Matières organiques des sols forestiers et changements climatique et atmosphérique

La matière organique des sols (MOS) constitue le plus grand réservoir de carbone des écosystèmes terrestres et elle est une composante majeure de la fertilité. Son évolution sous l’impact des changements atmosphériques et climatiques est porteuse d’enjeux essentiels à moyen et long terme, à l’échelle globale comme à l’échelle locale. Nous présentons ici une synthèse des connaissances sur cette évolution des MOS dans les forêts. Les principales méthodes d’étude sont les comparaisons d’inventaires pédologiques, l’interprétation de corrélations spatiales avec le climat en tendances temporelles, les suivis expérimentaux en laboratoire ou en forêt des flux d’entrée et de sortie du carbone dans le sol, et toute une gamme de modèles visant à assembler ces connaissances et à prédire l’évolution des MOS. Les résultats confirment qu’il faut s’attendre à plus ou moins long terme à un appauvrissement en MOS, dû au réchauffement, dans les forêts boréales et tempérées. Cependant, les dépôts azotés ont un effet positif sur le stockage de matière organique dans le sol, qui n’est pas encore intégré dans les modèles terrestres à l’échelle globale. Enfin, les expérimentations d’enrichissement de l’air en CO2 en forêt n’ont pour l’instant pas d’effet sur le stockage de carbone dans le sol, mais on peut s’attendre à des effets positifs à plus long terme. Sur le plan qualitatif, les dépôts azotés et le réchauffement contribuent à réduire la limitation de la fertilité par l’azote, et il est prévisible que la limitation par le phosphore gagne en importance relative

Associations between lamb survival and prion protein genotype: analysis of data for ten sheep breeds in Great Britain

BACKGROUND: Selective breeding programmes, based on prion protein (PrP) genotype, have been introduced throughout the European Union to reduce the risk of sheep transmissible spongiform encephalopathies (TSEs). These programmes could have negative consequences on other important traits, such as fitness and production traits, if the PrP gene has pleiotropic effects or is in linkage disequilibrium with genes affecting these traits. This paper presents the results of an investigation into associations between lamb survival and PrP genotype in ten mainstream sheep breeds in Great Britain (GB). In addition, the reasons for lamb deaths were examined in order to identify any associations between these and PrP genotype. RESULTS: Survival times from birth to weaning were analysed for over 38000 lambs (2427 dead and 36096 live lambs) from 128 flocks using Cox proportional hazard models for each breed, including additive animal genetic effects. No significant associations between PrP genotype and lamb survival were identified, except in the Charollais breed for which there was a higher risk of mortality in lambs of the ARR/VRQ genotype compared with those of the ARR/ARR genotype. Significant effects of birth weight, litter size, sex, age of dam and year of birth on survival were also identified. For all breeds the reasons for death changed significantly with age; however, no significant associations between reason for death and PrP genotype were found for any of the breeds. CONCLUSION: This study found no evidence to suggest that a selective breeding programme based on PrP genotype will have a detrimental effect on lamb survival. The only significant effect of PrP genotype identified was likely to be of little consequence because an increased risk of mortality was associated with a genotype that is selected against in current breeding strategies

The strain-rate sensitivity of high-strength high-toughness steels.

The present study examines the strain-rate sensitivity of four high strength, high-toughness alloys at strain rates ranging from 0.0002 s-1 to 200 s-1: Aermet 100, a modified 4340, modified HP9-4-20, and a recently developed Eglin AFB steel alloy, ES-1c. A refined dynamic servohydraulic method was used to perform tensile tests over this entire range. Each of these alloys exhibit only modest strain-rate sensitivity. Specifically, the strain-rate sensitivity exponent m, is found to be in the range of 0.004-0.007 depending on the alloy. This corresponds to a {approx}10% increase in the yield strength over the 7-orders of magnitude change in strain-rate. Interestingly, while three of the alloys showed a concominant {approx}3-10% drop in their ductility with increasing strain-rate, the ES1-c alloy actually exhibited a 25% increase in ductility with increasing strain-rate. Fractography suggests the possibility that at higher strain-rates ES-1c evolves towards a more ductile dimple fracture mode associated with microvoid coalescence

Mobiliser et valoriser les données sur les sols forestiers. Compte rendu de l’atelier 4

Une meilleure connaissance des sols forestiers et l’amélioration des référentiels pour interpréter leur fonctionnement est une attente des forestiers comme des acteurs des politiques publiques. Lors de REGEFOR 2013, l’atelier “Mobiliser et valoriser les données sur les sols forestiers” a identifié une ressource importante et sous-exploitée de données au niveau des organismes de développement et des laboratoires de recherche. Des outils existent pour les rendre plus visibles et accessibles sur le réseau internet. Face à la dispersion et à la faible harmonisation des jeux de données, des chantiers importants sont à mettre en oeuvre pour favoriser leur exploitation (exemple : mise en base de données, production de métadonnées et de référentiels sémantiques communs, clarification des droits de propriété, protocoles d’échanges de données entre applications). Dans cette optique, l’atelier a aussi conduit à s’interroger sur les possibilités d’améliorer la coordination entre production et gestion de données, notamment en discutant les intérêts et limites d’une centralisation sous un même système d’information

Modeling soil organic carbon dynamics in temperate forests with Yasso07

In a context of global changes, modeling and predicting the dynamics of soil carbon stocks (CSs) in forest ecosystems are vital but challenging. Yasso07 is considered to be one of the most promising models for such a purpose. We examine the accuracy of its prediction of soil carbon dynamics over the whole French metropolitan territory at a decennial timescale. We used data from 101 sites in the RENECOFOR network, which encompasses most of the French temperate forests. These data include (i) the quantity of above-ground litterfall from 1994 to 2008, measured yearly, and (ii) the soil CSs measured twice at an interval of approximately 15 years (once in the early 1990s and around 2010). We used Yasso07 to simulate the annual changes in carbon stocks (ACCs; in tC ha−1 yr−1) for each site and then compared the estimates with actual recorded data. We carried out meta-analyses to reveal the variability in litter biochemistry in different tree organs for conifers and broadleaves. We also performed sensitivity analyses to explore Yasso07's sensitivity to annual litter inputs and model initialization settings. At the national level, the simulated ACCs (+0.00±0.07 tC ha−1 yr−1, mean ± SE) were of the same order of magnitude as the observed ones (+0.34±0.06 tC ha−1 yr−1). However, the correlation between predicted and measured ACCs remained weak (R2<0.1). There was significant overestimation for broadleaved stands and underestimation for coniferous sites. Sensitivity analyses showed that the final estimated CS was strongly affected by settings in the model initialization, including litter and soil carbon quantity and quality and also by simulation length. Carbon quality set with the partial steady-state assumption gave a better fit than the model with the complete steady-state assumption. With Yasso07 as the support model, we showed that there is currently a bottleneck in soil carbon modeling and prediction due to a lack of knowledge or data on soil carbon quality and fine-root quantity in the litter

Multivalent dendrimers presenting spatially controlled clusters of binding epitopes in thermoresponsive hyaluronan hydrogels

The controlled presentation of biofunctionality is of key importance for hydrogel applications in cell-based regenerative medicine. Here, a versatile approach was demonstrated to present clustered binding epitopes in an injectable, thermoresponsive hydrogel. Well-defined multivalent dendrimers bearing four integrin binding sequences and an azido moiety were covalently grafted to propargylamine-derived hyaluronic acid (Hyal-pa) using copper-catalyzed alkyne-azide cycloaddition (CuAAC), and then combined with pN-modified hyaluronan (Hyal-pN). The dendrimers were prepared by synthesizing a bifunctional diethylenetriamine pentaacetic acid core with azido and NHBoc oligo(ethylene glycol) aminoethyl branches, then further conjugated with solid-phase synthesized RGDS and DGRS peptides. Azido terminated pN was synthesized by reversible addition-fragmentation chain transfer polymerization and reacted to Hyal-pa via CuAAC. Nuclear magnetic resonance (NMR), high performance liquid chromatography, size exclusion chromatography and mass spectroscopy proved that the dendrimers had well-defined size and were disubstituted. NMR and atomic absorption analysis confirmed the hyaluronan was affixed with dendrimers or pN. Rheological measurements demonstrated that dendrimers do not influence the elastic or viscous moduli of thermoresponsive hyaluronan compositions at a relevant biological concentration. Finally, human mesenchymal stromal cells were encapsulated in the biomaterial and cultured for 21days, demonstrating the faculty of this dendrimer-modified hydrogel as a molecular toolbox for tailoring the biofunctionality of thermoresponsive hyaluronan carriers for biomedical applications.The authors acknowledge the financial support from the AO Foundation (grant number C10-60S) and the consortium grant from AO Exploratory Research Board and Spanish Ministry of Economy and Competitiveness (SAF2011-30508-C02-01) and the Generalitat de Catalunya (2009SGR 1024). CIBER-BBN (DP) and La Caixa social program (PF) are also acknowledged for their financial support. The authors are grateful to Mr. Markus Glarner (AO Research Institute) and Mr. Matti Kesti (ETH Zurich) for their help with the polymer synthesis and rheology, respectively. The authors wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome.Peer reviewe

For public (and recontextualized) sociology: The promises and perils of public engagement in an age of mediated communication

This article argues for the analysis of public engagement as an essentially mediated activity. Although recent studies note that academic knowledge is increasingly available for consumption by nonacademic audiences, they tell us little about how it gets recontextualized while passing through the hands of media professionals on its way toward such audiences. In Burawoy’s (2005) influential call for the rebirth of public sociology, as in the debates his work provoked, the media is treated solely as a means for the transportation of knowledge. But as this article demonstrates, the media does not simply transport knowledge; it also, and at the same time, translates that knowledge in various, rhetorically consequential ways. Focusing on the mediated trajectory of an attempt by a group of academics to connect with audiences beyond academia, their initial contribution is compared to its subsequent translation(s) across various British newspapers. A discursive analysis reveals the techniques via which a classic form of public sociology came to be recontextualized such that, remarkably, these authors were left appearing to voice nothing but their own petty prejudices. The article concludes by noting that where public engagement involves mediation, public sociology should pay more attention to the recontextualizing affordances of media discourse