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Crotalaria is a genus of ~600 species of legumes predominantly found in (sub)tropical regions of Africa and Australia. Crotalaria novae‐hollandiae from Australia is a polymetallic zinc (Zn)‐cadmium(Cd)‐copper(Cu) hyperaccumulator, but only when growing in metalliferous soils. This study aimed to test metal tolerance in Australian Crotalaria species to establish whether metal tolerance is a trait shared between Crotalaria species not known to occur on metalliferous soils. The hyperaccumulator Crotalaria novae‐hollandiae and two non‐metallophytes, Crotalaria mitchellii and Crotalaria medicaginea, were exposed to different treatments containing Cu‐lead(Pb)‐Zn in the form of spiked soils. Foliar samples were analyzed for total elemental concentrations and spectrophotometric analysis was undertaken to assess photosynthetic pigments (chlorophyll a + b and carotenoids) as indicators of stress and polyphenols as an indicator of tolerance. No significant differences in metal accumulation were found in the Crotalaria species, and all exhibited a high level of tolerance toward Zn. However, C. novae‐hollandiae exhibited the greatest tolerance toward Zn but had low tolerance toward Cu, while none accumulated foliar Pb. Tolerance to Zn appears to be a trait shared between the Crotalaria species tested. None of the tested Crotalaria species exhibited tolerance toward Cu, and none accumulated Pb. [ABSTRACT FROM AUTHOR]

The 10th International Conference on Serpentine Ecology was held in Nancy, France on June 12–16, 2023. The main goals of the conference were to create a platform for the exchange of ideas and experiences and to promote scientific dialogue among scientists from numerous fields who share expertise in the study of ultramafic habitats worldwide. The proceedings of the conference are being published as two Special Issues of Ecological Research, of which this is the second. In this article, we present the major topics and provide some highlights of the contributions to the 10th International Conference on Serpentine Ecology. [ABSTRACT FROM AUTHOR]

This account presents information on all aspects of the biology of Silene uniflora Roth (S. maritima With., S. vulgaris Garcke subsp. maritima (With.) Á. & D. Löve), Sea Campion, that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of Britain and Ireland: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history and conservation.Silene uniflora is a mat‐like perennial herb that in Britain and Ireland is primarily distributed in coastal habitats, notably on sea cliffs and shingle banks but also at the drift line and rarely on sand; it also has populations on mountains and heavy metal mine waste tips. All of these substrates tend to be oligotrophic, loose‐textured and freely draining, and often with adverse ion concentrations. It is found in suitable habitats around much of the Atlantic and Baltic coasts of Europe.Its breeding system is gynodioecious and gynomonoecious (some individuals bearing female flowers only, some bearing hermaphrodite flowers only and others with both types of flower). The proportions of the three types of individual vary considerably between populations, but hermaphrodite flowers tend to predominate. The showy, white, nectar‐producing flowers are produced continuously over the entire summer and are pollinated mainly by long‐tongued Hymenoptera and night‐flying moths but autogamous selfing is also frequent.Silene uniflora and its close relative S. vulgaris were the subject of a classic, decadal study involving genetical and transplant experiments that was seminal in the development of 'experimental taxonomy'. More recently, attention has focused on the rapid evolution of Zn‐tolerant populations of S. uniflora growing on mine spoil and contaminated river gravels. It has also become a model organism for the study of sexually transmitted, castrating fungal diseases in plants (notably of the genus Microbotryum). [ABSTRACT FROM AUTHOR]

Self-sustaining vegetation in metal-contaminated areas is essential for rebuilding ecological resilience and community stability in degraded lands. Metal-tolerant plants originating from contaminated post-mining areas may hold the key to successful plant establishment and growth. Yet, little is known about the impact of metal toxicity on reproductive strategies, metal accumulation, and allocation patterns at the seed stage. Our research focused on the metal tolerant Atriplex lentiformis. Specifically, we examined the effects of toxic metal(loid) concentration in soils on variability in its reproductive strategies, including germination patterns, elemental uptake, and allocation within the seeds. We employed advanced imaging techniques like synchrotron X-ray fluorescence microscopy (2D scans and 3D tomograms) combined with inductively coupled plasma mass spectrometry to reveal significant differences in metal(loid) concentration and distribution within the seed structures of A. lentiformis from contrasting habitats. Exclusive Zn hotspots of high concentrations were found in the seeds of the metallicolous accession, primarily in the sensitive tissues of shoot apical meristems and root zones of the seed embryos. Our findings offer novel insights into phenotypic variability and metal tolerance and accumulation in plants from extreme environments. This knowledge can be applied to enhance plant survival and performance in land restoration efforts. [ABSTRACT FROM AUTHOR]

Background and aims: The abandoned Allchar Mine in the Republic of North Macedonia is a globally unique deposit with historical tailings from processing ore containing extremely toxic metal(loid)s concentrations, with up to 76.1 g kg−1 and 6.5 g kg−1 of As and Tl, respectively. Methods: Five pseudo-metallophyte species which naturally colonise the Allchar tailings were sampled: Alyssum kavadarcensis, Knautia caroli-rechingeri, Minuartia verna, Plantago lanceolata, and Silene vulgaris. Rhizosphere soils, roots and leaves were collected for each individual. The samples were subjected to elemental analysis to determine macro and micro-elemental concentrations. Results: The results show that the studied species exhibit different strategies in relation to the dominant elements in the substrate, with exclusion being the most common among them. Hyperaccumulation of Tl was found in M. verna and P. lanceolata (with 1770 and 1030 mg kg−1 as the mean concentration, respectively), whereas As was found in concentrations above the threshold for hyperaccumulation and leaf-to-root ratio > 1 in M. verna, S. vulgaris, and A. kavadarcensis (up to 1340, 2870 and 1330 mg kg−1, respectively). Conclusions: The studied plants have great potential for use in phytoremediation of mine wastes contaminated with As and Tl. [ABSTRACT FROM AUTHOR]

The lack of remediation of inactive mine sites is a serious global concern, as they pose risks to the environment, human health, and safety. The potential of Dianthus sylvestris subsp. sylvestris to remediate post‐mining sites contaminated with copper (Cu) at high altitudes, which is a challenging task for most management strategies, was explored in this study. More than 1300 mg Cu kg−1 in shoots were found in plants collected at the Monte Avanza legacy mine site (Alps). However, it is unclear whether this is due to hyperaccumulation or foliar contamination. To address this gap, field samples were washed with two different protocols, and a controlled Cu‐tolerance test was conducted. While very high Cu concentrations, exceeding the Cu hyperaccumulation threshold of 300 mg kg−1, were found in samples washed with water, results for the plants cleaned with a more rigorous approach with EDTA suggested Cu exclusion strategy. Under controlled conditions, the plant showed Cu hypertolerance but did not hyperaccumulate Cu. Thus D. sylvestris presents a Cu exclusion strategy rather than hyperaccumulation potential, making it a suitable candidate for Cu phytostabilization at high altitude legacy mine sites. The study emphasizes the need for experiments under controlled conditions when assessing the phytoremediation potential. [ABSTRACT FROM AUTHOR]

Pistacialentiscus L. is an excluder metallophyte proposed for the revegetation and phytostabilization of metal-contaminated sites in the Mediterranean area. The present study aims at evaluating the linking between bacterial communities and plants spontaneously growing in ecosystems chronically impacted by mining activities. Environmental properties and metal accumulation into hypogeal and epigeal tissues were analyzed in wild plants of two contrasting habitats with extreme metal contamination (> 2300 mg/kg for Zn, > 1100 mg/kg for Pb, > 10 mg/kg for Cd). The community structures of rhizospheric and root endophytic bacteria were fingerprinted by terminal restriction fragment length polymorphism of the 16S rRNA gene. The wild shrubs efficiently restrict the accumulation of the three major contaminants to the epigeal tissues in the two habitats under study (249 ± 68 mg/kg dw for Zn, 43 ± 21 mg/kg dw for Pb, and 1.4 ± 0.5 mg/kg dw for Cd). Evidence was provided that the combined but not individual effect of environmental conditions (moisture, inorganic carbon, pH) and proportion between Zn and Cd in the mine substrate play a role in structuring rhizosphere bacterial communities. The observed changes in community structures of root endophytes were found to be strongly associated with Pb level in roots and substrate properties (inorganic carbon and Zn/Cd ratio). Overall, our study highlights the importance of the analysis of multifactorial interactions among mine substrate, plant, and microbes for understanding how the environmental context affects phytoremediation under real conditions. [ABSTRACT FROM AUTHOR]

To examine the potential applications of hyperaccumulator plants in the Philippines, we reviewed current data on the extent of metal hyperaccumulation in native species and partitioning of metals within the plant tissue. Twenty-eight species had reported tissue concentrations above the hyperaccumulator threshold, 11 species were endemic to the Philippines. Nickel was present in higher concentrations in the aboveground tissue than in the belowground tissue, but the reverse was found for copper, aluminium and chromium. The fact that copper accumulates belowground rather than above, and most hyperaccumulators of nickel identified were trees, has implications for the potential of phytoextraction using native Philippines flora. Photograph of a native metal-accumulating plant in the Philippines. Soils of the Philippines often have high concentrations of heavy metals and low nutrient concentrations, which are conditions that are normally unfavourable for plant growth. However, many plants in the area have adapted to these conditions and can grow well. Here we have compiled data currently available on Philippine plants that can accumulate metals in their tissue, and the potential applications of these plants in restoration efforts. Photograph by Edwino S. Fernando. [ABSTRACT FROM AUTHOR]

This study investigated the impact of several priming agents on metal-tolerant and sensitive Silene vulgaris ecotypes exposed to environmentally relevant cadmium dose. We analyzed how priming-induced changes in the level of lipid, protein, and DNA oxidation contribute to calamine (Cal) and non-calamine (N-Cal) ecotype response to Cd toxicity, and whether the oxidative modifications interrelate with Cd tolerance. In non-primed ecotypes, the levels of DNA and protein oxidation were similar whereas Cal Cd tolerance was manifested in reduced lipid peroxidation. In both ecotypes protective action of salicylic acid (SA) and nitric oxide (NO) priming was observed. SA stimulated growth and reduced lipid and DNA oxidation at most, while NO protected DNA from fragmentation. Priming with hydrogen peroxide reduced biomass and induced DNA oxidation. In N-Cal, priming diminished Cd accumulation and oxidative activity, whereas in Cal, it merely affected Cd uptake and induced protein carbonylation. The study showed that priming did not stimulate extra stress resistance in the tolerant ecotype but induced metabolic remodeling. In turn, the lack of adaptive tolerance made the sensitive ecotype more responsive to the benefits of the primed state. These findings could facilitate priming exploitation with a view of enhancing metallophyte and non-metallophyte suitability for phytoremediation and land revegetation. [ABSTRACT FROM AUTHOR]

X-ray Fluorescence Spectroscopy (XRF) is a non-destructive analytical technique that has recently been developed as a tool for high throughput screening for the discovery of trace element hyperaccumulator species in herbarium collections. Herbarium XRF analysis was undertaken of representatives of the Brassicaceae family in the two herbaria in Belgrade (Serbia). This was coupled to field collection and chemical analysis of new samples of Cardamine waldsteinii. The data revealed a potentially new zinc hyperaccumulator species, C. waldsteinii, with 3050 mg kg−1 Zn in its leaves. This compares to 2210 mg kg−1 in the leaves of this species collected from the field. These values are below the notional hyperaccumulation threshold for zinc but are nevertheless unusual. The remarkably high accumulation factor for zinc are suggestive of the exceptional potential of C. waldsteinii for zinc uptake, even in non-metalliferous, zinc-deficient soils. We recommend following up this study with experimental investigations on C. waldsteinii to elucidate its ecophysiology and its zinc tolerance and accumulation characteristics. [ABSTRACT FROM AUTHOR]

Former mine sites can provide habitat for many rare specialised bryophyte species that have adapted to metal-rich soil conditions that are toxic to most other plant species. Some of the bryophyte species found in this habitat are facultative metallophytes, and others are regarded as strict metallophytes, the so-called 'copper mosses'. It is a general assumption in the literature that Cephaloziella nicholsonii and C. massalongoi, both categorised as Endangered in the IUCN Red List for Europe, are also strict metallophytes and obligate copper bryophytes. This in vitro experiment investigated the growth and gemma production of these two species from different sites in Ireland and Britain on treatment plates of 0 ppm, 3 ppm, 6 ppm, 12 ppm, 24 ppm, 48 ppm and 96 ppm copper. Results show that elevated copper is not an obligate requirement for optimum growth. Differences in response to the copper treatment levels among populations evident within both species could possibly be due to ecotypic variation. A case is also made for the taxonomic revision of the Cephaloziella genus. Implications for the species' conservation are discussed. [ABSTRACT FROM AUTHOR]

Ultramafic ecosystems are renowned for high endemism and habitat specialization. However, most of our understanding of ultramafic plant ecology comes from Mediterranean and temperate climes, raising questions about the generalizability of plant responses to ultramafic soils. This is especially apparent in tropical ultramafic ecosystems which exhibit a wide range of endemism and differentiation between ultramafic and adjacent non-ultramafic soils. Our objectives were two-fold: 1) synthesize our understanding of tropical ultramafic plant ecology, paying particular attention to generalities that may explain variation in endemism and habitat specialization among tropical ultramafic ecosystems; and 2) define an interdisciplinary research agenda using tropical ultramafic ecosystems as a macroecological model. We demonstrate that tropical ultramafic floras are diverse and variable in plant form and function due to the interactive effects of biogeography, climate, and edaphic properties. The variable rates of endemism, specialization, and stress tolerance traits across tropical ultramafic ecosystems have implications for the management and conservation of these diverse systems. Resumen. Los ecosistemas ultramáficos son reconocidos por su endemismo y especialización del hábitat. Sin embargo, la mayor parte de nuestra comprensión de la ecología vegetal ultramáfica proviene de climas mediterráneos y templados, lo que plantea dudas sobre la generalización de las respuestas de las plantas a los suelos ultramáficos. Esto es especialmente evidente en los ecosistemas tropicales ultramáficos que exhiben una amplia gama de endemismo y diferenciación entre suelos tropicales ultramáficos y no ultramáficos adyacentes. Nosotros teníamos dos objetivos: 1) sintetizar nuestra comprensión actual de la ecología de las plantas tropicales ultramáficas, prestando especial atención a las generalidades que pueden explicar la variación en el endemismo y la especialización del hábitat entre los ecosistemas tropicales ultramáficos; y 2) definir una agenda de investigación interdisciplinaria utilizando ecosistemas ultramáficos tropicales como modelo macroecológico. Las floras tropicales ultramáficas son diversas y variables en la forma y función de las plantas debido a los efectos interactivos de la biogeografía, el clima y las propiedades edáficas. Las tasas variables de endemismo, especialización y rasgos de tolerancia al estrés en los ecosistemas tropicales ultramáficos tienen implicaciones para el manejo y conservación de estos diversos sistemas. [ABSTRACT FROM AUTHOR]

Hyperaccumulator plants are able to tolerate extremely high concentrations of metals/metalloids in the soil in which they grow and to accumulate high concentrations in their shoots. To date, a total of 31 hyperaccumulator plant species have been identified in the Balkans, the centre of diversity and speciation in the European flora which is particularly rich in ultramafic areas. A further 8 species have yet to be confirmed through additional studies. Most of the 31 hyperaccumulator taxa (13 taxa or 41.9%) are species of the genus Odontarrhena, all hyperaccumulating Ni, but concentrations of this element above the hyperaccumulation threshold were also found in the genera Bornmuellera and Noccaea (all Brassicaceae), Orobanche (Orobanchaceae), Centaurea (Asteraceae) and Viola (Violaceae). The existence of hyperaccumulators of Tl and Zn is of particular interest because very few species worldwide hyperaccumulate these elements. Multiple metal hyperaccumulation was found in Noccaea kovatsii, as the hyperaccumulation of Zn was found in this species in addition to Ni, the primary accumulated element. Metal hyperaccumulation is discussed in terms of phylogenetic relationships and species distributions, with special attention to their systematics, the detection and recognition of new hyperaccumulating species and the possibilities for their future practical applications in phytotechnologies.

Ditrichum plumbicola Crundw. is a rare metallophyte that is threatened with global extinction. In this study, its population status and ecology on the Isle of Man were investigated. Surveys were carried out at all sites where the species may currently occur. Geographical coordinates of colonies were recorded using a GPS unit and counts made of occupied 1 m grid cells. Habitat and community composition were recorded by relevés. The chemical composition of occupied soil was also ascertained. Two subpopulations of the species have occurred, associated with the two main ore bodies on the island. One of the subpopulations has become extinct. The other subpopulation comprises colonies at four nearby disused metal mines. It occurs at each in small quantity, with a total population of 47 occupied 1 m grid cells. The species is confined to open metalliferous spoil with high concentrations of lead. Solenostoma gracillimum is the only frequent associate. Management intervention to re-expose open metalliferous spoil will be required ultimately to save the species from extinction. [ABSTRACT FROM AUTHOR]

Environmental changes are inevitable with time, but their intensification and diversification, occurring in the last several decades due to the combination of both natural and human-made causes, are really a matter of great apprehension. As a consequence, plants are exposed to a variety of abiotic stressors that contribute to their morpho-physiological, biochemical, and molecular alterations, which affects plant growth and development as well as the quality and productivity of crops. Thus, novel strategies are still being developed to meet the challenges of the modern world related to climate changes and natural ecosystem degradation. Innovative methods that have recently received special attention include eco-friendly, easily available, inexpensive, and, very often, plant-based methods. However, such approaches require better cognition and understanding of plant adaptations and acclimation mechanisms in response to adverse conditions. In this succinct review, we have highlighted defense mechanisms against external stimuli (mainly exposure to elevated levels of metal elements) which can be activated through permanent microevolutionary changes in metal-tolerant species or through exogenously applied priming agents that may ensure plant acclimation and thereby elevated stress resistance. [ABSTRACT FROM AUTHOR]

Serpentine soils are rich in heavy metals and poor in nutrients, limiting plant species' performance and survival. Nevertheless, specificities of such limitations as well as adaptability features required for thriving in serpentine environments are barely known. The Barberton Greenstone Belt in South Africa is an example of an area containing serpentine soil with adapted vegetation. In this study, a pot experiment was performed to compare development features (i.e., germination rates, leaf count, leaf length, biomass and photosynthetic capacity) during the early development of the non-serpentine species Berkheya radula, a genus consisting of known metal hyperaccumulators from serpentine areas in South Africa. B. radula was grown in serpentine soils taken from the Barberton region. B. radula leaves had heavy metals in concentrations that confirmed the species as a phytoextractor. There were trends for enhanced productivity and photosynthesis in the serpentine treatments compared to the control. Leaf count, leaf length, electron transport efficiency (ψEo/(1 − ψEo), density of reaction centers and PIABS,total were significantly and positively correlated with at least one of the heavy metals in the leaves. Germination rates were positively influenced by K, whereas biomass and the density of reaction centers were negatively affected by Ca and P, and only Ca, respectively. The heavy metals Zn, Ni and Co were positively correlated with each other, whereas they were negatively correlated with the macronutrients K, Ca and P. The latter correlated positively with each other, confirming higher fertility of the control soil. Our study suggests that B. radula exhibits metallophyte characteristics (i.e., preadapted), despite not naturally occurring on metal-enriched soil, and this provides evidence that the potential for bioaccumulation and phytoremediation is shared between serpentine and non-serpentine species in this genus. [ABSTRACT FROM AUTHOR]

Former mine sites can provide habitat for many rare specialised bryophyte species that have adapted to metal-rich soil conditions that are toxic to most other plant species. Some of the bryophyte species found in this habitat are facultative metallophytes, and others are regarded as strict metallophytes, the so-called ‘copper mosses’. It is a general assumption in the literature that Cephaloziella nicholsonii and C. massalongoi, both categorised as Endangered in the IUCN Red List for Europe, are also strict metallophytes and obligate copper bryophytes. This in vitro experiment investigated the growth and gemma production of these two species from different sites in Ireland and Britain on treatment plates of 0 ppm, 3 ppm, 6 ppm, 12 ppm, 24 ppm, 48 ppm and 96 ppm copper. Results show that elevated copper is not an obligate requirement for optimum growth. Differences in response to the copper treatment levels among populations evident within both species could possibly be due to ecotypic variation. A case is also made for the taxonomic revision of the Cephaloziella genus. Implications for the species’ conservation are discussed.

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The present report illustrates the first germination data of Limonium merxmuelleri subsp. merxmuelleri, a pioneer species of mine waste materials of Iglesiente region (South-West Sardinia). After harvesting, seeds were subjected to germination tests at the Sardinian Germplasm Bank (BG-SAR). The results show a high germination capability and germination rate at each tested temperature, with a slight germination reduction at the highest temperature (25°C) that simulates the aridity of the summer period. [ABSTRACT FROM AUTHOR]

Heavy metal-rich toxic soils and ordinary soils are both natural habitats of Arabidopsis halleri, a diploid perennial and obligate outcrosser in the sister clade of the genetic model plant Arabidopsis thaliana. The molecular divergence underlying survival in sharply contrasting environments is unknown. Here we comparatively address metal physiology and transcriptomes of A. halleri originating from the most highly heavy metal-contaminated soil in Europe, Ponte Nossa, Italy (Noss), and from non-metalliferous (NM) soils. Plants from Noss exhibit enhanced hypertolerance and attenuated accumulation of cadmium (Cd), and their transcriptomic Cd responsiveness is decreased, compared to plants of NM soil origin. Among the conditionindependent transcriptome characteristics of Noss, the most highly overrepresented functional class of 'meiotic cell cycle' comprises 21 transcripts with elevated abundance in vegetative tissues, in particular Argonaute 9 (AGO9) and the synaptonemal complex transverse filament protein-encoding ZYP1a/b. Increased AGO9 transcript levels in Noss are accompanied by decreased long terminal repeat retrotransposon expression. Similar to Noss, plants from other highly metalliferous sites in Poland and Germany share elevated somatic AGO9 transcript levels in comparison to plants originating from NM soils in their respective geographic regions. Transcript levels of Iron-Regulated Transporter 1 (IRT1) are very low and transcript levels of Heavy Metal ATPase 2 (HMA2) are strongly elevated in Noss, which can account for its altered Cd handling. We conclude that in plants adapted to the most extreme abiotic stress, broadly enhanced functions comprise genes with likely roles in somatic genome integrity maintenance, accompanied by few alterations in stress-specific functional networks. [ABSTRACT FROM AUTHOR]

The tolerance of Mentha crispa L. (garden mint) cultivated in cadmium-contaminated oxisol for 120 days was analyzed using plant growth variables such as height, the number of leaves and shoots in different Cd exposure periods, as well as assessing the metal concentration absorbed and accumulated in the plant parts (root, stem, and leaves). The maximum adsorption capacity was estimated at 9220 mg kg−1 and used as a reference to establish the different Cd concentrations to be applied in the soil. M. crispa showed tolerance and revealed a reduction of height, the number of leaves and shoots, root development, and secondary toxicity signs such as chlorosis and leaf wilting. Comparing to the stems and leaves, Cd was retained mainly in the roots. PERMANOVA showed that plant growth variables and Cd concentrations in the plant's part were affected by the Cd exposure time. The canonical discriminant analysis demonstrated height as the most affected variable until 45 growing days, and different responses were observed after 75 days. However, the number of shoots was the variable most affected by higher Cd concentrations. The bioaccumulation and translocation factors for all treatments were lower than one, indicating that M. crispa can be considered as an excluder plant and applied for a phytostabilization strategy. [ABSTRACT FROM AUTHOR]

Serpentine soils are rich in heavy metals and poor in nutrients, limiting plant species’ performance and survival. Nevertheless, specificities of such limitations as well as adaptability features required for thriving in serpentine environments are barely known. The Barberton Greenstone Belt in South Africa is an example of an area containing serpentine soil with adapted vegetation. In this study, a pot experiment was performed to compare development features (i.e., germination rates, leaf count, leaf length, biomass and photosynthetic capacity) during the early development of the non-serpentine species Berkheya radula, a genus consisting of known metal hyperaccumulators from serpentine areas in South Africa. B. radula was grown in serpentine soils taken from the Barberton region. B. radula leaves had heavy metals in concentrations that confirmed the species as a phytoextractor. There were trends for enhanced productivity and photosynthesis in the serpentine treatments compared to the control. Leaf count, leaf length, electron transport efficiency (ψEo/(1 − ψEo), density of reaction centers and PIABS,total were significantly and positively correlated with at least one of the heavy metals in the leaves. Germination rates were positively influenced by K, whereas biomass and the density of reaction centers were negatively affected by Ca and P, and only Ca, respectively. The heavy metals Zn, Ni and Co were positively correlated with each other, whereas they were negatively correlated with the macronutrients K, Ca and P. The latter correlated positively with each other, confirming higher fertility of the control soil. Our study suggests that B. radula exhibits metallophyte characteristics (i.e., preadapted), despite not naturally occurring on metal-enriched soil, and this provides evidence that the potential for bioaccumulation and phytoremediation is shared between serpentine and non-serpentine species in this genus.

Environmental changes are inevitable with time, but their intensification and diversification, occurring in the last several decades due to the combination of both natural and human-made causes, are really a matter of great apprehension. As a consequence, plants are exposed to a variety of abiotic stressors that contribute to their morpho-physiological, biochemical, and molecular alterations, which affects plant growth and development as well as the quality and productivity of crops. Thus, novel strategies are still being developed to meet the challenges of the modern world related to climate changes and natural ecosystem degradation. Innovative methods that have recently received special attention include eco-friendly, easily available, inexpensive, and, very often, plant-based methods. However, such approaches require better cognition and understanding of plant adaptations and acclimation mechanisms in response to adverse conditions. In this succinct review, we have highlighted defense mechanisms against external stimuli (mainly exposure to elevated levels of metal elements) which can be activated through permanent microevolutionary changes in metal-tolerant species or through exogenously applied priming agents that may ensure plant acclimation and thereby elevated stress resistance.

Ditrichum cornubicum is one of the world's rarest bryophytes and is undergoing a long-term decline as its habitat is gradually lost to vegetation succession in derelict mining areas. This study investigates short-term changes in abundance of the species at two sites in Cornwall (UK), including within trial management plots where turf-stripping occurred in September 2015. A detailed survey of D. cornubicum was undertaken in January 2020, and locations recorded using high accuracy GPS. The species has declined dramatically in trial management plots since January 2018, illustrated by a 93% loss in occupied 0.1 m grid cells. Outside trial management plots, such a decline did not occur over the same period. Within trial management plots, D. cornubicum underwent an initial dramatic increase soon after turf-stripping in September 2015, quickly followed by a rapid decline. Initial colonisation likely arose from germination of rhizoidal gemmae in the diaspore bank, exposed by turf-stripping. The subsequent decline is at least partly due to competitive exclusion by other colonists of exposed mine spoil, especially Ceratodon purpureus, and perhaps also changes in chemistry at the spoil surface, for example due to leaching. The life-strategy of D. cornubicum is poorly suited to the undisturbed conditions of derelict mining areas, and the species is critically dependent on conservation management interventions that re-expose areas of metalliferous substrate. Without such management, the long-term survival of the species is in serious jeopardy. [ABSTRACT FROM AUTHOR]

Increasing concentration of heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) in the soil may impose a serious threat to living organisms due to their toxicity and the ability to accumulate in plant tissues. The present review focuses on the phylogenetic relationships, sources, biotransformation and accumulation potential of hyperaccumulators for the priority HMs and PAHs. This review provides an opportunity to reveal the role of hyperaccumulators in removal of HMs and PAHs from soils, to understand the relationships between pollutants and their influence on the environment and to find potential plant species for soil remediation. The phylogenetic analysis results showed that the hyperaccumulators of some chemicals (Co, Cu, Mn, Ni, Zn, Cd) are clustered on the evolutionary tree and that the ability to hyperaccumulate different pollutants can be correlated either positively (Cd–Zn, Pb–Zn, Co–Cu, Cd–Pb) or negatively (Cu–PAHs, Co–Cd, Co–PAHs, Ni–PAHs, Cu–Ni, Mn–PAHs). Further research needs to be extended on the focus of commercializing the techniques including the native hyperaccumulators to remediate the highly contaminated soils. [ABSTRACT FROM AUTHOR]

Assessing the taxonomic status of closely related taxa is crucial in plant systematics and can have important implications for conservation and human plant use. Ericaandevalensis Cabezudo & Rivera is a metallophyte endemic species from highly metal-polluted soils of SW Iberian Peninsula, an area with a mining history going back more than 5,000 years. Ericaandevalensis is closely related to Ericamackayana Bab., a northern Iberian species also present in western Ireland. The status of E.andevalensis as a species or subspecies subordinated to E.mackayana is subject to debate. Here, we assessed the genetic and phenotypic relationship between both species, including the population structure of E.andevalensis . We used high throughput sequencing to determine genome-wide Single Nucleotide Polymorphisms (SNPs), and morphometric analyses from 35 reproductive and vegetative traits. The morphological analysis showed at least eight characters that can discriminate the two species, from which ovary hairiness and the size of leaf glandular hairs were the most informative. Genetic analyses showed that each species formed a monophyletic cluster with full support, separated by an interspecific genetic distance >4-fold higher than intra-specific distance. Population genetic analyses of E.andevalensis shows that populations are highly structured, with the Portuguese one as the most isolated and less variable. These results support the recognition of E.andevalensis as a distinct species with a highly constrained ecological requirements and a narrow geographic distribution, but with a limited gene flow between populations. We discuss the implications of these outcomes in conservation policies and potential uses of E.andevalensis such as decontamination of polluted soils., Competing Interests: The authors have declared that no competing interests exist., (Iván Rodríguez-Buján, Pilar Díaz-Tapia, Jaime Fagúndez.)

Aims: The study aimed at characterizing the patterns of natural variation in the tolerance and accumulation capacities for zinc (Zn), cadmium (Cd), and nickel (Ni) between and within edaphic ecotypes of the Zn/Cd/Ni hyperaccumulator, Noccaea caerulescens. Methods: Tolerance was assessed in a hydroponic 'sequential exposure' test, using the lowest concentration that completely arrested root growth as an end point. Accumulation was measured as the foliar metal concentration after six weeks of growth at 5 µM Zn, 2 µM Cd, or 1 µM Ni. Results: Zn and Cd tolerance were positively correlated, and highest in the calamine ecotype. Ni tolerance was without significant ecotypic variation. The ultramafic ecotype was as Zn-tolerant as the non-metallicolous one, but much more sensitive to Cd. The accumulation capacities for Zn, Cd and Ni were all positively correlated and without significant ecotypic variation. Zn hyperaccumulation capacity was species-wide, but Cd and Ni hyperaccumulation capacities were lacking in four populations (all calamine). Conclusions: There is considerable independent variation among populations regarding their Zn, Cd, and Ni accumulation capacities. This variation is most pronounced within the calamine ecotype, because some populations apparently had adopted an exclusion strategy for Zn or Cd hypertolerance, whereas others had not. [ABSTRACT FROM AUTHOR]

Summary: Lead (Pb) ranks among the most problematic environmental pollutants. Background contamination of soils is nearly ubiquitous, yet plant Pb accumulation is barely understood. In a survey covering 165 European populations of the metallophyte Arabidopsis halleri, several field samples had indicated Pb hyperaccumulation, offering a chance to dissect plant Pb accumulation.Accumulation of Pb was analysed in A. halleri individuals from contrasting habitats under controlled conditions to rule out aerial deposition as a source of apparent Pb accumulation. Several elemental imaging techniques were employed to study the spatial distribution and ligand environment of Pb.Regardless of genetic background, A. halleri individuals showed higher shoot Pb accumulation than A. thaliana. However, dose–response curves revealed indicator rather than hyperaccumulator behaviour. Xylem sap data and elemental imaging unequivocally demonstrated the in planta mobility of Pb. Highest Pb concentrations were found in epidermal and vascular tissues. Distribution of Pb was distinct from that of the hyperaccumulated metal zinc. Most Pb was bound by oxygen ligands in bidentate coordination.A. halleri accumulates Pb whenever soil conditions render Pb phytoavailable. Considerable Pb accumulation under such circumstances, even in leaves of A. thaliana, strongly suggests that Pb can enter food webs and may pose a food safety risk. [ABSTRACT FROM AUTHOR]

• Marrubium cuneatum is an endemic highly Pb-tolerant Iranian metallophyte. • M. cuneatum has high biomass with a relatively high Pb accumulation in its shoots. • M. cuneatum seems to be a suitable candidate for the phyto-extraction of Pb. Marrubium cuneatum is an endemic Iranian plant species, which can be found in lead-contaminated environments. This study aimed to investigate the effects of lead on the growth and germination in two M. cuneatum populations, from metalliferous, Pb-contaminated and uncontaminated soil, respectively. Soil and plant samples of the Tang-e Douzan Pb-Zn mine and Morghab Spring (non-contaminated site) were collected and analysed. Germination and growth were recorded under increasing Pb exposure in the non-metallicolous (NM) and the metallicolous (M) local M. cuneatum populations. Germination percentage (GP), mean germination time (MGT), germination index (GI), healthy plant percentage (HPP), seedling death (SD), fresh weight (FW) and dry weight (DW), were measured. Primary assessments showed toxic levels of lead in soil samples of the Tang-e Douzan mine and in leaves of plants growing at the mine site. Germination experiments showed that the germination parameters were stimulated by low concentrations of Pb in both populations, but inhibited by high concentrations. However, the adverse effects of Pb at high concentrations on GP, GI, and HPP were significantly less in the M population. The mortality of germinating seeds (SD) was consistently associated with fungal infection, which gradually decreased with increasing Pb exposure, but to the same degree in both populations. Growth experiments clearly demonstrated Pb hypertolerance in the M population. In the NM population, seedling growth is more sensitive to excess Pb than seed germination, compared to the M population. The M population has high biomass and a relatively high Pb accumulation in its shoots, which suggests it is a suitable candidate for phyto-extraction of Pb. [ABSTRACT FROM AUTHOR]

Abstract The current study aims to perform a field survey of three abandoned mining sites in the southern centre of Morocco to assess the recent metal pollution in soils and accumulation potential of plant species. Native plants and soils were sampled at several sites in the studied mines and analysed for Cu, Zn, Pb and Cd concentrations. Soils in the investigated sites proved to be deficient in major macronutrients and to contain toxic levels of Cu, Zn, Pb and Cd. Botanical survey of the prospected sites showed the abundance of diverse plant communities (46 species and 19 families), with no obvious toxicity symptoms. Results showed that the concentrations of heavy metals were different in the same plant species and from plant species to another. Eight plants of 46 species namely Hirschfeldia incana (L.) Lagr.-Foss, Citrullus vulgaris (L.) Schradi, Portulaca oleracea L., Stipa capensis Thunb., Lactuca viminea (L.) J.Presl & C.Presl, Forsskaolea tenacissima L., Lycium intricatum Boiss. and Hammada scoparia (Pomel) Iljin were considered as the best-performing specimens due to their high ability to accumulate multiple metals in their shoots and roots without being affected by excessive metal contents. This was confirmed by the transfer factors generally higher than 1. Consequently, these tolerant and native plant species could be used as tools for an effective phytorestoration of metal-contaminated sites. Highlights • Botanical survey, heavy metals analysis in plants and tailings were investigated. • Tailings from the three mining sites were seriously polluted by Cu, Zn, Pb and Cd. • 46 identified species represented all native and spontaneous metallophytes. • 8 species of 46 had great tolerance, accumulation and phytoremediation potential. • Native species could be useful tool for the phytorestoration strategies. [ABSTRACT FROM AUTHOR]

The metallophyte Imperata cylindrica inhabits copper (Cu) polluted soils in large areas from Central Chile. Here, we subjected clonal vegetative plantlets to 300 mg Cu kg−1 of substrate for 21 days to identify the main molecular pathways involved in the response to Cu stress. Transcriptomic analyses were performed for shoots and roots, with and without Cu supply. RNA-Seq and de novo transcriptome assembly were performed to identify the gene response associated with molecular mechanisms of Cu tolerance in I. cylindrica. De novo transcriptome revealed a total of 200,521 transcripts (1777 bp) comprising ~91% complete ultra-conserved genes in the eukaryote and Plantae database. The differentially expressed genes (DEGs) in roots were 7386, with 3558 of them being up-regulated and the other 3828 down-regulated. The transcriptome response in shoots was significantly less, showing only 13 up-regulated and 23 down-regulated genes. Interestingly, DEGs mainly related with actin and cytoskeleton formation, and to a minor degree, some DEGs associated with metal transporters and superoxide dismutase activity in root tissues were found. These transcriptomic results suggest that cytoskeleton could be acting as a mechanism of Cu-binding in the root, resulting in a high Cu tolerance response in this metallophyte, which deserve to be analyzed ultra-structurally. Our study contributes to reinforcing the potential of I. cylindrica as a candidate plant species to be used as a phytoremediation agent in Cu-contaminated environments.

This work examined the capability of Imperata cylindrica to respond, tolerate and accumulate Cu when growing at high Cu concentration (300 mg kg−1 of substrate) at different times of exposure (2, 14 and 21 days). The Cu accumulation in plants was examined by atomic absorption spectroscopy (AAS) and Cu localized by Scanning Electron Microscopy-Energy Dispersive X-Ray spectroscopy. Additionally, the phenolic compound identifications and concentrations were determined using liquid chromatography coupled to mass spectrometry. Our results showed that root biomass decreased significantly at high Cu levels, with a greater decrease at 21 days (39.8% less biomass in comparison to control). The root showed 328 mg Cu kg−1 dry weight at 21 days of exposure to Cu, being the tissue that accumulates most of the Cu. Lipid peroxidation was a clear indicator of Cu stress, principally in shoots. The exposure to Cu significantly increased the synthesis of phenolic compounds in shoots of plants exposed 21 days to Cu, where 5-caffeoylquinic acid reached the highest concentrations. Our results support that I. cylindrica is a Cu accumulator plant in root organs with a medium level of accumulation (between 200–600 mg Cu kg−1 biomass), which can tolerate the exposure to high Cu levels by means of increasing the synthesis of phenolic compound in shoots, suggesting a potential use as phytoremediation tool in Cu polluted environments.

The abandoned Allchar Mine in the Republic of North Macedonia is a globally unique deposit with the highest known grades of thallium (Tl) and arsenic (As) mineralization. We aimed to determine the distribution of As and Tl in whole dehydrated shoots of the three Viola taxa using synchrotron micro-X-ray fluorescence analysis. Additionally, soil and plant organ samples were collected from all three Viola taxa at the Allchar site and analysed using inductively coupled plasma-atomic emission spectrometry. Concentrations of Tl were extremely high in all three Viola taxa (up to 58 900 mg kg-1), but concentrations of As were highly variable with V. tricolor subsp. macedonica and V. allchariensis having low As (up to 20.2 and 26.3 mg kg-1, respectively) and V. arsenica having the highest concentrations (up to 381 mg kg-1). The extremely high Tl in all three species is endogenous and not a result of contamination. Arsenic in V. tricolor subsp. macedonica and V. allcharensis is strongly affected by contamination, but not in V. arsenica where it appears to be endogenous. The pattern of As enrichment in V. arsenica is very unusual and coincides with Ca-oxalate deposits and Br hotspots. The results of this study could form the basis for more detailed investigations under controlled conditions, including plant dosing experiments., (© The Author(s) 2023. Published by Oxford University Press.)

As a result of mining activities large portions of land have been degraded. In this work, different tolerance/resistance mechanisms of Erica andevalensis Cabezudo y Rivera, which allow thriving and growing in soils from mine areas enriched with potentially toxic elements are reported. Different strategies were identified in E. andevalensis to tolerate high concentrations of metal(loid)s in soils through field and laboratory studies. The response of this species to high concentrations of hazardous elements varies according to the element. Experimental evidence for E. andevalensis adaptation to polluted soils/sediments and the role of other chemical elements (e.g. silicon) to enhance metal(loid)s tolerance is described. The species acts as an excluder for almost all elements and its tolerance to the harsh environments is due to complex mechanisms that include defense and avoidance. [ABSTRACT FROM AUTHOR]

Cobalt (Co) tolerance and accumulation were studied in three Haumaniastrum species: the obligate metallophyte ( i.e. the strict endemic) Haumaniastrum robertii , its facultative metallophyte congener, H. katangense, and a species from nonmetalliferous soils, H. villosum . They were grown hydroponically and their growth during Co exposure was monitored. The two metallophytes did not grow in the absence of supplements, i.e., H. katangense required high concentrations of copper (Cu) to develop and H. robertii growth was conditional with regard to both Cu and Co. This discrepancy in metal requirement for growth originates from differences in ecological niches between the facultative and the absolute metallophytes. The beneficial effect of Co on plant growth was observed for all three species of Haumaniastrum . In the non-metallophyte, Co was beneficial at low concentrations and became toxic above 20 μM. In the two metallophytes the positive effect of Co was conditional on supplementation of Cu, and no toxicity was observed in the range of tested Co concentrations (3–150 μM). Co was essential to the growth of the absolute metallophyte. Mineral bulk analysis of plant parts by ICP-MS showed that Co accumulated more and was more mobile than Cu in all species investigated. This was confirmed by LA-ICP-MS mapping of root and leaf tissues, showing localisation of the two trace elements. H. katangense hyperaccumulated Co when exposed to 6 μM and H. robertii when exposed to 20 μM. None of the species studied hyperaccumulated Cu. Furthermore, Co and Cu did not occur in the same root tissues in any of the three Haumaniastrum species studied. In leaves of H. villosum and H. robertii , Cu and Co accumulated in different tissues while in those of H. katangense , Cu and Co were found to co-localize in the mesophyll cells. In summary our study supports the existence of effective Co tolerance mechanisms in the two Haumaniastrum metallophytes, mechanisms which are at least partially different from those for Cu and involve fitness costs. [ABSTRACT FROM AUTHOR]

The article presents a commentary on a study which employed X-ray elemental mapping techniques for examining the ecophysiology of hyperaccumulator plants. Topics covered include the ability of these mapping techniques to provide in situ information, features of nickel phytoextraction and phytomining, and the threats facing many hyperaccumulator plants such as mining, forestry development and fire or urban expansion.

The article reports on the Global Hyperaccumulator Database, a free online database aimed at providing a global database for plants that hyperaccumulate metal and metalloid trace elements. Topics covered include recognition of hyperaccumulator status and inclusion in the database, global numbers of hyperaccumulator plants, and impact of the lack of systematic screening of plant species on the discovery of hyperaccumulator plants.

Two species of Pb-adapted shrubs, Alyssum montanum and Daphne jasminea, were evaluated in vitro for their tolerance to elevated concentrations of cadmium. Shoot cultures were treated with 0.5, 2.5, and 5.0 μM CdCl for 16 weeks and analyzed for their organogenic response, biomass accretion, pigment content, and macronutrient status. Cadmium accumulation and its root-to-shoot translocation were also determined. In both species, rooted microplantlets, suitable for acclimatization, were obtained in the presence of Cd applied as selection agent. In A. montanum, low and moderate dose of Cd stimulated multiplication, rooting, and biomass production. Growth tolerance index (GTI) in Cd-treated shoots ranged from 120 to 215%, while in the roots 51-202%. In turn, in Cd-treated D. jasminea proliferation and rooting were inhibited, and GTI for shoots decreased with increasing doses of Cd. However, roots exposed to Cd had higher biomass accretion. Both species accumulated Cd in developed organs, and its content increased with increasing CdCl dose. Interestingly, D. jasminea accumulated higher amounts of Cd in the roots than A. montanum and immobilized this metal in the root system. On the contrary, A. montanum translocated some part of accumulated Cd to the shoots, but with low efficiency. In the presence of Cd, A. montanum maintained macronutrient homeostasis and synthesized higher amounts of phytosynthetic pigments in the shoots. D. jasminea accumulated root biomass, immobilized Cd, and restricted its translocation at the expense of nutrient balance. Considering remediation potential, A. montanum could be exploited in phytoextraction, while D. jasminea in phytostabilization of polluted substrate. [ABSTRACT FROM AUTHOR]

Ditrichum cornubicumis a rare and threatened acrocarpous moss found on copper-rich mine waste, characteristic of the EU protected habitat ‘Calaminarian grassland of theVioletalia calaminariae’. The species was once thought to be a British endemic, being known from two former copper/tin mine sites in Cornwall, until the discovery of a population in 2006 at Allihies Mountain Mine, Co. Cork, Ireland, a former copper mine. In light of this discovery, two theories of possible introduction from Britain to Ireland were put forward: (1) an introduction from the 1800s and (2) a more recent introduction (2000s). Only male plants of the species are known, and reproduction and dispersal are therefore solely through asexual propagules and fragmentation. In order to address the conservation questions of the origin of the Irish population and to determine whether diversity exists within this rare species, genetic fingerprinting (amplified fragment length polymorphism) was carried out on the three known global populations. Percent polymorphism was found to be 7.29% and Nei's total gene diversity (HT) was 0.0356. AMOVA revealed that, of the small amount of variation found, the majority was among the three populations (98%). The presence of five private alleles in the Allihies population suggests a longer period of isolation than would fit either theory of introduction. Cluster analyses reveal that the Allihies population is more genetically distinct than the two British populations are to each other, thus heightening the conservation priority for this population. [ABSTRACT FROM AUTHOR]

Divergence in functional traits and their plasticity can occur between metallicolous and non-metallicolous populations, driven by the selective pressure of metal toxicity in metalliferous soils, which is often associated with other edaphic constraints. The intraspecific variation of functional traits and their plasticity in response to cobalt in the soil, among populations of Anisopappus chinensis – a broad-niched metallophyte from southeastern D. R. Congo – have been experimentally investigated. Divergence in shoot height and leaf size was observed according to the ecological status of populations, with higher values occurring in plants from non-metalliferous soils. No clear differentiation in SLA was found between non-metallicolous and metallicolous populations. Metallicolous populations did not diverge in their leaf mineral composition and plastic response, with the exception of a lower leaf Co concentration on Co-contaminated soils. Functional leaf traits seemed to exhibit a homeostatic response to Co, which may account for the broad niche of the species. Further studies should include populations from other metallicolous and non-metallicolous habitats and include root and reproductive traits, to better understand resource acquisition strategies and adaptive response to Co toxicity. [ABSTRACT FROM AUTHOR]