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New Caledonia is known for the diversity of its geological substrates, which have shaped its highly original and diverse flora. Here, the effect of the soil on the vegetation is described for several contact zones between ultramafic and other substrates. The main vegetation formations on soils derived from ultramafic rocks are described: low and medium altitude rainforests, high altitude rainforests, and maquis. The main types of maquis and the biological characteristics of maquis species are also presented.

Plant and soil 475(1-2), 515 - 534 (2022). doi:10.1007/s11104-022-05388-3, PurposeThe Cunoniaceae are a major component of the New Caledonian flora with 91 endemic species that are highly unusual in that multiple metals are hyperaccumulated in different species. This makes it an ideal model system for studying the nature of the hyperaccumulation phenomenon.MethodsX-ray fluorescence spectroscopy (XRF) scanning of all herbarium collections of the Cunoniaceae was undertaken at the Herbarium of New Caledonia to reveal incidences of nickel (Ni) and manganese (Mn) accumulation. Following on, the Mn hyperaccumulating P. reticulata and the Ni hyperaccumulating P. xaragurensis were selected for detailed follow-up investigations using synchrotron-based X-ray fluorescence microscopy (XFM).ResultsThe systematic XRF screening of herbarium specimens showed that numerous species have high foliar Mn and Ni with species either accumulating Ni or Mn, but not both elements simultaneously. Soil ‘extractable’ Mn and Ni concentrations associated with Pancheria reticulata and P. xaragurensis greatly varies between the species. The XFM data shows that P. reticulata has a distinctive distribution pattern with Mn concentrated in large hypodermal cells. This contrasts with P. xaragurensis where Ni was mainly localized in and around the epidermis, and hypodermal cells were not observed., Published by Springer Science + Business Media B.V, Dordrecht [u.a.]

International audience

The OCBIL theory comprises a set of hypotheses to comprehend the biota of old, climatically buffered, infertile landscapes (OCBILs). Here, we review evidence from the literature to evaluate the extent to which this theory could apply to the biodiversity hotspot of New Caledonia. We present geological, pedological and climatic evidence suggesting how the island might qualify as an OCBIL. The predictions of OCBIL theory are then reviewed in the context of New Caledonia. There is evidence for a high rate of micro-endemism, accumulation of relict lineages, a high incidence of dioecy, myrmecochory and nutritional specializations in plants. New Caledonian vegetation also exhibits several types of monodominant formations that reveal the importance of disturbances on the island. Fires and tropical storms are likely to be important factors that contribute to the dynamic of New Caledonian ecosystems. Although naturally infertile, there is archaeological evidence that humans developed specific horticultural practices in the ultramafic landscapes of New Caledonia. Further comparisons between New Caledonia and other areas of the world, such as South Africa and Southwest Australia, are desirable, to develop the OCBIL theory into a more robust and generalized, testable framework and to determine the most efficient strategies to preserve their outstanding biodiversity.

Background and Aims Hybanthus austrocaledonicus (Violaceae) is a nickel (Ni) hyperaccumulator endemic to New Caledonia. One of the specimens stored at the local herbarium had a strip of bark with a remarkably green phloem tissue attached to the sheet containing over 4 wt% Ni. This study aimed to collect field samples from the original H. austrocaledonicus locality to confirm the nature of the green ‘nickel-rich phloem’ in this taxon and to systematically assess the occurrence of Ni hyperaccumulation in H. austrocaledonicus and Hybanthus caledonicus populations. Methods X-ray fluorescence spectroscopy scanning of all collections of the genus Hybanthus (236 specimens) was undertaken at the Herbarium of New Caledonia to reveal incidences of Ni accumulation in populations of H. austrocaledonicus and H. caledonicus. In parallel, micro-analytical investigations were performed via synchrotron X-ray fluorescence microscopy (XFM) and scanning electron microscopy with X-ray microanalysis (SEM-EDS). Key Results The extensive scanning demonstrated that Ni hyperaccumulation is not a characteristic common to all populations in the endemic Hybanthus species. Synchrotron XFM revealed that Ni was exclusively concentrated in the epidermal cells of the leaf blade and petiole, conforming with the majority of (tropical) Ni hyperaccumulator plants studied to date. SEM-EDS of freeze-dried and frozen-hydrated samples revealed the presence of dense solid deposits in the phloem bundles that contained >8 wt% nickel. Conclusions The occurrence of extremely Ni-rich green phloem tissues appears to be a characteristic feature of tropical Ni hyperaccumulator plants.

Parasitaxus usta (Podocarpaceae) is the only parasitic gymnosperm and endemic to New Caledonia. In this survey, 11 flavonoids and 6 phenolic compounds were isolated from the aerial parts. As for flavonoids, six flavones, apigenin 7- O-glucoside (1), luteolin (2), luteolin 7- O-glucoside (3), chrysoeriol (4), chrysoeriol 7- O-glucoside (5) and tricetin 3′- O-glucoside (6), one C-glycosylflavone, orientin (7), one flavonol, quercetin 3- O-glucoside (8), one anthocyanin, cyanidin 3- O-glucoside (9), and two biflavones, isoginkgetin (10) and agathisflavone (11) were identified by UV, liquid chromatograph–mass spectra (LC-MS), acid hydrolysis, NMR and/or HPLC comparisons with authentic samples. On the other hand, six phenolic compounds were identified as 5- O- E- p-coumaroyl quinic acid (12), 5- O- Z- p-coumaroyl quinic acid (13), 5- O- E- p-coumaroyl quinic acid methyl ester (14), 5- O- Z- p-coumaroyl quinic acid methyl ester (15), E-caffeic acid methyl ester 3- O-β-glucopyranoside (16), and Z-caffeic acid methyl ester 3- O-β-glucopyranoside (17) by UV, LC-MS and NMR. Chemical components of P usta were reported in this survey for the first time. Their chemical characters were chemotaxonomically compared with those of other Podocarpaceae species.

New Caledonia is a global biodiversity hotspot known for its metal hyperaccumulator plants. X-ray fluorescence technology (XRF) has enabled non-destructive and quantitative determination of elemental concentrations in herbarium specimens from the ultramafic flora of the island. Specimens belonging to six major hyperaccumulator families (Cunoniaceae, Phyllanthaceae, Salicaceae, Sapotaceae, Oncothecaceae and Violaceae) and one to four specimens per species of the remaining ultramafic taxa in the herbarium were measured. XRF scanning included a total of c. 11 200 specimens from 35 orders, 96 families, 281 genera and 1484 species (1620 taxa) and covered 88.5% of the ultramafic flora. The study revealed the existence of 99 nickel hyperaccumulator taxa (65 known previously), 74 manganese hyperaccumulator taxa (11 known previously), eight cobalt hyperaccumulator taxa (two known previously) and four zinc hyperaccumulator taxa (none known previously). These results offer new insights into the phylogenetic diversity of hyperaccumulators in New Caledonia. The greatest diversity of nickel hyperaccumulators occur in a few major clades (Malphigiales and Oxalidales) and families (Phyllanthaceae, Salicaceae, Cunoniaceae). In contrast, manganese hyperaccumulation is phylogenetically scattered in the New Caledonian flora.

Plant and soil 457(1-2), 293 - 320 (2020). doi:10.1007/s11104-020-04714-x, AimsThis study aimed to establish elemental profiles and to spatially resolve the elemental distribution in five New Caledonian woody Ni hyperaccumulator plant species (Geissois pruinosa var. pruinosa, Homalium francii, Hybanthus austrocaledonicus, Psychotria gabriellae, and Pycnandra acuminata) originating from the Cunoniaceae, Salicaceae, Violaceae, Rubiaceae, and Sapotaceae families respectively.MethodsUsing synchrotron-based micro-X-ray Fluorescence (��XRF) imaging of different plant tissues, from the roots to the shoots and reproductive organs, this study aimed to clarify how distribution patterns of nickel, and other physiologically relevant elements, differ between these species.ResultsThe results show that the tissue-level and cellular-level distribution of nickel in P. gabriellae, H. austrocaledonicus, G. pruinosa var. pruinosa, and H. francii conform with the majority of studied Ni hyperaccumulator plant species globally, including (temperate) herbaceous species, with localization mainly in epidermal cells and phloem bundles. However, P. acuminata has nickel-rich laticifers, which constitute an independent network of cells that is parallel to the vascular bundles and are the main sink for nickel.ConclusionsSynchrotron-based micro-X-ray Fluorescence (��XRF) is a powerful method for investigating how metal hyperaccumulation influences acquisition and spatial distribution of a wide range of elements. This non-invasive method enables investigation into the in vivo distribution of multiple elements and the structure and organisation of cells (e.g. laticifers)., Published by Springer Science + Business Media B.V, Dordrecht [u.a.]

International audience; Amborella trichopoda (Amborellaceae) is a shrub endemic to New Caledonia in the Southwest Pacific region. This plant suddenly became famous when molecular phylogenetic studies revealed that this sole species is likely the sister taxon to all other angiosperms. It has thus been a prime research model for reconstructing plant evolution and gaining insight into what the earliest angiosperms looked like. A wealth of studies on Amborella have now shed considerable light on its genome, morphology, anatomy, physiology, development, and architecture – this research is reviewed in this article. While Amborella likely retained some ancestral traits, critical character reconstructions have also highlighted some derived and sometimes unique characters in this species. The history of Amborella is also tied to the South Pacific archipelago of New Caledonia, its homeland. It was part of the New Caledonian biogeography puzzle and its genetic history shed light on the dynamics of its ecosystem, the rainforest understorey. Amborella is now cultivated in botanical gardens and has been the focus of some conservation measures that will also benefit other species in this biodiversity hotspot.

International audience; Aim: Alexander von Humboldt observed that plant communities on different continents but under similar climatic conditions shared few common species but often contained representatives of the same genera or higher taxonomic groups. To test if this observation can be extended to substrate type, we explored whether a phylogenetic signature could be seen among floras growing on ultramafic substrates that present challenging edaphic conditions for plant growth and are well-known for their distinctive vegetation. Location: Cuba, Madagascar, New Caledonia. Taxon Angiosperms. Methods We compared the floras of Cuba, Madagascar and New Caledonia to test whether the same plant families were under- or over-represented on the ultramafic substrates of the three islands. Results: Pairwise comparisons showed that plant orders and families tended to have the same behaviour on the three islands, i.e. ultramafic substrates filtered (in favour of or against) the same plant groups in the three biogeographical distinct areas. The COM clade (comprising Celastrales, Oxalidales and Malpighiales) appears to be over-represented on ultramafic substrates in all three islands and contains over half of the world's known nickel hyperaccumulators. Main conclusions: Our analyses provide support for Humboldt's observation by showing that ecological sorting can favour the same plant lineages in similar environments in different biogeographical regions.

This article is a Commentary on Reeves et al., 218: 407–411 and van der Ent et al., 218: 432–434.

The upper canopy of some rain forests in New Caledonia is dominated by single species. These monodominants are commonly secondary species, their dominance not persisting without disturbance. We tested whether dominance is associated with efficient uptake and use of nutrients (N, P and K), comparing between seedlings of monodominants (Nothofagus spp., Arillastrum gummiferum and Cerberiopsis candelabra) and 14 subordinates, grown in a nursery house. We also tested whether this trend applies more broadly to shade-intolerant trees that regenerate episodically (ER species) versus shade-tolerant trees that regenerate continuously (CR species). In the sun treatment, monodominants had higher photosynthetic nutrient-use efficiency and productivity for N and K, and uptake efficiency for N, P and K, than subordinates; ER species had higher photosynthetic nutrient-use efficiency for N, P and K, and uptake efficiency for N and P, than CR species. Uptake efficiency and productivity per nutrient mass were uncorrelated across species, yet Nothofagus spp., A. gummiferum and C. candelabra combined high levels of both traits for N, and Nothofagus spp. and A. gummiferum combined moderate to high levels for P, in sun-grown seedlings. This trait combination may contribute substantially to competitiveness and post-disturbance dominance on these nutrient-poor soils.

International audience

Some species-rich secondary forests in New Caledonia have a monodominant canopy. Here we investigate growth and biomass allocation traits that might explain single-species’ dominance of these post-disturbance stands, and their later decline in the absence of large-scale disturbance. Seedlings of 20 rain-forest trees were grown in two light treatments in a nursery house. In the sun treatment, monodominants grew faster (56.7 ± 1.4 mg g−1 wk−1) than subordinates (40.2 ± 2.6 mg g−1 wk−1). However, some episodically regenerating (ER) subordinates had high growth rates similar to those of monodominants. In the shade treatment, monodominants and subordinates had similar growth rates (33.7 ± 2.6 and 34.0 ± 1.9 mg g−1 wk−1 respectively). Notably, monodominants in both sun and shade treatments had lower root mass fraction (0.29 ± 0.02 and 0.27 ± 0.02 g g−1 respectively) than subordinates (0.39 ± 0.02 and 0.37 ± 0.02 g g−1). Fast growth in sunny conditions is probably imperative for these relatively shade-intolerant ER monodominants. In field conditions, high shoot mass fraction combined with efficient root performance may facilitate faster growth in monodominants competing with other ER species in sunlit sites. Slower growth in shade may contribute to loss of dominance over time in undisturbed forests.

International audience; New Caledonia is a widely recognised marine and terrestrial biodiversity hot spot. However, this unique environment is under increasing anthropogenic pressure. Major threats are related to land cover change and include fire, urban sprawling and mining. Resulting habitat loss and fragmentation end up in serious erosion of the local biodiversity. Mining is of particular concern due to its economic significance for the island. Open cast mines were exploited there since 1873, and scraping out soil to access ores wipes out flora. Resulting perturbations on water flows and dramatic soil erosion lead to metal-rich sediment transport downstream into rivers and the lagoon. Conflicting environmental and economic aspects of mining are discussed in this paper. However, mining practices are also improving, and where impacts are inescapable ecological restoration is now considered. Past and ongoing experiences in the restoration of New Caledonian terrestrial ecosystems are presented and discussed here. Economic use of the local floristic diversity could also promote conservation and restoration, while providing alternative incomes. In this regard, Ecocatalysis, an innovative approach to make use of metal hyperaccumulating plants, is of particular interest.

In New Caledonia, rain forests with an upper canopy dominated by single species of Nothofagus occur next to mixed-canopy forests, without discernible environmental cause. A potential explanation is that they are different successional stages. To test this hypothesis and predict long-term change in canopy dominance, population size structures of 61 canopy species were analysed in six Nothofagus-dominated forests and three adjacent mixed rain forests. Weibull analysis suggests that these Nothofagus forests are secondary forests, with recruitment insufficient to maintain monodominance, except at a high-altitude site. At low- to mid-altitudes the Nothofagus canopy is predicted to develop into a mixed canopy, unless moderate to severe disturbance occurs within its reproductive lifespan. However, adjacent mixed rain forests are also secondary, with 85% of analysed species showing no evidence of continuous regeneration. Fifteen species from both forest types showed reverse-J curves suggesting continuous regeneration, but only Calophyllum caledonicum did so consistently. Since few canopy species showed evidence of high shade tolerance and persistence, a small number of shade-tolerant species is predicted to dominate both forests in the long term, in the hypothetical absence of disturbance. Hence, temporal factors associated with disturbances play a key role in determining dominance in these forests.

Demographic and ecophysiological data for the endangered New Caledonian conifer, Araucaria muelleri (Araucariaceae), were analysed to: (i) evaluate population viability in relation to site conditions and human impacts; and (ii) advance our understanding of how stress-tolerator plant functional traits affect the population dynamic behaviour and conservation requirements of long-lived tree species. Growth, survivorship and recruitment in four A. muelleri populations were monitored across 9 years. Demographic rates were analysed using stage-based transition matrices. Leaf δ13C, %N and photosystem II stress (Fv/Fm) were measured for seedlings, saplings and trees, and leaf mass per area (LMA) for trees, and correlations among ecophysiological and demographic variables explored. Seedling, sapling and tree stem growth were among the slowest, and annual survivorship among the highest, reported for any tree. Transition matrix analyses yielded stable estimated population growth rates, λ, not significantly different from 1.0 for all populations. Leaf δ13C was positively correlated with seedling and sapling height growth, while daytime photosystem II stress (Fv/Fm) was high in seedlings, but low in saplings and trees. Ecophysiological measures suggest that individuals transition from moisture-limited growth at the seedling stage to nutrient-limited growth as adults. High levels of environmental stress result in slow stand dynamics, characterized by low recruitment and growth rates counterbalanced by equally low mortality rates. These dynamics result in populations with limited capacity to increase in size quickly, but potentially highly vulnerable to decline should the rate of adult mortality increase. This combination of traits is likely typical of extreme stress-tolerator woody species and suggests a conservation focus on the preservation of mature individuals.

International audience; Context: The biodiversity hotspot for conservation of New Caledonia has facing high levels of forest fragmentation. Remnant forests are critical for biodiversity conservation and can help in understanding how does forest fragmentation affect tree communities.Objective: Determine the effect of habitat configuration and availability on tree communities.Methods: We mapped forest in a 60 km2 landscape and sampled 93 tree communities in 52 forest fragments following stratified random sampling. At each sampling point, we inventoried all trees with a diameter at breast height ≥10 cm within a radius of 10 m. We then analysed the response of the composition, the structure and the richness of tree communities to the fragment size and isolation, distance from the edge, as well as the topographical position.Results: Our results showed that the distance from the forest edge was the variable that explained the greatest observed variance in tree assemblages. We observed a decrease in the abundance and richness of animal-dispersed trees as well as a decrease in the abundance of large trees with increasing proximity to forest edges. Near forest edges we found a shift in species composition with a dominance of stress-tolerant pioneer species.Conclusions: Edge-effects are likely to be the main processes that affect remnant forest tree communities after about a century of forest fragmentation. It results in retrogressive successions at the edges leading to a dominance of stress-tolerant species. The vegetation surrounding fragments should be protected to promote the long process of forest extension and subsequently reduce edge-effects.

Aims In situ species survival involves persistence at current sites and/or colonization of new locations. Determining the likelihood of these events requires an understanding of population dynamics and dispersal. We address these issues in populations of a critically endangered tropical conifer Araucaria nemorosa and provide conservation recommendations. Location Port Boise, island of Grand Terre, New Caledonia, Pacific Ocean. Methods We characterize the demographic structure of six populations of A. nemorosa based upon size class frequencies and relative basal area compared to competing angiosperm trees. Using genotype data from 280 adult individuals at seven microsatellite loci, we indirectly estimate dispersal distances and project a maximal dispersal envelope around the extant populations. Results Our survey detected marked differences in demographic parameters including the proportion of basal area occupied by A. nemorosa versus angiosperm trees (ranging from 25% to 77%), the size class frequency distributions of A. nemorosa and seedling densities (ranging from 500 to 37300 seedlings ha−1) among some populations. Wright’s genetic neighbourhood ranged from 22 to 876 trees, and historic gene dispersal ranged from 10.8 to 82.4 m, indicating that most seed dispersal is

Podocarp species and genus richness is higher in the Malesian region than anywhere else on earth, with maximum genus richness in New Guinea and New Caledonia and maximum species richness in New Guinea and Borneo. Members of the Podocarpaceae occur across the whole geographic and altitudinal range occupied by forests and shrublands in the region. There is a strong tendency for podocarp dominance of vegetation to be restricted either to high-altitude sites close to the limit of tree growth or to other sites that might restrict plant growth in terms of water relations and nutrient supply (e.g., skeletal soils on steep slopes and ridges, heath forests, ultramafic parent material). Although some species are widespread in lowland forests, they are generally present at very low density, raising questions concerning their regeneration ecology and competitive ability relative to co-occurring angiosperm tree species. A number of species in the region are narrowly distributed, being restricted to single islands or mountain tops, and are of conservation concern. Our current understanding of the distribution and ecology of Malesian podocarps is reviewed in this chapter, and areas for further research are identified.

This study compares demographic parameters and population dynamics for high disturbance (maquis) and low disturbance (rain forest) environments of the montane conifer, Araucaria laubenfelsii, in New Caledonia. The establishment, growth, survival and reproduction of ca 2500 individuals were followed in permanent plots over 10 yr. Growth and survival rates for A. laubenfelsii show that it is a long-lived, slow growing tree, with evidence of suppression in the sapling size classes in mature rain forest. Growth rates for all size classes are generally faster in maquis than rain forest. Transition matrix analyses estimated positive rates of population increase (λ values>1), with populations expanding in maquis, and stable in mature forest. Araucaria laubenfelsii is able to regenerate continuously in maquis and early successional rain forest, but recruitment is limited in older stands. Life table response experiment analyses showed that reproduction, and transitions from sapling to mature tree stage, contributed positively to λ in maquis, but negatively in forest. Araucaria laubenfelsii on Mont Do can be considered a long-lived pioneer, with early maquis colonizers helping to drive succession from maquis to forest. While opportunities for recruitment decline with time as rain forest sites develop a closed canopy, occasional gap phase recruitment, combined with disturbance by cyclones, landslides and fire, provide opportunities to ensure species persistence. Understanding contrasting population dynamics of A. laubenfelsii in maquis and rain forest will better facilitate conservation management of this species, particularly given current high rates of land conversion and degradation in New Caledonia.

A-09-41; International audience; 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.

Forest restoration programmes aim to use material for re-planting that is genetically diverse and not inbred. However, restricted seed sampling, high variance in reproductive output, and the production of inbred seeds that survive in the nursery but not in the wild can lead to forest restoration stock being genetically compromised. The aim of this study was to evaluate whether the reproductive biology of the New Caledonian endemic conifer Araucaria nemorosa makes it susceptible to these genetic problems and to assess whether there is evidence for genetic bottlenecks and elevated inbreeding in nursery stock compared to seedlings and adults from wild source populations. Reproductive output was low with high variance among trees (only 14% of adult trees surveyed produced mature cones, >50% of examined cones had

International audience; New Caledonia is renowned as one of the world's most significant biodiversity hotpots. The nutrient-deficiency and cations imbalances of ultramafic soils, which cover a third of the island, harbor a disproportionally high proportion of the plant diversity and endemism of New Caledonia. This review explores how ultramafic soils have influenced the exceptional endemism and richness of New Caledonia trough the concomitant occurrences of habitat patchiness, climatic instability, environmental gradient, and edaphic heterogeneity of ultramafic soils. We focus on the unique `maquis' vegetation where selective pressures by nutrient deficiency and trace element surplus are at their acme. We aim to synthesize our current understanding of diversification and speciation of lineages that have been phylogenetically studied to date. Fragmentation of the peridotite mantle in isolated massifs, and as such spatial heterogeneity of ultramafic soils types, appear to promote plant endemism and speciation. Repeated independent dispersal events of pre-adapted species and persistence of paleo-endemic lineages have contributed to the phylogenetic diversity and the endemism of the ultramafic flora. Finally, historical climatic instability has caused shifts of rain forest species in refugia thereby favoring the extension of maquis species.

Bradyrhizobium strains, isolated in New Caledonia from nodules of the endemic legume Serianthes calycina growing in nickel-rich soils, were able to grow in the presence of 15 mM NiCl 2 . The genomes of these strains harbored two Ni resistance determinants, the cnr and nre operons. By constructing a cnrA mutant, we demonstrated that the cnr operon determines the high nickel resistance in Bradyrhizobium strains.

Several monodominant rain-forest trees in New Caledonia have population size structures suggesting establishment following large-scale disturbance, with eventual replacement by shade-tolerant species predicted in the absence of future disturbance. Links of dominance and population dynamics to leaf-level photosynthesis were investigated in seedlings of 20 tree species from these forests, grown in experimental sun and shade conditions. In particular, we tested whether episodically regenerating (ER) species, including monodominants, have higher assimilation rates at high irradiances and lower tolerance of shade than continuously regenerating species (CR). ER species had higher maximum net assimilation rates (Amax-area) in sun plants (9.6 ± 0.4 μmol m−2 s−1) than CR species (6.2 ± 0.3 μmol m−2 s−1) and high plasticity, typical of shade-intolerant species, but monodominant species did not differ from other ER species. CR species had leaf-level traits consistent with shade tolerance, including lower dark respiration rates (Rd-area = 0.47 ± 0.03μmol m−2 s−1; Rd-mass = 7 ± 1 nmol g−1 s−1) than ER species (Rd-area = 0.63 ± 0.06 μmol m−2 s−1; Rd-mass = 11 ± 2 nmol g−1 s−1) in shade plants. Hence leaf-level assimilation traits were largely consistent with regeneration patterns, but do not explain why some shade-intolerant species can achieve monodominance.

International audience; Relationships between the trace-elements (TE) content of plants and associated soil have been widely investigated especially to understand the ecology of TE hyperaccumulating species to develop applications using TE phytoextraction. Many studies have focused on the possibility of quantifying the soil TE fraction available to plants, and used bioconcentration (BC) as a measure of the plants ability to absorb TE. However, BC only offers a static view of the dynamic phenomenon of TE accumulation. Accumulation kinetics are required to fully account for TE distributions in plants. They are also crucial to design applications where maximum TE concentrations in plant leaves are needed. This paper provides a review of studies of BC (i.e. soil-plant relationships) and leaf-age in relation to TE hyperaccumulation. The paper focuses of Ni and Mn accumulators and hyperaccumulators from New Caledonia who were previously overlooked until recent Ecocatalysis applications emerged for such species. Updated data on Mn hyperaccumulators and accumulators from New Caledonia are also presented and advocate further investigation of the hyperaccumulation of this element. Results show that leaf-age should be considered in the design of sample collection and allowed the reclassification of Grevillea meisneri known previously as a Mn accumulator to a Mn hyperaccumulator.

International audience; Increasing pressure on mineral resources has drawn research efforts into innovative supply and recycling. Metal-rich biomass produced in phytoextraction recently proved an interesting starting material for green chemistry. It allows the production of new catalysts, referred to as ecocatalysts. Ecocatalysts provide increased yields in chemical production and increased regio- and chemo-selectivity, which result in high added value. This new approach to using metal-rich biomass could spur the development of phytoextraction, a technique considered promising for long, yet without credible economic outlets. In this regard, metallophyte biodiversity hotspots, such as New Caledonia, are of particular interest for biomass supply. Potential phytoextraction from mine spoils using two species endemic to New Caledonia is discussed here. Geissois pruinosa, a hypernickelophore, and Grevillea exul, a Mn accumulator, were selected for these original experiments. The results presented here 20 months after plantation of young trees from a nursery show the interest of the approach. Mean Ni concentrations of up to 1513 mg kg−1 are reported in G. pruinosa, as well as 2000 mg kg−1 Mn in G. exul. Concentrations of Ni and Mn in the leaves of each species appear to be correlated with leaf age. Plantation of these species may also ensure mine reclamation, and experiments were conducted with the principles of ecological restoration in mind adding a further dimension to the approach.

Cerberiopsis candelabra is a long-lived monocarpic rain-forest tree endemic to New Caledonia that shows mass flowering across a substantial proportion of a population, and across a substantial number of populations. We investigated the relationship between tree size and flowering (and subsequent dying) across 18 populations from the flowering event of 2003 in order to understand the role of possible size thresholds for flowering in the life history and regeneration ecology of this monocarpic species. There was a strong positive correlation between trunk diameter and the incidence of flowering when population data were combined. However, the relationship between size and flowering was complex in that flowering occurred across a wide range of tree sizes, with almost complete overlap in size between flowering (5–79 cm dbh) and non-flowering trees (5–64 cm dbh), and with large trees in both the flowering and non-flowering state in the same population. In about half the populations studied there was no significant difference in mean trunk diameter of flowering and non-flowering trees. Nonetheless, we suggest that tree size may play a fundamental role in the life history and regeneration ecology of this species. The seedlings appear to be relatively shade-intolerant and dependent on large canopy gaps for recruitment. A significant effect of mass flowering and subsequent death of multiple large trees is the potential to form large canopy gaps and enhance seedling survival, as the gap is temporally linked with seed germination. However, it is unclear why there is such a large size range of flowering trees, i.e. whether this is just a consequence of the proximate cue, or whether the optimal size for flowering does indeed vary among individuals.

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 Ni- tolerant insects. The pentatomid heteropteran Utana viridipuncta, feeding on fruits of the Ni hyperaccumulator Hybanthus austrocaledonicus, contained a mean of 2 600 ∝g Ni/g in nymphs and 750 ∝g Ni/g in adults. The tephritid fly Bactrocera psidii, feeding on pulp of Sebertia acuminata fruits that contained 6 900 ∝g Ni/g, contained 420 ∝g Ni/g as larvae that had evacuated their guts and significantly less (65 ∝g Ni/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.

Two species of Pancheria (Cunoniaceae) described here, Pancheria minima J.C. Bradford and Pancheria ouaiemensis J.C. Bradford, draw attention to a recently recognized biodiversity pattern in New Caledonia. Montane maquis on acidic substrates, especially on the Roche Ouaieme, harbors numerous endemic species and is a rare and globally unique ecosystem. We cite 12 species, most described in the past several years, known only from the Roche Ouaieme in an area less than 10 km(2). Overall, 27 species are known only from montane maquis and currently not found in a well-protected area. The major local threat to montane maquis habitat is anthropogenic fire, with climate change a possible long-term problem. Those montane maquis species known from one or two localities, occupying very small areas, and with declining habitat quality are critically endangered or endangered based on IUCN Red List criteria. Adding the Roche Ouaieme to the reserve system of New Caledonia is recommended to protect and manage a representative area of montane maquis on acidic substrates. A research strategy is proposed to identify species most at risk, locate possible unknown areas of montane maquis, and update taxonomic knowledge. A review of characters that vary among Pancheria species is provided, and the inflorescence architecture is described and diagramed. Both new Pancheria species occur at upper elevations in shrubby habitats. P. minima is remarkable in that the size of plants, leaves and reproductive parts is highly reduced compared to other known species.

Nickel speciation in a nickel hyperaccumulating plant ( Sebertia acuminata ) and its associated soil of southern New Caledonia was studied using various analytical methods. The soil is formed of iron oxides (goethite, hematite), which contain almost all the nickel. The available nickel is probably linked to the organic matter in the litter. Sebertia acuminata , acts as a nickel pump, and concentrates the metal in its leaves. It partitions nickel and silica; nickel is concentrated in the cells (probably in the vacuoles) as organometallic complexes, whereas silica forms the framework of the cells, and the phytolithes. A thorough study of these plants seems essential in order to define the soil–plant relations, and to propose appropriate ways for ecological restoration. To cite this article: N. Perrier et al., C. R. Geoscience 336 (2004).

For a better understanding of pollen-tube guidance in relation to pollen-pistil interaction, we investigated the mode of pollen-tube growth in pistils of Casuarina equisetifolia, a monoecious, wind-pollinated species that undergoes chalazogamous fertilization. The pistil is bicarpellate, but only one of the two carpels develops with two ovules. One of these ovules develops more than four embryo sacs. Pistils usually require more than 1 month to reach maturity after pollen grains have been deposited on the stigmas. During that period, pollen-tube growth proceeds discontinuously in five distinct steps that lead up to fertilization: (1) from the stigma to the upper region of the style, (2) from the upper region of the style to a septum in the ovary, (3) from the septum to the surface of the funiculus, (4) from the funiculus to chalaza in the ovule, and (5) from the chalaza to an egg apparatus. Probably because of competitive interaction between male and female gametophytes (or ovules), one pollen tube is selected from among many during the first step (just before the second step), one ovule from the two during the second and third steps, and one embryo sac from more than four during the fourth and fifth steps. On the basis of our results, erroneous drawings and explanations reported in earlier publications on chalazogamy in Casuarinaceae should be brought into question.

Reproductive traits of 123 species of rain-forest tree from ultramafic regions of New Caledonia were assessed, mainly from herbarium specimens. Most species had extremely small, simple, pale-coloured flowers that are probably mainly pollinated by small insects, but not including bees. The seeds of most species were considered to be bird dispersed. However, wind is also important for pollination and seed dispersal. The phenological trend was for an increase in the number of species flowering and fruiting around the end of the warm dry season/start of the hot wet season, followed by a decline at the end of the wet season, and lower proportions during the cooler season. Seed size was significantly correlated with fruit size. Other correlations, between flower size and fruit size, and between seed size and seed number, were significant using species as independent observations, but did not hold following phylogenetic correction. Compared with non-dioecious species, dioecious species had significantly larger seeds, and a greater proportion of species with biotic dispersal, abiotic pollination and solitary (female) flowers. The long-term persistence of at least the larger-seeded tree species in New Caledonia is precarious, since the endemic giant pigeon, Ducula goliath, is probably their principal effective disperser, and this species is in decline.

International audience

This article focuses on the distribution of trees on a high-elevation tropical island of the New Caledonian archipelago. The aim was to determine how the variety of environments occurring on this island (in terms of elevation, rainfall, substrate and vegetation types) shapes the distribution of tree species. We analyzed the distribution of 702 native rainforest species through ca. 40,000 occurrence records and GIS environmental layers. Results showed that species exhibit high environmental tolerance while their distribution is spatially highly aggregated. We concluded that tree species distribution in New Caledonia is shaped by dispersal limitation rather than by environmental specialization., High-elevation tropical islands are ideally suited for examining the factors that determine species distribution, given the complex topographies and climatic gradients that create a wide variety of habitats within relatively small areas. New Caledonia, a megadiverse Pacific archipelago, has long focussed the attention of botanists working on the spatial and environmental ranges of specific groups, but few studies have embraced the entire tree flora of the archipelago. In this study we analyse the distribution of 702 native species of rainforest trees of New Caledonia, belonging to 195 genera and 80 families, along elevation and rainfall gradients on ultramafic (UM) and non-ultramafic (non-UM) substrates. We compiled four complementary data sources: (i) herbarium specimens, (ii) plots, (iii) photographs and (iv) observations, totalling 38 936 unique occurrences distributed across the main island. Compiled into a regular 1-min grid (1.852 × 1.852 km), this dataset covered ∼22 % of the island. The studied rainforest species exhibited high environmental tolerance; 56 % of them were not affiliated to a substrate type and they exhibited wide elevation (average 891 ± 332 m) and rainfall (average 2.2 ± 0.8 m year−1) ranges. Conversely their spatial distribution was highly aggregated, which suggests dispersal limitation. The observed species richness was driven mainly by the density of occurrences. However, at the highest elevations or rainfalls, and particularly on UM, the observed richness tends to be lower, independently of the sampling effort. The study highlights the imbalance of the dataset in favour of higher values of rainfall and of elevation. Projected onto a map, under-represented areas are a guide as to where future sampling efforts are most required to complete our understanding of rainforest tree species distribution.

International audience; Amborella trichopoda is the sole living angiosperm species belonging to the sister lineage of all other extant flowering plants. In the last decade, the species has been the focus of many phylogenetic, genomic and reproductive biology studies, bringing new highlights regarding the evolution of flowering plants. However, little attention has been paid to in situ A. trichopoda populations, particularly to their fruiting cycle. In this study, an A. trichopoda population was observed during three annual flowering cycles. Individuals and branches were labeled in order to monitor the fruiting cycle precisely, from the flowering stage until the abscission of the fruit. Fruit exocarp was green during the first 9 months following flowering, turned red when the next flowering started a year later then remained on the branch during another year, between fruit ripping and abscission. Presence of fruits with two stages of maturity on shrubs was always noticed. Germination tests showed that seeds acquired their germination capacity 1 year after flowering, when fruits changed color. A. trichopoda’s fruiting cycle is a long process overlapping two annual flowering periods. These results introduce a new model for flowering and fruiting cycles. The availability of mature seeds on shrubs for more than 1 year is likely to maximize opportunities to be dispersed, thus promoting the survival of this basal angiosperm

International audience; In the Australia–Pacific Region ultramafic outcrops are both widespread and extensive, covering thousands of km2. Soils derived from ultramafic bedrock impose edaphic challenges and are widely known to host highly distinctive floras with high levels of endemism. In the Australia–Pacific Region, the ultramafics of the island of New Caledonia are famed for harbouring 2150 species of vascular plants of which 83% are endemic. Although the ultramafic outcrops in Western Australia are also extensive and harbour 1355 taxa, only 14 species are known to be endemic or have distributions centred on ultramafics. The ultramafic outcrops in New Zealand and Tasmania are small and relatively species-poor. The ultramafic outcrops in Queensland are much larger and host 553 species of which 18 (or possibly 21) species are endemic. Although New Caledonia has a high concentration of Ni hyperaccumulator species (65), only one species from Western Australia and two species from Queensland have so far been found. No Ni hyperaccumulator species are known from Tasmania and New Zealand. Habitat destruction due to forest clearing, uncontrolled fires and nickel mining in New Caledonia impacts on the plant species restricted to ultramafic soils there. In comparison with the nearby floras of New Guinea and South-east Asia, the flora of the Australia–Pacific Region is relatively well studied through the collection of a large number of herbarium specimens. However, there is a need for studies on the evolution of plant lineages on ultramafic soils especially regarding their distinctive morphological characteristics and in relation to hyperaccumulation.

Retrophyllum is a genus in the Podocarpaceae consisting of five species with a disjunct distribution in the Southern Hemisphere. Support for the monophyly of the genus, and its sister group relationship to an Afrocarpus‐Nageia clade, was obtained from trnL‐F sequences. Within Retrophyllum, the Melanesian species (R. minus, R. comptonii, R. vitiense) formed a monophyletic group, sister to the South American species R. rospigliosii. This topology is consistent with Gondwanan fragmentation, although the amount of nucleotide substitutions between taxa is surprisingly small for such an ancient disjunction. We were unable to distinguish between historical long distance dispersal or slow substitution rates as the source of this discrepancy. Two of the Retrophyllum species are endemic to New Caledonia; one of these (R. minus) is endangered with less than 2500 individuals remaining in the wild. The other endemic species (R. comptonii) is more widespread. We have used a combination of chloroplast RFLPs and...

To measure nickel (Ni) bioavailability experiments were conducted in the field using ion exchange resin (IER) method. Resin bags were inserted into the upper layer of soils developed on ultramafic rocks in New Caledonia. Their Ni contents were determined after four weeks and compared to those of plant leaves of five species. Significant correlations were obtained so that the IER appeared to be successful for routine applications. Furthermore, the use of chemical reactants such as diethylenetriaminepentaacetic acid (DTPA) and KCl demonstrated to be much less reliable for assessing the bioavailability of Ni.

To identify forests of high priority for conservation in tropical dry forests of New Caledonia, Fiji, the Marquesas and Hawaii, we examined patterns of woody plant species richness (total, native and endemic) and threatened species (IUCN categorization and density) at the stand level, using Gentry's transect method. There were associations between total, native and endemic plant species richness in all four Pacific dry forest regions but we found no significant association with the presence or density of species listed on the IUCN Red List. Dry forests in New Caledonia and Hawaii merit the highest conservation priority in the Pacific, based on level of endemism and number of threatened species. The study sites that merit high conservation priority are Metzdorf, Nekoro and Pindai, in New Caledonia, Kokee and Kaupulehu, in Hawaii, and Vatia, in Fiji. New Caledonia and Fiji have a small dry forest extent and protected area extent compared with other dry forests in biodiversity hotspots. Although we identified priority areas for dry forest conservation, more comparative plot data, presence/absence data in fragments and regional geographical data are needed to adequately manage and protect dry forests in the Pacific.

(1310 bp) and matK (1014 bp), using 15 species representing the family. The study included analyses of Ticodendron (Ticodendraceae) and three species of Betulaceae as close relatives, and one species each of Juglandaceae and Myricaceae as outgroups. Analyses based on matK gene sequences, which provided a much better resolution than the analyses based on rbcL gene sequences alone, resulted in a single most parsimonious tree whose topology is almost identical with the strict consensus tree generated by the combined data set of rbcL and matK gene sequences. Results showed that Casuarinaceae are monophyletic, comprising four distinct genera, Allocasuarina, Casuarina, Ceuthostoma and Gymnostoma, which were not recognized until recently. Within the family, Gymnostoma is positioned at the most basal position and sister to the remainder. Within the remainder Ceuthostoma is sister to the Allocasuarina-Casuarina clade. Morphologically the basalmost position of Gymnostoma is supported by plesiomorphies such as exposed stomata in the shallow longitudinal furrows of the branchlets, a basic chromosome number x=8 and the gynoecium composed of two fertile, biovulate carpels. The three other genera, Allocasuarina, Casuarina, and Ceuthostoma, have invisible stomata in the deep longitudinal furrows of the branchlets, a higher basic chromosome number x=9 or 10–14 (unknown in Ceuthostoma), the gynoecium composed of one fertile and one sterile carpel with a single ovule (unknown in Ceuthostoma). The diversity of infructescence morphology found in the latter three genera suggests that they may have evolved in close association with the elaboration of fruit dispersal mechanisms.

Eight Frankia-Gymnostoma nitrogen-fixing symbioses endemic to New Caledonia were studied using a range of techniques including molecular typing of Frankia , infectivity/effectivity and host spectrum of the isolates. The study was conducted on 128 Frankia isolates from the eight Gymnostoma species. The RFLP analysis of the rRNA 16S-23S ITS allowed us to cluster the strains in four groups. Symbiotic characterization of the four groups failed to reveal any host specificity both in term of infectivity or effectivity. The characteristics of the strains were those of Eleagnaceae -infective Frankia strains. Co-inoculation of two Gymnostoma species with mixtures of strains evidenced 11 % of mixed RFLP profiles. In such controlled conditions, this was interpreted as co-infections. This work evidenced original features of these Gymnostoma isolates: (i) they were closer to Eleagnaceae -infective Frankia than Casuarina -infective Frankia ; (ii) closer to atypical Frankia from Casuarina ; (iii) poorly host-specific; and (iv) they had a tendency of co-infection. They could represent a primitive group of Frankia able to survive in a wide range of habitats.

l~l~~~~~i~i~~~ll ABSTRACT Plants that hyperaccumulate Ni contain > 1000 ppm (dry wt.) in their tissues. Variation of Ni content within hyperaccumulating plant species is poorly explored. Using the Ni-hyperaccumulating shrub Psychotria douairei, we documented variation of leaf Ni levels within individual shrubs, and variation with respect to plant size and leaf age. Plant size did not correlate significantly with leaf Ni content, and leaf Ni content did not correlate significantly with soil Ni content. Older leaves contained twice as much Ni as younger leaves. Older leaves also contained greater concentrations of Ca, Fe, and Cr but less K, P, and Cu. Five elements (Zn, Pb, Co, Mn, Mg) showed no significant variation due to leaf age. We also examined the effect of leaf age on epiphyll cover, finding increased epiphyll cover on the upper surface of older leaves. The dominant leafy liverwort epiphyll had a relatively high Ni content (400 ppm), suggesting that epiphylls of Ni hyperaccumulators obtain some Ni from host leaves. Individual shrubs differed in mean leaf Ni content almost two-fold (14,900-27,700 ppm). Variation among branches within individuals also ranged widely; however, this intraplant variability was not strongly correlated with the mean leaf Ni content of an individual shrub. We concluded that Ni contents in leaves of I? douarrei vary considerably due to leaf age, among individual shrubs, and among branches within a shrub.

Summary Aim This study investigates the role of fire and post fire succession in determining the structure and composition of vegetation on ultramafic iron crust soils. Location The study was conducted in the Plaines des Lacs region of southern New Caledonia. Methods A survey was made of eighty-eight sites, recording floristic composition, trunk size-class distributions, regeneration after fire, growth ring counts of Dacrydium araucarioides (Podocarpaceae) and historical information on past fires. Floristic data was ordinated using multidimensional scaling and an index of succession based on structural and historical information. A transition matrix model was developed to predict the effect of fire frequency on vegetation composition. Results The vegetation is undergoing postfire succession from maquis to forest, after about 75 years, and eventually to rainforest. Gymnostoma deplancheanum has a key role as an early colonist that produces shade, the bulk of the litter, and forms nitrogen fixing nodules with Frankia sp. However, the open canopy of Gymnostoma and slow litter decay creates flammable conditions. Though many species resprout from rootstocks, only thirty-nine persist through fires while 114 others colonize at later successional stages, as the litter layer and shade increase. Some early successional species are later excluded but these can persist locally in swamps and on rocky hill tops. Forest and rainforest are less flammable and the matrix model suggests that ignition frequency has a critical role in determining the abundance of maquis or forest. Main conclusions The vegetation mosaic represents a post fire succession from open maquis to forest. Palynological and charcoal records from late Pleistocene sediments suggest that fire has been a major factor determining the development of maquis vegetation since before the arrival of humans. Recently, frequent fires have converted much of the vegetation to maquis, posing a threat to some forest species and largely eliminating rainforest from iron crust soils.

Despite its small size, New Caledonia has a flora which includes 43 endemic species of conifer. This study examines the stand structure of the New Caledonian conifer, Araucaria laubenfelsii Corbasson, a species which occurs on ultramafic soils as an emergent tree in rainforest and in an unusual structural association with maquis vegetation. Fire and cyclone blow-down are the primary disturbances in the maquis, but fire is infrequent in the rainforests which is evident from the low proportion of fire scarred trees. Preliminary results show abundant seedlings and saplings of A. laubenfelsii both in maquis and forest. Size class distributions of individuals suggest that the species is continuously regenerating in the maquis and immature forests. Variability in the stand structure in maquis communities reflects the probable patchy nature of disturbance from small-scale fires and blow-down from tropical cyclones. In mature forests, Nothofagus codonandra (Baillon) Steenis is the dominant canopy species and 'other tree species' are continuously regenerating, while the size class distributions and basal area of A. laubenfelsii suggest that there is, at present, limited regeneration of this species. Tree ring counts indicate that individuals in forest areas grow at a slower rate than those in maquis, but attain greater age, probably as a result of greater protection from fire.