Foliar manganese accumulation by Maytenus founieri (Celastraceae) in its native New Caledonian habitats: populational variation and localization by X-ray microanalysis.

Hyperaccumulation by plants is a rare phenomenon that has potential practical benefits. The majority of manganese (Mn) hyperaccumulators discovered to date occur in New Caledonia, and little is known about their ecophysiology. This study reports on natural populations of one such species, the endemic shrub Maytenus founieri. Mean foliar Mn concentrations of two populations growing on ultramafic substrates with varying soil pHs were obtained. Leaf anatomies were examined by light microscopy, while the spatial distributions of foliar Mn in both populations were examined by qualitative scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). Plants growing on two different substrates were found to have very different mean dry weight (DW) foliar Mn concentrations. Light microscopy showed that the leaves had very distinct thick dermal structures, consisting of multiple layers of large cells in the hypodermis. In vivo X-ray microprobe analyses revealed that, in both populations, Mn sequestration occurred primarily in these dermal tissues. The finding here that foliar Mn is most highly localized in the nonphotosynthetic tissues of M. founieri contrasts with results from similar studies on other woody species that accumulate high Mn concentrations in their shoots.

Identifying the early genetic consequences of habitat degradation in a highly threatened tropical conifer, Araucaria nemorosa Laubenfels.

The early genetic effects of habitat degradation were investigated in the critically endangered conifer Araucaria nemorosa. This species occurs in New Caledonia, a global biodiversity hotspot where the world's greatest concentration of endemic conifer species coincides with an extremely high level of habitat destruction due to fire and mining. Using seven microsatellite loci, estimates were made of genetic marker variation, inbreeding coefficients and population differentiation of adult and seedling cohorts of A. nemorosa. These were contrasted with equivalent estimates, made over similar spatial scales and with the same marker loci, in the locally common and more widespread sister species Araucaria columnaris. There were no significant differences in population genetic parameters between adult populations of the two species, despite their different abundances. However, in A. nemorosa, the juvenile cohort showed a loss of rare alleles and elevated levels of inbreeding when compared to the adult cohort. These genetic differences between the cohorts were not observed in the locally common A. columnaris. This suggests that recent environmental degradation is influencing the genetic structure of A. nemorosa populations. Although this is not detectable among predisturbance adult populations, an early warning of these impacts is evident in more recently established seedling cohorts. The conservation implications of these results are discussed.

Chorology of New Caledonian palms and possible evidence of Pleistocene rain forest refugia.

The distribution of the 36 palm species of New Caledonia is studied in relation to several parameters: elevation, rainfall, geological substrate, phytogeographical sectors and vegetation types. The climate (thermal gradient and rainfall) appears to be the principal factor influencing the distribution of palms, the substrate effect being subordinate to the climatic pattern. Nearly all palm populations are included within the 1,500 mm isoline. Maximum levels of species richness and endemism are located in four areas receiving more than 3,000 mm of annual rainfall. We interpret these areas as former Pleistocene refugia of lowland rain forest based on three lines of evidence: 1) all locally endemic lowland palm species and genera are restricted to these areas; 2) local endemics occur on east-facing slopes receiving the highest rainfall and most likely to have sustained rain forests during the driest periods; and 3) several pairs of sister species are disjunct between the southeastern and northeastern high rainfall areas.

Distribution of gymnostoma spp. microsymbiotic frankia strains in new caledonia is related to soil type and to host-plant species

The diversity of the Frankia strains that are naturally in symbiosis with plants belonging to the Gymnostoma genus in New Caledonia was investigated. A direct molecular characterization of DNA extracted from nodules was performed, followed by characterization by restriction fragment length polymorphism (RFLP) of the ribosomal rrs-rrl (16S-23S) intergenic spacer (IGS) polymerase chain reaction (PCR)-amplified region. Seventeen different patterns were identified among the 358 microsymbiotic strains studied in the eight species of host plant present in New Caledonia. This genotypical approach permitted us to show that a large diversity existed among the patterns and that these did not exhibit a strict specificity to any host-plant species comparable with that previously found in the Casuarina and Allocasuarina symbioses in Australia. Despite this lack of specificity, a correspondence analysis nevertheless showed that the distribution of these patterns was related to soil type and to host-plant species. Furthermore, several Frankia strains were exclusively associated with the ultramafic soils.

Phylogenetic relationships within Araucariaceae based on rbcL gene sequences.

Phylogenetic relationships were determined in the Araucariaceae, which are now found mainly in the Southern Hemisphere. This conifer family was well diversified and widely distributed in both hemispheres during the Mesozoic era. The sequence of 1322 bases of the rbcL gene of cpDNA was determined from 29 species of Araucariaceae, representing almost all the species of the family. Phylogenetic trees determined by the parsimony method indicate that Araucariaceae are well defined by rbcL sequences and also that the monophyly of Agathis or Araucaria is well supported by high bootstrap values. The topology of these trees revealed that Wollemia had derived prior to Agathis and Araucaria. The rbcL phylogeny agrees well with the present recognition of four sections within Araucaria: Araucaria, Bunya, Eutacta, and Intermedia. Morphological characteristics of the number of cotyledons, position of male cone, and cuticular micromorphologies were evaluated as being phylogenetically informative. Section Bunya was found to be derived rather than to be the oldest taxon. Infrageneric relationships of Agathis could not be well elucidated because there are few informative site changes in the rbcL gene, suggesting the more recent differentiation of the species as their fossil records indicate. The New Caledonian Araucaria and Agathis species each formed a monophyletic group with very low differentiation in rbcL sequences among them, indicating rapid adaptive radiation to new edaphic conditions, i.e., ultramafic soils, in the post-Eocene era.

Nickel uptake by Flacourtiaceae of New Caledonia.

Herbarium and field specimens (over 300) of all of the Flacourtiaceae of New Caledonia were analysed for nickel in order to identify hyperaccumulators (greater than 1000 microgram/g dry mass) and to assess nickel accumulation in relation to the evolutionary status of 'nickel plants' of New Caledonia. One hyperaccumulator was identified in the genus Lasiochlamys, ten among Xylosoma, one among Casearia and seven among Homalium. Although these Homalium nickel plants had previously been recorded, fresh data for these and other Homalium are presented. The remarkable tolerance of Flacourticeae to ultrabasic rocks is shown by the fact that 75% of the species are found on such substrates. The number of hyperaccumulators was greatest in the genera Xylosoma and Homalium. The Flacourtiaceae are among the most primitive of all angiosperms and in common with other primitive hyperaccumulators, contain nickel as a complex with citric acid. The only advanced New Caledonian nickel plant (Psychotria douarrei) has most of its nickel bound with ligands other than citric acid, a feature of other advanced hyperaccumulators. It is postulated that nickel complexing with citric acid may be a primitive character. Most of the New Caledonian nickel plants belong to the order Violales of subclass Dilleniidae. It is suggested that hyperaccumulation of nickel is an evolutionary character which occurs in long-indisturbed floras such as that of New Caledonia.

Sebertia acuminata: A Hyperaccumulator of Nickel from New Caledonia.

Sebertia acuminata (Sapotaceae) from New Caledonia has been shown to be a hyperaccumulator of nickel. The nickel content of the latex (25.74 percent on a dry weight basis) is easily the highest nickel concentration ever found in living material. The nickel is in the form of a low-molecular-weight, water-soluble organic complex.