Abstract
Acacia spirorbis is a legume tree species distributed all over the Melanesian arc and mainly in New Caledonia where it is ubiquitous over a wide range of variety of soils. Indeed, from North to South of the territory and up to an altitude of 400m, this species is very dynamic in terms of implantation, growth and renewal capacity, demonstrating an amazingly wide range of adaptation, probably unique among vascular plants. New Caledonia offers an extreme diversity of soils, inducing different types of stresses (for exemple: water stress in metalliferous, calcareous and silty soils, heavy metal toxicity in metalliferous soils and aluminium toxicity in bauxite soils). /nAnother important feature of A. spirorbis is its ability to develop nitrogen-fixing nodules, arbuscular mycorrhizas and ectomycorrhizas. This ability to establish a triple symbiosis is known only for a very limited number of angiosperms: some species among australian Acacia and some actinorhizal plants. Each of these symbioses has been characterized as important actors in adaptation of plants to edaphic stresses and this triple symbiosis is often mentioned to explain the high adaptive plasticity of their hosts. However, few of the “trisymbiotic” acacias are naturally facing such contrasted edaphic situations on a such reduced areas as A. spirorbis in New Caledonia. One plant species, three different symbioses naturally living in a contrasted range of more or less toxic edaphic conditions : such is the context of ADASPIR. /nThe main objective of ADASPIR is to analyze the weight of each symbiosis in the adaptation of A. spirorbis to its different environments from the community to the individual and gene levels. As part of a multidisciplinary project ADASPIR proposes to study the mechanisms of adaptation of A. spirorbis and its associated microorganisms face to different abiotic stresses. The project is organized in three work packages: Coordination, dissemination and exploitation of results (WP1), A. spirorbis and its environments (WP2) and Role of symbiotic microorganisms in A. spirorbis adaptation to abiotic constrainsts (WP3) through 9 tasks: (1) coordination and development of work, (2) selection of study sites: 7 A. spirorbis stands will be selected on their contrasted edaphic characteristics, (3) pedological, geochemical and mineralogical characterization of the soils in the 7 studied sites, (4) genetypic and phenotypic characterisation of A. spirorbis : being in a context of high endemism, in dispersed geographical locations, these points will be analyzed, (5) In situ quantification of nitrogen fixation in A. spirorbis and live traits history: the impact of environment on A. spirorbis nitrogen fixation ability will be studied in the 7 sites through 15N natural abundance determinations, (6) diversity and functionality of the nitrogen-fixing bacteria associated with A. spirorbis, (7) diversity and functionality of arbuscular mycorrhizal fungi of A. spirorbis, (8) diversity and functionality of ectomycorrhizal fungi of A. spirorbis, (9) functioning of the Pisolithus albus/ A. spirorbis symbiosis under abiotic stresses. /nIn conclusion, the ADASPIR project proposes to conduct basic research to characterize the mechanisms of adaptation of a species, A. spirorbis to various abiotic soil tresses: polymetallic toxicities (Ni, Cr, Mn, Co), unbalanced Ca/Mg ratio (1/40), aluminum toxicity, excess of Ca carbonate, poverty in major elements, in metalliferous, bauxite, limestone and siliceous or acid soils. It should be noted that this species is able to grow and form very dynamic stands on a very diverse range of soils: limestone, siliceous (acid and neutral), aluminum, ferralitic, serpentine... On a industrial point of view, A. spirorbis is a widely used species in revegetation programs of former mining sites in New Caledonia. The ADASPIR project aims to better target the use of this species and to optimize the management of sustainable restoration of degraded ecosystems. /n
France