Diversity and P-solubilizing ability of mycorrhizosphere bacteria associated with Pinus pinaster in the Landes forest ecosystem

Ectomycorrhizal fungi (ECM) and their associated mycorrhizosphere bacteria (MB) play a major role in phosphorous (P) nutrition of maritime pine, particularly in the Landes forest ecosystem considering the low bioavailability of P in its sandy-acidic soils. In order to characterize the MB associated to ECM, three collection campaigns of ECM root tips were performed from autumn 2005 to autumn 2006 throughout three forest stations. Five MB and nine ECM genera were identified overall through sequencing of 16S rDNA and mitochondrial large subunit rDNA fragment respectively. Dramatic seasonal changes were observed in the different MB-ECM associations especially in Burkholderia-Lactarius and Bacillus-Russula that were the most abundant ones. P-solubilizing ability of MB was shown to be taxon-dependent with a large majority of P-solubilizing isolates among Burkholderia, Pseudomonas and Paenibacillus contrary to Bacillus. Relationships between functional diversity of the MB-ECM associations and bioavailability of soil P remain to be investigated. (Résumé d'auteur)

Nodular diagnosis for ecological engineering of the symbiotic nitrogen fixation with legumes

As a major contributor to the reduced nitrogen pool in the biosphere, symbiotic nitrogen fixation by legumes plays a critical role in a sustainable production system. However this legume contribution varies with the physico-chemical and biological conditions of the nodulated-root rhizosphere. In order to assess the abiotic and biotic constrains that might limit this symbiosis at the agroecosystem level, a nodular diagnosis is proposed with common bean as a model grain-legume, and a major source of plant proteins for world human nutrition. The engineering of the legume symbiosis is addressed by participatory assessment of bean recombinant inbred lines contrasting for their efficiency in use of phosphorous for symbiotic nitrogen fixation. With this methodology, in field-sites chosen with farmers of an area of cereal-cropping in the Mediterranean basin, a large spatial and temporal variation in the legume nodulation was found. Soil P availability was a major limiting factor of the rhizobial symbiosis. In order to relate the field measurements with progress in functional genomics of the symbiosis, in situ RT-PCR on nodule sections has been implemented showing that the phytase gene is expressed in the cortex with significantly higher number of transcripts in P-efficient RILs. It is concluded that various tools and indicators are available for developing the ecological engineering of the rhizobial symbiosis, in particular for its beneficial contribution to the bio-geochemical cycle of N, and also P and C

Effects of eight neuropsychiatric copy number variants on human brain structure

Many copy number variants (CNVs) confer risk for the same range of neurodevelopmental symptoms and psychiatric conditions including autism and schizophrenia. Yet, to date neuroimaging studies have typically been carried out one mutation at a time, showing that CNVs have large effects on brain anatomy. Here, we aimed to characterize and quantify the distinct brain morphometry effects and latent dimensions across 8 neuropsychiatric CNVs. We analyzed T1-weighted MRI data from clinically and non-clinically ascertained CNV carriers (deletion/duplication) at the 1q21.1 (n = 39/28), 16p11.2 (n = 87/78), 22q11.2 (n = 75/30), and 15q11.2 (n = 72/76) loci as well as 1296 non-carriers (controls). Case-control contrasts of all examined genomic loci demonstrated effects on brain anatomy, with deletions and duplications showing mirror effects at the global and regional levels. Although CNVs mainly showed distinct brain patterns, principal component analysis (PCA) loaded subsets of CNVs on two latent brain dimensions, which explained 32 and 29% of the variance of the 8 Cohen’s d maps. The cingulate gyrus, insula, supplementary motor cortex, and cerebellum were identified by PCA and multi-view pattern learning as top regions contributing to latent dimension shared across subsets of CNVs. The large proportion of distinct CNV effects on brain morphology may explain the small neuroimaging effect sizes reported in polygenic psychiatric conditions. Nevertheless, latent gene brain morphology dimensions will help subgroup the rapidly expanding landscape of neuropsychiatric variants and dissect the heterogeneity of idiopathic conditions

Calcification des cellules corticales des racines en milieu calcaire

National audienc

Mise en évidence de la néogenèse de sables calcaires sous l'influence des racines : incidence sur la granulométrie du sol

National audienceA microstructural study of calcareous soil from marl weathering showed the presence of calcareous features developing along structural discontinuities. These corresponded with the traces of roots, composed of calcified cells of size ca 100 μm, still arranged in a tissue, but independent one from another. The tissues concerned were mostly the epidermis, the cortical parenchyma and the endodermis. The central cylinder was generally represented by a gap. Detailed granulometric analysis of the fine sand fraction (50-200 μm) showed a peak at about 80 μm. The observation of granulometric fractions both with binocular lens and by scanning electron microscopy allowed the distinction (by shape and colour) of cytomorphic sands from sands coming from the parent material and their quantification (by counting). The cytomorphic sands were sparitic calcite crystals. The calcification of root cells thus apparently gives rise to cytomorphic sands forming up to quarter of the mineral phase of the soil near the surface, a silt-sandy soil developing from a silt-clayey marl.L’étude microstructurale d’un sol calcaire issu de l’altération de marnes révèle la présence de nombreuses micro-structures calcaires se développant au niveau des discontinuités fissurales. Il s’agit de vestiges de racines de graminées, constitués de cellules calcifiées d’environ 100 μm de diamètre, indépendantes les unes des autres mais ayant conservé leur arrangement tissulaire. D’un autre côté, l’analyse granulométrique détaillée des sables fins (50-200 μm) met en évidence un pic aux alentours de 80 μm. L’observation des fractions granulométriques correspondantes, à la loupe binoculaire et au microscope à balayage électronique, nous permet de distinguer (par leur forme et leur couleur) les sables cytomorphes des sables hérités de la marne et de quantifier (par comptage) les proportions de chacune des deux formes. Il apparaît ainsi que la calcification des cellules des racines est à l’origine de sables (cytomorphes) qui constituent jusqu’au quart de la phase minérale du sol au voisinage de la surface

Techniques for studing the ionic environment at the soil/root interface

International audienc

Pédologie. Mise en évidence de la calcitisation des cellules corticales de racines de graminées en milieu carbonaté

National audienc

Activité racinaire et rhizostructures en milieu carbonaté

25 ref.National audienc