405 research outputs found
Postdispersal weed seed predation ranged between 19 to 84% per week following a species preference rank
Postdispersal weed seed predation ranged between 19 to 84% per week following a species preference ran
PrĂ©dire lâoccurrence des espĂšces adventices : quelles Ă©chelles de temps et dâespace ?
Comprendre la distribution spatiale des communautĂ©s vĂ©gĂ©tales et les processus Ă©cologiques sous-jacents constituent un enjeu majeur en particulier pour la gestion intĂ©grĂ©e de la flore adventice. Le projet europĂ©en PURE ("Pesticide Use-and-risk Reduction in European farming systems with Integrated Pest Management") vise Ă concevoir, Ă partir dâĂ©tudes empiriques identifiant les dĂ©terminants locaux et rĂ©gionaux de la distribution dâespĂšces nuisibles, des paysages qui leur soient dĂ©favorables. Les dĂ©terminants de la distribution des adventices sont gĂ©nĂ©ralement Ă©tudiĂ©s Ă lâĂ©chelle de la parcelle or, de rĂ©centes Ă©tudes suggĂšrent quâil est Ă©galement nĂ©cessaire de tenir compte du contexte paysager. Par ailleurs, les paysages agricoles constituent des systĂšmes dynamiques dans lesquels les cultures et les pratiques se succĂšdent. Nous faisons lâhypothĂšse que la flore adventice qui sâexprime dans une parcelle une annĂ©e donnĂ©e dĂ©pend Ă la fois des pratiques appliquĂ©es lâannĂ©e donnĂ©e mais Ă©galement les annĂ©es prĂ©cĂ©dentes et des pratiques sur les parcelles voisines. Notre Ă©tude vise ainsi Ă identifier quelles Ă©chelles de temps et dâespace sont les plus pertinentes pour prĂ©dire lâoccurrence des espĂšces adventices. La flore adventice a Ă©tĂ© Ă©chantillonnĂ©e dans 58 parcelles de la zone de FĂ©nay pendant 4 annĂ©es consĂ©cutives. Les pratiques de ces parcelles ont Ă©tĂ© recensĂ©es de 2004 Ă 2011 par enquĂȘtes auprĂšs des agriculteurs. Nous avons adoptĂ© une approche de sĂ©lection de modĂšles basĂ©e sur le critĂšre dâAIC, complĂ©tĂ©e par une validation croisĂ©e pour quantifier les capacitĂ©s prĂ©dictives du meilleur modĂšle. Les premiers rĂ©sultats montrent que lâintĂ©gration dâĂ©chelles de temps et dâespace larges amĂ©liore la description de la distribution des adventices
Origine et intĂ©rĂȘt Ă©cologique des sols limoneux des dĂ©pressions humides du massif dunaire dâHatainville (Manche)
Sur les cĂŽtes europĂ©ennes, les massifs dunaires sont caractĂ©risĂ©s par de nombreux habitats Ă forte valeur Ă©cologique quâexplique la prĂ©sence dâune nappe phrĂ©atique. Depuis une vingtaine dâannĂ©es, les plantes pionniĂšres et prairiales de ces habitats subissent une tendance trĂšs importante Ă la rĂ©gression. Le massif dunaire dâHatainville en est un parfait exemple. La protection des espĂšces herbacĂ©es rares passe par une meilleure connaissance des sols et de leur fonctionnement. Une Ă©tude pĂ©dologique a Ă©tĂ© menĂ©e sur les sols limoneux des dĂ©pressions humides du massif, sols dont la dĂ©couverte fut inattendue. Ces sols prĂ©sentent en effet la particularitĂ© de dĂ©tenir les espĂšces pionniĂšres et prairiales les plus riches. Les rĂ©sultats analytiques ont permis de prĂ©ciser lâorigine et lâintĂ©rĂȘt Ă©cologique des sols limoneux. Ils soulignent Ă©galement la nĂ©cessitĂ© de prĂ©server ce matĂ©riel Ă©daphique dans le cadre dâune gestion conservatoire de la biodiversitĂ© du massif dunaire.Along the European coasts, dune massifs are characterized by numerous settlements with great ecological value in relation to phreatic water. Since about twenty years, pioneer and grassy species of those settlements are subjected to substantial decline. Dune massif of Hatainville is a perfect sample of this regressive trend. Protection of scarce grassy species requires a better knowledge of soils and their dynamics. Pedological investigation has been carried out concerning unexpected silty soils of massif dune slacks. These soils are original insofar as they own richest pioneer and grassy species. Origin and ecological value of the silty soils have been cleared by analytic data. These data also underline the need for preserving this edaphic material within the conservatory management of the biodiversity of dune massif
Prise en compte de la diversité végétale arborée chez les paysagistes
Cet article vise Ă interroger la relation entre la diversitĂ© arborĂ©e et la pratique du projet de paysage Ă travers la littĂ©rature existante dâhistoire des jardins publiĂ©e au cours des trois derniers siĂšcles. La lecture de ces documents a permis dâidentifier quatre grandes « Úres » qui ont non seulement fait Ă©voluer des maniĂšres de penser et de dessiner les projets, mais aussi dâintĂ©grer et de conduire lâarbre dans les amĂ©nagements de grands parcs et domaines privĂ©s du xviie siĂšcle Ă ceux dâaujourdâhui, rendus publics et urbains. Ainsi, du xviie au xxe siĂšcle, de lâart des jardins classique Ă lâurbanisme fonctionnaliste, nous verrons comment il est dĂ©jĂ possible de dĂ©gager des paramĂštres dâorganisation, de structure et de fonctionnement qui tĂ©moignent avant lâheure dâune dimension de la diversitĂ© arborĂ©e. Cela a pour objectif de replacer dans lâhistoire cet Ă©lĂ©ment de nature prĂ©sent dans les villes comme un vecteur et/ou un support de biodiversitĂ©.This article focuses on the relation between arborescent plant diversity and the landscape project in the literature of the history of gardens published during the last three centuries. The study if these documents has made it possible to identify four major âerasâ which not only contributed to changing the way of thinking about and designing projects, but also integrated and used the arborescent plant as a defining component in the development of major parks and private domains from the 17th century up until today, and which have now become public and urban spaces. Thus, from the 17th to the 20th century, spanning from the art of classic gardens to the trend of functional urbanism, the article shows how it is possible to identify the parameters relating to forms of organisation, structure and practise which point to the early presence of tree diversity. The objective is to place within the historical framework this natural element present in cities as a vector of and/or a support for biodiversity
THE IMPACT OF STORAGE CONDITIONS ON THE FOREST BIOMASS QUALITY FOR BIOFUELS PRODUCTION
Biomass quality is an essential parameter for the production of biofuels both by thermal ways (gasification, pyrolysis, torrefaction, etc) or biochemical ways (enzymatic hydrolysis and yeast saccharification). Storage is one of the most important parameters to be taken in account in the logistics chains of biomass supply for biofuel conversion sites. Morever, some benefits in terms of biomass quality can be obtained by storing biomass prior transportation or usage. In this case, storage can be considered as a pre-treatment of biomass for biofuel production.
In this project, we have studied the evolution of biomass quality of different wooden resources (softwoods and hardwoods; short/very-short rotation coppices and residues of forest exploitation) stored under different conditions : seasons (spring/summer or autumn/winter), sites (forest roadside and storage platforms; uncovered and covered; under water sprinkling). Two locations were also tested, one in Bordeaux area (southwest of France) and the second in Dijon area (northeast of France). Different piles of approximately 10 m3 (2.5 to 3.5 tons of wood chips) were constituted for each modality. Samples were taken from two different levels of the piles at different intervals of storage (0 to 6 months).
The following biomass quality parameters were followed : moisture content, elemental (C, H, O, N, S, Cl) and chemical (extractives, lignin, polysaccharides â cellulose and hemicelluloses, C5 and C6 sugars contents) composition; heating value; ash content, fusibility behaviour and composition.
The results obtained indicated that the conditions of storage strongly influence the biomass quality, especially for the thermal conversion. The type of initial raw material (softwoods or hardwoods / short/very-short rotation coppices and residues of forest exploitation) are also of major importance, especially if the biomass material is stored with or without leaves. In that way, the season aspect becomes very important. Water sprinkling is an interesting way to remove certain compounds, such ash constituents or extractives, partially responsible for tar formation. On the other way, in this case a compulsory drying step is needed and a careful energy balance is needed in order to evaluate the pertinence or not of this technology. Concerning the biochemical conversion, no major differences were observed for the mono/polysaccharides contents. However, the removal of certain elements/substances could impact the enzymatic hydrolysis and fermentation for bioethanol production
Col-OSSOS: The Colours of the Outer Solar System Origins Survey
The Colours of the Outer Solar System Origins Survey (Col-OSSOS) is acquiring
near-simultaneous , , and photometry of unprecedented precision with
the Gemini North Telescope, targeting nearly a hundred trans-Neptunian objects
(TNOs) brighter than mag discovered in the Outer Solar System
Origins Survey. Combining the optical and near-infrared photometry with the
well-characterized detection efficiency of the Col-OSSOS target sample will
provide the first flux-limited compositional dynamical map of the outer Solar
System. In this paper, we describe our observing strategy and detail the data
reduction processes we employ, including techniques to mitigate the impact of
rotational variability. We present optical and near-infrared colors for 35
TNOs. We find two taxonomic groups for the dynamically excited TNOs, the
neutral and red classes, which divide at . Based on simple
albedo and orbital distribution assumptions, we find that the neutral class
outnumbers the red class, with a ratio of 4:1 and potentially as high as 11:1.
Including in our analysis constraints from the cold classical objects, which
are known to exhibit unique albedos and colors, we find that within our
measurement uncertainty, our observations are consistent with the primordial
Solar System protoplanetesimal disk being neutral-class-dominated, with two
major compositional divisions in color space.Comment: Accepted to ApJS; on-line supplemental files will be available with
the AJS published version of the pape
Influence du paysage et des pratiques agricoles sur le contrĂŽle biologique des graines d'adventices par les carabiques
Farmland biodiversity and its associated ecosystem services are affected by agricultural activities at multiple spatial scales. Among these services, the regulation of weeds by invertebrate seed predators has received much attention recently but little is known about the relative effect of local management and landscape context of fields on this process. We monitored seed predation on four common weed species and carabid communities in 28 winter-cereals fields during five consecutive weeks in spring 2010. These fields were situated in contrasted landscape contexts and varied in terms of intensity of pesticide treatments and soil tillage regimes. Weed seed predation was strongly and positively related to the Shannon diversity of (strictly) granivorous carabids and to the activityâdensity of omnivorous carabids but negatively to the richness of omnivorous carabids. Weed seed predation and granivore diversity were positively related to landscape diversity and the proportion cover of temporary grassland within a 1000 m radius around focal fields and were negatively affected by the intensity of local pesticide treatments. No-till systems sheltered higher diversity of granivorous carabids but did not show higher seed predation rates. We showed that landscape composition factors had a higher relative influence than local practices factors on weed seed predation service. Consequently, weed management strategies should not only consider the management of single fields but also the surrounding landscape to preserve carabid biodiversity and enhance weed seed predation service
Humid Evolution of Haze in the Atmosphere of Super-Earths in the Habitable Zone
Photochemical hazes are expected to form and significantly contribute to the
chemical and radiative balance of exoplanets with relatively moderate
temperatures, possibly in the habitable zone of their host star. In the
presence of humidity, haze particles might thus serve as cloud condensation
nuclei and trigger the formation of water droplets. In the present work, we are
interested in the chemical impact of such a close interaction between
photochemical hazes and humidity on the organic content composing the hazes and
on the capacity to generate organic molecules with high prebiotic potential.
For this purpose, we explore experimentally the sweet spot by combining
N-dominated super-Earth exoplanets in agreement with Titan's rich organic
photochemistry and humid conditions expected for exoplanets in habitable zones.
A logarithmic increase with time is observed for the relative abundance of
oxygenated species, with O-containing molecules dominating after 1 month only.
The rapidity of the process suggests that the humid evolution of N-rich organic
haze provides an efficient source of molecules with high prebiotic potential
Evaluation of the sterilization effect on biphasic scaffold based on bioactive glass and polymer honeycomb membrane
The sterilization is a core preoccupation when it comes to implantable biomaterials. The most common in industry is the gamma sterilization; however, the radiation used in this method can induce modifications in the material properties. This study investigates the impact of such radiations on the physicochemical properties and biological toxicity of a new biomaterial based on a poly-l-co-d,l-lactide polymer honeycomb membrane and bioactive glass (BG), combined, to form an assembly (membrane/BG assembly). The investigated BGs are the S53P4, which is FDA approved and clinically used, and 13-93B20, a BG containing boron promising for bone regeneration. Infrared and photoluminescence measurements revealed that, upon irradiation, defects are created in the BGs molecular matrix. Defects were identified to be mainly non-bridging oxygen hole center and occur in higher proportion in the 13-93B20 making it more sensitive to irradiation compared to the S53P4. However, the irradiation does not significantly impact the structure of the BGs. On the membrane side, the molecular weight is divided by two resulting in a lower shear stress resistance. However, the membrane honeycomb topography does not seem to be impacted by the irradiation. In contact with cells, no toxicity effect was observed, and BGs keep their bioactive properties by releasing ions beneficial to the cell fate and with no influence on apatite precipitation speed. Overall, this study showed that, despite some impact on the physicochemical properties, the irradiation does not induce deleterious effect on the membrane/BG assemblies and is therefore a suitable method for the sterilization of this novel biomaterial.Peer reviewe
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