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Serpentine
Serpentine soils have long fascinated biologists for the specialized floras they support and the challenges they pose to plant survival and growth. This volume focuses on what scientists have learned about major questions in earth history, evolution, ecology, conservation, and restoration from the study of serpentine areas, especially in California. Results from molecular studies offer insight into evolutionary patterns, while new ecological research examines both species and communities. Serpentine highlights research whose breadth provides context and fresh insights into the evolution and ecology of stressful environments.
eBook
Adaptation and divergence in edaphic specialists and generalists
Premise Adaptation to harsh edaphic substrates has repeatedly led to the evolution of edaphic specialists and generalists. Yet, it is unclear what factors promote specialization versus generalization. Here, we search for habitat use patterns associated with serpentine endemics (specialists) and serpentine tolerators (generalists) to indirectly test the hypothesis that trade‐offs associated with serpentine adaptation promote specialization. We predict that (1) endemics have adapted to chemically harsher and more bare serpentine habitats than tolerators, and (2) edaphic endemics show more habitat divergence from their sister species than tolerators do among on‐ and off‐serpentine populations. Methods We selected 8 serpentine endemic and 9 serpentine tolerator species representing independent adaptation to serpentine. We characterized soil chemistry and microhabitat bareness from one serpentine taxon of each species and from a paired nonserpentine sister taxon, resulting in 8 endemic and 9 tolerator sister‐taxa pairs. Results We find endemic serpentine taxa occur in serpentine habitats averaging twice as much bare ground as tolerator serpentine taxa and 25% less soil calcium, a limiting macronutrient in serpentine soils. We do not find strong evidence that habitat divergence between sister taxa of endemic pairs is greater than between sister taxa of tolerator pairs. Conclusions These results suggest serpentine endemism is associated with adaptation to chemically harsher and more bare serpentine habitats. It may be that this adaptation trades off with competitive ability, which would support the longstanding, but rarely tested, competitive trade‐off hypothesis.
Journal Article
Microbial diversity and mineral composition of weathered serpentine rock of the Khalilovsky massif
Endolithic microbial communities survive nutrient and energy deficient conditions while contributing to the weathering of their mineral substrate. This study examined the mineral composition and microbial communities of fully serpentinized weathered rock from 0.1 to 6.5 m depth at a site within the Khalilovsky massif, Orenburg Region, Southern Ural Mountains, Russia. The mineral composition includes a major content of serpentinite family (mostly consisting of lizardite and chrysotile), magnesium hydrocarbonates (hydromagnesite with lesser amounts of hydrotalcite and pyroaurite) concentrated in the upper layers, and clay minerals. We found that the deep-seated weathered serpentinites are chrysotile-type minerals, while the middle and surface serpentinites mostly consist of lizardite and chrysotile types. Microbial community analysis, based on 16S rRNA gene sequencing, showed a similar diversity of phyla throughout the depth profile. The dominant bacterial phyla were the Actinobacteria (of which unclassified genera in the orders Acidimicrobiales and Actinomycetales were most numerous), Chloroflexi (dominated by an uncultured P2-11E order) and the Proteobacteria (predominantly class Betaproteobacteria). Densities of several groups of bacteria were negatively correlated with depth. Occurrence of the orders Actinomycetales, Gaiellales, Solirubrobacterales, Rhizobiales and Burkholderiales were positively correlated with depth. Our findings show that endolithic microbial communities of the Khalilovsky massif have similar diversity to those of serpentine soils and rocks, but are substantially different from those of the aqueous environments of actively serpentinizing systems.
Journal Article
nature of serpentine endemism
Serpentine soils are a model system for the study of plant adaptation, speciation, and species interactions. Serpentine soil is an edaphically stressful, low productivity soil type that hosts stunted vegetation and a spectacular level of plant endemism. One of the first papers on serpentine plant endemism was by Arthur Kruckeberg, titled “Intraspecific variability in the response of certain native plant species to serpentine soil.” Published in the American Journal of Botany in 1951, it has been cited over 100 times. Here, I review the context and content of the paper, as well as its impact. On the basis of the results of reciprocal transplant experiments in the greenhouse, Kruckeberg made three important conclusions on the nature of serpentine plant endemism: (1) Plants are locally adapted to serpentine soils, forming distinct soil ecotypes; (2) soil ecotypes are the first stage in the evolutionary progression toward serpentine endemism; and (3) serpentine endemics are restricted from more fertile nonserpentine soils by competition. Kruckeberg’s paper inspired a substantial amount of research, especially in the three areas reviewed here: local adaptation and plant traits, speciation, and the interaction of climate and soil in plant endemism. In documenting soil ecotypes, Kruckeberg identified serpentine soils as a potent selective factor in plant evolution and helped establish serpentine soils as a model system in evolution and ecology.
Journal Article
Application of Al2O3/water nanofluid as the coolant in a new design of photovoltaic/thermal system: An experimental study
A new geometry of photovoltaic/thermal (PVT) system is introduced in this study, and the application of Al2O3/water nanofluid as the coolant on the electrical and thermal behavior of a solar system is experimentally evaluated. To intensify the thermal ability of the solar collector, a serpentine half‐pipe cooling system is designed and fabricated behind the solar panel for better cooling. The cells of the panel are assembly on a 3‐mm‐thick aluminum plate, and the Tedlar removes from the system to maximize the heat transfer in the cooling section. A special layer arrangement for the composite panel is used to minimize thermal resistance of the system. Different concentrations of nanofluid samples (0.05–0.5 wt.%) prepared. To increase the stability of prepared nanofluids, suitable surfactants are also used. Based on the obtained results, adding the nanoparticles to the pure water can remarkably raise the efficiency of the PVT apparatus. The best behavior of the solar collector is observed for 0.5 wt.% of nanofluid samples. 126.71% and 7.38% enhancement in terms of thermal and electrical efficiency can be gained by the application of nanofluid in the system compared with pure water, respectively. The best obtained value of the overall efficiency is around 93.73% for the studied system. The maximum temperature rise for water and nanofluid is around 5.5 and 9.1°C, respectively, which confirms the better cooling ability of PVT system by nanofluid compared with water. Layer arrangement of proposed model and overall efficiency of photovoltaic/thermal system versus flow rate and different concentrations of nanofluids.
Journal Article
Plant mortality on ultramafic soils after an extreme heat and drought event in the Mediterranean area
Aims
Plant mortality associated with the growing frequency and intensity of heatwaves and dry spells is increasingly occurring in various ecosystems worldwide. However, the impacts of extreme events on plant communities of ultramafic soils are still unknown. Here, we describe a first case of plant mortality on serpentine outcrops in Italy following a heat and drought event that occurred between autumn 2016 and summer 2017.
Methods
Mortality of perennial plants was assessed in thirty plots representing ten major serpentine areas along a SW-NE gradient, with the sparse vegetation of ultramafic soils. Statistical modelling was based on temperature and precipitation data and local site conditions.
Results
Responses of single species were largely different and not related to their taxonomic position, growth form or level of edaphic specialization for serpentine soils. Notably, obligate serpentine endemics were not less impacted than non-endemics. As expected, species mortality decreased with increasing chromosome number, suggesting higher tolerance and adaptive capacity in taxa of likely polyploid origin. Mortality increased with decreasing number of rainy days and duration of the heatwave and decreased with increasing distance from the Tyrrhenian coastline, reaching 60% in the southern and western areas with a Mediterranean climate. Local site conditions such as increasing soil depth and north-facing aspect significantly increased plant survivorship.
Conclusions
Our findings show that extreme drought and heat can have a previously unrealized impact on ultramafic plant communities in the short term. Further studies should examine the recovery capacity and resilience of serpentine plants, together with the long term effects.
Journal Article
Parallel adaptation in autopolyploid Arabidopsis arenosa is dominated by repeated recruitment of shared alleles
Relative contributions of pre-existing vs de novo genomic variation to adaptation are poorly understood, especially in polyploid organisms. We assess this in high resolution using autotetraploid
Arabidopsis arenosa
, which repeatedly adapted to toxic serpentine soils that exhibit skewed elemental profiles. Leveraging a fivefold replicated serpentine invasion, we assess selection on SNPs and structural variants (TEs) in 78 resequenced individuals and discover significant parallelism in candidate genes involved in ion homeostasis. We further model parallel selection and infer repeated sweeps on a shared pool of variants in nearly all these loci, supporting theoretical expectations. A single striking exception is represented by
TWO PORE CHANNEL 1
, which exhibits convergent evolution from independent de novo mutations at an identical, otherwise conserved site at the calcium channel selectivity gate. Taken together, this suggests that polyploid populations can rapidly adapt to environmental extremes, calling on both pre-existing variation and novel polymorphisms.
Relative contributions of pre-existing versus de novo genomic variation to adaptation remain unclear. Here, the authors address this problem by examining the adaptation of autotetraploid
Arabidopsis arenosa
to serpentine soils and find that both types of variations contribute to rapid adaptation.
Journal Article
Lotus corniculatus-rhizobia symbiosis under Ni, Co and Cr stress on ultramafic soil
Aims
Ultramafic/serpentine soils constitute a stressful environment with many plant growth constrains such as a lack of macronutrients and high levels of potentially toxic metals. We considered the adaptive strategy of
Lotus corniculatus
L.-rhizobia symbiosis to Ni, Co and Cr stress conditions.
Methods
L. corniculatus
nodulating rhizobia from ultramafic soil were isolated, identified and tested for nitrogen fixation, metal tolerance and plant growth promoting abilities. The structural and immunocytochemical analyses of root nodules were also performed.
Results
The isolates effective in nitrogen fixation were identified as
Rhizobium
and
Mesorhizobium
tolerant to Ni, Co, and Cr. Some strains directly promoted root growth of
L. corniculatus
and non-legume
Arabidopsis thaliana
under metal stress. The metal treated nodules showed structural alternations, i.e. enhanced accumulation of phenols and wall thickening with higher cellulose, hemicellulose, pectins, glycoproteins and callose content.
Conclusions
Our results revealed that metal tolerant, growth promoting rhizobacteria inhabiting
L. corniculatus
root nodules may improve plant growth in the ultramafic environment. Accumulation of phenols and reorganization of nodule apoplast can counteract harmful effects of Ni, Co and Cr on the symbiosis. These findings imply that
L. corniculatus
-rhizobia symbiosis is an important element of plant adaptation to metal stress occurring on the ultramafic soils.
Journal Article
Serpentine environment prevails over geographic distribution in shaping the genetic diversity of Medicago lupulina L
Edaphic conditions of serpentine soils, naturally rich in heavy metals, act as a strong selection pressure that shapes specific metal-tolerant ecotypes. Medicago lupulina L. (black medick) is not only a widespread plant species that prefers calcareous and dry soil types but also grows at the borders of serpentine formations. It can also be found in waste and disturbed habitats. This is a species with reported phytoremediation potential, however, there is no published data regarding the impact of the environment on the genetic distribution of this species. The aim of our research was to explore how selection pressure of serpentine soils affects genetic diversity of M. lupulina and to test heavy-metal accumulation capacity of this species. Specimens of 11 M. lupulina populations were collected from serpentine outcrops located in Central and Eastern Bosnia as well as from non-serpentine sites. Soil and plant samples were analyzed for the total contents of heavy metals using air-acetylene flame atomic absorption spectroscopy. Genetic diversity was analyzed using AFLP (Amplified Fragment Length Polymorphism) markers. Serpentine soils showed high nickel, cobalt, chromium and iron concentrations. Nickel and manganese concentrations in soil samples and plant material showed statistically significant correlation. Although plants in two populations show the ability to extract Ni, M. lupulina does not show hyperaccumulating properties. Despite severe selective pressure, genetic diversity in serpentine populations is not reduced. Analyses of intrapopulation and interpopulation genetic diversity showed significant genetic differentiation among populations which is not related to their geographic distance. Population from non-metalliferous soil showed clear separation from all other populations. Diversity data suggest that serpentine populations maintain genetic diversity by undetected mechanisms and that edaphic factors rather than geography influence genetic structure analyzed M. lupulina populations.
Journal Article