Non-serpentine Soils Research Articles

Plant species within Streptanthoid Complex associate with distinct microbial communities that shift to be more similar under drought.

Prolonged water stress can shift rhizoplane microbial communities, yet whether plant phylogenetic relatedness or drought tolerance predicts microbial responses is poorly understood. To explore this question, eight members of the Streptanthus clade with varying affinity to serpentine soil were subjected to three watering regimes. Rhizoplane bacterial communities were characterized using 16S rRNA gene amplicon sequencing and we compared the impact of watering treatment, soil affinity, and plant species identity on bacterial alpha and diversity. We determined which taxa were enriched among drought treatments using DESeq2 and identified features of soil affinity using random forest analysis. We show that water stress has a greater impact on microbial community structure than soil affinity or plant identity, even within a genus. Drought reduced alpha diversity overall, but plant species did not strongly differentiate alpha diversity. Watering altered the relative abundance of bacterial genera within Proteobacteria, Firmicutes, Bacteroidetes, Planctomycetes, and Acidobacteria, which responded similarly in the rhizoplane of most plant species. In addition, bacterial communities were more similar when plants received less water. Pseudarthrobacter was identified as a feature of affinity to serpentine soil while Bradyrhizobium, Chitinophaga, Rhodanobacter, and Paenibacillus were features associated with affinity to nonserpentine soils among Streptanthus. The homogenizing effect of drought on microbial communities and the increasing prevalence of Gram-negative bacteria across all plant species suggest that effects of water stress on root-associated microbiome structure may be predictable among closely related plant species that inhabit very different soil environments. The functional implications of observed changes in microbiome composition remain to be studied.

Temporal Variation in Selection Influences Microgeographic Local Adaptation.

AbstractEcological heterogeneity can lead to local adaptation when populations exhibit fitness trade-offs among habitats. However, the degree to which local adaptation is affected by the spatial and temporal scale of environmental variation is poorly understood. A multiyear reciprocal transplant experiment was performed with populations of the annual plant Leptosiphon parviflorus living on adjacent serpentine and nonserpentine soil. Local adaptation over this small geographic scale was observed, but there were differences in the temporal variability of selection across habitats. On serpentine soil, the local population had a consistently large survival advantage, presumably as a result of the temporal stability in selection imposed by soil cation content. In contrast, a fecundity advantage was observed for the sandstone population on its native soil type but only in the two study years with the highest rainfall. A manipulative greenhouse experiment demonstrated that the fitness advantage of the sandstone population in its native soil type depends critically on water availability. The temporal variability in local adaptation driven by variation in precipitation suggests that continued drought conditions have the potential to erode local adaptation in these populations. These results show how different selective factors can influence spatial and temporal patterns of variation in fitness trade-offs.

Interactive effects of light, water, soil type and competition on the endangered Minuartia smejkalii vary over time

Understanding drivers of species performance is crucial for their effective conservation. Despite a range of studies on the effects of single biotic and abiotic factors on plant performance, very little is known about interactions among multiple factors and their effects over time. We studied competition and abiotic interactions in an endemic species of the Czech Republic, serpentinophyte Minuartia smejkalii, over four years. In a full factorial experiment, we evaluated the performance of M. smejkalii alone, in the presence of a competitor, Festuca ovina, and under different abiotic conditions, including different types of soil, light exposure and water regime, and observed its changes over time. The results indicate very complex interactions among these factors. Competition had negative effects on the performance of M. smejkalii (1.2 times larger plants and 1.8 times more flowers in the absence of the competitor), but abiotic factors had stronger effects than competition alone. The effects of F. ovina on M. smejkalii also varied depending on whether shaded or not and soil conditions. Biotic and abiotic factors had contrasting effects on plant and number of flowers, suggesting that investment in growth and reproduction are context dependent. The size of plants grown in shaded areas was 2.7 times larger than those grown in full sun, whereas plants under full sun produced 1.7 times more flowers than those grown in shaded conditions. Type of soil did not affect plant area, but plants produced 1.5 times more flowers in non-serpentine soils. Our results suggest that the effects of competition are very complex, interact with abiotic factors and vary over time. We highlight the importance of long-term studies to identify competitive interactions and the importance of studying competition under multiple conditions. Understanding how competition might affect performance of the endangered M. smejkalii, under certain abiotic conditions (i.e. soil, water, shading), provides essential information for implementation of more efficient long-term conservation strategies.

Unravelling the ultramafic rock-driven serpentine soil formation leading to the geo-accumulation of heavy metals: An impact on the resident microbiome, biogeochemical cycling and acclimatized eco-physiological profiles

In the present study, we have underpinned the serpentine rock, serpentinized ultramafic soil and rhizosphere's microbial communities, signifying their heavy metals-exposed taxa signatures and functional repertoires in comparison to non-serpentine soils. The results revealed that the serpentine rock embedded soil highlighted the geo-accumulation of higher amount of Cr and Ni impacting soil microbial diversity negatively by metal stress-driven selection. Biolog Ecoplate CLPP defined a restricted spectrum of C-utilization in the higher heavy metal-containing serpentine samples compared to non-serpentine. The linear discriminant analysis (LDA) score identified a higher abundance of Desulfobacterota, Opitutales, and Bacteroidales in low Cr and Ni-stressed non-serpentine-exposed samples. Whereas the abundance of Propionibacteriales and Actinobacteriota were significantly enriched in the serpentine niche. Further, the C, N, S, Fe, and methane biogeochemical cycles linked functional members were identified, and showing higher functional diversity in low Cr and Ni concentration-containing rhizosphere JS-soils. The Pearson correlation coefficient (r) value confirmed the abundance of functional members linked to specific biogeochemical cycle, positively correlated with relevant pathway enrichment. Ultimately, this study highlighted the heavy metal stress within a serpentine setting that could limit the resident microbial community's metabolic diversity and further select the bacteria that could thrive in the serpentine-associated heavy metal-stressed soils. These acclimatized microbes could pave the way for the future applications in the soil conservation and management.

Plant community data from a statewide survey of paired serpentine and non-serpentine soils in California, USA.

Soils derived from ultramafic parent materials (hereafter serpentine) provide habitat for unique plant communities containing species with adaptations to the low nutrient levels, high magnesium : calcium ratios, and high metal content (Ni, Zn) that characterize serpentine. Plants on serpentine have long been studied in evolution and ecology, and plants adapted to serpentine contribute disproportionately to plant diversity in many parts of the world. In 2000-2003, serpentine plant communities were sampled at 107 locations representing the full range of occurrence of serpentine in California, USA, spanning large gradients in climate. In 2009-2010, plant communities were similarly sampled at 97 locations on nonserpentine soil, near to and paired with 97 of the serpentine sampling locations. (Some serpentine locations were revisited in 2009-2010 to assess the degree of change since 2000-2003, which was minimal.) At each serpentine or nonserpentine location, a north- and a south-facing 50 × 10 m plot were sampled. This design produced 97 "sites" each consisting of four "plots" (north-south exposure, serpentine-nonserpentine soil). All plots were initially visited three or more times over two years to record plant diversity and cover, and a subset were revisited in 2014 to examine community change after a drought. The original question guiding the study was how plant diversity is shaped by the spatially patchy nature of the serpentine habitat. Subsequently, we investigated how climate drives plant diversity at multiple scales (within locations, between locations on the same and different soil types, and across entire regions) and at different levels of organization (taxonomic, functional, and phylogenetic). There are no copyright restrictions and users should cite this data paper in publications that result from use of the data.

Comparison of bacterial communities and their functional profiling using 16S rRNA gene sequencing between the inherent serpentine-associated sites, hyper-accumulator, downgradient agricultural farmlands, and distal non-serpentine soils

This study aims to determine and compare the bacterial community and functional profiles associated with serpentine sites, innate hyper-accumulating weed, downgradient agricultural farmlands and non-serpentine sites using 16S rRNA gene sequencing. Elemental analysis revealed that the serpentine rock and weathered soil have higher magnesium, nickel, chromium, magnesium/calcium and lower calcium/magnesium ratios and agricultural farmlands have recorded elevated chromium. Proteobacteria were found predominant, except the non-serpentine site which was rich in Cyanobacteria. PCA analysis at the genus level indicates the uniqueness of different experimental groups, except the hyperaccumulators which exhibited relatively less dissimilarity. The shift analysis showed the serpentine sites were characterized by the abundance of bacteria having heavy metal effluxion. The hyper-accumulating weeds were higher in plant growth-promoting bacteria expressing tolerance against heavy metals toxicity such as nickel, chromium, cobalt and arsenic. Besides, the agricultural lands were abundant in wetland-associated methanogens and metal (manganese, iron and zinc) transporting function related bacteria. The results suggest that the inherent edaphic factors including heavy metal content, the interacting behavior of hyperaccumulator’s rhizosphere microbiota with soil and anthropogenic activities such as agricultural practices could be a major determinant of the variation in the bacterial community selection and abundance in the respective study sites.

Plant phenology influences rhizosphere microbial community and is accelerated by serpentine microorganisms in Plantago erecta.

Serpentine soils are drought-prone and rich in heavy metals, and plants growing on serpentine soils host distinct microbial communities that may affect plant survival and phenotype. However, whether the rhizosphere communities of plants from different soil chemistries are initially distinct or diverge over time may help us understand drivers of microbial community structure and function in stressful soils. Here, we test the hypothesis that rhizosphere microbial communities will converge over time (plant development), independent of soil chemistry and microbial source. We grew Plantago erecta in serpentine or nonserpentine soil, with serpentine or nonserpentine microbes and tracked plant growth and root phenotypes. We used 16S rRNA gene barcoding to compare bacterial species composition at seedling, vegetative, early- and late-flowering phases. Plant phenotype and rhizosphere bacterial communities were mainly structured by soil type, with minor contributions by plant development, microbe source and their interactions. Serpentine microorganisms promoted early flowering in plants on nonserpentine soils. Despite strong effects of soil chemistry, the convergence in bacterial community composition across development demonstrates the importance of the plant-microbe interactions in shaping microbial assembly processes across soil types.

Soil physicochemical properties shape distinct nematode communities in serpentine ecosystems

Serpentine ecosystems have unique plant communities that have overcome the chemical and physical challenges presented by these soils. However, such a specific soil fauna community has not been identified. It is presumed that such communities are affected directly by the chemical and physical properties of serpentine soils. Here, we focused on nematodes, which comprise a ubiquitous and an abundant group in soil fauna, for comparing their community structure in serpentine and in non-serpentine soils based on morphological approaches. Root biomass, Mg, and Ni were higher in serpentine habitats than non-serpentine ones. In contrast, the soil water content, NO3− and Ca/Mg ratio were higher at non-serpentine habitats than serpentine ones. Among the nematode community indices, the channel index, which indicates the degree of fungal participation in the decomposition channels of soil food webs, was greater in serpentine (94.5 ± 4.8) than in non-serpentine (44.8 ± 3.2) habitats, whereas the enrichment index, which indicates the abundance and activity of primary detrital consumers, was greater in non-serpentine (56.2 ± 3.7) than in serpentine (40.2 ± 2.9) habitats. A non-metric multidimensional scaling scatterplot showed that nematode communities clustered into both serpentine and non-serpentine habitats by a permutational multivariate analysis of variance. Ca/Mg ratio accounted for the most variation in nematode communities: 90 % of the variation between the sites by envfit. Furthermore, relative frequencies of nine taxa (Filenchus, Malenchus, Mesodorylaimus, Monhystera, Paratylenchus, Plectus, Prodesmodora, Teratocephalus, and Tripyla) were greater in serpentine than in non-serpentine habitats, and those of five taxa (Alaimus, Bastiania, Cervidellus, Diptherophora, and Rhabditidae) were greater in non-serpentine than in serpentine ones by indicator species analysis. Although our study was a small sample size and unit, our findings suggest that the structure of nematode communities reflects the physicochemical properties of serpentine soils.

Response of Three Greek Populations of Aegilops triuncialis (Crop Wild Relative) to Serpentine Soil.

A common garden experiment was established to investigate the effects of serpentine soil on the photosynthetic and biochemical traits of plants from three Greek populations of Aegilops triuncialis. We measured photosynthetic and chlorophyll fluorescence parameters, proline content, and nutrient uptake of the above plants growing in serpentine and non-serpentine soil. The photochemical activity of PSII was inhibited in plants growing in the serpentine soil regardless of the population; however, this inhibition was lower in the Aetolia-Acarnania population. The uptake and the allocation of Ni, as well as that of some other essential nutrient elements (Ca, Mg, Fe, Mn), to upper parts were decreased with the lower decrease recorded in the Aetolia-Acarnania population. Our results showed that excess Ni significantly increased the synthesis of proline, an antioxidant compound that plays an important role in the protection against oxidative stress. We conclude that the reduction in the photosynthetic performance is most probably due to reduced nutrient supply to the upper plant parts. Moreover, nickel accumulation in the roots recorded in plants from all three populations seems to be a mechanism to alleviate the detrimental effects of the serpentine soil stress. In addition, our data suggest that the population from Aetolia-Acarnania could be categorized among the nickel excluders.

Variation of Phenolic and Pigment Composition Depending on Soil Type in Three Serpentinovag Plant Species

Serpentine soils are stressful for plant growth, due to nutrient deficiencies, especially Ca, low water-holding capacity, and high levels of heavy metals and Mg. Determination of biochemical differences of plants grown in serpentine and non-serpentine soil can contribute to understanding tolerance to serpentine soil. In this study, samples of three plant species (Alyssum sibiricum Willd., Salvia absconditiflora (Montbret & Aucher ex Bentham) Greuter & Burdet and Centaurea urvillei DC. subsp. stepposa Wagenitz) were compared in terms of the composition of phenolic compounds and chloroplast pigments. Higher amounts of phenolic compounds were measured in serpentine soil-grown forms of all three species. Total soluble phenolic content, in samples grown in serpentine and non-serpentine soil, respectively, S. absconditiflora 731.8 - 161.7, C. urvillei 121.0-49.7 and A. sibiricum 50.2- 47.3 µg g-1 DW). It was determined that the amount of chlorophyll a was higher in the serpentine soil grown forms of all three species while the amount of chlorophyll b was variable. In plants grown in serpentine soil, β-carotene values are higher than non-serpentine forms. Total xanthophyl values are also parallel with β-carotene findings, but lower. The findings in the present study show that antioxidant compounds such as phenolics and carotenoids may play a role in the stress tolerance of plants growing in serpentine habitats.

Intraspecific trait variability and genetic diversity in the adaptive strategies of serpentine and non-serpentine populations of Silene paradoxa L.

AimsWe investigated whether individuals of Silene paradoxa L., grown in serpentine and non-serpentine soils, displayed variation in functional traits and adaptive strategies together with a differentiation of the gene pool. We hypothesised that individuals growing in serpentine sites may be exposed to a higher degree of stress, resulting in measurable differences in leaf traits and adaptive strategies, and as well that the differences in the soil type were associated with a genetic process of differentiation.MethodsWe analysed a specific set of leaf functional traits of populations of S. paradoxa grown on serpentine and non-serpentine soils. Furthermore, DNA-fingerprinting techniques were used to further dissect the emergence of genetic processes of differentiation linked to the different soil types.ResultsWe detected a relevant intraspecific trait variation in S. paradoxa, with the populations from serpentine sites significantly polarised towards the stress-tolerant adaptive strategy. This polarisation came with a shift in gene pool selection, even if we did not detect quantitative differences in the genetic diversity or evidence of genetic drift.ConclusionsThe results indicate that particular edaphic conditions acted on the selection of some regions of the species’ genome, independently of the site, with various portions of the genome being exclusive to or prevalent in the serpentine or non-serpentine populations.

Influence of soil properties on the bioaccessibility of Cr and Ni in geologic serpentine and anthropogenically contaminated non-serpentine soils in Taiwan

Serpentine minerals with high levels of geologic chromium (Cr) and nickel (Ni) and non-serpentine farmlands polluted by irrigation water causing high anthropogenic Cr and Ni levels are both found in Taiwan. Elevated levels of Cr and Ni in these soils are a concern due to their potential to promote cancer mortality in humans. Bioaccessibility is a crucial factor determining the actual health risk via oral ingestion when children are exposed to metal-contaminated soils. Furthermore, the bioaccessibility of metals varies with the source, soil properties, and fractionation of metals in the soil. Therefore in this study, soil pH, total organic carbon (TOC), texture, and the total concentrations, fractionation, and bioaccessibility of Cr and Ni were analyzed and correlated for soils collected from serpentine mineral-containing deposits and contaminated non-serpentine farmlands. The low bioaccessibility and low mobility of Cr and Ni in serpentine soils suggested that incidental ingesting of soils posed a low health risk; however, the higher bioaccessibility and mobility of Ni in non-serpentine soils contaminated by electroplating wastewater could lead to potential risks for humans. Additionally, a significant difference in the bioaccessibility of Ni was observed between serpentine and non-serpentine soils, but this was not shown for Cr. Accordingly, a correlation analysis showed that Cr bioaccessibility was positively correlated with TOC, with no distinction between serpentine and non-serpentine soils. In contrast, TOC and the fractions of the sequential extraction procedure were significantly correlated with Ni bioaccessibility both in anthropogenically contaminated non-serpentine soils and in natural serpentine soils.

Generalists are more specialized in low-resource habitats, increasing stability of ecological network structure

Linking mechanistic processes to the stability of ecological networks is a key frontier in ecology. In trophic networks, "modules"-groups of species that interact more with each other than with other members of the community-confer stability, mitigating effects of species loss or perturbation. Modularity, in turn, is shaped by the interplay between species' diet breadth traits and environmental influences, which together dictate interaction structure. Despite the importance of network modularity, variation in this emergent property is poorly understood in complex natural systems. Using two years of field data, we quantified interactions between a rich community of lepidopteran herbivores and their host plants across a mosaic of low-resource serpentine and high-resource nonserpentine soils. We used literature and our own observations to categorize herbivore species as generalists (feeding on more than one plant family) or specialists (feeding on one plant family). In both years, the plant-herbivore network was more modular on serpentine than on nonserpentine soils-despite large differences in herbivore assemblage size across years. This structural outcome was primarily driven by reduction in the breadth of host plant use by generalist species, rather than by changes in the composition of species with different fundamental diet breadths. Greater modularity-and thus greater stability-reflects environmental conditions and plastic responses by generalist herbivores to low host plant quality. By considering the dual roles of species traits and ecological processes, we provide a deeper mechanistic understanding of network modularity, and suggest a role for resource availability in shaping network persistence.

Profiling of proteasome activity in Alyssum species on serpentine soils in Turkey reveals possible insight into nickel tolerance and accumulation

In crops and most plants, nickel induces oxidative stress resulting in oxidized and misfolded proteins. Proteasomes maintain cellular homeostasis during stress by removing these damaged proteins. Although mild stress tolerance is mediated by proteasomal proteolysis of misfolded and oxidized proteins, previous studies have observed that severe nickel stress decreases proteasome activity in nickel-sensitive plants. Whether or not proteasome function is impaired in nickel-tolerant plants is not know. Therefore, we tested the hypothesis that proteasome activity is elevated in nickel-tolerant Alyssum species capable of accumulating nickel to unusually high levels. Our field studies examined Alyssum sibiricum and Alyssum caricum, a moderate nickel accumulator and hyper-accumulator respectively, growing on their native serpentine soil in Turkey. A. sibiricum had higher proteasome activity on serpentine soil compared to non-serpentine soil; these plants also had elevated levels of nickel accumulation and higher proteasome activity compared to other low accumulating plants in the genus Festuca or Astragalus. In A. caricum, proteasome activity was very weakly correlated with nickel soil bioavailability or accumulation in leaf tissue, suggesting that proteasome function was not impaired in plants that accumulated the highest concentration of nickel. We discuss if maintained proteasome activity might underpin nickel tolerance and the unique ecophysiology of nickel hyper-accumulation in plants.

Antimicrobial Properties of Selected Plant Species in the Ussangoda and Yodhaganawa Serpentines.

Serpentine are the soils derived from ‘serpentinised’ (altered by hydration) ultramaffic rocks. These are poor in plant-essential nutrients, organic matter, water availability, etc., but, rich in Mg, Fe, and heavy metals Ni, Cr and Co. Serpentine flora may be assisted by various bioactivities beneficial for mankind. This study aimed to investigate the antimicrobial properties of selected serpentine plant species from two serpentine sites in Sri Lanka: Ussangoda (in Hambantota District) and Yodhaganawa (inside Wasgomuwa National Park). Eleven (11) plant samples from 10 species were collected from the two serpentines for screening for antimicrobial activity against Gram positive (Bacillus cereus, Staphylococcus aureus) and Gram negative (Escherichia coli, Pseudomonas aeruginosa) bacteria, and fungi (Aspergillus niger, Candida albicans, Trichodermavirens). Plant materialsof 04 species were collected from both the serpentine and the neighboring non-serpentine soils in Ussangoda, for comparative analysis of the effect of substrate on the antimicrobial activity of these plants. Crude extracts were obtained by soaking dried, powdered leaf material in 1:1 mixture of Methanol: Dichloromethane for two weeks and subsequent concentrating. Samples re-dissolved in 10% DMSO in methanol were used in the Kirby- Bauer Antibiotic Disc Diffusion Assay and Micro-Titre Plate Based Resazurin Assay. Data obtained from the assays were analyzed using SPSS 16.0 software. When screened, 10 extracts (Azadirachta indica, Lantana camara, Toddalia asiatica, Eupatorium odoratum, Bauhinia racemonsa, Carissa spinarum, Garcinia spicata, Atalantia monophylla, Tarenna asiatica) showed activity against at least one test microorganism. The extract of Tarennaasiatica showed activity against all the test microorganisms. Sapindus saponaria extract did not show activity against any of the test organisms. When comparing, Azadirachta indica extract did not show any significant difference (P>0.05) in the mean diameter of the inhibition zone (±SD) between the serpentine site and the adjacent non-serpentine site for all the tested bacterial species. However, significantly higher (P<0.05) mean diameter of the inhibition zone (±SD) against E. coli was shown by the serpentine Lantana camara extract (13.3±1.1mm) compared with the non-serpentine plant extract(mean diameter of the inhibition zone 9.5±0.9mm). In contrast, non-serpentine extract of Eupatorium odoratum showed slightly higher activity than that of the serpentine plant extract against the same bacterial strain, with respective mean diameters (±SD) of inhibition zones being 10±0.9 mm and 8±0.8 mm. The results indicate that serpentine flora may have altered antimicrobial activities compared to the plants of the same species growing in non-serpentine soils, probably due to the influence of the serpentine substrate. Keywords: Serpentine, Ultramaffic, Plants, Bioactivities, Antimicrobial, Properties

Effects of soil metals on pollen germination, fruit production, and seeds per fruit differ between a Ni hyperaccumulator and a congeneric nonaccumulator

Developmentally distinct soil formations (e.g., serpentine vs. non-serpentine soils) can vary markedly in chemical composition, including elements known to alter plant reproduction. Here we evaluate the effects of soil Ca and Ni on pollen germination and fruit and seed production for two species: Streptanthus polygaloides, a serpentine endemic and Ni hyperaccumulator, and S. tortuosus, a non-endemic, non-Ni-accumulating, serpentine-tolerant species. In a factorial experiment, we grew each species in soils that were amended to have high or low concentrations of Ca and Ni. We then performed hand pollinations and measured pollen germination, fruit production, and seeds per fruit. While Ca soil supplementation did not affect reproduction for either species, soil Ni had a strong influence, which varied by species. For S. tortuosus, the high Ni recipient treatment resulted in reduced pollen germination and fruit/seed production. For S. polygaloides, recipient effects were detected, but in the opposite direction of S. tortuosus: high Ni recipient treatment had a neutral (or slightly positive) effect on S. polygaloides pollen germination and fruit/seed production. Soil chemistry can greatly influence plant reproduction by altering pollen-pistil interactions, and may determine patterns of plant species abundance and distribution on novel soils by directly affecting pollen germination and subsequent reproductive success.

Drought Response Strategies ofClarkia gracilis(Onagraceae) Populations from Serpentine and Nonserpentine Soils

Premise of research. The serpentine grassland system provides the opportunity to examine whether drought response traits may have contributed to differentiation in the stress-tolerant genus Clarkia. Commonly utilized drought responses might be indicative of traits important to species diversification in stressful environments.Methodology. We examined the drought response strategies of populations of Clarkia gracilis (Onagraceae) from both serpentine and nonserpentine soils. Physiological, morphological, and biomass data were collected under controlled greenhouse conditions.Pivotal results. Serpentine-derived plants exhibited faster growth and germination rates and larger leaf size than nonserpentine-derived plants under increasing water stress, indicating drought escape strategies. However, serpentine-derived plants also employed dehydration avoidance by increasing their water-use efficiency (decreased transpiration rate) under drought stress. In terms of biomass, serpentine-derived plants had a higher fitness potential than nonserpentine-derived plants. Nonserpentine-derived plants tended toward dehydration avoidance through decreased growth rate, decreased transpiration, and smaller leaf size.Conclusions. Our data support transpiration rate as a trait important to stress tolerance. Moreover, serpentine-derived plants avoid drought with drought escape strategies more than nonserpentine plants and may have a higher fitness potential, particularly in water-limiting conditions. Thus, serpentine populations may be competitively superior to nonserpentine populations under drought stress conditions.

Nickel speciation in several serpentine (ultramafic) topsoils via bulk synchrotron-based techniques

Serpentine soils have elevated concentrations of trace metals including nickel, cobalt, and chromium compared to non-serpentine soils. Identifying the nickel bearing minerals allows for prediction of potential mobility of nickel. Synchrotron-based techniques can identify the solid-phase chemical forms of nickel with minimal sample treatment. Element concentrations are known to vary among soil particle sizes in serpentine soils. Sonication is a useful method to physically disperse sand, silt and clay particles in soils. Synchrotron-based techniques and sonication were employed to identify nickel species in discrete particle size fractions in several serpentine (ultramafic) topsoils to better understand solid-phase nickel geochemistry. Nickel commonly resided in primary serpentine parent material such as layered-phyllosilicate and chain-inosilicate minerals and was associated with iron oxides. In the clay fractions, nickel was associated with iron oxides and primary serpentine minerals, such as lizardite. Linear combination fitting (LCF) was used to characterize nickel species. Total metal concentration did not correlate with nickel speciation and is not an indicator of the major nickel species in the soil. Differences in soil texture were related to different nickel speciation for several particle size fractionated samples. A discussion on LCF illustrates the importance of choosing standards based not only on statistical methods such as Target Transformation but also on sample mineralogy and particle size. Results from the F-test (Hamilton test), which is an underutilized tool in the literature for LCF in soils, highlight its usefulness to determine the appropriate number of standards to for LCF. EXAFS shell fitting illustrates that destructive interference commonly found for light and heavy elements in layered double hydroxides and in phyllosilicates also can occur in inosilicate minerals, causing similar structural features and leading to false positive results in LCF.

Evolution of nickel hyperaccumulation and serpentine adaptation in the Alyssum serpyllifolium species complex.

Metal hyperaccumulation is an uncommon but highly distinctive adaptation found in certain plants that can grow on metalliferous soils. Here we review what is known about evolution of metal hyperaccumulation in plants and describe a population-genetic analysis of the Alyssum serpyllifolium (Brassicaceae) species complex that includes populations of nickel-hyperaccumulating as well as non-accumulating plants growing on serpentine (S) and non-serpentine (NS) soils, respectively. To test whether the S and NS populations belong to the same or separate closely related species, we analysed genetic variation within and between four S and four NS populations from across the Iberian peninsula. Based on microsatellites, genetic variation was similar in S and NS populations (average Ho=0.48). The populations were significantly differentiated from each other (overall FST=0.23), and the degree of differentiation between S and NS populations was similar to that within these two groups. However, high S versus NS differentiation was observed in DNA polymorphism of two genes putatively involved in adaptation to serpentine environments, IREG1 and NRAMP4, whereas no such differentiation was found in a gene (ASIL1) not expected to play a specific role in ecological adaptation in A. serpyllifolium. These results indicate that S and NS populations belong to the same species and that nickel hyperaccumulation in A. serpyllifolium appears to represent a case of adaptation to growth on serpentine soils. Further functional and evolutionary genetic work in this system has the potential to significantly advance our understanding of the evolution of metal hyperaccumulation in plants.

Is it worth hyperaccumulating Ni on non-serpentine soils? Decomposition dynamics of mixed-species litters containing hyperaccumulated Ni across serpentine and non-serpentine environments.

Nickel (Ni)-hyperaccumulating species produce high-Ni litters and may potentially influence important ecosystem processes such as decomposition. Although litters resembling the natural community conditions are essential in order to predict decomposition dynamics, decomposition of mixed-species litters containing hyperaccumulated Ni has never been studied. This study aims to test the effect of different litter mixtures containing hyperaccumulated Ni on decomposition and Ni release across serpentine and non-serpentine soils. Three different litter mixtures were prepared based on the relative abundance of the dominant species in three serpentine soils in the island of Lesbos, Greece where the Ni-hyperaccumulator Alyssum lesbiacum is present. Each litter mixture decomposed on its original serpentine habitat and on an adjacent non-serpentine habitat, in order to investigate whether the decomposition rates differ across the contrasted soils. In order to make comparisons across litter mixtures and to investigate whether additive or non-additive patterns of mass loss occur, a control non-serpentine site was used. Mass loss and Ni release were measured after 90, 180 and 270 d of field exposure. The decomposition rates and Ni release had higher values on serpentine soils after all periods of field exposure. The recorded rapid release of hyperaccumulated Ni is positively related to the initial litter Ni concentration. No differences were found in the decomposition of the three different litter mixtures at the control non-serpentine site, while their patterns of mass loss were additive. Our results: (1) demonstrate the rapid decomposition of litters containing hyperaccumulated Ni on serpentine soils, indicating the presence of metal-tolerant decomposers; and (2) imply the selective decomposition of low-Ni parts of litters by the decomposers on non-serpentine soils. This study provides support for the elemental allelopathy hypothesis of hyperaccumulation, presenting the potential selective advantages acquired by metal-hyperaccumulating plants through litter decomposition on serpentine soils.