Ultramafic Outcrops Research Articles

Grassland flora of ultramafic areas in Northern Pindus (Greece)

AbstractIn Europe, the largest and most floristically diverse ultramafic (serpentine) outcrops are located on the Balkan Peninsula. In Greece, the Northern Pindus mountain range is characterized as a floristic diversity hotspot, due to the presence of large ultramafic outcrops that harbor a large number of nickel (Ni) hyperaccumulators with potential use in agromining. The work presented here is part of a more in‐depth study of floristic composition and ecology of plant communities in ultramafic grasslands of the Northern Pindus mountain range. In 2021–2022, 120 relevés in three subareas (sA1, sA2, and sA3) were sampled according to the Braun‐Blanquet method. We identified 493 plant taxa belonging to 61 families. The most abundant families were Asteraceae, Poaceae, Fabaceae, Lamiaceae, and Caryophyllaceae. A total of 22 plant taxa are endemic to Greece. Ninety‐five taxa are of Balkan origin while 158 taxa are distributed to the broader Mediterranean region. The highest number of plant life‐forms are hemicryptophytes (56.39%) and therophytes (23.33%). Eight Ni hyperaccumulators including Centaurea thracica, Bornmuellera baldaccii, Bornmuellera emarginata, Bornmuellera tymphaea, Noccaea boeotica, Noccaea tymphaea, Odontarrhena chalcidica, and Odontarrhena smolikana were recorded.

Metal concentrations in invasive Ailanthus altissima vs native Fraxinus ornus on ultramafic soils: Evidence for higher efficiency in Ni exclusion and adjustments to Mg and Ca imbalance

AbstractAilanthus altissima is one of the major invasive trees at a global scale. Despite numerous reports about its invasiveness in different habitats, so far it was not observed on harsh ultramafic soils and to colonize the vegetation of these outcrops. In this paper we show that the species can also spread in these habitats in the Mediterranean region and is able to cope with the severe anomalies of ultramafic soils. We sampled A. altissima in four ultramafic outcrops of central Italy and in control sites to unravel the behavior of this species toward the typically high soil concentrations of trace metals, such as Ni, Cr and Co, as well the imbalance of the Ca:Mg quotient. A similar sampling was performed for the native Fraxinus ornus that occurs naturally on a broad range of soils, including those from ultramafic rocks. Trace metal concentrations in leaves of both species were below toxicity thresholds, but A. altissima showed lower translocation and bioaccumulation factors (TF and BF, respectively) for Ni. Compared with F. ornus, the invasive species displayed higher leaf concentrations of Mg, thus suggesting a higher tolerance of potentially toxic levels of this element. Moreover, the higher TF and BF values for Ca in both control and serpentine populations suggested that A. altissima was more able to extract and accumulate this macronutrient in leaves in respect to F. ornus. Given the inherent deficiency of this element in ultramafic soils, efficient use of Ca could be a key trait contributing to the invasiveness of A. altissima on these soils.

Plant–pollinator interactions in ultramafic and non-ultramafic environments in New Caledonia

ABSTRACT Edaphic conditions operate major environmental filtering on plant assemblages and their community structure. Soils derived from ultramafic outcrops (i.e. ultramafic substrates) are characterized by high concentrations of metal and metalloid and nutrient deficiencies constraining plant growth. Due to the coupled effects of edaphic conditions and climate, tropical ultramafic substrates harbour a very particular flora. New Caledonia, one of the main plant biodiversity hotspots worldwide, owes much of its exceptional biodiversity to ultramafic substrates. While the flora of the New Caledonian ultramafic substrates is well known, its pollinating fauna remains to be described. Here, we describe plant–pollinator interactions in some ultramafic and non-ultramafic environments in New Caledonia, with a particular focus on wild alien, native and domestic bees. Wild alien bees were less diverse and less present in ultramafic environments than in non-ultramafic ones; we only recorded six interactions realised by wild alien bee species in ultramafic environments. Apis mellifera was also less present in ultramafic environments. Regarding native bees, they were equally present in both environments but less diverse in non-ultramafic environments. Our results suggest that ultramafic environments may filter alien pollinators. Due to beekeeping, Apis mellifera thrived and was the most active species in both environments. Further studies are needed to explore the diversity of interactions in ultramafic environments and to test whether metal and metalloid found in ultramafic substrates such as nickel may transfer to pollinators through plant rewards.

Interpopulation variation in nickel hyperaccumulation and potential for phytomining by Odontarrhena penjwinensis from Western Iran

The Ni hyperaccumulator Odontarrhena penjwinensis (Brassicaceae) is a species endemic to the ultramafic soils of Western Iran. Seven ultramafic outcrops and the populations of O. penjwinensis they support were investigated for Ni and other elemental concentrations to assess their potential for future Ni agromining operations. Nickel hyperaccumulation was confirmed in at least one individual plant sampled from all seven populations. The highest and lowest concentrations of Ni in leaves were recorded for two sites (3270 and 660 mg kg−1, respectively). The highest concentrations of Mn, Cr, and Co were 3110, 79, and 193 mg kg−1, respectively. A positive relationship was found between the concentrations of Ni and Fe, and Mg and Ca in roots and shoots. Correlation analysis of edaphic factors also revealed positive correlations between Ni concentration in the shoots, water-holding capacity, and soil pH, whereas it was negatively correlated for soil organic matter. The highest Ni yield (c. 0.4 g per plant), biomass (115 g per plant) and maximum plant height (43 cm) were recorded for one population where the total soil Ni concentration was 2550 mg kg−1. This O. penjwinensis population is likely to be a promising candidate for the development of Ni agromining in the region.

Metal accumulation by Alyssum serpyllifolium subsp. malacitanum Rivas Goday (Brassicaceae) across different petrographic entities in South-Iberian ultramafic massifs: plant-soil relationships and prospects for phytomining

In the ultramafic area of Spain, a high quantity of petrographic entities is present. Data on the variability among populations of hyperaccumulation are scarce. We investigated Alyssum serpyllifolium subsp. malacitanum for variations in eleven elements among populations growing in different ultramafic massifs in different petrographic entities (dunites, harzburgite-pyroxenic dunite, harzburgite-lherzolite, pyroxenite, and serpentinites). Samples of leaves and soils were collected from the ultramafic outcrops of Sierra Bermeja and Sierra de Mijas (Andalusia, Spain). The concentrations of Ni, Fe, Mg, Si, Cr, Co, Sr, Mn, Cu, Zn, and Ba and the bioaccumulation factors (BAF) were determined. Although analysis of variance of the data for each element revealed considerable variation in soil chemistry (for Fe, Mg, Sr, and Ba) among the different petrographic entities, population-level variation with regard to the hyperaccumulation in the leaves was not detected. BAF values >1 were obtained for Sr and Ni depending on the petrographic entities. The correlation detected between the concentration of Ni in leaves and concentration in soil is relevant. The population-level variation obtained in the BAF values for Sr and Ni provides comprehensive information on the natural variation of hyperaccumulation. The BAF obtained for Ba is an important result for phytomining. Novelty statement To date, studies of hyperaccumulation in plant tissues on ultramafic rocks have not considered the great diversity of petrographic entities in the world's outcrops. One of them is the one that we studied in Spain with more than eight petrographic entities and different soils. Our hypothesis is that the different chemical compositions of the soils in ultramafic rocks significantly affect the hyperaccumulation of metals by specialized plants, which may have consequences for phytomining. For this purpose, individuals, populations, and different soils have been tested and the results have been subjected to the corresponding statistical tests. The obtained knowledge reflects the different behavior of the studied plant not only for the Ni: the obtained results for Sr and for Ba revealed interesting results for the hyperaccumulation in Alyssum of both metals.

Nickel distribution in

Context Hyperaccumulator plants are of considerable interest for their extreme physiology. Stackhousia tryonii is a nickel (Ni) hyperaccumulator plant endemic to ultramafic outcrops in Queensland (Australia) capable of attaining up to 41 300 μg g−1 foliar Ni. Aims This study sought to elucidate the distribution of Ni in S. tryonii by using synchrotron X-ray fluorescence micro-computed tomography (XFM-CT), complemented with elemental maps acquired from physically sectioned plant organs. Its Ni-enriched cylindrical photosynthetic stems make them particularly well suited samples for synchrotron XFM-CT. Methods XFM-CT enables ‘virtual sectioning’ of a sample, avoiding artefacts arising from physical sample preparation. The method can be used on fresh samples that are frozen during the analysis, which preserves ‘life-like’ conditions by limiting radiation damage. It also prevents/minimises other artefacts. Key results The results showed that Ni is mainly concentrated in the apoplastic space surrounding epidermal cells, and in some epidermal cell vacuoles. This finding is significant because this ‘free’ solute Ni is likely to be lost during physical sectioning. Conclusions and implications This case study has highlighted the utility of the XFM-CT approach for visualising metals within intact plant organs, which may be used across the plant sciences.

Assessment of plant diversity and foliar chemistry on the Sri Lankan ultramafics reveals inconsistencies in the metal hyperaccumulator trait

AbstractSome of the largest expanses of ultramafic soils occur in South Asia, but knowledge of the plant diversity and biogeochemistry of these systems in Sri Lanka is very limited. This study aimed to assess the plant diversity and bedrock and foliar chemistry of all known Sri Lankan ultramafic outcrops. The field survey yielded a total of 132 plant taxa from 44 families. The enigmatic nickel hyperaccumulator Rinorea bengalensis (Violaceae), first reported in Sri Lanka over four decades ago, was rediscovered at a newly surveyed ultramafic site, however, it did not hyperaccumulate nickel. No new metal hyperaccumulator plants were identified, suggesting that R. bengalensis is a facultative nickel hyperaccumulator. This study is the first to highlight the floristic diversity of all known Sri Lankan ultramafic outcrops while revealing the facultative nature of nickel and copper hyperaccumulation among some of Sri Lanka's ultramafic plants.

Contribution to the knowledge of Portuguese serpentine flora: ecological characteristics, endemic plants, and implications for biodiversity conservation

Serpentine areas are scarce in the world, but contain a large number of endemic taxa. These areas have, in many cases, been little or not at all surveyed from a vegetation and biodiversity conservation point of view. The most important Portuguese serpentine outcrops are found in northeastern Portugal, particularly in the Bragança-Vinhais and Morais massifs. Here, we present a complete ecological-floristic check-list of serpentinophites that are found in these areas since this knowledge is essential for their evaluation, management and conservation. A total of 25 taxa, classified into three categories with different grades of serpentinophily, were included in the list: (1) obligate serpentinophytes (exclusively on serpentine), (2) endemic or widespread taxa that in Portugal occur exclusively in ultramafic outcrops, and (3) preferential serpentinophytes (most of the distribution range, at least 90% of populations, are found on serpentine). Genera common to other Iberian serpentine areas (Andalusian serpentine flora) are Odontarrhena, Arenaria, Armeria, Asplenium, Paragymnopteris, Saxifraga and Silene. The majority of the studied serpentinophytes (72%) occurred in endemic and highly specialized plant communities. About half of the studied serpentinophytes (48%) are assigned in some IUCN threat category. Consequently, it is necessary to implement conservation measures to guarantee the protection of these habitats. Supplemental data for this article is available online at https://doi.org/10.1080/11263504.2021.2013337 .

Using multivariate statistical analysis in assessment of surface water quality and identification of heavy metal pollution sources in Sarough watershed, NW of Iran.

The Sarough watershed in NW Iran hosts a large amount of mineral occurrences and ore deposits which may be considered as the source of heavy metals in the region. The area has been studied previously; however, the methodology of this paper was less focused on previous studies. This study aimed to assess water quality, determine the spatial distribution pattern, and identify the sources of heavy metals in the main tributaries of Sarough watershed using pollution indexes, multivariate statistical methods, and processing data by geographic information system. Totally, 51 water samples were collected along the main rivers to determine the concentrations of heavy metals by ICP-MS. Regarding the drinking water, agriculture, and freshwater aquatic life guidelines, the rivers were assumed unsafe considering most of toxic elements' content, especially As. The mean values for heavy metal pollution indexes (HPI: 237.32) and metal indexes (MI: 25.37) indicated the intensive heavy metal pollution. The cluster analysis categorized the 51 sampling sites into four clusters with respect to pollution level. The results obtained from the Kruskal-Wallis and multiple comparison tests had the harmony with the results of CA in introducing the most impacted sampling sites and the parameters responsible for water quality degradation. The results of PCA showed the maximum similarity between As, Sb, Se, Fe, and Mn as well as base metals which was attributed to anthropogenic input from mining and mineral processing wastes. Association of Cr and Ni may suggest a lithology source (weathering of metamorphosed ultramafic outcrops). The maps prepared in the GIS system showed the spatial distribution pattern of toxic elements with maximum values nearby mining sites which decreases gradually toward downstream areas. Finally, the results showed that the Sarough River and its tributaries are influenced by high concentrations of heavy metals from the drainages of mining and ore processing sites and naturally occurring metal loadings as well as the geogenic sources such as weathering of geologic formations and hot springs.

Geo-ecological insights on the island of Inchcailloch in Loch Lomond, Scotland: a small serpentine outcrop in a mixed geological setting

Inchcailloch hosts a small serpentine (ultramafic) site in Loch Lomond that is unusual in the Scottish context in being covered with broad-leaved woodland; along with serpentinite, serpentine breccias and sandstones are also found. In order to look at plant-soil relationships in more detail here, I analysed soil and foliar chemistry from sampling locations on and around the ultramafic outcrop. Soils situated directly on the outcrop had elevated concentrations of metals such as Co, Cr, Mg, Mn, Ni and Zn and a lower Ca-to-Mg ratio. Foliar elemental composition was influenced more by species than sampling location although some metals (Ni and Mn) were at greater concentrations in plants on the ultramafic outcrop. Foxgloves (Digitalis purpurea) had the highest foliar Ni concentration as well as Al and Zn, indicating an ability to accumulate multiple metals. Overall, the high Ca-to-Mg ratio indicating the calcareous nature of the soils due to mixing of soils from contrasting geologies, the low metal concentrations, and the high soil P are all considered to act together to prevent this site from exhibiting some of the more extreme features, such as skeletal soils and sparse vegetation cover, found at other Scottish serpentine sites.

Accumulation of Potentially Toxic Elements in Viola L. (Sect. Melanium Ging.) from the Ultramafic and Non-ultramafic Soils of the Balkan Peninsula

The aim of the present study was to assess the metal concentrations in five species of the genus Viola L. (section Melanium) from 12 ultramafic outcrops and two non-ultramafic (prolluvium and dolomite) soils from Serbia and Bosnia and Herzegovina. The concentrations of P2O5, K2O, Ca, Mg, Fe, Mn, Zn, Cu, Cr, Co, Cd and Pb in soils and plant samples, as well as their shoot-to-root ratio, biological concentration and accumulation factors were determined. Five investigated Viola species growing on 14 different localities displayed considerable differences in concentration of potentially toxic elements in their roots and its accumulation in their shoots. Viola kopaonikensis and V. beckiana from ultramafic soils could be classified as strong Ni accumulators, since moderately high level of Ni was measured in their shoots (up to 266 mg kg−1 and 337 mg kg−1, respectively), while in V. tricolor high amount of the same element was accumulated in the roots (up to 395 mg kg−1). Population of V. beckiana from dolomitic site in Bosnia and Herzegovina accumulated high concentrations of Pb in the shoots (67.1 mg kg−1), as well as of Cd in both roots and shoots (81.1 mg kg−1 and 60.5 mg kg−1). The results also suggest that V. kopaonikensis populations from the ultramafic soils of Serbia emerge as Cr accumulators, which is quite rare trait within the genus Viola. It seems that species from Melanium section apply quite different strategies against toxic elements. Future studies should strive to explain what adaptive mechanisms are hidden behind it.

Spontaneous Serpentine Carbonation Controlled by Underground Dynamic Microclimate at the Montecastelli Copper Mine, Italy

Understanding low temperature carbon sequestration through serpentinite–H2O–CO2 interaction is becoming increasingly important as it is considered a potential approach for carbon storage required to offset anthropogenic CO2 emissions. In this study, we present new insights into spontaneous CO2 mineral sequestration through the formation of hydromagnesite + kerolite with minor aragonite incrustations on serpentinite walls of the Montecastelli copper mine located in Southern Tuscany, Italy. On the basis of field, petrological, and geochemical observations coupled with geochemical modeling, we show that precipitation of the wall coating paragenesis is driven by a sequential evaporation and condensation process starting from meteoric waters which emerge from fractures into the mine walls and ceiling. A direct precipitation of the coating paragenesis is not compatible with the chemical composition of the mine water. Instead, geochemical modeling shows that its formation can be explained through evaporation of mine water and its progressive condensation onto the mine walls, where a layer of serpentinite powder was accumulated during the excavation of the mine adits. Condensed water produces a homogeneous film on the mine walls where it can interact with the serpentinite powder and become enriched in Mg, Si, and minor Ca, which are necessary for the precipitation of the observed coating paragenesis. The evaporation and condensation processes are driven by changes in the air flow inside the mine, which in turns are driven by seasonal changes of the outside temperature. The presence of “kerolite”, a Mg-silicate, is indicative of the dissolution of Si-rich minerals, such as serpentine, through the water–powder interaction on the mine walls at low temperature (~17.0 to 18.1 °C). The spontaneous carbonation of serpentine at low temperature is a peculiar feature of this occurrence, which has only rarely been observed in ultramafic outcrops exposed on the Earth’s surface, where instead hydromagnesite predominantly forms through the dissolution of brucite. The high reactivity of serpentine observed, in this study, is most likely due to the presence of fine-grained serpentine fines in the mine walls. Further study of the peculiar conditions of underground environments hosted in Mg-rich lithologies, such as that of the Montecastelli Copper mine, can lead to a better understanding of the physical and chemical conditions necessary to enhance serpentine carbonation at ambient temperature.

Unravelling soil and plant metal relationships in Albanian nickel hyperaccumulators in the genus Odontarrhena (syn. Alyssum sect. Odontarrhena, Brassicaceae)

Based on a recent taxonomic revision of the genus Odontarrhena in Albania, our work aimed at comparing the taxa and populations of this genus in terms of nickel accumulation and levels of other metals in relation to their concentrations in the soil at distinct Albanian ultramafic outcrops. Several populations of different Odontarrhena species were sampled from 20 different outcrops across the entire Albanian territory. Concentrations of Ni, Co, Cr, Mg, Ca, K, Fe and Mn were determined in soil, roots and shoots of all specimens sampled. Ultramafic soils across Albania showed variable metal composition, with significant differences between sites. Large differences in mineral element concentrations were also found between the plants which were not related to species identity or geographical distribution of their populations. Shoot Ni concentrations in Albanian Odontarrhena taxa depend on soil Ni concentrations but not on species identity. For O. chalcidica, the more widely distributed species, the environmental fingerprint for shoot metal composition was found not only for Ni, but also for Ca and Mg, the latter showing a positive linear relationship between soil and plant concentrations.

Effects of reclamation effort on the recovery of ecosystem functions of a tropical degraded serpentinite dump site

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.

Can organic amendments replace chemical fertilizers in nickel agromining cropping systems in Albania?

In Albania, ultramafic outcrops cover 11% of the surface and have the potential to support nickel phytomining. In a large-scale in-situ experiment on an ultramafic Vertisols in Pojskë we are studying the influence of agronomical practices on Ni phytoextraction yield of Odontarrhena chalcidica (syn. Alyssum murale). Three cropping systems were compared in three plots in 2016–2017; POJ-1 Plot (0.3 ha) was established with plants that had germinated spontaneously without any treatments; POJ-2 plot (0.3 ha) was covered by plants that had germinated spontaneously and was treated with mineral fertilizer (N50P50K50 kg ha−1); and POJ-3 Plot (400 m2) was divided in four sub plots, where O. chalcidica was planted at a density of 4 plants m−2 on which, we neither applied fertilizer, nor NPK fertilizer (N65P65K65), pig (FPM; N260:P105:K260 + 15 kg ha−1N, P, K) or chicken manure (FCHM; N260:P390:K260 +15 kg ha−1 N, P, K. Irrigation and mechanical control of weeds was done on POJ-3. After 8 months, shoot Ni concentration, biomass, and Ni yields were higher in O. chalcidica treated with manure and the cost of biomass production was smaller. Nickel yield was more promising (145 kg ha−1) than in previous field trials. This study highlights that, using manure, the Ni yield increases Ni phytomining net values, thus agromining can become an economically justifiable agricultural cropping system.

Implementing nickel phytomining in a serpentine quarry in NW Spain

In Galicia (NW Spain), ultramafic outcrops represent approximately 5% of the land surface and several mining and quarrying activities take place in these areas. Resulting mine-soils present physical, chemical and biological properties which limit plant growth and soil functioning. Nickel phytomining, an eco-friendly strategy for metal recovery, could potentially be applied to these areas. A one-year field experiment was carried out in a serpentine quarry to evaluate the performance of four Ni hyperaccumulating plant species, comparing the Mediterranean spp. Bornmuellera emarginata and Odontarrhena muralis with the native populations of Noccaea caerulescens and Odontarrhena serpyllifolia. Field plots were established and amended with inorganic NPK fertilisers or composted sewage sludge. Three replicate plots (4 m2) were planted for each plant species and fertilisation regime. Amending with compost reduced pH from 7.8 to 6.6, and increased soil cation exchange capacity (CEC), nutrient concentrations and Ni availability. Moreover, compost-amended mine-soil presented higher microbial density and activity, parameters which were further stimulated by plant growth. Plant biomass production of all plant species was significantly higher in compost-amended soils than that after NPK fertilisation, being most pronounced for O. muralis and B. emarginata. Despite the reduction in shoot Ni concentrations observed in plants (except O. muralis) grown in compost-amended plots, the increased biomass production led to significantly higher Ni yields (in kg ha−1) in B. emarginata (2.9), N. caerulescens (1.9) and O. muralis (2.3). All plant species were able to establish and grow in the mine-soil (with the Mediterranean species showing a higher capacity for adaptation) and to generate moderate Ni yields. Nonetheless, the results highlight the need for further optimisation in order to enhance the Ni phytoextraction efficiency. Finally, the improvement in soil quality after compost amendment and plant growth support the idea that phytomining systems can be effective approaches for the rehabilitation of soils affected by quarrying operations after mine closure.

The native status of Pinus pinaster on serpentine soils: charcoal analysis and palaeoenvironmental history in Sierra Bermeja (southern Iberian Peninsula, Spain)

Pinus pinaster (maritime pine), a conifer native to the western Mediterranean, has a broad distribution, occupying a wide variety of habitats. On certain substrata such as ultramafic (ultrabasic) rock, the indigenous nature of this conifer has traditionally been questioned by the scientific community, which has regarded it as an introduction. In Sierra Bermeja, mountains forming the largest ultramafic outcrop in western Europe, the dominant woodland formations on serpentine soils are P. pinaster and Abies pinsapo. However the variable presence, albeit isolated, of various species of arboreal Quercus and the frequent forestry plantation of P. pinaster in recent centuries have led to broad-leaved woods being generally considered as the dominant natural communities in this mountain range, so marginalizing the role of these conifers. In an attempt to settle this scientific controversy, we have carried out soil charcoal analyses from seven localities in Sierra Bermeja. The palaeoecological data we have gathered show that P. pinaster has a natural status and has been present in this mountain range during a large part of the Holocene before the changes to its natural landscape by human activities. These results are of great importance for the management and conservation of rare serpentine ecosystems.

Comparative RNA-seq analysis of nickel hyperaccumulating and non-accumulating populations of Senecio coronatus (Asteraceae).

Most metal hyperaccumulating plants accumulate nickel, yet the molecular basis of Ni hyperaccumulation is not well understood. We chose Senecio coronatus to investigate this phenomenon as this species displays marked variation in shoot Ni content across ultramafic outcrops in the Barberton Greenstone Belt (South Africa), thus allowing an intraspecific comparative approach to be employed. No correlation between soil and shoot Ni contents was observed, suggesting that this variation has a genetic rather than environmental basis. This was confirmed by our observation that the accumulation phenotype of plants from two hyperaccumulator and two non-accumulator populations was maintained when the plants were grown on a soil mix from these four sites for 12months. We analysed the genetic variation among 12 serpentine populations of S.coronatus, and used RNA-seq for de novo transcriptome assembly and analysis of gene expression in hyperaccumulator versus non-accumulator populations. Genetic analysis revealed the presence of hyperaccumulators in two well supported evolutionary lineages, indicating that Ni hyperaccumulation may have evolved more than once in this species. RNA-Seq analysis indicated that putative homologues of transporters associated with root iron uptake in plants are expressed at elevated levels in roots and shoots of hyperaccumulating populations of S.coronatus from both evolutionary lineages. We hypothesise that Ni hyperaccumulation in S.coronatus may have evolved through recruitment of these transporters, which play a role in the iron-deficiency response in other plant species.

After fire regeneration in a Mediterranean serpentine mountain

Abstract: The management of Mediterranean mountains need to know whether or not the flora is adapted to respond to fire and, if so, through what mechanisms. Serpentine outcrops constitute particular ecosystems in the Mediterranean Basin, and plants need to make an additional adaptive effort. The objective of this study is to know the response to fire of the main members of the group of serpentine plants, which habit the Spanish Mediterranean ultramafic mountain, to help in their management. For this purpose, monitoring plots were established on a burned ultramafic outcrop, which was affected by fire in August 2012.They were located in the Mediterranean south of the Iberian Peninsula, Andalusia region. The dominant vegetation of this serpentine ecosystem had been studied previously to fire; it was a shrubland composed of endemic serpentinophytes (small shrubs and perennial herbs) included in Digitali laciniatae-Halimietum atriplicifolii plant association (Cisto-Lavanduletea class) in an opened pine forest. The post-fire response of the plants was studied in the stablished burned plots by field works through permanent 200 x 10 m transect methods, consisting on checking whether they were resprouters, seeders, both of them or if they showed no survival response. Additional information about fire related functional traits is provided for the studied taxa from other studies. Of the total of plants studied (23 taxa), 74% acted as resprouters, 30% as seeders, some of which also had the capacity to resprout (13%), and only 9% of the plants did not show any survival strategy. The presence of a resprouting burl was not high (17%), although serpentine small shrubs such as Bupleurum acutifolium and the generalist Teucrium haenseleri had this kind of organ. The herbaceous taxa Sanguisorba verrucosa, Galium boissieranum and Linum carratracense were seen to be resprouters and seeders. The serpentine obligated Ni-accumulator, Alyssum serpyllifolium subsp. malacitanum, did not show any survival strategy in the face of fire and therefore their populations need monitoring after fires. In the studied ecosystems no species had traits that would protect the aerial part of the plant against fire, although most of the species are capable of post-fire generation by below ground buds. Our results show that the ecosystem studied, composed of taxa with a high degree of endemism and some of them threatened, is predominantly adapted to survival after a fire, although their response capacity may be decreased by environmental factors.

Impacts of ultramafic outcrops in Peninsular Malaysia and Sabah on soil and water quality.

This study focused on the influence of ultramafic terrains on soil and surface water environmental chemistry in PeninsularMalaysia andinthe State of Sabah also inMalaysia. The sampling included 27 soils from four isolated outcrops atCheroh, Bentong, Bukit Rokan, and Petasih from Peninsular Malaysia and sites near Ranau inSabah. Water samples were also collected from rivers and subsurface waters interacting with the ultramafic bodies in these study sites. Physico-chemical parameters (including pH, EC, CEC) as well as the concentration of major and trace elements were measured in these soils and waters. Geochemical indices (geoaccumulation index, enrichment factor, and concentration factor) were calculated. Al2O3 and Fe2O3 hadrelatively high concentrations in the samples. A depletion in MgO, CaO, and Na2O was observed as a result of leaching in tropical climate, and in relation to weathering and pedogenesis processes. Chromium, Ni, and Co were enriched and confirmed by the significant values obtained for Igeo, EF, and CF, which correspond to the extreme levels of contamination for Cr and high to moderate levels of contamination for Ni and Co. The concentrations of Cr, Ni, and Co in surface waters did not reflect the local geochemistry and were within the permissible ranges according to WHO and INWQS standards. Subsurface waters were strongly enriched by these elements and exceeded these standards. The association between Cr and Ni was confirmed by factor analysis. The unexpected enrichment of Cu in an isolated component can be explained by localized mineralization in Sabah.