Calamine Soils Research Articles

Forms of metal(loid)s in soils derived from historical calamine mining waste and tailings of the Olkusz Zn–Pb ore district, southern Poland: A combined pedological, geochemical and mineralogical approach

Historical calamine mining in Poland has resulted in the deposition of trace element contaminated waste on the land surface. Further, the elements occurring in calamines may become bioavailable in calamine soils, depending on their properties and the mineral composition related to past mining processing. The goal of this study was to determine the forms of selected elements (Zn, Pb, Cd, and As) in technogenic soils developed from diverse calamines (calamine mining wastes and tailings) in the Olkusz region of southern Poland in relation to soil properties and mineralogy. The following soil properties were measured: pH, the content of carbonates and soil organic matter. Mineral and chemical composition was determined using XRD, SEM-EDS, and EPMA. Further, the total concentrations of Zn, Pb, Cd, and As were determined, and the chemical forms of soil elements were identified using a BCR sequential extraction procedure. The soils developed from calamine mining waste had higher pH (7.3–8.3) and higher carbonate content (<67%) compared to soils from calamine tailings (4.8–7.8 and < 19%, respectively). All soils contained high total contents of Zn, Pb, Cd, and As. In the past, different calamine processing techniques influenced the properties, mineralogy, and chemical forms of toxic trace elements (Zn, Pb, Cd, As) in the parent material of soils developing on the surface of calamine disposal sites. It was found that higher percentages of Zn, Pb, and Cd occurred in more mobile forms in acidic soils developed from calamine tailings compared to soils from calamine mining waste, which was caused by the lower pH values and lower carbonate content of the former soils.

A core seed endophytic bacterial community in the hyperaccumulator Noccaea caerulescens across 14 sites in France

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

Cadmium tolerance and accumulation in Excluder Thlaspi arvense and various accessions of hyperaccumulator Noccaea caerulescens

Cadmium (Cd) accumulation and tolerance were analyzed in hyperaccumulator Noccaea caerulescens F.K. Mey and excluder Thlaspi arvense L.. Five accessions of N. caerulescens (La Calamine (LC, Belgium), Saint Felix de Pallieres (SF, France), Col du Mas de l’Aire (CMA, France), Ganges (GA, France) from metalliferous soils and Lellingen (LE, Luxembourg) from nonmetalliferous soils) were grown in halfstrength Hoagland solution for 8 weeks in the presence of 1, 5, 25, and 50 μM Cd(NO3)2 and T. arvense in the presence of 0.1, 0.2, 1.0, and 5.0 μM Cd(NO3)2. The toxic effect of Cd was assessed by changes in root and shoot dry weight. The content of Cd in roots and shoots was determined by atomic absorption spectrophotometry and expressed in mg/kg dry weight of plant material and calculated per plant root system or shoot. The tolerance of N. caerulescens to Cd was higher than that of T. arvense and increased in various accessions of N. caerulescens in the row GA < CMA < LE < SF ≈ LC. The ability to accumulate Cd in roots of N. caerulescens accessions increased in the row LC < LE ≈ GA < CMA ≈ SF, while that in shoots were in the row LC < LE ≈ GA < SF < CMA. Reduction in accumulation of root biomass of hyperaccumulator N. caerulescens started at lower Cd content in them compared with that in shoots, while an opposite pattern was observed for excluder T. arvense. Thus, accessions of hyperaccumulator N. caerulescens, having a higher tolerance to Cd compared with excluder T. arvense, differed significantly from each other not only in their capacity to accumulate heavy metals but also in tolerance to them. LC accession from calamine soils accumulated less Cd and, possibly, this was the reason why it was more tolerant than the other accessions. SF accession, also growing on calamine soils, was characterized both by high Cd tolerance and accumulation, which is probably due to more efficient mechanisms of Cd detoxification. The results obtained suggest that there are differences in the mechanisms and causes of tolerance to Cd in various accessions of hyperaccumulator N. caerulescens.

Nickel and zinc accumulation capacities and tolerance to these metals in the excluder Thlaspi arvense and the hyperaccumulator Noccaea caerulescens

Representatives of Brassicaceae species—the hyperaccumulator Noccaea caerulescens F.K. Mey and the metal excluder Thlaspi arvense L.—were compared in terms of their ability to accumulate nickel (Ni) and zinc (Zn) and their tolerance to these metals. Four ecotypes of N. caerulescens were used: the ecotypes La Calamine (LC, Belgium) and Saint Felix de Pallieres (SF, France) grow naturally on calamine soils rich in Zn, Cd, and Pb; the ecotype Monte Prinzera (MP, Italy) originates from serpentine soils rich in Ni, Co, and Cr; and the ecotype Lellingen (LE, Luxembourg) inhabits non-metalliferous soils. The plants of N. caerulescens were grown for 8 weeks in a half-strength Hoagland solution supplemented with 25, 100, 200, 300, and 400 μM Ni(NO3)2 (ecotypes LC, SF, MP, LE) or 100, 200, 400, 800, and 1000 μM Zn(NO3)2 (ecotypes LC, SF, LE); the plants of T. arvense were grown in the presence of 10, 20, 25, and 30 μM Ni(NO3)2 or 40, 50, 60, 70, 80 μM Zn(NO3)2. The toxic effect of Ni and Zn was assessed from changes in dry matter of roots and shoots of treated plants compared to untreated. The content of metals in roots and shoots was determined by means of atomic absorption spectrophotometry. The Ni-accumulating capacity of N. caerulescens ecotypes increased in the order: LC < SF < LE < MP, and the Zn-accumulating capacity increased in the row: LC < SF < LE. In the hyperaccumulating plant N. caerulescens, the increments of biomass started to decrease at a lower metal content in roots than in shoots, whereas the opposite pattern was observed in the metal excluder T. arvense. Since T. arvense plants accumulated Ni and Zn in roots, whereas N. caerulescens accumulated these metals in shoots, one may assume that the greater sensitivity of root growth compared with shoots in N. caerulescens was determined by more effective mechanisms of metal detoxification in shoots. Conversely, the higher sensitivity of shoot growth compared to root growth in T. arvense was determined by more effective mechanisms of metal detoxification in roots. Being more tolerant to Ni and Zn than T. arvense plants, the N. caerulescens ecotypes differed substantially in terms of metal-accumulating capacity and their tolerance to heavy metals. The ecotype originating from non-metalliferous soils (LE) accumulated larger amounts of Zn, but was less tolerant compared with ecotypes growing naturally on calamine soils (SF and LC), whereas the ecotype occurring on serpentine soils (MP) exhibited a markedly greater tolerance to Ni, compared with other ecotypes examined, as well as the largest accumulation of this metal. The results indicate the existence of different mechanisms responsible for plant tolerance to Ni and Zn; the study of these mechanisms is a promising direction for future research.

Life history traits of the pseudometallophyte Thlaspi caerulescens in natural populations from Northern Europe

We examined recruitment, survival, life cycle and fecundity of two metallicolous (M, on metalliferous calamine soils) and two non-metallicolous (NM, on normal soils) populations of Thlaspi caerulescens in Belgium and Luxemburg. In each population, permanent plots were monitored over two reproductive seasons. In M populations, plots were located in two contrasting environments (grass versus grove) in order to test the influence of vegetation cover on life strategy. Our results show that the monocarpic life cycle is dominant in all populations of T. caerulescens. However the length of the pre-reproductive period varies from several months (winter annuals) to 1 year or more (perennials), and is partly related to plant origin (M versus NM). Most plants growing in metalliferous environments were annuals, whereas NM plants were mostly perennials. These differences in life cycle were related to differences in survival during summer, which was better in NM than in M populations. Within each M population, different survival conditions and life cycles were observed according to vegetation cover. Plants growing in grass areas were mostly annuals and had a low survival rate in summer whereas grove plants were mostly perennials and survived better in summer. Our results suggest the selection of stress avoiders (shortening of life cycle) in M populations of T. caerulescens but only for individuals growing in grass areas. Summer survival seems to play a key role in selection of life strategy in T. caerulescens.

Fitness and genetic variation of Viola calaminaria, an endemic metallophyte: implications of population structure and history

We investigated variations in genetic diversity and plant fitness in a rare endemic metallophyte of calamine soils, Viola calaminaria, in relation to population size, population connectivity and population history in order to evaluate and discuss potential conservation strategies for the species. Mean population genetic diversity (H(s) = 0.25) of V. calaminaria was similar to endemic non-metallophyte taxa. Twenty-one per cent of the genetic variation was partitioned among populations and a low (9%) but significant differentiation was found among geographical regions. Our results did not support the hypothesis that the acquisition of metal tolerance may result in reduced genetic diversity, and suggested that strict metallophytes do not exhibit higher inter-population differentiation resulting from scattered habitats. There were no relationships between population genetic diversity and population size. Significant correlations were found between plant fitness and (i) population size and (ii) connectivity index. Recently-founded populations exhibited the same level of genetic diversity as ancient populations and also possessed higher plant fitness. There was no indication of strong founder effects in recently-established populations. The results suggest that the creation of habitats through human activities could provide new opportunities for conservation of this species.

Within‐population genetic structure and clonal diversity of a threatened endemic metallophyte, Viola calaminaria (Violaceae)

We studied the within-population genetic structure and the clonality extent of Viola calaminaria, a rare endemic species of calamine soils, by means of RAPD markers in two populations (one recent and one ancient) with expected harsh and heterogeneous heavy-metal stress. At a very local scale (0.2-3 m), clonal propagation was detected in both populations, but the levels of clonal diversity were high (number of genets/number of ramets sampled = 0.9 [recent] and 0.76 [ancient]) and the maximal observed extension of the clones was 0.4 m. This indicated that clonality is not, for the species, an important mode of propagation and that clonal growth cannot be interpreted as a strategy for propagating or perpetuating adapted genotypes under harsh ecological constraints. Spatial autocorrelations revealed a significant (P < 0.001) negative value of correlogram slope in the two populations even when a single individual per clone was considered (i.e., analysis at the genet level). We conclude that spatial genetic structure at a very local scale reflects limited gene flow due to restricted seed dispersal rather than variation in clonal pattern in response to environmental heterogeneity. At a larger scale (2-30 m), spatial autocorrelations revealed a positive (P < 0.001) correlation at < 3 m and a random pattern at larger distances for the two populations. This suggested a patchy distribution of the genetically linked individuals associated with a disrupted pattern at a longer distance probably due to gene flow by pollen dispersal and a seed bank effect. The implications for the conservation of V. calaminaria are discussed.

Development of Issoria lathonia (Lepidoptera: Nymphalidae) on zinc‐accumulating and nonaccumulating Viola species (Violaceae)

The larvae of Issoria lathonia L. feed in natural conditions on several Viola spp., among which are the zinc-accumulating Viola calaminaria (Gingins) Lej. and the nonmetal-accumulating Viola tricolor L. To examine how I. lathonia caterpillars cope with the naturally high foliar zinc concentration of V. calaminaria, we compared the growth of caterpillars reared on leaves varying in zinc concentration. Larvae were fed in controlled conditions with V. calaminaria and V. tricolor grown on noncontaminated soil (i.e., two low-Zn diets) and with V. calaminaria grown on zinc-enriched soil (i.e., one high-Zn diet). Larvae had a higher growth rate when fed with noncontaminated V. calaminaria compared to zinc-enriched V. calaminaria, suggesting that zinc slows down larval growth. However, larvae consumed more leaves of zinc-enriched V. calaminaria (+45%; estimated from fecal mass) compared with noncontaminated V. calaminaria, suggesting that zinc accumulation would not be advantageous to plants. Caterpillars reared on high-zinc leaves regulate their internal zinc concentration through excretion of highly metal-concentrated feces. When kinetics of growth on both low-zinc diets were compared, it appeared that larval development was faster on noncontaminated V. calaminaria than on V. tricolor. This suggests that more nutrients or less feeding inhibitors in V. calaminaria account for fastest growth. Developmental rates on V. tricolor and on zinc-enriched V. calaminaria were similar, despite the high leaf zinc concentration of the latter species. Together with the abundance of V. calaminaria on calamine soils, this may explain why the largest populations of I. lathonia develop on V. calaminaria in Belgium.

Real-time PCR analysis of metallothionein-2b expression in metallicolous and non-metallicolous populations of Silene vulgaris (Moench) Garcke

In this paper we aimed to assess the role of metallothionein-2b in Zn or Cd hypertolerance by analyzing the expression of SvMT 2 b in roots of metallicolous and non-metallicolous Silene vulgaris populations, as well as in interpopulation crosses segregating for tolerance to Zn or Cd. Plants were grown in hydroponic nutrient solution and Zn and Cd were supplied as sulphates after 1 week of preculture. After 14 d of growth, RNA samples were taken from roots of plants exposed to different concentrations of Zn or Cd (2, 20, 200 μM Zn; 0, 2.5, 12.5 μM Cd) for 72 h. SvMT 2 b transcript levels were analyzed by real-time qPCR and compared to an Actin II control. Populations from cupriferous and calamine soil had significantly higher expression than non-metallicolous populations ( P < 0.001). Although there was variation between the means of SvMT 2 b transcript levels among selection lines ( P < 0.001), there was no overall significant difference between the Zn-hypertolerant and non-Zn-hypertolerant lines ( P > 0.10) Metals did not significantly affect SvMT 2 b expression in any of the populations ( P > 0.10). No co-segregation of Zn and Cd tolerance was observed, nor was any co-segregation of SvMT 2 b expression and Zn or Cd tolerance seen. It is concluded that Zn and Cd tolerance are genetically independent traits. Further we conclude that enhanced SvMT 2 b expression is not a primary determinant of naturally selected Zn or Cd hypertolerance. The enhanced expression in populations from calamine soils without Cu enrichment could be related to Cu homeostasis or, alternatively, point to a role as a non-metal specific hypostatic enhancer in metal hypertolerance. The possible role for SvMT 2 b in heavy metal tolerance is discussed.

Metal Accumulation by Some Plants Growing on Zinc-Mine Deposits

Zinc accumulation by Thlaspi cepeaefolium (Wulfen) Koch, Biscutella levigata L. and Anthyllis vulneraria L. growing on calamine soils was studied in shoots, leaves and roots at different times during one season. Measurements were made polarographically. A. vulneraria and B. levigata accumulate the highest ammounts of zinc in the roots and leaves during spring: the metal is then removed and translocated to the shoots. T. cepeaefolium always shows the lowest zinc accumulation in the roots, suggesting that in this species there is no metal inactivation by root cells.