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In this study, soils and plants of ultramafic areas of Neyriz, in the south of Iran, were collected, identified, and analyzed for “serpentine” metals. Soil analysis of total element concentrations indicated that maximum total concentrations (µg g-1) of Ni = 1250, Cr = 200, Co = 295, Mn = 1850, Fe = 105,300, Mg = 73,000, and Ca = 2800. The maximum concentration of exchangeable Ni in these soils was of 4.7 µg g-1. During this study, 116 plant species belonging to 30 families were collected and a few species were endemic to ultramafic soils of these areas. Analysis of the plant leaves did not reveal any hyperaccumulators of Ni or any other “serpentine” metals. The highest concentrations of Ni (140 µg g-1) and Co (47 µg g-1) were found in Rheum ribes. The highest concentration of Cr (76 µg g-1) was measured in Nepeta glomerulosa.
The Ni hyperaccumulator Strepthanthus polygaloides (Brassicaceae) is one of a handful of Ni hyperaccumulators known from continental North America. Surveys have revealed four distinctive morphs of this species, relying primarily on floral traits (sepal color and shape): a purple sepal morph (P), a yellow sepal morph (Y), a morph in which sepals start yellow and mature to purple (Y/P), and a morph with light yellow undulate sepals (U). In this study, we raised plants from ten populations (five Y, three P, one Y/P, and one U) under uniform greenhouse conditions to determine if morphs varied in morphology and elemental concentrations when grown on Ni-amended potting soil in a common garden. Morphological data included measurements of leaf form (length, width, and degree of lobing) and plant size (height to first flower as they bolted in summer). Phenology was documented by noting flowering timing of plants. Elemental concentrations of plants were also determined for nine elements (Ca, Cu, Fe, K, Mg, Mn, Ni, P, and Zn). All morphological/phenological traits measured varied significantly between at least some morphs. The U and Y/P morphs were larger than Y and P morphs, with larger leaves as well. Leaves of U morph plants had wide sinuses and shallow lobes, whereas Y/P plants had narrow sinuses and long narrow lobes. P morph plants were shortest in stature, with the smallest leaves. Morphs also varied significantly in concentrations of all elements except Fe. All populations hyperaccumulated Ni, but the P morph contained significantly greater Ni levels than the other three morphs. The P morph also had more Mg, and less Mn and P, than the other morphs. The U morph had more K and Zn, but less Ca, than the other morphs. Principal components analysis revealed all four morphs to be distinctive from one another, and also suggested both morphological/phenological and elemental differences between Y morph populations along a north—south gradient. We conclude that there is considerable genetic divergence between morphs. If additional information shows that morphs are reproductively isolated, then these morphs may require taxonomic subdivision.
Teucrium chamaedrys is the most variable species in the genus Teucrium, fitting Kruckeberg's category of a bodenvag species. Six populations distributed on serpentine and 3 populations off serpentine were investigated, and 23 morphological features were studied by univariate and multivariate statistical analyses. The variation was higher for the vegetative features and not clearly expressed for the generative ones. In addition, metal concentration in the populations and soil were studied. The species tolerant to the serpentine conditions demonstrated specific morphological differences in stem length, stem length up to the first leave pair, and internode length between second and third leave pairs. Morphological differences, geographical isolation, and preliminary results on the karyology of T. chamaedrys in Bulgaria, suggest that the populations studied were different ecotypes.
The western Betic Mountain Range contains the largest ultramafic rock area in the Iberian Peninsula. The predominant flora of this southern territory (over two hundred taxa) was screened for Ni accumulation. Only two species showed important concentrations of Ni in their tissues, Alyssum serpyllifolium subsp. malacitanum (Brassicaceae), a Ni hyperaccumulator, and Saxifraga gemmulosa (Saxifragaceae). Saxifraga gemmulosa is a rare endemic species restricted to the ultramafic outcrops of Málaga (South Spain), mainly growing in basic or ultrabasic rock crevices, where it appears with other serpentinophytes such as Asplenium adiantum-nigrum subsp. corunnense (Aspleniaceae). Nickel and other representative elements present in Saxifraga gemmulosa and its soils from Sierra Bermeja (Málaga) were studied by inductively coupled plasma-mass spectrometry (ICP-MS). The structures of the plant were micromorphologically analysed by scanning electron microscopy (SEM) coupled to an Energy-Dispersive X-Ray Probe (EDX). The results showed the Ni hyperaccumulating characteristics of S. gemmulosa. As observed in other Ni hyperaccumulator plants, accumulation was mainly detected in leaf epidermis.
In the serpentine area in Hokkaido, 46 taxa of serpentine plant species were recognized, and 44 of them were endemic to Hokkaido. The P concentration in the serpentine plants was lower, while the concentrations of K, Ca, and N were higher, than those in nonserpentine plants and trees. The Ni concentration of the serpentine plants increased proportionally to that of the exchangeable Ni concentration in the soil up to 10 mg kg-1 soil, but did not increase further. Among the plants investigated, a nonserpentine plant, Thlaspi japonicum, was recognized for its extraordinary Ni accumulation (1300 mg kg-1 on average), indicating that this plant is the first Ni-hyperaccumulator identified in Japan.
Compartmentation of metals in specific tissues, cells, and subcellular compartments is considered a metal-tolerance mechanism in metal hyperaccumulator plants. In this study, we investigated the accumulation of Ni in the trichomes of a serpentine endemic Ni hyperaccumulator plant, Alyssum inflatum, native to western Iran. Elemental analysis of plants from their natural habitat showed that the Ni concentration of trichomes was not higher than in the shoot, suggesting that Ni does not preferentially accumulate in trichomes. Treatment of plants by adding different concentrations of Ni to the growth medium showed that staining of trichomes with dimethylglyoxime (a specific stain for Ni) increased as concentrations of external Ni increased. Accumulation occurred in the base of trichomes and, by increasing the concentration of Ni, accumulation extended to the rays and cell walls. The results showed that trichomes can accumulate high concentrations of Ni and that Ni accumulation can be under the control of Ni concentration in the shoot.
We investigated accumulation of elements (Ca, Co, Cr, Cu, Fe, K, Mg, Mn, P, Pb, and Zn) in leaves of different ages for 11 evergreen woody plant species from serpentine soils of New Caledonia. Species were classified into four categories of Ni accumulation ability: one species was a non-accumulator (<100 mg Ni/ kg), three were accumulators (100–1000 mg Ni/kg), two were hyperaccumulators (1000–10,000 mg Ni/kg), and five were hypernickelophores (>10,000 mg Ni/kg). We harvested leaves from each species, separating them into three (four in one case) relative age categories based upon their position along branches (younger toward the apex, older far from it). Leaf samples were dried, ground, and dry-ashed, and their elemental concentrations were determined by inductively coupled plasma spectrometry (all elements except Ni) or atomic absorption spectrophotometry (Ni). Great variation was found for most elements both within and among species, but Ni varied most (1050-fold between species for oldest leaves). Correlations between Ni and other transition metals showed no significant relationships within samples of any species, but, we found significant positive correlations between Ni and Pb (correlation coefficient = 0.97) and Ni and Fe (correlation coefficient= 0.87) among species. Leaf Ni concentrations varied significantly with leaf age for two species, the hypernickelophores Geissois pruinosa and Homalium kanaliense. We conclude that Ni concentration varies markedly between species, but generally does not vary with leafage within species. We also suggest that four Ni accumulation category terms— non-accumulator, hemi-accumulator, hyperaccumulator, and hypernickelophore—be used to subdivide the wide variation found in Ni concentrations in plant leaves.
Serpentine outcrops around the world are known to harbor disproportionately high rates of plant endemism. Remarkable cases of serpentine endemism occur in New Caledonia and Cuba, with 3178 and 920 endemic taxa, respectively, found solely on serpentine. Despite the patchy occurrence of serpentine in eastern North America from Québec and Newfoundland south to Alabama, only one taxon, Cerastium velutinum var. villosissimum, has been broadly recognized as a serpentine endemic for the region. Based on reports in the literature, we suggest that Adiantum viridimontanum, Minuartia marcescens, and Symphyotrichum rhiannon be considered endemic to serpentine soils from the east coast of North America. Aspidotis densa, with several disjunct populations on and off serpentine in western North America, is known solely from serpentine soils where it occurs in eastern North America and should be considered endemic to the substrate there. The geobotany of eastern North America in general is poorly understood, and additional taxonomic studies on the region's unique geologic substrates will likely yield further edaphic endemics.
Serpentine endemics and other soil-restricted taxa may be presumed to face extraordinarily high risk from climate change because their narrow edaphic niches limit their possibilities to adapt through migration. However, their distinctive life-history traits and their competitive relationships with faster-growing soil generalists may complicate this picture and produce unexpected outcomes. Here we propose a conceptual framework for how serpentine endemics will fare under climate change, together with three potential tests of its predictions. We believe climate change should be embraced by serpentine plant ecologists as a critical area for greater study.
Alyssum bracteatum is the first Ni hyperaccumulator reported from serpentine soils of western Iran. In this study, uptake and accumulation of Co by a serpentine and a non-serpentine population of this species were tested under controlled conditions. Seedlings of A. bracteatum were grown in different concentrations of Co (0, 2, 5, 10, 15, and 30 mg Co L-1) in solution culture (perlite) for 21 days. Tolerance to Co of serpentine population seedlings was significantly greater than the Co tolerance of seedlings from the non-serpentine population. Analysis of shoots and roots showed that the concentration of Co in both populations of A. bracteatum increased with increasing Co in solution culture, but amounts of Co in the shoots of non-serpentine plants were significantly less than those in serpentine plants. Plants of the serpentine population contained as much as 1830 µg Co g-1 dry weight when grown in 15 mg Co L-1 conditions, showing that this species is capable of hyperaccumulating Co under solution culture conditions.
Hyperaccumulator plants mobilize large amounts of certain elements from the soil into their tissues. Those elements then may be transferred to other organisms in those communities. Using a humid tropical forest site in New Caledonia, we tested whether epiphytes (mosses and liverworts) growing on Ni hyperaccumulator hosts contained greater levels of Ni (and seven other metals) than those growing on non-hyperaccumulator hosts. We selected two Ni hyperaccumulator species, Psychotria douarrei and Hybanthus austrocaledonicus, pairing individuals of each species with similar-sized non-hyperaccumulators and collecting epiphytes from each for elemental analysis. Samples of epiphytes and host plant leaves were analyzed for concentrations of eight metals (Co, Cr, Fe, Mg, Mn, Ni, Pb, and Zn). Two-way ANOVA was used to assess the influence of host type (hyperaccumulator or non-hyperaccumulator), epiphyte group, and the interaction term. Leaves of both Ni hyperaccumulator species had greater Ni concentrations than the paired non-hyperaccumulator species, but leaf concentrations of other metals (Co, Cr, Fe, Pb, and Zn) were higher as well in one or both cases. The strongest influence on epiphyte elemental composition was found to be the host type factor for Ni. Epiphytes collected from hyperaccumulator hosts had significantly greater Ni concentrations than those collected from non-hyperaccumulator hosts. Epiphyte Ni concentrations often exceeded the threshold used to define Ni hyperaccumulation (1000 µg/g), showing that some epiphytes (in most cases those growing on Ni hyperaccumulators) also hyperaccumulate Ni. Six of the epiphytes we analyzed, four liverworts (Frullania ramuligera, Schistochila sp., Morphotype #1 and Morphotype #13) and two mosses (Calyptothecium sp. and Aerobryopsis wallichii), had at least one specimen containing more than 1000 µg Ni/g and hence qualify as Ni hyperaccumulators. We conclude that Ni could move from Ni hyperaccumulator hosts to their epiphytes, either from leachates/exudates from tissues or from accumulated external dust, thus potentially mobilizing Ni still further into the food webs of these humid tropical forests.
Most plants that hyperaccumulate metals are restricted to soils with elevated concentrations of those metals. Recent reports have suggested that some Phytolacca species in China can hyperaccumulate manganese (Mn). Phytolacca americana L. (Pokeweed) is a ubiquitous weed of roadsides and waste areas in its native range in the southeastern United States, and has no known association with high-Mn soils. We investigated whether Mn hyperaccumulation also occurs among such plants. Field-collected samples contained approximately 2000 µg Mn g-1 dry weight, whereas other species from the same site ranged from 50 to 450 µg g-1. Seedlings of P. americana were transplanted to the laboratory and grown in nutrient solutions ranging up to 8 mM Mn. After three weeks, Mn concentration in leaves exceeded 32,000 µg/g or 3.2%. This result suggests that P. americana possesses a latent physiological ability to hyperaccumulate Mn, even if this trait is rarely, if ever, expressed within its native range.
Asbestos exposure has been linked to adverse human health effects including asbestosis and mesothelioma. As such, mining and utilization of asbestos is restricted or has been banned in about 50 countries since 1990. Nevertheless, abandoned asbestos mines, mostly in serpentine areas, persist as sources of hazardous airborne fibers. Revegetation of asbestos mine spoils has been proposed as a way by which to stabilize asbestos-bearing substrate, thereby reducing fiber dispersion into the air. No study to date, however, has evaluated the revegetation's effectiveness of reducing airborne asbestos pollution. In this study, we evaluated the effect of natural revegetation on the air dispersion of asbestos fibers from asbestos-rich serpentine lithosoils at an abandoned chrysotile mine. Air sampling of vegetated and barren plots within the mine demonstrated that vegetative cover significantly reduced asbestos dispersion into the air (50% reduction with 15–40% vegetative cover). Additionally, the effectiveness of several native, locally collected serpentine-tolerant species to revegetate the asbestos mine spoil, including Minuartia and Thymus species, was evaluated. Mat-forming, serpentine endemic Thymus sp. proved to be particularly effective at revegetating the mine spoil, having high transplantation survival, growth rates, and reproductive output.
Pedologists and ecologists generally consider peridotite and serpentinite together as common serpentine soils or substrates. A detailed survey in the Klamath Mountains, CA, with separate soil map units on peridotite and serpentinite revealed appreciable differences in geomorphic and pedologie features between these types of ultramafic rocks. Slopes tend to be steeper on peridotite and the soils redder. More Alfisols (Luvisols) were found on peridotite, and more Mollisols (Phaeozems) on serpentinite. Very shallow soils (7% of the area), which are mostly Mollisols and Entisols (Leptosols), are more common on serpentinite. Barrens are commonly fragmental colluvium (talus) on peridotite and erodible, slightly to moderately stony summits and slopes on serpentinite. The most obvious vegetation differences related to parent material are on very shallow and shallow soils, with more coniferous trees (Pinus jeffreyi [Jeffrey Pine] > Calocedrus decurrens [Incense Cedar] > Pseudotsuga menziesii [Douglas Fir]) and Quercus durata (Leather Oak) on peridotite, and more Ceanothus cuneatus (Buckbrush) and Vulpia microstachys (Annual Fescue) on serpentinite soils.
Soils on ultramafic rocks are usually colonized by plant species and communities adapted to high heavy-metal content and low Ca/Mg ratio. However, the effects of metal speciation on microbial activity and arthropodal communities have scarcely been studied, especially under coniferous forests in boreal or subalpine areas. Six typical subalpine soils, in the ophiolitic area of Mont Avic Natural Park, located in the Western Italian Alps, were studied in order to verify the chemical speciation of Ni, Co, Mn, and Cr and their effects on soil biological properties and microbial activity. Five soils, developed from till composed of mafic and ultramafic materials, showed strong signs of podzolization, while the sixth was polluted by mine spoil. All the samples had high metal content, high acidity, and high metal mobility and bioavailability. These edaphic properties deeply influenced both arthropodal communities and microbial activity, all of which were strictly correlated with parent material and bioavailable Ni, Co, and Mn.
Nickel (Ni) is essential for all plants due to its role in urease activation. Demonstration of Ni essentiality has required exceptional effort to purify nutrient solutions to remove Ni; thus, an improved technique would make study of Ni deficiency more available to diverse researchers. As part of our research on Ni hyperaccumulation by plants, we developed chelator-buffered nutrient solutions with very low buffered activity of free Ni2 , and tested growth of Alyssum murale (Goldentuft Madwort), A. corsicum (Madwort), A. montanum (Mountain Alyssum) and Lycopersicon esculentum (Tomato). We used a modified Hoagland nutrient solution with 2 mM Mg and 1 mM Ca to simulate serpentine soil solutions. We could use hydroxyethyl-ethylene-diaminetriacetate (HEDTA) to achieve Ni2 activity levels as low as 10-16 M, and cyclohexane-ethylenediamine-tetraacetate (CDTA) to supply higher activities of buffered Ni2 compared with HEDTA; however, we were unable to obtain proof of induced Ni-deficiency, even with urea-N supply in a 6-week growth period, apparently because seeds supplied enough Ni for growth.
Yields were somewhat reduced at lower Ni activity by the end of the test period, but strong deficiency symptoms did not occur, apparently due to the supply of Ni from hyperaccumulator species seeds (contained 7000–9000 mg Ni kg-1). Chelator buffering supplied controlled levels of Ni2 for all test species; very low plant Ni levels were attained when seed Ni was low. Reaching clear and strong Ni deficiency appears to require longer growing periods, using seed with exceedingly low initial endogenous Ni, or species possessing higher Ni requirements.
Most of the ultramafic rocks from Newfoundland to Alabama, inland from the Atlantic Ocean, and from Arkansas to Texas, inland from the Gulf of Mexico, are peridotites and serpentinites derived from the mantle in oceanic or magmatic-arc settings. They were accreted to a precursor of the North American continent more than 0.25 Ga ago. The serpentine soils range from very cold Entisols and Histosols in Newfoundland and Quebec to cold or cool Inceptisols southward to the limit of late Pleistocene glaciation about latitude 41°N. They are warm to hot Alfisols in the unglaciated areas from New Jersey south to Alabama, with some Mollisols in the Blue Ridge Mountains. Mollisols are the dominant serpentine soils in the drier Llano uplift of Texas. The woody vegetation on the serpentine soils is relatively sparse or stunted, or both. Many of the plant species grow mainly or only on serpentine soils, and some that are common on other soils do not grow on serpentine soils. Some of the species are circumpolar and are common on serpentine soils in both eastern and western North America, and some have distributions that are disjunct from populations on nonserpentine soils of midcontinental prairies. The most distinctive features of serpentine soils are low exchangeable Ca/Mg ratios and high first-transition element concentrations from Cr through Mn, Fe, and Co to Ni. Although some of the serpentine plants have relatively high Ni contents that are toxic to some plants, it is mostly the low Ca/Mg ratios that are responsible for the unique plant assemblages on serpentine soils. The serpentine soils have soil organic matter contents comparable to those of nonserpentine soils.
Centuries of mining economically valuable minerals from serpentine have left a legacy of drastically disturbed landscape. Asbestos and nickel-laterite mining from serpentine is estimated to have degraded 11,130 and 19,070 ha, respectively, in 18 countries. Increasing mineral extraction, fueled by increasing global demand for industrial commodities, will continue to have devastating impacts on serpentine landscapes. Simultaneously, increasing environmental awareness is motivating nations to balance economic advancement with environmental protection. Revegetation of landscapes degraded by mining provides a way to address these issues. This review highlights some advances of the past decades in serpentine revegetation and ecology, and provides a framework of concepts, including physical stabilization, substrate amendment, and plant-materials selection, by which drastically disturbed serpentine substrates may be revegetated.
Hydrogen produced by serpentinization has the potential to fuel subsurface microbial metabolisms. In the serpentinizing subsurface, the solids comprise ultramafic parent rocks derived from the Earth's mantle, serpentine minerals, veins of hydroxides, and accessory magnetite and/or other metal-rich grains. Fluid that occurs with these solids is altered seawater and/or meteoric water and is predicted to be reducing. Hydrogen, a powerful reducing agent, is generated when Fe2 in Fe(OH)2 is oxidized to magnetite, coupled to the reduction of water. Theoretical considerations and experimental work suggest that serpentinization may generate fluid H2 concentrations as high as ≈75 millimolar, and that related seeps on land should have ≈300 micromolar. Field observations have shown that submarine serpentinizing seeps contain fluid H2 concentrations of 1 to 15 millimolar H2, subseafloor sediments have ≈7–100 nanomolar H2, and thermal springs have ≈13 nanomolar H2. Fluid H2 has the potential to drive a variety of metabolic processes in oxygen- and organic carbon-deprived environments, such that considerable interest has developed in the potential of serpentinizing systems as an abode of deep subsurface life. Based on empirical parameters, we have modeled the free-energy change for an array of metabolic reactions that may be associated with serpentinization, and find that metabolic niches do exist for methanogenesis, ferric iron reduction, sulfate reduction, and nitrate reduction, given environmentally realistic fluid chemistries.
“Serpentinomics” is an emerging field of study which has the potential to greatly advance our understanding of serpentine ecology. Several newly developing —omic fields, often using high-throughput tools developed for molecular biology, will advance the field of serpentine ecology, or, “serpentinomics.” Using tools from the fields of ionomics, metabolomics, proteomics, transcriptomics and genomics, researchers will be able to address new (and old) ecological questions in powerful and creative ways. In particular, “serpentinomics” has the potential to uncover the mechanistic and genetic basis of the complexities of tolerance of and adaptation to serpentine soils, including the biochemistry of hyperaccumulation. Here we outline each of these —omic fields and describe possible applications to the field of serpentine ecology.
This study evaluated relationships between the serpentine soil from a waste-rock dump of the abandoned Libiola sulphide mine (NW Italy) and its pioneer vegetation. We identified the tolerance of various species to environmental conditions and evaluated physical or chemical factors that influenced the first plants to colonize this stressful environment. Thirteen sampling sites were identified in the rock dump from characterization of surface or near-surface oxidation zone and vegetation type. Sampling sites were analyzed for slope, pH, mineralogy, soil chemistry, floristic composition, and the percent coverage of each species. In all the plots, species richness and vegetation cover were extremely low. The flora showed an acidophilous character.
The geoecology of a serpentinite-dominated site in the Czech Republic was investigated by rock, soil, water, and plant analyses. The 22-ha Pluhův Bor watershed is almost entirely forested by a nearly 110-year old plantation of Picea abies (Norway Spruce) mixed with native Pinus sylvestris (Scots Pine) in the highest elevations. It is mainly underlain by serpentinite, with occassional tremolite and actinolite schists and amphibolite outcrops. Tremolite schists and especially serpentinites are characterized by extremely high concentrations of Mg, Ni, and Cr and by negligible concentrations of K, creating an unusual environment for plants. The spruce growth rate is very slow, apparently as a result of K deficiency, Mg oversupply, and Ni toxicity. Foliar Ca is in the upper part of the optimum range because schists and amphibolites are important sources of Ca to the soil exchangeable pool and vegetation. Mineral weathering and atmospheric deposition generate near-neutral magnesium-bicarbonate-sulfate streamwater with a high concentration of Ni.
Serpentine soils are extreme habitats known to be involved in processes of local adaptation and speciation of plants. Here I use a greenhouse reciprocal-transplant experiment to compile baseline data for describing patterns of serpentine local adaptation in Quercus ilex subsp. ballota (Holm Oak). I also tested the role of mycorrhizal fungi on the establishment and growth of seedlings on serpentine and non-serpentine soil. Non-serpentine seedlings grew more than serpentine seedlings in all treatments. Plants grew more on non-serpentine soil and mycorrhizal fungi positively influenced seedling growth. I did not find evidence of better seedling performance in their home environment, suggesting the absence of local adaptation. However, I document significant growth differences between serpentine and non-serpentine seedlings, which suggest physiological differences between seedlings from these two soil origins.
Serpentine outcrops in the Middle Urals, Russia, supported 113 species of lichens. These rocks had a more diverse lichen flora and lower specificity (only 9 species) than other rocks types of the region. Pyroxenite's lichen flora was the most similar to that of serpentine. Rocky outcrops along different rivers varied in species richness, the highest being at the southernmost site (River Iset; 81 species) and the lowest at the northernmost site (River Neiva; 57 species).
Root ultrastructure and histochemistry of Ni-hyperaccumulating and non-hyperaccumulating genotypes of Senecio coronatus were compared using transmission electron and light microscopy. Distinct groups of inner cortical cells in the Ni-hyperaccumulator had an organelle-rich cytoplasm, while indistinct groups of these cells in the non-hyperaccumulator had few organelles. The inner cortical-cell groups and adjacent endodermis in both genotypes appeared to be sites for the synthesis of an alkaloid which was produced more abundantly in the Ni-hyperaccumulator. Casparian bands in exodermal cells were better defined in the non-hyperaccumulator, suggesting a more efficient barrier for exclusion of Ni. Results are discussed in relation to the differential uptake of Ni by the genotypes and ultrastructural aspects of alkaloid production.
This study examined woody vegetation, edaphic factors, bedrock geochemistry, petrography, and outcrop structure to evaluate some of the community-structuring factors in an ultramafic terrain of Maryland. Analyzing the dynamic nature of combined geological and ecological processes can detect correlative relationships between factors that are typically considered as independent such as tectonically driven bedrock fracturing and ecological community interaction. This study provides evidence for structural variation in fracture density of bedrock as a partial control on tree species distribution in an ultramafic woodland/forest ecosystem. Increases in the number of bedrock fractures correlates negatively with plot-level volumetric soil moisture. Additionally, the degree of serpentinization of the ultramafic parent material results in compositional variation in Ca, Mg, and Ni of parent materials and soils. The combination of these factors provides a significant level of control on the distribution of xeric tree species.
Ultramafic soils are widespread in the Balkans. Albania and Greece are the richest in the number of endemics, including several hyperaccumulator species, growing on serpentine. The objectives of this study were to understand the potential of Ni hyperaccumulation of these species in close relation with the characteristics of their native soil environments. Collection of both plant samples (analysis of element concentrations in aerial parts) and soil samples (analysis of total elements, DTPA-extractable Ni, Fe, and Ni distribution in mineral phases) allowed evaluation of phenotypic efficacy in hyperaccumulating Ni. Nickel availability in soils is controlled by soil weathering and mineral-bearing phases. Unsurprisingly, the highest levels of Ni availability were associated with amorphous Fe-oxides in moderately weathered Cambisols or with high-exchange capacity clays in well-evolved Vertisols. The highest Ni concentrations in leaves were found in Alyssum murale in Pojska (Albania; 2.0%), Alyssum markgrafii in Gjegjan (Albania; 1.9%), Bornmuellera baldacii subsp. markgrafii in Gramsh (Albania; 1.4%), and Leptoplax emarginata in Trigona (Greece; 1.4%). We identified a new member in the Albanian Ni-hyperaccumulator flora: Thlaspi ochroleucum in Pojska (Albania: 0.13% Ni) and in Pishkash (0.14% Ni). With regard to Ni availability in soils, A. markgrafii (Albania) is the most efficient Ni-hyperaccumulator among all species. Alyssum murale, which is widespread in the serpentines of the Balkans, accumulates Ni, with leaf concentration being negatively correlated to total Ca content of soils regardless of Ni availability (DTPA extractable Ni). If this relationship is confirmed, it would mean that genetic variability is not the main factor that explains the hyperaccumulation performance of this species.
Cerastium utriense Barberis (Caryophyllaceae) is an endemic plant growing on ultramafic outcrops in northwestern Italy. Despite its great phytogeographical importance, little is known about its ecological requirements and environmental range. Thus, the main objective of the present work was to examine and clarify these aspects. On the basis of a preliminary survey on its range, 28 plots were sampled, and Ellenberg ecological indices of the flora growing with C. utriense were defined. Furthermore, on the basis of the floristic diversity and physical, chemical, and biological properties of the soils, 10 of these plots were selected and more closely investigated. This preliminary study characterized C. utriense as a strictly Ni-excluding serpentinophyte with no apparent relationship with typical chemical characteristics of serpentine soils. On the contrary, the species showed a direct association with physical traits typical of serpentine substrates.