP markers were amplified and a potential adaptive value was identified in 34 of those markers. Conclusions Phenotype regression analyses were found to be more powerful than outlier analyses and indicated that regulation of foliar concentrations of Ni, Ca, Mg and P are the main factors involved in serpentine adaptation. More research is needed in order to resolve the ancestral or recently -evolved nature of Ni-hyperaccumulation.

International audience; AbstractKey messageSlash and burn practices affect tropical forests. Our results showed strong introgression between Inga ingoides and Inga edulis in the species contact area. Interspecific hybridization could be sought to improve yield and tolerance to flooding and further increase the economic potential of the poorly drained Amazonian soils and minimize deforestation.ContextInga species are important components of tropical American forests, as well as a local food source. Little is known about the genetic structure of these species; in particular the amount of introgression among species remains unknown.AimsWe assessed the degree of genetic divergence and introgression among populations of I. ingoides (Rich.) Willd. and I. edulis Mart. (Fabaceae) from three Peruvian Amazon tributary rivers.MethodsUsing microsatellite markers we determined the genetic structure of populations using an analysis of molecular variance and a Bayesian analysis of population structure in areas affected by seasonal river fluctuations and in ‘terra firme’ forests.ResultsOverall genetic differentiation was weak. The degree of genetic variation was similar in the two species. A putatively strong introgression was detected between the two species and an intense gene flow was identified among populations. This indicates that an intense gene flow had happened in the past, leading also to a small differentiation among populations within species.ConclusionSelection of natural hybrids or artificial hybridization between I. edulis and I. ingoides could be applied to improve legume size and yield in the later species, while maintaining tolerance to flooding. Improved I. ingoides could be used in multipurpose agroforestry on open areas along the rivers, instead of using the usual slash and burn practice to create inland open areas.

Foliar ionome, photosystem II activity, and leaf growth parameters of Ranunculus acris L., a potential biomonitor of trace element (TE) contamination and phytoavailability, were assessed using two riverbank soil series. R. acris was cultivated on two potted soil series obtained by mixing a TE (Cd, Cu, Pb, and Zn)-contaminated technosol with either an uncontaminated sandy riverbank soil (A) or a silty clay one slightly contaminated by TE (B). Trace elements concentrations in the soil-pore water and the leaves, leaf dry weight (DW) yield, total leaf area (TLA), specific leaf area (SLA), and photosystem II activity were measured for both soil series after a 50-day growth period. As soil contamination increased, changes in soluble TE concentrations depended on soil texture. Increase in total soil TE did not affect the leaf DW yield, the TLA, the SLA, and the photosystem II activity of R. acris over the 50-day exposure. The foliar ionome did not reflect the total and soluble TE concentrations in both soil series. Foliar ionome of R. acris was only effective to biomonitor total and soluble soil Na concentrations in both soil series and total and soluble soil Mo concentrations in the soil series B.

To assess the genetic patterns of colonisation of metalliferous areas by the pseudometallophyte Cistus ladanifer with AFLP genome scan, to compare those estimates with previous cpSSR results, and to identify loci potentially linked to tolerance to metalliferous soils. Thirty-three populations were screened with AFLP markers. Statistical analyses included estimation of genetic diversity, hierarchical analysis of molecular variation and Bayesian analysis of geographical partitioning of genetic diversity. Mantel tests and Spearman’s correlation index were used to compare results obtained with AFLP and cpSSR. Generalized Estimating Equations (GEE) models were applied to correlate allele frequency distribution and soil variables (pH, Ca:Mg ratio and total contents of different trace metals). Metallicolous and non-metallicolous populations of C. ladanifer showed neither different levels of genetic diversity, nor genetic differentiation between population types. Incongruence in genetic diversity estimates between AFLP and cpSSR due to marker-specific properties was observed. Nonetheless, pairwise distance matrices computed with both markers were concordant. GEE analyses showed that the Mn total soil content has an important effect on the allele distribution in C. ladanifer. In contrast, the Ca:Mg ratio seems to have no selective effect. Moreover, we identified a particular band with a putative role in the species’ tolerance to high Mn concentrations in the soil. The soil type had no influence over this species’ genetic structure. GEE showed their usefulness in revealing the association between soil variables and AFLP loci.

This study investigated the phylogeographic structure of Cistus ladanifer, in order to locate its Quaternary refugia, reconstruct its recolonisation patterns and assess the role of geographical features (mountain ranges, rivers and the Strait of Gibraltar) as barriers to its seed flow and expansion through the Western Mediterranean. Thirty-eight populations were screened for length variation of polymorphic chloroplast simple sequence repeats (cpSSRs). Statistical analyses included estimation of haplotypic diversity, hierarchical analysis of molecular variation (AMOVA) and fixation indices. Mantel tests, SAMOVA and BARRIER analyses were applied to evaluate the geographical partitioning of genetic diversity across the entire species range. Pollen data from bibliography were used to complement molecular inferences. Chlorotype diversity within populations was similar throughout the natural range of C. ladanifer (mean haplotypic diversity = 0.32). High differentiation among populations was estimated (GST = 0.60). Our data suggest that the barriers of the Strait of Gibraltar and the Betic ranges may have favoured the divergence during glacial periods of four different lineages of populations inferred with SAMOVA. The main northward colonisation of in the Iberian Peninsula occurred from refugia in southwest Iberia. This process may have been influenced by human activities (forest clearance, livestock grazing and even commerce) in the Iberian Peninsula. In contrast, populations in the Betic area have conserved a specific haplotype.

The genetic diversity of Cistus ladanifer ssp. ladanifer (Cistaceae) growing on ultramafic and non-ultramafic (basic and schists) soils in the NE of Portugal was studied in order to identify molecular markers that could distinguish the metal-tolerant ecotypes of this species. Random Amplified Polymorphic DNA (RAPD) markers were used in order to estimate genetic variation and differences between populations. The RAPD dataset was analysed by means of a cluster analysis and an analysis of molecular variance (AMOVA). Our results indicate a significant partitioning of molecular variance between ultramafic and non-ultramafic populations of Cistus ladanifer, although the highest percentage of this variance was found at the intra-population level. Mantel’s test showed no relationship between inter-population genetic and geographic distances. A series of RAPD bands that could be related to heavy metal tolerance were observed. The identification of such markers will enable the use of Cistus ladanifer in phytoremediation procedures.

Intra-specific variability of root biomass production (RP) of six rooted macrophytes, i.e. Juncus effusus , Phragmites australis , Schoenoplectus lacustris , Typha latifolia , Phalaris arundinacea , and Iris pseudacorus grown from clones, in response to Cu exposure was investigated. Root biomass production varied widely for all these macrophytes in control conditions (0.08 μM) according to the sampling site. Root biomass production of T. latifolia and I. pseudacorus in the 2.5–25 μM Cu range depended on the sampling location but not on the Cu dose in the growth medium. For P. australis , J. effusus , S. lacustris , and P. arundinacea , an intra-specific variability of RP depending on both the sampling location and the Cu-dose was evidenced. This intra-specific variability of RP depending on the sampling location and of Cu-tolerance for these last four species suggests that Cu constitutive tolerance for all rooted macrophytes is not a species-wide trait but it exhibits variability for some species.

Cistus ladanifer L. (Cistaceae) is a Mediterranean shrub covering different kinds of soils in the Western Mediterranean area. This species has colonised several metalliferous areas (serpentine outcrops as well as human-polluted sites) throughout its distribution range, and is therefore an interesting species to study the possible effects on genetic diversity and differentiation produced by the colonisation of areas polluted with heavy metals. The genetic structure of 33 natural populations distributed across its entire natural distribution range (Morocco, Portugal and Spain) and growing on either metalliferous or non-metalliferous soils was investigated using chloroplast microsatellites. Population genetic parameters were estimated and genetic groups were identified using Bayesian inference. In addition, we compared the genetic diversity and differentiation among metallicolous and non-metallicolous populations within each Bayesian-defined group. The cpSSR data suggested that metallicolous populations of Cistus ladanifer have arisen through multiple independent evolutionary origins within two different chloroplast lineages. Evidence that the soil type provoked genetic bottlenecks in metallicolous populations or genetic differentiation among metallicolous and non-metallicolous populations was not observed. Historical factors are the main cause of the present genetic structure of C. ladanifer. The nature of tolerance to heavy metals as a species-wide trait in this shrub is discussed.

Aim To characterize the genetic structure and diversity of Pinus cembra L. populations native to two disjunct geographical areas, the Alps and the Carpathians, and to evaluate the rate of genetic differentiation among populations. Location The Swiss Alps and the Carpathians. Methods We screened 28 populations at three paternally inherited chloroplast simple sequence repeats (cpSSRs) for length variation in their mononucleotide repeats. Statistical analysis assessed haplotypic variation and fixation indices. Hierarchical analysis of molecular variance (AMOVA), Mantel test, spatial analysis of molecular variance (SAMOVA) and barrier analyses were applied to evaluate the geographical partitioning of genetic diversity across the species’ range. Results Haplotypic diversity was generally high throughout the natural range of P. cembra, with the mean value substantially higher in the Carpathians (H = 0.53) than in the Alps (H = 0.35). The isolated Carpathian populations showed the highest haplotype diversity among the populations originating from the High Tatras (Velka Studena Dolina) and South Carpathians (Retezat Mountains). AMOVA revealed that only 3% of the total genetic variation derived from genetic differentiation between the two mountain ranges. Differentiation among Carpathian populations was higher (FST = 0.19) than among Alpine populations (FST = 0.04). Low, but significant, correlation was found between the geographical and genetic distances among pairs of populations (r = 0.286, P