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Soil microorganisms could be one of the principal lever for conservation and ecological restoration, owing to their crucial role in ecosystems functioning and their ability to rapidly respond to environmental changes.. However, despite their major role, this hidden biodiversity has beenwidely neglected, particularly in southern hemisphere. New Caledonia is an archipelago located in the southwest Pacific renowned for its exceptional biological diversity, and recognized as a world priority area for conservation and restoration. With one third of its territory covered by soils originated from ultramafic rocks, which contain 20-30% of the global nickel ore reserve, mining has occurred since more than a century and has drastically increased in the past decades. Mining has led to a massive land degradation throughout the entire main island. In this context, we have conducted complementary studies on soil fungal and bacterial communities within diverse ultramafic ecosystems. Their aims were to characterize (i) the taxonomical diversity within these organisms, (ii) the underlying mechanisms that may impact them, as well as (iii) their probable functional roles, and (iv) their potential to be used as monitoring and evaluation tools for restoration. Our investigations relied on different molecular approaches, especially the emergent and revolutionary molecular methods that are next-generation sequencing technologies (NGS). Our results revealedthe incredible soil microbial diversity, notably of the symbiotic group of ectomycorrhizal fungi, which may harbour an endemism rate of 87-95%. We highlighted a plant and site effects on both fungal and bacterial communities. Such site effect suggests that each location, or ultramafic massif, displays its own soil microbial community, and could thus represent distinct conservation units. We also showed that microbial composition influence ultramafic soils' susceptibility to erosion. Lately, our findings pointed out the great promise that represent the combination of soil microbial communities and high-throughput amplicon sequencing of environmental DNA (eDNA) to monitor ecosystems recovery. Soil eDNA metabarcoding could then contribute to the identification of suitable symbionts for plant inoculation. Overall, our findings underpin the great interest of considering soil microorganisms and the emergent new sequencing technologies for conservation and restoration.

International audience; Background. Recent climatic history has strongly impacted plant populations, but little is known about its effect on microbes. Alders, which host few and specific symbionts, have high genetic diversity in glacial refugia. Here, we tested the prediction that communities of root symbionts survived in refugia with their host populations. We expected to detect endemic symbionts and a higher species richness in refugia as compared to recolonized areas. Methods. We sampled ectomycorrhizal (EM) root tips and the nitrogen-fixing actino-mycete Frankia communities in eight sites colonized by Alnus glutinosa subsp. barbata close to the Caucasus in Georgia. Three sites were located in the Colchis, one major Eurasian climatic refugia for Arcto-Tertiary flora and alders, and five sites were located in the recolonized zone. Endemic symbionts and plant ITS variants were detected by comparing sequences to published data from Europe and another Tertiary refugium, the Hyrcanian forest. Species richness and community structure were compared between sites from refugia and recolonized areas for each symbionts. Results. For both symbionts, most MOTUs present in Georgia had been found previously elsewhere in Europe. Three endemic Frankia strains were detected in the Colchis vs two in the recolonized zone, and the five endemic EM fungi were detected only in the recolonized zone. Frankia species richness was higher in the Colchis while the contrary was observed for EM fungi. Moreover, the genetic diversity of one alder specialist Alnicola xanthophylla was particularly high in the recolonized zone. The EM communities occurring in the Colchis and the Hyrcanian forests shared closely related endemic species. Discussion. The Colchis did not have the highest alpha diversity and more endemic species, suggesting that our hypothesis based on alder biogeography may not apply to alder’s symbionts. Our study in the Caucasus brings new clues to understand symbioses biogeography and their survival in Tertiary and ice-age refugia, and reveals that isolated host populations could be of interest for symbiont diversity conservation.

Comunicación oral presentada en la Sesión 4: Biodiversidad asociada a bosques y matorrales.

9 pages, 4 tables, 3 figures, 63 references. We thank the Consejería de Medio Ambiente (Andalusian Government) and Marco Antonio Tena, then Director of Los Alcornocales Natural Park, for the facilities and support to carry out our field work. We are grateful to Nacho Pérez-Ramos, Ana Pozuelos, María Navarro, Eduardo Gutiérrez, Sophie Manzi and Juliet Rochet for field and lab assistance., Host trees can modify their soil abiotic conditions through their leaf fall quality which in turn may influence the ectomycorrhizal (ECM) fungal community composition. We investigated this indirect interaction using a causal modelling approach. We identified ECM fungi on the roots of two coexisting oak species growing in two forests in southern Spain e Quercus suber (evergreen) and Quercus canariensis (winter deciduous)-using a PCR-based molecular method. We also analysed the leaf fall, litter and soil sampled beneath the tree canopies to determine the concentrations of key nutrients. The total mycorrhizal pool was comprised of 69 operational taxonomic units (OTUs). Tomentella and Russula were the most species-rich, frequent and abundant genera. ECM fungi with epigeous and resupinate fruiting bodies were found in 60% and 34% of the identified mycorrhizas, respectively. The calcium content of litter, which was significantly higher beneath the winter-deciduous oak species due to differences in leaf fall quality, was the most important variable for explaining ECM species distribution. The evaluation of alternative causal models by the d-sep method revealed that only those considering indirect leaf fallmediated host effects statistically matched the observed covariation patterns between host, environmen (litter, topsoil, subsoil) and fungal community variables., This study was supported by an FPI-MEC grant to CA, by the Spanish MEC projects Dinamed (CGL2005-5830- C03-01) and Interbos (CGL2008-4503-C03-01), and the European FEDER funds. This research is part of the Globimed (www. globimed.net) network in forest ecology.

11 páginas, 1 tabla, 2 figuras, 38 referencias.-- Congreso celebrado del 21-25 de septiembre 2009, en Ávila, España., La supervivencia de las quercíneas en condiciones naturales depende de la micorrización, una asociación simbiótica establecida entre plantas y hongos. A través de esta relación los hongos proveen a la planta de agua, nutrientes y beneficios tales como una mayor protección ante el estrés hídrico, los contaminantes o los agentes patógenos. Cambios en la cubierta vegetal, en las condiciones de humedad o la aplicación de fertilizantes y pesticidas pueden reducir las poblaciones de hongos micorrícicos, afectando a las interacciones entre plantas y llegando a alterar la composición de la comunidad vegetal. Este trabajo se realizó en los bosques de quercíneas del sur de la península ibérica. Nuestro objetivo fue estudiar, mediante el uso de métodos moleculares, la diversidad y estructura de la comunidad de hongos micorrícicos asociados a las raíces de dos especies coexistentes en estos bosques, el alcornoque (Q. suber L.) y el quejigo moruno (Q. canariensis Willd.), y describir la relación entre la especie huésped, las condiciones ambientales y la composición de la comunidad fúngica. Entre los resultados, destaca la gran diversidad de especies micorrícicas encontradas, resultado de un elevado número de taxones raros, rasgo característico de las comunidades de micorrizas. Las familias Thelephoraceae y Russulaceae se mostraron como las más abundantes, taxonómicamente diversas y con mayor dispersión espacial. Un número limitado de especies presentaron especificidad por la especie huésped mientras que el efecto de las condiciones del medio en la composición de la comunidad de hongos micorrícicos fue notable. La coexistencia de especies vegetales huéspedes y la heterogeneidad del medio parecen ser factores clave para sostener la diversidad de la comunidad micorrícica., Este estudio esta financiado por una beca FPI-MEC otorgada a C.A., los proyectos de Investigación Nacional Dinamed (CGL2005-5830-C03-019) e Interbos (CGL2008-4503-C03-01) concedidos por el Ministerio de Educación y Ciencia y los fondos Europeos FEDER. Esta investigación forma parte de la red Globimed de cambio global y biodiversidad en los ecosistemas mediterráneos (www.globimed.net).

1 página. Presentación oral a EURECO-GFOE, 15-18 de septiembre, 2008, Leipzig. Dicho congreso posteriormente dió lugar a la publicación de un libro de 865 páginas. Esta presentación está en el Capítulo 4.7: Diversity and ecological role of mycorrhizal fungi in ecosystems., Mediterranean oak forests have a high ecologic and economic value. The sustainability these forests relies on the symbiosis established between tree species and tomycorrhizal (EM) fungal community. Oaks provide fungi with photosynthesized products that are used to generate an underground fangal network. In turn this network enlarges hosts nutrient and water foraging area and allows the exchange of resources between connected tree individuals that may be of the same or different species. In addition, oak seedlings rapidly integrate into the EM fungal network enhancing their nutrient acquisition. Therefore the EM community directly affects the productivity and regeneration of oak forest.

Le Genévrier thurifère (Juniperus thurifera L.) est une espèce ligneuse à répartition méditerranéenne, rare dans les Pyrénées où il est distribué en deux populations principales entourées chacune par de petites populations satellites plus ou moins menacées. Ces populations se situent dans des sites proposés au titre de la directive “habitats” pour le réseau Natura 2000. Les thuriféraies françaises sont classées comme “ habitats prioritaires ” par la Directive Habitats de l’Union européenne (code Corine Biotope 42.A27) et l’espèce devrait être inscrite prochainement par l’U.I.C.N. dans la catégorie des espèces vulnérables (V) au niveau mondial. L’objectif du projet est d’approfondir les connaissances sur les populations pyrénéennes afin de mieux évaluer leur valeur patrimoniale et de guider les opérations de gestion in situ, voire de renforcement de population et de conservation ex situ. Il se concrétisera par la rédaction d’un plan de conservation. Pour cela, trois axes d’étude sont mis en oeuvre : l’étude de l’origine et de la dynamique passée des populations pyrénéennes,l’étude de leur dynamique récente et la recherche de facteurs pouvant affecter les capacités de régénération d’une population : rôle de l’avifaune dans la dispersion des graines, influence des ravageurs de galbules sur les potentialités de régénération et influence de champignons mycorhiziens., Juniperus thurifera L. is a woody species growing in the mediterranean area. Rare in the Pyrenees, it is distributed in two main populations surrounded by a few small populations more or less endangered. These populations are located in sites proposed for the Natura 2000 Network. French J. thurifera woodlands are classified as a priority habitat in the european Habitats Directive and the species will soon be included in the IUCN Red List as vulnerable (VU) species. The purpose of the project is to collect more information about pyrenean populations to evaluate their patrimonial value and to elaborate proposals for in situ management, population reinforcement and ex situ conservation. A conservation plan will then be written. Three different kinds of studies are implemented : - the origin and past dynamic of pyrenean populations, - their recent dynamic, - the factors influencing plant regeneration: the role of birds in seed dispersal, the effect of specialists seed insects and the influence of mycorhizal fungi.

Une planche photographique composée de 10 clichés; National audience; Juniperus thurifera L. is a woody species growing in the mediterranean area. Rare in the Pyrenees, it is distributed in two main populations surrounded by a few small populations more or less endangered. These populations are located in sites proposed for the Natura 2000 Network. French J. thurifera woodlands are classified as a priority habitat in the european Habitats Directive and the species will soon be included in the IUCN Red List as vulnerable (VU) species. The purpose of the project is to collect more information about pyrenean populations to evaluate their patrimonial value and to elaborate proposals for in situ management, population reinforcement and ex situ conservation. A conservation plan will then be written. Three different kinds of studies are implemented : - the origin and past dynamic of pyrenean populations, - their recent dynamic, - the factors influencing plant regeneration: the role of birds in seed dispersal, the effect of specialists seed insects and the influence of mycorhizal fungi.; Le Genévrier thurifère (Juniperus thurifera L.) est une espèce ligneuse à répartition méditerranéenne, rare dans les Pyrénées où il est distribué en deux populations principales entourées chacune par de petites populations satellites plus ou moins menacées. Ces populations se situent dans des sites proposés au titre de la directive “habitats” pour le réseau Natura 2000. Les thuriféraies françaises sont classées comme “ habitats prioritaires ” par la Directive Habitats de l’Union européenne (code Corine Biotope 42.A27) et l’espèce devrait être inscrite prochainement par l’U.I.C.N. dans la catégorie des espèces vulnérables (V) au niveau mondial. L’objectif du projet est d’approfondir les connaissances sur les populations pyrénéennes afin de mieux évaluer leur valeur patrimoniale et de guider les opérations de gestion in situ, voire de renforcement de population et de conservation ex situ. Il se concrétisera par la rédaction d’un plan de conservation. Pour cela, trois axes d’étude sont mis en oeuvre : l’étude de l’origine et de la dynamique passée des populations pyrénéennes,l’étude de leur dynamique récente et la recherche de facteurs pouvant affecter les capacités de régénération d’une population : rôle de l’avifaune dans la dispersion des graines, influence des ravageurs de galbules sur les potentialités de régénération et influence de champignons mycorhiziens.

International audience; Tetrachaetum elegans Ingold is a saprobic aquatic hyphomycete for which no sexual stage has yet been described. It occurs most commonly during the initial decay of tree leaves in temperate freshwater habitats and typically sporulates under water. Dispersal of the aquatic fungus takes place primarily in the water column and has a large passive component. Differences in substrate composition (e.g. quality of leaf litter) may also play a role in the distribution of different species or genotypes. The population genetic structure of T. elegans was studied using amplified fragment length polymorphism (AFLP) multilocus fingerprints. The populations were isolated from the leaf litter of three different tree genera, sampled in nine streams distributed throughout a mixed deciduous forest. Molecular markers were developed for 97 monosporic isolates using four selective primer pairs. A total of 247 fragments were scored, of which only 32 were polymorphic. Significant stream differentiation was detected for the isolates considered in this study. Analysis of molecular variance revealed that 20% of the genetic variation observed was the result of differences between streams. No correlation between genetic and geographical distances was found but a few multilocus genotypes were observed in different locations. Altogether these results suggest that environmental barriers play a role in the population structure of this aquatic fungus. No clear-cut effect of leaf litter composition on genetic variation could be demonstrated. Finally, tests of linkage disequilibrium between the 32 polymorphic AFLP loci as well as simulations did not provide a final answer regarding clonality in T. elegans. Indeed, it was possible to reject linkage equilibrium at different sampling levels and show that full linkage was unlikely.

Tricholoma populinum et Tricholoma scalpturatum sont deux champignons basidiomycètes formant des symbioses ectomycorhiziennes avec les racines des plantes ligneuses. Ces deux espèces phylogénétiquement proches, diffèrent cependant par leur niveau de spécificité envers la plante-hôte: T. populinum est Inféodé aux peupliers tandis que T. scalpturatum présente un spectre d'hôtes très large. Ces deux espèces peuvent se rencontrer ensemble, sous peupliers noirs (Populus nigra), dans des environnements très variés quant aux perturbations qu'ils subissent. Dans ce travail, nous examinons dans quelle mesure les différences de spécificité d'hôtes et les contraintes environnementales peuvent se traduire par des différences au niveau des caractéristiques des populations de ces deux espèces. Nous comparons les structures de populations et les stratégies de colonisation de ces deux espèces fongiques dans deux sites: une peupleraie noire naturelle en bordure de Garonne régulièrement soumise à des crues et une pelouse bordée de peupliers noirs, indemne de toute perturbation. Les carpophores apparus sur les deux sites, ont été récoltés et les génets différenciés à l'aide de marqueurs RAPD et RFLP dans l'espaceur intergénique (IGS) de l'ADNr nucléaire. En zone non perturbée, seulement 2 génets regroupant chacun de nombreux carpophores distribués sur plusieurs dizaines de m2 ont été trouvés au sein de la population de T. populinum. Ce résultat indiquait une stratégie de colonisation de type C, privilégiant la croissance végétative du mycélium dans le sol pour cette espèce. Les carpophores de T. scalpturatum se distribuaient en 12 génets, petits (représentés par 1 ou quelques carpophores) ou plus grands (30 à 40 m2). Cette population semblait ainsi structurée à la fois par la croissance végétative et la reproduction sexuée selon une stratégie mixte (r et C). En zone perturbée, la même tendance a été mise en évidence avec cependant une prépondérance accrue de la reproduction sexuée pour les 2 espèces. Ainsi, la population de T. scalpturatum était exclusivement constituée de multiples petits génets et donnait l'image d'une population à stratégie r fortement structurée par la reproduction sexuée, la colonisation s'opérant uniquement par spores. Chez T. populinum, un génet, parmi 7 identifiés, présentait une croissance végétative importante tandis que les autres apparaissaient petits. Ce résultat indiquait une population à stratégie mixte (r et C) pour cette espèce sur ce site perturbé. La caractérisation des carpophores a donc révélé, quelque soit le site, une diversité génétique beaucoup plus élevée, des génets moins pérennes et un mode de colonisation par reproduction sexuée plus marqué chez T. scalpturatum, l'espèce à large spectre d'hôtes, que chez T. populinum, l'espèce spécialiste du peuplier.