Un exemple de roman géographique (et pédagogique) au xixe siècle : Les Enfants du capitaine Grant (Jules Verne, 1867‑68)

Les « Voyages extraordinaires » de Jules Verne (1828‑1905) sont des romans géographiques qui ont permis au xixe siècle de transmettre autrement le savoir géographique. La présentation et l’analyse de « Les Enfants du capitaine Grant » illustre notamment comment l’articulation du réel et de l’imaginaire géographique assure ainsi une dimension pédagogique à un récit pourtant fictif mais cautionné par certains géographes de l’époque considérée.The « Extraordinary Journeys » of Jules Verne (1828‑1905) are geographical novels that allowed for an alternative transmission of geographical knowledge during the 19th century. Through a presentation and analysis of « In Search of the Castaways » (« The Children of Captain Grant »), the present study shows how linking reality and the geographical imaginary provides an educational dimension to an fictional account, yet supported by some geographers of the time

Modélisation de l'ancrage racinaire des arbres forestiers

Les récentes tempêtes en Europe ont occasionné de lourds dégâts et des pertes économiques dramatiques dans les forêts. Les questions relatives à l'ancrage de l'arbre ont émergé. Cependant, les moyens actuels pour répondre à ces attentes sont limités, l'accès par l'expérience aux mécanismes souterrains étant limité. L'analyse des phénomènes du déracinement a donc été abordée par la modélisation mécanique. Plusieurs phases ont été nécessaires pour atteindre cet objectif. Dans un premier temps, la mesure des systèmes racinaires a permis d'acquérir des données concernant l'architecture des racines. Ensuite, les formes racinaires mesurées étant très variables et complexes, des modèles de la structure racinaire ont été développés. Ceux-ci permettent de construire des géométries idéalisées dont la complexité et la variabilité sont maîtrisées. La troisième phase de ce travail s'est attachée à développer des outils informatiques permettant l'analyse par éléments finis d'une structure racinaire quelconque, issue de mesures où bien de simulations. Enfin, la dernière étape a été consacrée à la simulation de scenarii d'enracinement très variés afin de comprendre les mécanismes et d'identifier les facteurs déterminants. Finalement, l'utilisation des méthodes numériques a permis d'apporter des éléments nouveaux pour la compréhension du phénomène de déracinement. Le sol, et particulièrement le frottement interne, influe sur la cinématique du basculement et sur la forme de la motte racinaire soulevée. En ce qui concerne les racines, la profondeur et le diamètre des racines latérales sont apparus comme essentiels dans la résistance et les mécanismes de déracinement.The recent storms in Europe have caused much damage and huge economic losses in forests. Questions related to the anchorage of individual trees have emerged. However, the current investigation techniques to answer them are limited, experimental methods to investigate underground mechanisms being limited. Analysis of uprooting mechanism was conducted using mechanical modelling. This objective was reached following four steps. Firstly, root system measurements were carried out in order to collect data concerning root architecture. Then, as root structures discovered were much variable and complex, models of root systems were developed. They allowed to build idealised geometries whose complexity and variability is controlled. The third stage of this work concentrates on the design of computing tools which enable finite element analysis of any root structure, from either measured or simulated root systems. The final part focused on the simulation of various rooting scenario in order to understand the mechanisms and identify the determinant factors. The use of numerical methods brought new elements for the understanding uprooting phenomenon. The soil, notably its internal friction, modifies the toppling movement and the shape of the root/soil ball. As for the influence of roots, the depth and diameter of laterals showed to be essential factors of the resistance to uprooting

L’imaginaire géographique au cœur d’un Voyage Extraordinaire

Jules Verne est l’auteur des Voyages extraordinaires, 62 romans où s’articule systématiquement le passage d’une géographie scientifique, campant le récit dans un réel confirmé, vers une géographie plus fictive. Appliquée au roman Le Superbe Orénoque (1898), l’analyse des sources et des figures de rhétorique utilisées par Jules Verne illustre comment fonctionne l’imaginaire géographique dans un roman « vernien ».Jules Verne is the author of a series of 62 novels known as The Extraordinary Voyages. These stories exemplify a shift from scientific geography, where action takes place in a confirmed reality, to a more fictitious geography. By analysing the inspirational sources and the rhetorical figures used by Jules Verne in his novel The Mighty Orinoco (1898), we show how the geographical imaginary works in a « vernian » novel

Light Sheet Tomography (LST) for <i>in situ</i> imaging of plant roots

The production of crops capable of efficient nutrient use is essential for addressing the problem of global food security. The ability of a plant's root system to interact with the soil micro-environment determines how effectively it can extract water and nutrients. In order to assess this ability and develop the fast and cost effective phenotyping techniques which are needed to establish efficient root systems, in situ imaging in soil is required. To date this has not been possible due to the high density of scatterers and absorbers in soil or because other growth substrates do not sufficiently model the heterogeneity of a soil's microenvironment. We present here a new form of light sheet imaging with novel transparent soil containing refractive index matched particles. This imaging method does not rely on fluorescence, but relies solely on scattering from root material. We term this form of imaging Light Sheet Tomography (LST). We have tested LST on a range of materials and plant roots in transparent soil and gel. Due to the low density of root structures, i.e. relatively large spaces between adjacent roots, long-term monitoring of lettuce root development in situ with subsequent quantitative analysis was achieved

Smoothed particle hydrodynamics for root growth mechanics

International audienceA major challenge of plant developmental biology is to understand how cells grow during the formation of an organ. To date, it has proved dicult to develop computational models of entire organs at cellular resolution and, as a result, the testing of hypotheses on the biophysics of self-organisation is currently limited. Here, we formulate a model for plant tissue growth in an SPH framework. The framework identies the SPH particle with individual cells in a tissue , but the tissue growth is performed at the macroscopic level using SPH approximations. Plant tissue is represented as an anisotropic poro-elastic material where turgor pressure deforms the cell walls and biosynthesis and cell division control the density of the tissue. The performance of the model is evaluated through a series of tests and benchmarks. Results demonstrate good stability and convergence of simulations as well as readiness of the technique for more complex biological problems

Transparent soil for imaging the rhizosphere

Understanding of soil processes is essential for addressing the global issues of food security, disease transmission and climate change. However, techniques for observing soil biology are lacking. We present a heterogeneous, porous, transparent substrate for in situ 3D imaging of living plants and root-associated microorganisms using particles of the transparent polymer, Nafion, and a solution with matching optical properties. Minerals and fluorescent dyes were adsorbed onto the Nafion particles for nutrient supply and imaging of pore size and geometry. Plant growth in transparent soil was similar to that in soil. We imaged colonization of lettuce roots by the human bacterial pathogen Escherichia coli O157:H7 showing micro-colony development. Micro-colonies may contribute to bacterial survival in soil. Transparent soil has applications in root biology, crop genetics and soil microbiology

Framework for quantification of the dynamics of root colonization by pseudomonas fluorescens isolate SBW25

Colonization of the root surface, or rhizoplane, is one of the first steps for soil-borne bacteria to become established in the plant microbiome. However, the relative contributions of processes, such as bacterial attachment and proliferation is not well characterized, and this limits our ability to comprehend the complex dynamics of microbial communities in the rhizosphere. The work presented here addresses this knowledge gap. A model system was developed to acquire quantitative data on the colonization process of lettuce (Lactuca sativa L. cultivar. All Year Round) roots by Pseudomonas fluorescens isolate SBW25. A theoretical framework is proposed to calculate attachment rate and quantify the relative contribution of bacterial attachment to colonization. This allows the assessment of attachment rates on the root surface beyond the short time period during which it can be quantified experimentally. All techniques proposed are generic and similar analyses could be applied to study various combinations of plants and bacteria, or to assess competition between species. In the future this could allow for selection of microbial traits that improve early colonization and maintenance of targeted isolates in cropping systems, with potential applications for the development of biological fertilizers

Mobility and growth in confined spaces are important mechanisms for the establishment of Bacillus subtilis in the rhizosphere

The rhizosphere hosts complex and abundant microbiomes whose structure and composition are now well described by metagenomic studies. However, the dynamic mechanisms that enable micro-organisms to establish along a growing plant root are poorly characterized. Here, we studied how a motile bacterium utilizes the microhabitats created by soil pore space to establish in the proximity of plant roots. We have established a model system consisting of Bacillus subtilis and lettuce seedlings co-inoculated in transparent soil microcosms. We carried out live imaging experiments and developed image analysis pipelines to quantify the abundance of the bacterium as a function of time and position in the pore space. Results showed that the establishment of the bacterium in the rhizosphere follows a precise sequence of events where small islands of mobile bacteria were first seen forming near the root tip within the first 12–24 h of inoculation. Biofilm was then seen forming on the root epidermis at distances of about 700–1000 µm from the tip. Bacteria accumulated predominantly in confined pore spaces within 200 µm from the root or the surface of a particle. Using probabilistic models, we could map the complete sequence of events and propose a conceptual model of bacterial establishment in the pore space. This study therefore advances our understanding of the respective role of growth and mobility in the efficient colonization of bacteria in the rhizosphere

Poly(fluoroacrylate)s with tunable surface hydrophobicity via radical copolymerization of 2,2,2-trifluoroethyl α-fluoroacrylate and 2-(trifluoromethyl)acrylic acid

International audienceThe synthesis of poly(fluoroacrylate)s with tunable wettability and improved adhesion for potential applicationas functional coatings was achieved via radical copolymerization of 2,2,2-trifluoroethylα-fluoroacrylate (FATRIFE) with 2-(trifluoromethyl)acrylic acid (MAF), an adhesion-promoting monomer.These copolymerizations, initiated by tert-butyl peroxypivalate at varying comonomer feed ([FATRIFE]0/[MAF]0) ratios led to a series of poly(FATRIFE-co-MAF) copolymers with different molar compositions infair to good conversions (32–87%) depending on the MAF feed content. The microstructures of the synthesizedpoly(FATRIFE-co-MAF) copolymers were determined by 19F NMR spectroscopy. Even at MAFfeed contents higher than 50%, MAF incorporation into the copolymers was lower than 50%, since MAFdoes not undergo any homopolymerization under radical polymerization conditions. The reactivity ratiosof the (FATRIFE; MAF) monomer pair were also determined (rFATRIFE = 1.65 ± 0.07 and rMAF = 0 at 56 °C)evidencing the formation of statistical copolymers. Initiation involving a highly branched perfluorinatedradical that released a •CF3 radical enabled the demonstration of the regioselective attack of the latterradical onto the CH2 of FATRIFE. The resulting poly(FATRIFE-co-MAF) copolymers exhibited various glasstransition temperatures (Tgs) depending on their compositions. Tg values increased with increasing MAFcontents in the copolymer. In addition, their thermal stability (the temperature for 10% weight loss in air,Td10%) increased with increasing FATRIFE content in the copolymer and reached 348 °C (for that containing93 mol% FATRIFE). Finally, a high copolymer MAF content led to both a good adhesion onto metalsubstrates and to improved hydrophilicity, as revealed by the decrease of the water contact angle from107° (for a reference PFATRIFE homopolymer) to 81° (for a copolymer containing 42 mol% MAF)