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This study explores how chemical and microbial properties of litters can be affected by coastal environments across the Mediterranean basin. A litterbag experiment includingPinus halepensisMill. andPistacia lentiscusL., collected from both inland and coastal areas, was set up in France, Greece and Algeria. Control litterbags were left in their sampling sites and a transfer of litterbags from inland to coastal areas was performed to test whether the effect of the specific constraints of coastal environments varies according to the country and the litter type. After 10 months, litter chemical composition (CP/MAS(13)C-NMR) and microbial activities (cellulase activity, basal respiration, catabolic diversity using Biolog) and community structure (TRFLP) were analysed. Coastal conditions led to various responses: (i) litter aromaticity differed in the coastal zones depending on the country (high in the Greek coastal area, low in the Algerian coastal zone), (ii) fewer functionally diversified microbial communities were found in the Greek coastal area compared to the French and Algerian coasts, (iii) genetic diversity and richness were strongly impacted after transfer to the coastal zone whatever the country. The type of litter shaped microbial communities: (i) at a local scale (i.e., in either coastal or inland areas) catabolic profiles and cellulase activities varied with the plant species, (ii) at a regional scale, the effect of coastal conditions differed with the plant species (basal respiration, Shannon-Weaver index, catabolic diversity H ', cellulases and catabolic profiles). Thus, litter microbial properties differed in coastal environments across the Mediterranean basin and plant litter type plays a major role in microbial properties at a large spatial scale. Highlights The environmental drivers of litter microbial sensitivity to water potential stress were investigated Litterbag transfers from inland to coastal areas were performed in the Mediterranean. Soil and land system units conform to long-tail or heavy tail distributions. Microbial diversity of inland litters decreased when exposed to coastal conditions Litter plant species shape microbial functioning even at wide spatial scales. Coastal areas and plant litter drive microbial responses to water potential stress.

The extent to which nanoparticles may impact the environment is largely dependent on their mobility in soils and in surface and groundwater systems. Size and aggregation/dispersion state are obvious parameters, whose determination (and prediction) requires a detailed knowledge of the surface chemistry of the nanophases and their reactivity with a variety of organic and inorganic nutrients and pollutants, taking into account possible competition between ligands. Hydrophobicity is another important parameter to take into consideration. The hydrophobicity can be either intrinsic (e.g. fullerene) or acquired (intentional coating during manufacturing or reaction with natural organics), and this hydrophobic quality may evolve during transport in the environment. Here we examine the mechanisms by which even minor changes in the physico-chemical conditions may results in drastic modifications of the ability of nanoparticles to be transported in environmental systems. The present work will focus on commercially available products, viz. C60, TiO2 and CeO2 based nanomaterials, as well as naturally occurring nanostructured alumino-silicates. The transformations at the surface of this nanomaterials and the structure and mobility of the resulting phases have been examined by several analytical tools (TEM, X-ray absorption and scattering, NMR...) so as to obtain an observation scale spanning over at least three orders of magnitude. The results underline the difficulty to obtain a global view of the phenomena due to competing mechanisms.

In a Mediterranean climate, water stress is one of the principal constraints on proper forest ecosystem functioning. Drought influences rates of organic matter degradation by affecting microbial growth and enzyme activities. The objectives of this study were: (i) to evaluate the effect of repeated drying-rewetting cycles on cellulase, alkaline phosphatase and fluorescein diacetate (FDA) hydrolase activities of three distinct Quercus ilex L. litter layers, and (ii) to investigate the effect of these cycles on gamma-irradiated litters in order to distinguish the abiotic influence on the fluctuations observed. Results, for all three layers, showed high correlations between litter water content and enzyme activities. Under mesocosm conditions, and using non-sterilized litter samples, cellulase, alkaline phosphatase, and FDA activities significantly decreased or increased during drying or rewetting cycles respectively. Significant differences were also found when evaluating the effect of litter depth on enzyme activities, the intermediate depth (OLv layer) generally being the most active. For gamma-sterilized samples, FDA activity still fluctuated with drying-rewetting cycles. Assays showed that pre-humidification of gamma-irradiated litter increased FDA activity two-fold in the first 30 min. All these results have shown that following drying-rewetting cycles, some of the fluctuations occur independently of microbial growth, suggesting abiotic interactions, such as desorption, in combination with both solvatation status and conformational changes of enzymes.

Climate change marked by an increased frequency and duration of severe droughts favours the recurrence of wildfires. These repeated disturbances, considered as a deciding factor in the processes of ecosystem degradation, were little studied. Our general hypothesis is that the Mediterranean ecosystems are balanced with fire regime in a limit which depends on fire frequency. High frequencies would lead to an impoverishment of the environment, an erosion of biodiversity and a decrease of its resistance to droughts. To test this hypothesis, we selected in the Maure massif (Var - south-eastern France) 17 plots characterized by different fire regimes(variable in number of fires, at time since the last fire and in interval of time between fires). In the laboratory, these soils were subjected either to only one, or to 4 successive water stresses to assess the resistance of microbial diversity, studied by the technique of micropatches Biolog ®. The quality of the organic matter of 17 samples of soils was studied by MNR of C13. Our results show that 4 fires in 40 years, compared with unburnt control soils, decrease soil organic matter quantity by 42 %, while increasing by 70 % its degree of aromaticity. The modifications of the quality of the organic matter are correlated to a decrease of microbial diversity (r 0,86, p < 0,001). Soils with the highest level of OM aromaticity (high fire frequency) also possess the strongest resistance of microbial diversity for many water stresses. NIRS analyses were used to build predictive PLS models for microbial diversity and its resistance to water stress which are controlled by fire frequency. This frequency was also modelled by NIRS. This work suggests that microbial diversity and its stability are strongly controlled by organic matter quality, itself strongly modified beyond 3 successive fires., Les changements climatiques marqués par une augmentation de la fréquence et de la durée des grandes sècheresses favorisent la récurrence des incendies. Ces perturbations répétitives, pourtant considérées comme décisives dans les processus de dégradation des écosystèmes, ont été très peu étudiées. Notre hypothèse générale est que les écosystèmes méditerranéens sont en équilibre avec le feu dans une limite qui dépend de la fréquence des incendies. Une trop grande fréquence conduirait à un appauvrissement du milieu, une érosion de la biodiversité et une diminution de leur résistance aux sécheresses. Pour tester cette hypothèse, nous avons sélectionné dans le massif des Maures (Var) 17 parcelles caractérisées par une histoire d'incendies différente (variable en nombre de feux, en temps depuis le dernier feu et en intervalle de temps entre les feux). Au laboratoire, ces sols ont été soumis soit à un seul, soit à un nombre important de stress hydriques successifs (4) afin d'évaluer la résistance de la diversité microbienne étudiée par la technique des microplaques Biolog®. La qualité de la matière organique des 17 échantillons de sols a été étudiée par RMN du solide du 13C. Nos résultats montrent que 4 incendies en 40 ans, comparativement aux sols non incendiés, diminuent la quantité de matière organique des sols de 42%, tout en augmentant son degré d'aromaticité de 70%. Les modifications de la qualité de la matière organique sont corrélées avec une diminution de la diversité microbienne (r=-0,86, p

Organic matter mineralization of forest litter is catalysed by the action of different extracellular enzymes produced by microorganisms. Coupling enzyme activities with data on the general macromolecular structure of organic matter, provided by cross-polarization magic angle spinning C-13 nuclear magnetic resonance (C-13 CPMAS NMR), allows researchers new insights into organic matter degradation processes. In this paper, the effect of the temperature of incubation on the degradation processes was evaluated in three distinct layers (OhLn, OhLv and OhLf) of an evergreen oak litter (Quercus ilex L.), located in the Mediterranean area of south-eastern France. We studied degradation phenomena by a combination of C-13 CPMAS NMR and microbiological analysis. In order to determine the microbial activity of litter layers, three enzyme activities (laccase, cellulase and butyrate esterase) were measured in a 6-month mesocosm study. Results showed an increase in the alkyl C to O-alkyl-C ratio and an increase of the phenolic C and carboxyl C regions, indicating a preferential degradation of polysaccharides. The aromaticity also increased with litter depth and degradation, and humification processes were more elevated at 30 degrees C. ANOVA showed significant effects (P < 0.001) of increased temperature, depth and time of degradation on microbiological variables. Further information is needed about the variations in temperature and temperature-litter response and soil functions to link fundamental understanding of carbon stabilization, climate change and global C cycling.

We introduce an analytical method that combines in one pot the advantages of column chromatography separation and NMR structural analysis. The separation of the NMR spectra of the components of a mixture can be achieved according to their apparent diffusion rates [James, T. L. and McDonald, G. G. (1973) J. Magn. Reson. 58, 58–61]. We show that the separation of the spectral components, corresponding to single molecular species, can be enhanced by order of magnitudes upon addition of a typical stationary phase used in HPLC. The solid phase imbibed by the mixture for analysis is an heterogeneous ensemble, so that solidstate NMR methods (high-resolution magic angle spinning) are necessary to recover high-resolution spectra. We demonstrate applications of this combination of high-resolution magic angle spinning and NMR diffusometry on test mixtures for direct (silica gel) and inverse (C18) columns. However, many common chromatographic supports available for HPLC should be readily adaptable for use with this technique

In this study, the preparation of polybutadiene/polysilsesquioxane nanocomposites (NCs) having tunable thermomechanical and dielectric properties is reported. This was achieved by using different amounts of a filler consisting of a silsesquioxane with a defined ladder-like molecular structure (LPMASQ) bearing reactive methacrylate functionalities. In detail, solid-state nuclear magnetic resonance (NMR) investigation revealed that an increasing amount of filler leads to a progressive homopolymerization of LPMASQ units resulting in the generation of domains in the composites, which induce a kind of polymer chain confinement in proximity of the hybrid interface. The evolution of the molecular organization of the inorganic nanobuilding blocks as a function of their concentration has been highlighted also by small-angle X-ray scattering (SAXS) experiments. The gradual assembly of LPMASQ units gives rise to peculiar dielectric properties along with enhanced thermal and mechanical stability of the final NCs, thus supplying suitable materials for applications in high performance dielectrics. Furthermore, these outcomes support the idea that a careful control of the molecular architecture and organization of the silsesquioxanes in a polymer matrix allows to simultaneously modulate two or more distinct functional features of polymer NCs

International audience; We compared a calcareous soil developed from a lignite vein (natural outcrop) and a control adjacent soil without lignite in order to assess the impact of lignite on pedogenetic processes and microbial functions in Mediterranean soils. Lignite was evidenced by the C-14 analysis, delta C-13 signature and SS C-13 CPMAS NMR spectroscopy in the various soil horizons. Physico-chemical (particle size analysis, pH, total organic carbon, carbonate content, nitrogen, sulfur, cation exchange capacity, crystalline and amorphous Fe and Al, mineralogy, bulk density) and biological (enzyme activities: beta-glucosidase, arylsulfatase, acid phosphatase, arylamidase, fluorescein dilaurate hydrolase and fluorescein diacetate hydrolase; basal respiration and Biolog (R) catabolic profile) properties were also analyzed in all horizons. We showed that the naturally-occurring lignite modified soil organic matter quality and mineralogy and improved some soil properties such as clay content, C-org, CEC and porosity. On the contrary, lignite had a higher C/N and higher recalcitrant C content compared to recent soil organic matter, which resulted in a decrease in the expression of microbial soil functions involved in the turn-over of the main bio-elements C, N, P and S due to lignite acting as a diluting factor (i.e. inert regarding microbial activities). The information derived from this study offers insight on the long term fate of lignite in soil, especially relevant if lignite is aimed at being used as amendment. (C) 2014 Elsevier B.V. All rights reserved.

A 2-oxoglutaric acid (2-OG) probe bearing a methylene group introduced at the C4 position and a vinyl group to replace the carbonyl group at the C2 position elicited characteristic affinity for NtcA, the 2-OG receptor, while maintaining the signaling function of the parent natural metabolite 2-OG. This discovery opens new perspectives in the design, synthesis, and implementation of specific 2-OG analogues as molecular probes for investigating the complex 2-OG signaling pathways.

2-Difluoromethylene-4-methylenepentanoic acid (DFMPA), a seemingly deviated analog of 2-oxoglutaric acid (2-OG), could surprisingly mimic its signaling function in cyanobacteria. Computer modeling revealed the favorable binding of DFMPA toward the 2-OG receptor, NtcA, via mutual conformational changes, suggesting that structural alteration of 2-OG is tolerated for it to exercise its signaling role. This extremely useful finding could be exploited for the design of affinity probes with which to study new 2-OG receptors in related signaling pathways.