Agroforesterie et services écosystémiques en zone tropicale

Respectueux de l’environnement et garantissant une sécurité alimentaire soutenue par la diversification des productions et des revenus qu’ils procurent, les systèmes agroforestiers apparaissent comme un modèle prometteur d’agriculture durable dans les pays du Sud les plus vulnérables aux changements globaux. Cependant, ces systèmes agroforestiers ne peuvent être optimisés qu’à condition de mieux comprendre et de mieux maîtriser les facteurs de leurs productions. L’ouvrage présente un ensemble de connaissances récentes sur les mécanismes biophysiques et socio-économiques qui sous-tendent le fonctionnement et la dynamique des systèmes agroforestiers. Il concerne, d’une part les systèmes agroforestiers à base de cultures pérennes, telles que cacaoyers et caféiers, de régions tropicales humides en Amérique du Sud, en Afrique de l’Est et du Centre, d’autre part les parcs arborés et arbustifs à base de cultures vivrières, principalement de céréales, de la région semi-aride subsaharienne d’Afrique de l’Ouest. Il synthétise les dernières avancées acquises grâce à plusieurs projets associant le Cirad, l’IRD et leurs partenaires du Sud qui ont été conduits entre 2012 et 2016 dans ces régions. L’ensemble de ces projets s’articulent autour des dynamiques des systèmes agroforestiers et des compromis entre les services de production et les autres services socio-écosystémiques que ces systèmes fournissent

Energy transfer in polymers submitted to ionizing radiation: A review

International audienceAs a result of the energy deposition of ionizing radiation in organic polymers and in organic compounds in general, excited and ionized species are formed. The latter can readily react with emitted electrons to form excited species that will eventually lead to macromolecular defects and gas emission - their counterpart. Charges from ionized species and excitations can also be transferred, and trapped, far from their creation sites before leading to defects creation. In dense materials submitted to irradiation, excitations, charge transfer or mass transport from one molecule to the other has been proven to happen since the early 1930's in organic molecules mixtures and the 1950's in polymers. Radical stemming from the evolution of the excited molecules, which results either from direct energy deposition by the radiations or from the electron-hole recombination, can also migrate before being trapped or reacting, on a site far from its creation site. Radical, excitation, electron and hole transfers are gathered in the generic term of energy transfer. In this review is presented an overview on the research performed in this field. We evaluate the influence of different parameters that can alter the efficiency of energy transfer: these can be related to the polymer composition (chemical structure of the molecules composing the monomers or the additives inserted in the bulk) or to the irradiation characteristics (radiation type among ionizing radiations, dose and temperature for example). To get rid of the complexity brought by the polymer structure and the existence of different levels of organization, polymers are sometimes modelled by molecules, either pure or as mixtures. To take this into account, some studies on energy transfer in molecule mixtures are also presented

Kinetic Monte Carlo simulation of heterogeneous and homogeneous radio-oxidation of a polymer

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Chemical modifications induced by ionizing radiations on polymers the specificity of Swift Heavy Ions (SHI)

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Genetic diversity of Cameroon native goat populations revealed by caprine microsatellites

A total of seventeen caprine microsatellite markers were used on 169 goats to investigate genetic diversity of eight Cameroon native goats and to assess genetic differentiation with the east African small goat. All microsatellites showed a high polymorphic content (PIC) of more than 0.5 in almost all ecotypes. Thus demonstrating that these microsatellite markers were useful for within and between ecotypes variability appraisal of domestic goat. Expected heterozygosity of all ecotypes was above 0.5, varying from 0.2 to 0.7. Only goats from Rain forest-east ecotype deviated from Hardy-Weinberg Equilibrium test (P>0.001). Although geographic distribution was a good indication of differentiation there appeared a tendency of genetic exchange between various ecotypes in Cameroon native goats.Key words : Characterization, biodiversity, goat, ecotypes, selectio

Intermediate LET-like effect in distal part of proton Bragg peak revealed by track-ends imaging during super-Fricke radiolysis

Abstract Upstream of the efficiency of proton or carbon ion beams in cancer therapy, and to optimize hadrontherapy results, we analysed the chemistry of Fricke solutions in track-end of 64-MeV protons and 1.14-GeV carbon ions. An original optical setup is designed to determine the primary track-segment yields along the last millimetres of the ion track with a sub-millimetre resolution. The Fe3+-yield falls in the Bragg peak to (4.9 ± 0.4) × 10–7 mol/J and 1.9 × 10–7 mol/J, under protons and carbon ions respectively. Beyond the Bragg peak, a yield recovery is observed over 1 mm for proton beams. It is attributed to the intermediate-LET of protons in this region where their energy decreases and energy distribution becomes broader, in relation with the longitudinal straggling of the beam. Consequently to this LET decrease in the distal part of the Bragg peak, Fe3+-yield increases. For the first time, this signature is highlighted at the chemical level under proton irradiation. Nevertheless, this phenomenon is not identified for carbon ion beams since their straggling is lower. It would need a greater spatial resolution to be observed

Cameroon native goat populations’ genetic diversity and maternal origin assessed by D-loop mtDNA polymorphisms

Our study aimed to estimate genetic diversity and maternal origin of Cameroon native goat populations. Blood samples were randomly collected on 50 native goats belonging to 8 country agro ecological zones representing indigenous sub populations. They are morphologically known in 3 main groups, which are dwarf, medium and long legged. A selected goat mtDNA primer of expected size 778bp from literature was applied. A total of 28 caprine sequences from GenBank were used for edition, correction and alignment using Chromas Lite, Clustal X.2; ATGC PhySic Online software. Our findings showed that mtDNA D-loop sequence is highly variable in studied populations with moderately high frequency of mutations. Mitochondrial diversity of native goat populations was high (Hd = 69, with haplotype diversity = 0.9945) indicating a rich genetic diversity with 5 clades. The Cameroon goat populations belong to Haplogroup A, the most abundant in the world. Based on the previous migratory scenarios, the Cameroon native goats may have various maternal origins, Indian, Middle East and south Mediterranean regions. The results are useful for conservation and subsequent investigations may be undertaken to broaden genetic diversity particularly for production purpose.Key words: Diversity, mtDNA, D-loop sequence, goat populations, Cameroo

Hydration effect on ion exchange resin irradiated by swift heavy ions and gamma rays

International audienceGamma radiolysis of ion exchange resins (IER) is widely studied since the sixties, as a function of different parameters (resin type, dose, atmosphere, water content …). However, to our knowledge, there are very few data concerning hydrogen emission from anionic and cationic resins irradiated at high Linear Energy Transfers (LET). In the present work, we focus on the influence of hydration on hydrogen emission, in anionic and cationic resins irradiated under inert atmosphere using Swift Heavy Ions (SHI) and gamma irradiations. The radiation chemical yield of molecular hydrogen is nonlinear with water content for both resins. The molecular hydrogen production depends first on the water form in IER (free or linked) and second on the solubility of degradation products. Three steps have been observed: at lower water content where G(H2) is stable, at 50%, G(H2) increases due to reactions between water radiolytic species and the resin functional groups and at high water content, G(H2) decreases probably due to its accumulation in water and its consumption by hydroxyl radicals in the supernatant

Energy migration effect on the formation mechanism of different unsaturations in ethylene/styrene random copolymers

International audienceTo evaluate the influence of specific parameters, i.e. energy sink concentration and excitons and/or radical migration, on the mechanisms underlying the formation of double bonds in aliphatic polymers, materials with energy sinks in the chain were synthesized. By following the radiation-induced modifications in ethylene/styrene random copolymers, as a function of the styrene content and of the irradiation temperature, we were able to understand the formation mechanisms of trans-vinylenes, trans-trans-dienes, allyl radicals and vinyls. The irradiation temperature allows the discrimination between energy transfers (at 11 K and at room temperature, RT) and of radical migration (at RT). Irradiations were performed using swift heavy ions, and we could show that track overlapping has also an influence on the studied chemical group concentrations. For instance, trans-vinylenes are influenced by excitation transfer and radical migration: their formation decreases in presence of styrene aromatic rings, whatever the dose range and the irradiation temperature. On the opposite, vinyls are formed only at high ionizing density and are not influenced by excitation transfer; however, their concentration is influenced by radical migration