Influence relative des semenciers, du type de couvert végétal et des variables abiotiques sur l'établissement des semis arborescents en milieu forestier après déboisement

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal

Homogeneous light in shade-house experiment overestimates carbon gains in Norway maple seedlings

We set up a shade-house experiment with Norway maple growing at two light intensities typical of a disturbed and undisturbed forest canopy from either a homogeneous or a dynamic regime that mimics sunflecks. We show that although horticultural-grade shade-cloths can be finely tuned to provide daily averages of any light intensity, they do not appropriately mimic natural forest understories which are characterized by dynamic light environments composed of intense but short direct light events interspaced with prolonged period of low diffuse light. The results suggest that replicating the dynamic light environment of forests could be very important in experiments aimed at identifying the traits responsible for invasiveness in exotic species in forest understories, such as Norway maple in North America

Nitrogen resorption in Acer platanoides and Acer saccharum : influence of light exposure and leaf pigmentation

We investigated the effects of leaf color change in the fall on photosynthetic production and nitrogen resorption. Seedlings of Acer platanoides L. and A. saccharum Marsh. were grown in a shade house for 5 months in either 21 % (intermediate light, M) or 4.9 % (low light, L) of incident irradiance. After this period, a subset of the intermediate-light grown seedlings was transferred to a high-light stress treatment (H). Gas exchange, chlorophyll fluorescence, pigments, antioxidant activity, and nitrogen (N) resorption were examined at three leaf senescence stages during September and October. Our results show that plants of both species produce more anthocyanins in the H treatment. In comparison with plants grown in the L and M treatments, plants of both species in the H treatments had lower chlorophyll, carotenoid and chlorophyll fluorescence parameters (F (v)/F (m), I broken vertical bar (PSII), NPQ and ETR) at the third sampling date (October 12-18), and indicating higher levels of photoinhibition in the seedlings exposed to high light. Our results imply that autumn leaf redness is inducible and closely linked to photo-oxidative stress. However, anthocyanins did not enhance antioxidant capacity in red leaves in either species, when exposed to high light. For both species, our results showed a higher N-resorption for high-light stressed plants. We also observed that the number of abscised leaves at the second sampling dates (September 10) was higher than at the third sampling dates. The intra-leaf distribution of anthocyanin, the association between anthocyanin production and the high-light environments, the retention of red leaves, the substantial physiological gain of photosynthetic activity, as well as the links between anthocyanins and increased N resorption led us to assume that one primary role of autumn anthocyanin could be to protect the photosynthetic apparatus from photo-oxidative damage as light filters rather than as antioxidant. Another major role is to extend carbon capture and help supply the energy needed for N resorption from senescing leaves in both A. saccharum and A. Platanoides during high-light stress. Nevertheless, photoprotective capacity of anthocyanins was not able to fully compensate for photoinhibitory stress as the anthocyanins are not optimally located to efficiently reduce light within the leaves.Peer reviewe

A Methodology to Assess Vulnerabilities and Countermeasures Impact on the Missions of a Naval System

International audienceThe paper proposes a methodology to assess the impacts of vulnerabilities, attacks and countermeasures on a vessel's missions, and a metric designed to express and compare these impacts. A behavioral modeling approach for depicting naval systems and missions is presented. Then the paper introduces a model-checking based impact assessment method. The cyber events are integrated in the behavioral model through model mutation. Then, for each mission, their impact is computed by performing a series of model checks. The paper also discusses the algorithmic complexity of the impact assessment method

Science citoyenne et qualité des données sur la biodiversité : un faux problème ?

International audienc

Maîtrise des Correctifs de Sécurité pour les Systèmes Navals

National audienceUn navire est un système complexe, opéré dans le but d'accomplir un ensemble de missions. Les composants d'un tel système peuvent être affectés de vulnérabilités dont l'exploitation peut avoir des conséquences sur les missions en cours. Il est donc nécessaire d'appliquer des correctifs réduisant le risque lié à ces vulnérabilités. Mais il est important de s'assurer que ces correctifs n'ont pas eux-mêmes d'impact négatif sur les missions du navire. Nous proposons, dans cet article, l'architecture d'un processus de gestion des correctifs appliqué au contexte des systèmes navals. Nous extrayons de ce processus les problématiques principales qu'il pose : la modélisation d'un système complexe, et le calcul des impacts liés aux correctifs et vulnérabilités. Nous évoquons ensuite l'intérêt de la fédération de modèles pour représenter le système naval, puis nous proposons une mesure de l'impact des correctifs et vulnérabilités sur la sûreté de fonctionnement du système, basée sur l'utilisation d'automates temporisés

Science citoyenne et qualité des données sur la biodiversité : un faux problème ?

International audienc

Light acclimation strategies change from summer green to spring ephemeral as wild-leek plants age

PREMISE OF THE STUDY : Spring‐ephemeral forest‐herbs emerge early to take advantage of the high‐light conditions preceding canopy closure; they complete their life cycle in a few weeks, then senesce as the tree canopy closes. Summer greens acclimate their leaves to shade and thus manage to maintain a net carbon gain throughout summer. Differences in phenology among life stages within a species have been reported in tree saplings, whose leaf activity may extend beyond the period of shade conditions caused by mature trees. Similar phenological acclimation has seldom been studied in forest herbs. METHODS : We compared wild‐leek bulb growth and leaf phenology among plants from seedling to maturity and from under 4 to 60% natural light availability. We also compared leaf chlorophyll content and chl a/b ratio among seedlings and adult plants in a natural population as an indicator of photosynthetic capacity and acclimation to light environment. KEY RESULTS : Overall, younger plants senesced later than mature ones. Increasing light availability delayed senescence in mature plants, while hastening seedling senescence. In natural populations, only seedlings acclimated to the natural reduction in light availability through time. CONCLUSIONS : Wild‐leek seedlings exhibit a summer‐green phenology, whereas mature plants behave as true spring ephemerals. Growth appears to be more source‐limited in seedlings than in mature plants. This modulation of phenological strategy, if confirmed in other species, would require a review of the current classification of species as either spring ephemerals, summer greens, wintergreens, or evergreens

Le concept de l'œuvre bizarre dans Les Grotesques de Théophile GautierLa rhétorique du texte et de l’image sous le signe de l’excès

International audienceRésumé: Le musée de Gautier se dessine dans Les Grotesques à travers un parcours esthétique permettant de cerner la sensibilité grotesque et d’appréhender l’imaginaire de l’excès, de la marginalité, de l’anormalité, de l’excentricité, revendiqué par le critique d’art, et s’exprimant à travers le baroque et le romantisme, invitant à une contemplation littéraire et picturale, des motifs symboliques, des figures mythiques et des visages de l’œuvre, sous le signe d’une rhétorique du texte et de l’image

Note d’opportunité sur la valorisation des logiciels issus de la recherche

Software is a hybrid object in the world research as it is equally a driving force (as a tool), a result (as proof of the existence of a solution) and an object of study (as an artefact). This specific status means we need to define strategies, tools and procedures which are adapted to the various issues it raises. These include the citation of contributions to software design and production, the reproducibility of research results involving software and the wider usage and long-term sustainability of the software heritage created. This opportunity note by the Committee for Open Science's Free Software and Open Source Project Group describes the issues at stake and formulates actionable recommendations.Le logiciel est un objet hybride au sein de la recherche, dont il est à la fois moteur (comme outil), résultat (comme preuve d’existence d’une solution) et objet d’études (comme artefact). Ce statut spécifique doit amener à la définition de stratégies, d’outils et de procédures adaptés aux différents enjeux qu’il soulève, tels que notamment : la citation des contributions relatives à la conception et à la production de logiciels, la reproductibilité des résultats de recherche faisant intervenir des logiciels, la valorisation et la pérennisation du patrimoine logiciel créé