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[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; In the last twenty years, several studies have stressed the importance of including a historical approach in ecological studies. It helps understand structure and functioning of present ecosystems but also assess conservation objectives. In temperate regions, several studies showed that forest vascular plants differ according to forest temporal continuity. This difference is caused by a modification of forest habitats by past land use, especially soil physico-chemical properties, but is also conditioned by species colonisation potential. For instance, species more frequent in forests with a long temporal continuity, also known as ancient forest species, have life-history traits associated to poor dispersal abilities. However, the effect of past land use on the present flora has not yet been investigated in the Mediterranean. Our aim is thus to analyse floristic differences between ancient and recent forests and to identify life-history traits associated to those differences in the Natural Regional Park of Luberon. We also explore the effect of past land use on forest plant communities and soil physico-chemical properties. We hypothesised that: (1) species more frequent in ancient forests were typical forest species, more shade-tolerant and with poor dispersal ability (dispersal syndrome, soil seedbank); (2) ancient forest soils had less nutrients, more organic matter and are more superficial compared to recent forests; (3) those differences varied according to past land use (pastoral vs. cultural); (4) those differences are less pronounced than in temperate regions because former pasturelands were dominant in the Mediterranean. This study will enable us to better understand past land use effects on vegetation and soil dynamics in Mediterranean forests, and to compare our results with other biogeographical and sociological contexts.

The taxonomic status of eleven rhizospheric bacterial strains belonging to the genus Burkholderia and isolated from roots of Costularia (Cyperaceae), tropical herbaceous pioneer plants growing on ultramafic soils in New Caledonia, was investigated using a polyphasic taxonomic approach. The genetic analyses (16S rRNA genes, gyrB, recA, nreB and cnr) confirmed that all strains are Burkholderia and cluster into two separated groups. The DNA hybridization results showed low relatedness values to the closest relatives Burkholderia species. The phenotypic analyses confirmed that the two groups of strains could be differentiated from each other and from other known Burkholderia species. This polyphasic study revealed that these two groups of strains represent each a novel species of Burkholderia, for which the names Burkholderia novacaledonica sp. nov. (type strain STM10272(T)=LMG28615(T)=CIP110887(T)) and B. ultramafica sp. nov. (type strain STM10279(T)=LMG28614(T)=CIP110886(T)) are proposed, respectively. These strains of Burkholderia presented specific ecological traits such as the tolerance to the extreme edaphic constraints of ultramafic soils: they grew at pH between 4 and 8 and tolerate the strong unbalanced Ca/Mg ratio (1/19) and the high concentrations of heavy metals i.e. Co, Cr, Mn and Ni. Noteworthy B. ultramafica tolerated nickel until 10mM and B. novacaledonica up to 5mM. The presence of the nickel (nreB) and cobalt/nickel (cnr) resistance determinants encoding for protein involved in metal tolerance was found in all strains of both groups. Moreover, most of the strains were able to produce plant growth promoting molecules (ACC, IAA, NH3 and siderophores). Such ecological traits suggest that these new species of Burkholderia might be environmentally adaptable plant-associated bacteria and beneficial to plants.

Microbial species richness and assemblages across ultramafic ecosystems were investigated to assess the relationship between their distributional patterns and environmental traits. The structure of microorganism communities in the Koniambo massif, New Caledonia, was investigated using a metagenetic approach correlated with edaphic and floristic factors. Vegetation cover and soil properties significantly shaped the large phylogenetic distribution of operational taxonomic unit within microbial populations, with a mean per habitat of 3,477 (± 317) for bacteria and 712 (± 43) for fungi. Using variance partitioning, we showed that the effect of aboveground vegetation was the most significant descriptor for both bacterial and fungal communities. The floristic significant predictors explained 43% of the variation both for the bacterial and fungal community structures, while the edaphic significant predictors explained only 32% and 31% of these variations, respectively. These results confirm the previous hypothesis, that the distribution of microorganisms was more structured by the vegetation cover rather than the edaphic characteristics and that microbial diversity is not limited in ultramafic ecosystems.

To investigate the effects of microbial inocula and Erythrina poeppigiana pruning residues on soil K, NO3-, and NH4? concentrations, a greenhouse trial, a field experiment in an organic farm, and three in vitro tests were conducted. Under controlled conditions, weak, temporary effects (10 %) on maize seedling growth were observed on poor soils (taken from the 10-20 cm layer) in the first 2 weeks after application. Positive effects of pruning residue applications on soil K levels (0.09 cmol kg-1, on average) were detected in both the field and greenhouse study. However, significant effects due to the addition of microbial inocula on soil K concentrations were not detected in the field; thus, microbial applications were ineffective at enhancing nutrient availability under field conditions. In contrast, in the in vitro experiments, CO2 production was 31 % greater than that of untreated soil on the 8th and 15th days of incubation. These results highlight the importance of adding tree pruning residues to support coffee-plant nutrition. Experimental outcome data could be valuable for further studies focused on microbial application dosage and timing.

Introduction. Aux Antilles francaises, les planteurs considerent generalement qu'il est necessaire d'effectuer periodiquement un travail du sol pour regenerer la porosite du sol et maintenir un fort rendement. Cependant, dans les bananeraies perennes d'altitude, le sol qui n'est jamais travaille presente de meilleures proprietes physiques et biologiques que dans bananeraies conduites de maniere conventionnelle. Pour determiner si le travail du sol avant la plantation est necessaire au bon fonctionnement d'une culture de bananiers et pour evaluer l'effet du labour sur la qualite du sol, une plantation de bananiers apres travail du sol classique a ete comparee a la plantation directe de bananiers sur un paillis de residus de recolte en parcelle experimentale. Materiel et methodes. La qualite du sol a ete evaluee par des indicateurs tels que la porosite, le statut organique, la biomasse microbienne et la structure des populations de nematodes. Le fonctionnement de la culture a ete evalue par la croissance de la plante, la distribution des racines, et la disponibilite de l'eau et de l'azote du sol. Resultats. Nous avons constate que le travail du sol a reduit la biomasse microbienne du sol et le nombre de guildes fonctionnelles de nematodes. Le travail du sol a eu seulement un effet a court terme sur la porosite du sol et n'a pas permis un enracinement plus profond. Bien que la mineralisation de l'azote organique du sol ait ete plus elevee avec le travail du sol conventionnel, la nutrition en azote des bananiers n'a pas ete meilleure, probablement parce que la fertilisation azotee elevee a compense les variations de la disponibilite de l'azote d'origine organique. Nous avons constate que la croissance des bananiers etait meilleure dans le traitement sans travail du sol. Cela a pu etre explique par un plus faible dessechement du sol du au paillis de residus de recolte laisse sur la surface du sol pour le traitement sans travail du sol. Conclusion. Par rapport au travail du sol classique, une plantation sans labour a ameliore la qualite du sol et les performances de la culture.

International audience; Although it is usually admitted that arbuscular mycorrhizal (AM) fungi are key components in soil bio-functioning, little is known on the response of microbial functional diversity to AM inoculation. The aims of the present study were to determine the influence of Glomus intraradices inoculum densities on plant growth and soil microflora functional diversity in autoclaved soil or non-disinfected soil. Microbial diversity of soil treatments was assessed by measuring the patterns of in situ catabolic potential of microbial communities. The soil disinfection increased sorghum growth, but lowered catabolic evenness (4.8) compared to that recorded in the non-disinfected soil (6.5). G. intraradices inoculation induced a higher plant growth in the autoclaved soil than in the non-disinfected soil. This AM effect was positively related to inoculum density. Catabolic evenness and richness were positively correlated with the number of inoculated AM propagules in the autoclaved soil, but negatively correlated in the non-disinfected soil. In addition, after soil disinfection and AM inoculation, these microbial functionality indicators had higher values than in the autoclaved or in the non-disinfected soil without AM inoculation. These results are discussed in relation to the ecological influence of AM inoculation, with selected fungal strains and their associated microflora on native soil microbial activity

Rhizobial lipo-chitooligosaccharides (LCOs) are signaling molecules involved in host-range recognition for the establishment of the symbiosis with leguminous plants. The major LCO of Rhizobium meliloti , the symbiont of Medicago plants contains four or five N -acetylglucosamines, O-acetylated and N-acylated with a C16:2 fatty acid on the terminal nonreducing sugar and O-sulfated on the reducing sugar. In this paper, the ligand specificity of a high-affinity binding site (Nod factor binding site 2 or NFBS2), enriched in a plasma membrane-enriched fraction of Medicago cell suspension cultures, is reported. By using chemically synthesized LCOs, the role of structural elements, important for symbiotic activities, as recognition motifs for NFBS2 was determined. The results show that the substitutions on the nonreducing sugar of the LCOs (the O -acetate group, the fatty acid, and the hydroxyl group on the C 4 of the sugar) are determinants for high-affinity binding to NFBS2. In contrast, the sulfate group, which is necessary for all biological activities on Medicago , is not discriminated by NFBS2. However, the reducing sugar of the LCO seems to interact with NFBS2, because ligand binding is affected by the reduction of the free anomeric carbon and depends on the number of N -acetyl glucosamine residues. These results suggest that the recognition of the LCOs by NFBS2 is mediated by structural elements in both the lipid and oligosaccharidic moities, but not by the sulfate group.

8 pages; International audience; Agricultural practices should modify the diversity of soil microbes. However, the precise relationships between soil properties and microbial diversity are poorly known. Here, we study the effect of agricultural management on soil microbial diversity and C turnover in tropical grassland of north-eastern Laos. Three years after native grassland conversion into agricultural land, we compared soils from five land use management systems: one till versus two no-till rotational cropping systems, one no-till improved pasture and the natural grassland. Soils were incubated in microcosms during 64 days at optimum temperature and humidity. Bacterial and fungal diversity were evaluated by metagenomic 454-pyrosequencing of 16S and 18SrRNA genes, respectively. Changes in soil respiration patterns were evaluated by monitoring 12C- and 13C-CO2 release after soil amendment with 13C-labelled wheat residues. Results show that residue mineralization increased with bacterial richness and diversity in the tilled treatment 7 days after soil amendment. Native soil organic C mineralization and priming effect increased with fungal richness and diversity in improved pasture and natural grassland. No-till cropping systems represented intermediate situations between tillage and pasture systems. Our findings evidence the potential of controlling soil microbial diversity by agricultural practices to improve soil biological properties. We suggest the promotion of no-till systems as a fair compromise between the need for agriculture intensification and soil ecological processes preservation.

The responses of the soil microbial community features associated to the legume tree Acacia senegal (L.) Willd. including both arbuscular mycorrhizal fungal (AMF) diversity and soil bacterial functions, were investigated under contrasting environmental conditions. Soil samples were collected during dry and rainy seasons in two contrasting rainfall sites of Senegal (Dahra and Goudiry, in arid and semiarid zone, resp.). Soils were taken from the rhizosphere of A. senegal both in plantation and natural stands in comparison to bulk soil. A multiple analysis revealed positive correlations between soil physicochemical properties, mycorrhizal potential and enzyme activities variables. The positive effects of A. senegal trees on soil mycorrhizal potential and enzyme activities indicates that in sahelian regions, AMF spore density and diversity as well as soil microbial functions can be influenced by land-use systems (plantation versus natural population of A. senegal) and environmental conditions such as moisture and soil nutrient contents. Our study underlines the importance of prior natural AMF screening for better combinations of A. senegal seedlings with AMF species to achieve optimum plant growth improvement, and for restoration and reforestation of degraded lands.

The objectives of this study were to determine the impact of two exotic tree species (pine and eucalypts) on the early growth of Uapaca bojeri (an endemic tree species from Madagascar) via their influence on soil chemical, microbial characteristics, on ectomycorrhizal fungal community structures in a Madagascarian highland forest and to test the ability of an early-successional ectomycorrhizal shrub, Leptolena bojeriana, to mitigate the impacts of these exotic species. Finally, we hypothesized that L. bojeriana could act as a natural provider for ectomycorrhizal propagules. Soil bioassays were conducted with U. bojeri seedlings grown in soils collected under the native tree species (U. bojeri and L. bojeriana) and two exotic tree species (Eucalyptus camaldulensis and Pinus patula) and in the same soils but previously cultured by L. bojeriana seedlings. This study clearly shows that (1) the introduction of exotic tree species induces significant changes in soil biotic and abiotic characteristics, (2) exotic-invaded soil significantly reduces the early growth and ectomycorrhization of U. bojeri seedlings and (3) L. bojeriana decreased these negative effects of the exotic tree species by facilitating ectomycorrhizal establishment and consequently improved the U. bojeri early growth. This study provides evidence that L. bojeriana can facilitate the ectomycorrhizal infection of U. bojeri and mitigates the negative effects of the introduction of exotic tree species on the early growth of the native tree species. From a practical point of view, the use of ectotrophic early-successional shrub species should be considered to improve forest resaturation after exotic invasion.

Use of the Australian genusEucalyptusin short rotation plantations in Africa and Madagascar has developed over the last century to such an extent that it is becoming the most frequently planted genus in Africa. In order to find ecologically well-adapted eucalypts, foresters have tested different species of various origins and the number of testedEucalyptusspecies now exceeds 150 in Africa. Due to the ability of eucalypts to naturally form ectomycorrhizae, even in the absence of any controlled introduction of compatible ectomycorrhizal fungal partners, their introduction in new ecosystems has direct consequences for ectomycorrhizal fungus communities. A bibliographical compilation, together with original field observations on putative ectomycorrhizal fungi associated with eucalypts in Africa and in Madagascar, has been drawn up in two lists: one for Africa and one for Madagascar where surprisingly high fungal diversity was observed. The level of diversity, the putative origin of the fungi, and their potential impact on native ectomycorrhizal fungi are discussed. The development of eucalypts plantations will inexorably lead to the increase of exotic fungal species being potentially invasive in the considered region.

Les bois ont longtemps été traités avec des fongicides et "impact de ces fongicides sur les sols après lessivage constitue un vrai problème écologique. Dans cette perspective nous nous proposons d'étudier des communautés fongiques de ces bois contaminés dans un but de biorémédiation. La plupart des études précédentes se sont focalisées sur la capacité de certains Basidiomycètes et de certains champignons de la pourriture blanche à dégrader ces produits biocides. Des échantillons de bois traités et témoins ont été incubés dans des containers de sols forestiers en Guyane. Deux premiers échantillonnages de ces bois et du sol des containers ont été réalisés à S mois d'écart. Une étude culturale et moléculaire a permis l'isolement et l'identification de 40 souches d'Ascomycètes qui sont capables de se développer sur le bois et de résister à des xénobiotiques. D'autre part, une étude des communautés fongiques du bois et du sol a été effectuée par D-HPLC et CE-SSCP puis analysée par ACP. D'après ces analyses les produits biocides sont lessivés dans le sol et ont un impact sur les communautés fongiques. Celles-ci sont en effet différentes selon le temps d'échantillonnage et selon le traitement du bois. Ces résultats intéressants sont cependant à approfondir par d'autres échantillonnages et une étude culturale plus approfondie.

Présentation de l'éditeur : Les substrats ultramafiques - ou terrains miniers - à l'origine du minerai de nickel, couvrent près du tiers de la Nouvelle-Calédonie, qui se place parmi les premiers producteurs de ce métal dans le monde. Mais l'exploitation minière à ciel ouvert nécessite d'importants décapages qui génèrent des problèmes d'érosion des sols, de dérèglement des débits hydriques, de pollution des cours d'eau et de perte de biodiversité. Ces substrats datant de 37 millions d'années portent une flore riche et originale, qui a largement contribué au classement de la Nouvelle-Calédonie comme un des principaux hotspots de biodiversité de la planète. Elle comprend environ 2150 espèces végétales dont 82 % sont endémiques. Ces espèces sont en outre spécialisées, adaptées à des sols très pauvres en plusieurs éléments nutritifs et inversement très riches en magnésium, en nickel et en d'autres métaux. Ces milieux abritent également une faune d'une grande diversité. Ainsi la Nouvelle-Calédonie est confrontée à un double défi : celui d'exploiter une ressource minière considérable à même d'assurer au pays un développement économique important, et celui de protéger cette biodiversité exceptionnelle au nom des principes fondamentaux édictés mondialement. Dans ce contexte, la conservation des milieux abritant la plus grande part de la biodiversité, ainsi que la restauration des sites dégradés par l'exploitation minière s'imposent comme des nécessités incontournables. L'ouvrage décrit et illustre tout d'abord la variété des substrats ultramafiques, ainsi que la diversité des écosystèmes et de leurs composantes floristiques, zoologiques et microbiologiques. Le concept de restauration écologique des sites dégradés et les moyens nécessaires pour sa mise en oeuvre sont ensuite développés ; puis les modes de collecte, de germination, de conservation des semences et de production de plants d'espèces locales sont décrits, de même que les méthodes de revégétalisation. Enfin près de 100 espèces végétales utiles pour la restauration sont présentées. Cet ouvrage est destiné à un large public, allant des professionnels du secteur minier (sociétés minières, opérateurs de la revégétalisation, bureaux d'étude...) aux personnels des collectivités impliquées dans la gestion du patrimoine minier et biologique du pays, ainsi qu'aux scientifiques, enseignants, étudiants, et plus largement à toute personne intéressée par les terrains miniers et leur gestion environnementale

International audience

Erratum paru dans Plant and soil (2009) 325 (1-2) p. 351-352 http://dx.doi.org/10.1007/s11104-009-0100-4. Diversity, structure and productivity of above-ground compartment of terrestrial ecosystems have been generally considered as the main drivers of the relationships between diversity and ecosystem functioning. More recently it has been suggested that plant population dynamics may be linked with the development of the below-ground community. The biologically active soil zone where root-root and rootmicrobe communications occur is named "Rhizosphere" where root exudates play active roles in regulating rhizosphere interactions. Root exudation can regulate the soil microbial community, withstand herbivory, facilitate beneficial symbioses, modify the chemical and physical soil properties and inhibit the growth of competing plant species. In this review, we explore the current knowledge assessing the importance of root exudates in plant interactions, in communications between parasitic plants and their hosts and how some soil microbial components could regulate plant species coexistence and change relationships between plants. This review will be focussed on several well documented biological processes regulating plant-plant communications such as exotic plant species invasions, negative root-root communication (allelopathy) and parasitic plant / host plant interactions and how some soil microbial components can interfere with signal traffic between roots. The reported data show that the overall effect of one plant to another results from multiple interacting mechanisms where soil microbiota can be considered as a key component.

/ Le mémoire présente les travaux effectués depuis 1999 au Cemagref de Clermont-Ferrand (jusqu'en 2004) puis au Cemagref d'Aix-en-Provence concernant l'étude des boisements spontanés. Trois thématiques sont abordées. La première traite de l'étude de la dynamique ligneuse après abandon cultural ou pastoral. Après l'analyse des différents processus de l'afforestation spontanée, un simulateur a été produit permettant de modéliser la dynamique de colonisation par le pin sylvestre et mettant en exergue le rôle des fenêtres de régénération. La deuxième thématique aborde les conséquences de la mise en place des boisements spontanés sur la végétation et les propriétés des sols. Les travaux ont souligné en particulier le rôle des héritages liés aux pratiques culturales anciennes sur les compositions de flore et les caractéristiques des sols. Enfin la troisième thématique concerne la gestion des boisements spontanés notamment pour les pinèdes à pin d'Alep en région méditerranéenne. Les travaux font appel à l'ingénierie écologique et portent sur le pilotage des dynamiques naturelles de succession et l'obtention de peuplements mélangés pin/chêne.

Many Acacia species are known to improve soil fertility and yields of associated crops. Their capacity to form symbiotic associations with soil bacteria called Rhizobium and mycorrhizal fungi improves growth and mineral nutrition. Associated crops can take benefits of this by acquiring some N and organic matter (mainly through litter). Acacia species are therefore very important in arid and semi arid zones, where land degradation and deforestation induce soil fertility decline. Acacia Senegal is a species of major importance because it produces gum arable. This gum has very high economic value and it is an important source of cash income for farmers. Growth and vigour of the trees can be improved by inoculation by specific Rhizobium strains. This inoculation also has a positive effect on the production of gum Arabic. This study, conducted using soils from Senegal, Burkina Faso and Niger assesses the changes caused by the inoculation by Sinorhizob^um strains on bacterial and fungal communities from different periods : rainy and dry (gum production) seasons. Bacterial and fungal diversity are assessed by DGGE and Shannon indexes based statistical analysis. Results show different effects on microbial diversity, depending on countries. In Senegal, bacterial diversity is affected by inoculation, and bacterial and fungal diversities are increased in dry season. Bacterial diversity is increased in dry season in Niger as well, but there is no significant effect of both factors in Burkina Faso. More studies will be conducted by PCR-DGGE to target specific communities, which are involved in nitrogen cycle.

The hypothesis of the present study was that bacterial communities would differentiate under Eucalyptus camaldulensis and that an enhancement of arbuscular mycorrhizal (AM) density would minimize this exotic plant species effect. Treatments consisted of control plants, preplanting fertilizer application and AM inoculation. After 4 months of culture in autoclaved soil, E. camaldulensis seedlings were either harvested for growth measurement or transferred into containers filled with the same soil but not sterilized. Other containers were kept without E. camaldulensis seedlings. After 12 months, effects of fertilizer amendment and AM inoculation were measured on the growth of Eucalyptus seedlings and on soil microbial communities. The results clearly show that this plant species significantly modified the soil bacterial community. Both community structure (assessed by denaturing gradient gel electrophoresis profiles) and function (assessed by substrate-induced respiration responses including soil catabolic evenness) were significantly affected. Such changes in the bacterial structure and function were accompanied by disturbances in the composition of the herbaceous plant species layer. These results highlight the role of AM symbiosis in the processes involved in soil bio-functioning and plant coexistence and in afforestation programmes with exotic tree species that target preservation of native plant diversity.

En Nouvelle-Calédonie, les espèces végétales envahissantes constituent un problème préoccupant sur les plans agricole, environnemental et socio-économique. Elles sont essentiellement localisées dans les zones d'élevage allaitant qui occupent 11% du territoire. L'écologie systèmique, la phytosociologie et l'écologie du paysage sont mobilisées pour mettre en évidence les effets du milieu et des pratiques de gestion sur l'évolution de la flore des pâturages. Plus de 30 espèces envahissantes majeures ont été inventoriées, beaucoup d'entre elles sont présentes sur les îles du Pacifique et en Australie. Des cartes de leur répartition en Nouvelle-Calédonie ont été dressées. Les dynamiques d'évolution et les relations entre les espèces invasives, la végétation pastorale, le milieu et les pratiques de gestion ont été établies. Les stratégies de reproduction et de propagation ont été étudiées sur 2 espèces modèles. Une étude diachronique de la dynamique d'envahissement a été reconstituée à l'échelle du paysage. (Texte intégral)

La période de décembre 1992 à mai 1993 a été consacrée à la mise en place du projet. Avant d'engager les mesures de réceptivité dans les zones de culture du palmier, la méthode expérimentale a été mise au point à Dijon sur des échantillons venant de Côte d'Ivoire, du Cameroun et de Malaisie. Des enquêtes ont également été réalisées en zone fusariée en Côte d'Ivoire pour identifier les sites caractéristiques où l'incidence de la fusariose est suspectée d'être associée avec un facteur de l'environnement. Les activités en cours et les premiers résultats sont donnés sur : la réceptivité et les analyses de la microflore tellurique (INRA, Dijon); l'analyse minérale des sols (Universisade de la Laguna, Espagne); les enquêtes de terrain (IDEFOR/DPO, Côte d'Ivoire)