Tolerance and induction of tolerance to Ni of arbuscular mycorrhizal fungi from New Caledonian ultramafic soils

The influence of Ni on arbuscular mycorrhizal fungi (AMF) has not been studied yet. We tested the tolerance to Ni of five AMF isolates from New Caledonian ultramafic soils. Spore germination indicated that these isolates were clearly more tolerant to Ni than three other isolates from non-ultramafic soils. They were able to germinate at 30 μg g⁻¹ Ni, whereas spores of the non-ultramafic isolates were totally inhibited at 15 μg g⁻¹ Ni. Among the ultramafic isolates, two were obtained from roots of Ni-hyperaccumulating plants. Their tolerance to Ni was clearly higher than all the other isolates. The proportion of germinated spores of the different isolates in contact with ultramafic soils showed the same tendencies as those observed with Ni solutions. Tolerance to Ni increased when spores were produced from mycorrhiza on plants grown on sand containing 20 μg g⁻¹ Ni, in comparison with those produced on sand without Ni. These results indicate that the tolerance to Ni of AMF spores can be induced by the presence of this metal in the substrate.

Arbuscular mycorrhizal fungi from New Caledonian ultramafic soils improve tolerance to nickel of endemic plant species

In order to improve knowledge about the role of arbuscular mycorrhizal fungi (AMF) in the tolerance to heavy metals in ultramafic soils, the present study investigated the influence of two Glomus etunicatum isolates from New Caledonian ultramafic maquis (shrubland), on nickel tolerance of a model plant species Sorghum vulgare, and of two ultramafic endemic plant species, Alphitonia neocaledonica and Cloezia artensis. In a first step, plants were grown in a greenhouse, on sand with defined concentrations of Ni, to appreciate the effects of the two isolates on the alleviation of Ni toxicity in controlled conditions. In a second step, the influence of the AMF on A. neocaledonica and C. artensis plants grown in a New Caledonian ultramafic soil rich in extractable nickel was investigated. Ni reduced mycorrhizal colonization and sporulation of the fungal isolates, but the symbionts increased plant growth and adaptation of endemic plant species to ultramafic conditions. One of the two G. etunicatum isolates showed a stronger positive effect on plant biomass and phosphorus uptake, and a greater reduction in toxicity symptoms and Ni concentration in roots and shoots. The symbionts seemed to act as a barrier to the absorption of Ni by the plant and reduced root-to-shoot Ni translocation. Results indicate the potential of selected native AMF isolates from ultramafic areas for ecological restoration of such degraded ecosystems.     

Extractability of nickel and its concentration in cultivated plants in Ni rich ultramafic soils of New Caledonia

The presence of higher-than-normal quantities of nickel is one of the most general features of ultramafic soils and is often suspected as the reason for their infertility. This study on the bioavailability of Ni in ultramafic soils derived from peridotites in New Caledonia showed important variations depending on the position of the soil in the landscape. In piedmont and non hydromorphic colluvio-alluvial soils, Ni was poorly absorbed by cultivated plants. In contrast, crops species grown in the plain soils, especially those found in the colluvio-alluvial and plain soils subject to temporary reducing conditions, possessed very high and even toxic Ni concentrations. Extraction of Ni by DTPA 5 mM was an effective method of estimating Ni bioavailability in these soils. The regression equation developed with only DTPA-extractable ni explained 88% of the variability in tomato Ni concentration. Extractable Ni might originate from the association of Ni with primary alterable minerals, organic matter and goethite. ei]Section editor: L V Kochian     

Mycorrhizal status of Cyperaceae from New Caledonian ultramafic soils: effects of phosphorus availability on arbuscular mycorrhizal colonization of Costularia comosa under field conditions

Plants from the Cyperaceae family (sedges), usually considered as non-mycorrhizal, constitute almost exclusively the herbaceous stratum of the ultramafic maquis in New Caledonia. These plants are pioneers and are important for the ecological restoration of mined areas. Costularia comosa, one of the most common sedges in this environment, was grown under field conditions on ultramafic soil, fertilized or not with phosphate and/or nitrogen. Results showed that the addition of phosphate to the soil induced a clear increase in mycorrhizal colonization of C. comosa and an increase in arbuscule abundance, reflecting the establishment of a functional mycorrhizal symbiosis. Significant positive correlations were found among mycorrhizal parameters and plant or soil phosphorus concentrations. Nitrogen fertilization did not affect mycorrhizal colonization of C. comosa. The improvement in mycorrhizal colonization by phosphate fertilization did not influence significantly nickel concentrations in the roots and shoots of plants. This study demonstrated that phosphate fertilization of ultramafic soil improved mycorrhizal colonization of C. comosa, with formation of a functional symbiosis under field conditions.     

New insights into the mycorrhizal status of Cyperaceae from ultramafic soils in New Caledonia

In New Caledonia, a hot spot of biodiversity, plants from the Cyperaceae family are mostly endemic and considered pioneers of the nickel-rich natural serpentine ecosystem. The aim of the study was to highlight the mycorrhizal status of these Cyperaceae and to bring new insights into the role of this symbiosis in plant tolerance to ultramafic soils. Nine Cyperaceae species were studied and presented evidence of root colonization by arbuscular mycorrhizas (AMs), with frequencies ranging from 8% to 57%. The highest level of AM colonization was observed in plants from the endemic dominant genus Costularia. Molecular evidence demonstrated the presence of Glomus sp. inside the roots. In a controlled greenhouse assay, AM inoculation of Costularia comosa grown under ultramafic conditions significantly enhanced plant growth, with an increase in biomass by up to 2.4-fold for shoots and 1.2-fold for roots, and also reduced nickel content in roots by 2.5-fold, as compared with the controls. All these data support our hypotheses (i) that a relationship exists between the mycorrhizal status of Cyperaceae and their habitat, and (ii) that AM have a positive role in plant tolerance to ultramafic soils (mineral nutrition and metal tolerance), suggesting the use of these pioneer plants with AM management as potential tools for nickel mine site rehabilitation in New Caledonia.     

Microbial communities of ultramafic soils in maquis and rainforest at Mont Do,New Caledonia

We analysed variation in microbial community richness and function in soils associated with a fire‐induced vegetation successional gradient from low maquis (shrubland) through tall maquis to rainforest on metal‐rich ultramafic soils at Mt Do, New Caledonia. Random amplified polymorphic DNA fingerprinting was used to determine the extent of genetic relatedness among the microbial communities and indicated that the open and tall maquis microbial communities were more similar to each other than they were to the rainforest community. Sole‐source carbon utilization indicated variation in the microbial communities, again with greater diversity in rainforest soils. Plate counts showed that both rainforest and maquis soils contained bacteria that can grow in the presence of up to 20 mmol L^?1 nickel and 10 mmol L^?1 chromium. Understanding microbial community composition and dynamics in these ultramafic soils may lead to a better understanding of the processes facilitating vegetation succession from shrubland to forest on these high‐metal substrates, and of approaches to successful revegetation following mining for metals including nickel, chromium and cobalt.     

Microbial biomass,respiration and diversity in ultramafic soils of West Dome,New Zealand

Ultramafic soils are colonised by plant communities adapted to naturally elevated heavy metal content but it is not known whether soil microbial communities are similarly adapted to heavy metals. We measured microbial properties of six ultramafic soils that ranged in heavy metal content to test whether microbial diversity would decrease and respiratory quotient (microbial respiration:biomass) increase due to the stress imposed by increasing metal content. Soil samples were collected from beneath Nothofagus solandri var. cliffortioides tall forest, tall Leptospermum scoparium shrubland, open Leptospermum scoparium shrubland, an open Leptospermum scoparium shrubland with the rare ultramafic endemic Celmisia spedenii, a mixed divaricate shrubland, and a red tussock (Chionochloa rubra) grassland on the Dun Mountain Ophiolite belt, New Zealand. Samples were analysed for catabolic evenness using the catabolic response profile technique, microbial biomass, microbial respiration, and soil properties (pH, total carbon, total nitrogen, magnesium and total or extractable chromium and nickel). The sites differed in base saturation, pH and concentrations of metals, particularly magnesium, chromium and nickel, properties that are a major determinant of the plant communities that develop. Microbial biomass and respiration, catabolic evenness (range of 19.1 to 22.7) and the respiratory quotient were not correlated to any of the measured soil chemical properties. Factor analysis of the respiratory responses showed that the microbial communities under each vegetation type were distinct. The second factor extracted was correlated to total carbon (r ²=0.62, P<0.01), basal respiration (r ²=0.55, P<0.01) and microbial biomass (r ²=0.65, P<0.01). Increasing metals concentrations had no direct impact on microbial diversity, biomass, respiration or community energetics. However, we suggest that metal concentrations may have exerted an indirect effect on the structure of the microbial communities through control of the vegetation community and litter inputs of carbon to the soil.     

Host effects in high ectomycorrhizal diversity tropical rainforests on ultramafic soils in New Caledonia

Tropical rainforests have been thought to have low prevalence and diversity of ectomycorrhizal symbioses. However, to date, tropical regions have been poorly sampled for ectomycorrhizal fungi. Here, we investigated ectomycorrhizal fungal community diversity and the role of host plants in shaping this diversity in three main ultramafic rainforests in New Caledonia, an archipelago renowned for its exceptional plant diversity and recognized as a biodiversity hotspot. Sampling of ectomycorrhizal root tips and fruit bodies in Nothofagus aequilateralis-dominated, Arillastrum gummiferum-dominated and mixed rainforests showed high fungal diversity with, in total, 28 lineages and 311 operational taxonomic units (OTUs), of which 95% might be endemic. We also found that host preference and host density influenced ectomycorrhizal community composition and contributed to the high fungal diversity of New Caledonian rainforests. Finally, the /cortinarius lineage dominated the below- and above-ground communities, which suggests that this lineage plays a central role in ultramafic ecosystems functioning.     

Spontaneous metatool use by New Caledonian crows

A crucial stage in hominin evolution was the development of metatool use -- the ability to use one tool on another [1, 2]. Although the great apes can solve metatool tasks [3, 4], monkeys have been less successful [5-7]. Here we provide experimental evidence that New Caledonian crows can spontaneously solve a demanding metatool task in which a short tool is used to extract a longer tool that can then be used to obtain meat. Six out of the seven crows initially attempted to extract the long tool with the short tool. Four successfully obtained meat on the first trial. The experiments revealed that the crows did not solve the metatool task by trial-and-error learning during the task or through a previously learned rule. The sophisticated physical cognition shown appears to have been based on analogical reasoning. The ability to reason analogically may explain the exceptional tool-manufacturing skills of New Caledonian crows.     

Vegetation and soils of the Meikle Kilrannoch ultramafic sites

Summary

The vegetation of two ultramafic sites (MK1 and MK2) at Meikle Kilrannoch are described. MK1 is dome shaped and has much weathering bedrock whilst MK2 is flatter, lacks weathering bedrock and has probably been entirely peat covered. Six vegetation Groups were recognized: I, high-level blanket bog; II and III, grass heath (with II more sedge-rich); IV, dwarf shrub heath; V and VI, debris (an open vegetation on stony skeletal soils). Vegetation maps were produced which had five mapping units: Group I, Groups II and IH combined, Group IV, Groups V and VI combined, and non-vegetated eroding peat. Three main soil types occur: peat, which underlies Group I; a complex of freely draining magnesian brown soils and imperfectly drained magnesian gleys which bear Groups II–IV; and skeletal soils, derived either from weathering bedrock (MK1 only) or ultramafic drift, which bear vegetation in Groups V or VI. The rare plants are commonest in, but not restricted to, debris vegetation on skeletal soils. The likely plant toxicity of soil magnesium at the sites is reaffirmed but it is suggested that the low plant cover in the debris is more likely to result from low nutrients or intensive frost action or both. Floristic differences between MK1 and MK2 are discussed and quantified for Lychnis alpina (which had 68000individuals on the former site and 46 on the latter) but the causes of the differences remain unexplained.     

Comparison of different microbial biomass and activity measurement methods in metal-contaminated soils

The aims of this study were: (1) to compare different microbial methods of detecting the effects of heavy metals on the functioning of the soil ecosystem; and (2) to evaluate the effect of incubation on microbial biomass and microbial activity in soils that were not pre-incubated after sampling in order to determine their suitability for measuring the effects of heavy metals on the soil microbial ecosystem. The microbial biomass methods (included: biomass C, N and ninhydrin-N by fumigation-extraction (FE); substrate-induced respiration (SIR); soil ATP content and microbial activity as evolved CO2-C and arginine ammonification. All were tested in soils from the Woburn Market Garden Experiment. Due to past sludge application the soils contained, Zn, Cu or Ni at around current European Union upper limits and Cd at up to three times the limit. The amount of microbial biomass in metal-contaminated soils was about half of that found in soils from the experiment that received uncontaminated organic manure or inorganic fertilizer. The amount of biomass measured by FE and soil ATP content in incubated soils showed little change over 20 days incubation. However, SIR measurements were statistically affected over the first few days of incubation. The rates of arginine ammonification were higher in this order: farmyard manure (FYM)>inorganic fertilizer>sewage-sludge throughout the incubation. However, the evolved CO2-C rates were not significantly different among the treatments. Discriminant analysis confirmed smaller amounts of biomass in the metal-contaminated soils than in the other treatments. Linked properties, such as relationships between biomass and soil organic matter, or biomass-specific respiration rates, may provide "internal control" which may help overcome problems of establishing suitable control, or comparative measurements, when moving from experimental to natural environments.     

Some observations on the microbial activity in remoistened air-dried soils

Summary Comparative studies on the respiration of four air-dried and fresh soils show that in all cases a higher level of metabolic activity is attained in the air-dried soils following remoistening. The degree by which metabolic activity increases in remoistened air-dried soils varies directly with the concentrations of free amino acids and other nitrogenous materials released by the air drying process. No appreciable gas exchange was noted through chemical action alone and it is felt that the increased respiration of air-dried samples over fresh soils is due mainly to biological activity.Quantitative studies of the bacterial flora of air-dried soils indicate a short lag period followed by a phase of logarithmic increase during the early stages following remoistening. These results are discussed in terms of the bacterial population existing after air drying and its relationship to the high respiratory activity observed.Contribution No. 411.     

Nickel levels in arthropods associated with Ni hyperaccumulator plants from an ultramafic site in New Caledonia

Arthropods (mainly insects) were collected from a forest site that contained at least six species of Ni hyperaccumulators. Whole body Ni analysis was performed for 12 arthropod taxa, two of which were studied at different life cycle stages. We found two Nitolerant insects. The pentatomid heteropteran Utana viridipuncta, feeding on fruits of the Ni hyperaccumulator Hybanthus austrocaledonicus, contained a mean of 2 600 μNi/g in nymphs and 750 μNi/g in adults. The tephritid fly Bactrocera psidii, feeding on pulp of Sebertia acuminata fruits that contained 6 900 μNi/g, contained 420 μNi/g as larvae that had evacuated their guts and significantly less (65 μNi/g) as adults. European honeybees (Apis mellifera) visiting flowers of the Ni hyperaccumulator H. austrocaledonicus contained significantly more Ni (8‐fold more) than those collected from flowers of Myodocarpus fraxinifolius, a non‐hyperaccumulator. Our results show that some insects feed on Ni hyperaccumulator plants and that their feeding mobilizes Ni into local food webs.     

Recent advances in New Caledonian biogeography

The biota of New Caledonia is one of the most unusual in the world. It displays high diversity and endemism, many peculiar absences, and far‐flung biogeographic affinities. For example, New Caledonia is the only place on Earth with both main clades of flowering plants – the endemic Amborella and ‘all the rest’, and it also has the highest concentration of diversity in conifers. The discovery of Amborella's phylogenetic position led to a surge of interest in New Caledonian biogeography, and new studies are appearing at a rapid rate. This paper reviews work on the topic (mainly molecular studies) published since 2013. One current debate is focused on whether any biota survived the marine transgressions of the Paleocene and Eocene. Total submersion would imply that the entire fauna was derived by long‐distance dispersal from continental areas since the Eocene, but only if no other islands (now submerged) were emergent. A review of the literature suggests there is little actual evidence in geology for complete submersion. An alternative explanation for New Caledonia's diversity is that the archipelago acted as a refugium, and that the biota avoided the extinctions that occurred in Australia. However, this is contradicted by the many groups that are anomalously absent or depauperate in New Caledonia, although represented there by a sister group. The anomalous absences, together with the unusual levels of endemism, can both be explained by vicariance at breaks in and around New Caledonia. New Caledonia has always been situated at or near a plate boundary, and its complex geological history includes the addition of new terranes (by accretion), orogeny, and rifting. New Caledonia comprises ‘basement’ terranes that were part of Gondwana, as well as island arc and forearc terranes that accreted to the basement after it separated from Gondwana. The regional tectonic history helps explain the regional biogeography, as well as distribution patterns within New Caledonia. These include endemics on the basement terranes (for example, the basal angiosperm, Amborella), disjunctions at the West Caledonian fault zone, and great biotic differences between Grande Terre and the Loyalty Islands.     

Warming and drying suppress microbial activity and carbon cycling in boreal forest soils

Climate warming is expected to have particularly strong effects on tundra and boreal ecosystems, yet relatively few studies have examined soil responses to temperature change in these systems. We used closed‐top greenhouses to examine the response of soil respiration, nutrient availability, microbial abundance, and active fungal communities to soil warming in an Alaskan boreal forest dominated by mature black spruce. This treatment raised soil temperature by 0.5 °C and also resulted in a 22% decline in soil water content. We hypothesized that microbial abundance and activity would increase with the greenhouse treatment. Instead, we found that bacterial and fungal abundance declined by over 50%, and there was a trend toward lower activity of the chitin‐degrading enzyme N‐acetyl‐glucosaminidase. Soil respiration also declined by up to 50%, but only late in the growing season. These changes were accompanied by significant shifts in the community structure of active fungi, with decreased relative abundance of a dominant Thelephoroid fungus and increased relative abundance of Ascomycetes and Zygomycetes in response to warming. In line with our hypothesis, we found that warming marginally increased soil ammonium and nitrate availability as well as the overall diversity of active fungi. Our results indicate that rising temperatures in northern‐latitude ecosystems may not always cause a positive feedback to the soil carbon cycle, particularly in boreal forests with drier soils. Models of carbon cycle‐climate feedbacks could increase their predictive power by incorporating heterogeneity in soil properties and microbial communities across the boreal zone.     

土壤微生物总活性研究方法进展

微生物总活性是指在某一时段内微生物所有生命活动的总和,它直接决定着微生物行使生理、生态功能的能力,是微生物学研究的热点,也是难点。迄今为止,还没有建立直接测定微生物总活性的方法,只能用一些相关指标来间接反映它。目前常用的指标主要包括微生物的呼吸速率、生长速率以及胞内RNA含量等。与其它一些基质和环境相比,测定土壤中的微生物总活性更为困难。通过总结研究土壤微生物总活性常用的3种方法,在简略概括传统的土壤微生物呼吸测定法的基础上,详细介绍了放射性同位素标记法和RNA直接表征法的原理和操作流程,整理归纳了一些重要应用案例,比较分析了不同方法的优缺点,以期为选择研究土壤微生物总活性的适宜方法提供依据。     

Vegetation of tuscan ultramafic soils in relation to edaphic and physical factors

Vegetation and soil sampling were carried out in 80 plots located in five different ultramafic (serpentine) sites of Tuscany, central Italy. The physical and chemical features of each plot were determined and the species composition and cover recorded. The exchangeable fraction of soil metals was analysed because it gives a measure of their concentrations available to plants. The plots were classified by cluster analysis and ANOVA was used to compare the environmental variables of the groups of plots. Canonical correspondence analysis was used to detect the principal factors for gradients of species composition within the plant communities. A higher content of exchangeable metals was found under the more evolved and structured plant communities, suggesting that serpentine vegetation of Tuscany is not strongly limited by soil metals, such as chromium, cobalt, nickel and magnesium, typically associated with ultramafic soils. The low nutrient content of the soils and drought stress mainly due to topographical features, appear to have a more significant role in determining the typical scattered vegetation of the Tuscan ultramafics.     

Ecotypic response to ultramafic soils by some plant species of northwestern United States

Soils high in magnesium derived from ultramafic rocks (serpentine, peridotite, and dunite) in northwestern United States support endemic as well as wide-ranging but edaphically indifferent(bodenvag) species. The latter occur widely on diverse rock formations of the region. Severalbodenvag species are shown to respond ecotypically to ultramafic soils. Of 18 species tested, all but three are differentiated into strains either tolerant or intolerant of ultramafic soils. Tests for edaphic preferences were conducted with seedlings and mature transplants on ultramafic soils. Growth performances were determined in greenhouse pot tests, outdoor soil bins, and by transplants in the wild. Herbaceous perennials (e.g.,Achillea millefolium, Fragaria virginiana, Prunella vulgaris, Rumex acetosella) gave the clearest ecotypic differences. Woody species either showed only slight ecotypic response(Spiraea douglasii var.menziesii andGaultheria shallon) or delayed the expression of their genotypic adaptability(Pinus contorta). Where ultramafic abut non-ultramafic soils, those populations ofbodenvag species that grow in non-ultramafic habitats can have a significant proportion of individuals tolerant to ferromagnesian soils (e.g.,Achillea millefolium). This suggests gene flow between populations of contrasting edaphic sites and possibly preadaptedness for the ultramafic habitat. Strains of two introduced weeds(Prunella vulgaris andRumex acetosella) have become ecotypically tolerant to ultramafic soils, probably within the last 75 years.