Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Intercropping, defined as two or more crops grown on the same land area at the same time, is a sustainable alternative to sole crops. Intercropping has been associated with multiple benefits, such as increased nutrient and soil organic carbon (SOC) cycling, decreased soil erosion and increased carbon (C) sequestration. A common intercropping practice is to integrate cereal and legume crops such as maize (Zea mays L.), and soybean (Glycine max (L.) Merr.). Most studies on intercropping have focused on yield, weed control, and land use efficiency in the tropics. Few studies have researched C and nitrogen (N) dynamics in temperate intercrops, with respect to soybean and maize residue stabilization. Soil from Balcarce, Argentina, was incubated for 140 days with soybean, maize, or no residue. Throughout the incubation, results illustrated the effect of residue application upon the soil, specifically through significantly higher amounts of light fraction (LF) C and LFN concentrations, soil microbial biomass (SMB) C and SMBN concentrations, higher microbial diversity, lower N2O production rates, in addition to distinct isotopic values in soil fractions and CO2 (p<0.05). Furthermore, it was observed from δ15N-TN and δ15N-LF that treatments with soybean residues included had higher N cycling (p<0.05), emphasizing the importance of including N-fixing legumes in complex agroecosystems. Significant changes over time in SMB and SMCS characteristics, and isotope values (p<0.05) indicated the preferential utilization of relatively young and easily accessible litter. Furthermore, the loss of labile material over the incubation resulted in more recalcitrant forms (such as older C and lignin) to be utilized. Slightly higher SOC, TN, LFC and LFN concentrations, as well as lower CO2 production rates suggested 2:3 (rows of maize:rows of soybean) as a more desirable intercrop design for C sequestration. The 1:2 intercrop design was observed to be more beneficial for microbial community structure, furthering the idea that intercropping is a beneficial alternative to sole cropping. This study improves knowledge in residue stabilization and C sequestration in complex agroecosystems, providing encouragement for the implementation of more sustainable management practices.

Temperate Midwestern oak savannas are considered imperiled ecosystems with < 1 % remaining since the time of European settlement and are identified as critical areas for preservation. Restoration of Midwestern oak savannas is challenging due to the lack of accurate historical data, few intact remnants remaining to study, and lack of restoration ecology studies. A plant trait-based approach was used to evaluate the ability of six C3 and three C4 native bunchgrasses to restore functionality to a remnant savanna–woodland of the Bluegrass Region of Kentucky. The response and effect framework was used to assess the response of the nine native grasses according to the habitat filters of interannual precipitation, inter- vs. intra-specific competition, and simulated grazing. The effect traits associated with plant-soil nitrogen and carbon cycling were also assessed. The response traits of interannual competition and inter- vs. intra-specific competition along with the effect traits plant-soil nitrogen and carbon cycling were measured in a monoculture experiment conducted at Griffith Woods WMA. The simulated grazing or clipping experiment was conducted over three months in a heated greenhouse experiment. Four of the C3 species were of the genus Elymus which had significant differences in life history traits compared to the other species and made them particularly well adapted to the Bluegrass Savanna-Woodland. The Elymus species were not well adapted to the most intense clipping treatment. For the other two C3 species, C. latifolium would be a better competitor than D. clandestinum under normal conditions. D. clandestinum had the most number of plastic traits and was the only species to exhibit all three grazing strategies. Comparing the C4 species, T. flavus and P. anceps grew well in the monoculture but A. virginicus did not. The life history traits of A. virginicus does not make this species a good candidate for restoration at this site. The three C4 species were well adapted to clipping. The results of this study suggest that the C3 species, particularly the Elymus, are well adapted to the eutrophic mesic conditions of the Bluegrass Savanna-Woodland, and that the C4 species are better adapted to disturbance.

Intercropping, defined as two or more crops grown on the same land area at the same time, is a sustainable alternative to sole crops. Intercropping has been associated with multiple benefits, such as increased nutrient and soil organic carbon (SOC) cycling, decreased soil erosion and increased carbon (C) sequestration. A common intercropping practice is to integrate cereal and legume crops such as maize (Zea mays L.), and soybean (Glycine max (L.) Merr.). Most studies on intercropping have focused on yield, weed control, and land use efficiency in the tropics. Few studies have researched C and nitrogen (N) dynamics in temperate intercrops, with respect to soybean and maize residue stabilization. Soil from Balcarce, Argentina, was incubated for 140 days with soybean, maize, or no residue. Throughout the incubation, results illustrated the effect of residue application upon the soil, specifically through significantly higher amounts of light fraction (LF) C and LFN concentrations, soil microbial biomass (SMB) C and SMBN concentrations, higher microbial diversity, lower N2O production rates, in addition to distinct isotopic values in soil fractions and CO2 (p<0.05). Furthermore, it was observed from δ15N-TN and δ15N-LF that treatments with soybean residues included had higher N cycling (p<0.05), emphasizing the importance of including N-fixing legumes in complex agroecosystems. Significant changes over time in SMB and SMCS characteristics, and isotope values (p<0.05) indicated the preferential utilization of relatively young and easily accessible litter. Furthermore, the loss of labile material over the incubation resulted in more recalcitrant forms (such as older C and lignin) to be utilized. Slightly higher SOC, TN, LFC and LFN concentrations, as well as lower CO2 production rates suggested 2:3 (rows of maize:rows of soybean) as a more desirable intercrop design for C sequestration. The 1:2 intercrop design was observed to be more beneficial for microbial community structure, furthering the idea that intercropping is a beneficial alternative to sole cropping. This study improves knowledge in residue stabilization and C sequestration in complex agroecosystems, providing encouragement for the implementation of more sustainable management practices.

Diss. (sammanfattning) Linköping : Linköpings universitet, 2005. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 4 uppsatser.

Dans le but de développer des matériaux et des dispositifs avec de nouvelles propriétés, l’élaboration de monocouches auto-assemblées (SAM) est un sujet d'intérêt croissant dans le domaine des nanosciences. Les SAM sont des agrégats bidimensionnels formés par des molécules régulièrement espacées sur une surface et liées entre elles par des forces non covalentes. Le domaine des biocapteurs électrochimiques pour la reconnaissance des brins d'ADN est parmi les applications les plus récentes des SAM. Dans ce cadre, nous avons mené une étude théorique des mécanismes fondamentaux engagés lors de l’adsorption de la molécule quinone Jug-C4-thiol sur la surface Au (111). Les résultats ont été confrontés aux mesures expérimentales accessibles réalisées par l’équipe « nano 2D » au laboratoire ITODYS (Université Paris7). Tout d’abord, la théorie de la fonctionnelle de la densité PBE et PBE-D2 a été utilisée pour étudier les mécanismes mis en jeu (physisorption ou chimisorption) lors de l’adsorption de la molécule isolée à la surface de Au (111) et déterminer le site le plus favorable pour chaque mécanisme. La nature de la liaison entre la molécule et la surface de a été finement analysée à l’aide de calculs de densité d’états (DOS) et de différences de densités de charge. Ensuite, l'assemblage de la molécule quinone Jug-C4-thiol sur la surface Au (111) a été étudié. Cet assemblage des molécules a été initié par la formation de configurations de dimère à travers la formation de liaisons intermoléculaires (liaison hydrogène et π-stacking, …). Les spectres infrarouges des configurations les plus stables ont été simulés et confrontés à l’expérience. Et enfin, le mécanisme d’échange entre des molécules « hôtes » (alcanethiols C12H25SH préalablement assemblés sur la surface) et « invitées » (Jug-C4-thiols) a été exploré avec les outils théoriques. L’analyse des résultats a mis en évidence des informations structurales et énergétiques importantes sur la formation de la monocouche moléculaire mixte. / In order to develop materials and devices with new properties, the development of self- In order to develop materials and devices with new properties, the development of self-assembled monolayers (SAM) is a topic of growing interest in the field of nanoscience. SAM are two-dimensional aggregates formed by molecules regularly spaced on a surface and bonded together by non-covalent forces. The field of electrochemical biosensors for DNA strand recognition is among the most recent applications of SAM. In this context, we conducted a theoretical study of the fundamental mechanisms involved in the adsorption of the quinone Jug-C4-thiol molecule on the Au (111) surface. The results were compared to the accessible experimental measurements from the "nano 2D" team at the ITODYS laboratory (Paris 7 University). First, the density functional theory at PBE and PBE-D2 levels was used to study the mechanisms involved (physisorption or chemisorption) during the adsorption of the isolated molecule on the surface of Au (111) and access to the most favorable site for each mechanism. The nature of the binding between the molecule and the surface was finely analyzed using density of states (DOS) calculations and differences in charge densities.Then, the assembly of the quinone Jug-C4-thiol molecule on the Au (111) surface was studied. This assembly of molecules was initiated by the formation of dimer configurations through the formation of intermolecular bonds (hydrogen bonding and π-stacking, etc.). The infrared spectra of the most stable configurations were simulated and compared with the experiment. And finally, the mechanism of exchange between "host" molecules (C12H25SH alkanethiols previously assembled on the surface) and "invited" molecules (Jug-C4-thiols) was explored with the theoretical tools. The analysis of the results revealed important structural and energetic informations on the formation of the mixed molecular monolayer.

No description available.

C4 plants have a biochemical carbon concentrating mechanism (CCM) that increases CO2 concentration around Rubisco in the bundle sheath (BS). Maize CCM has two CO2 delivery pathways to the Bundle Sheath (BS) (respectively via malate, MAL or aspartate, ASP); rates of PGA reduction, carbohydrate synthesis and PEP regeneration vary between BS and Mesophyll (M) cells. For these anatomical and biochemical complexities, C4 plants are highly sensitive to light conditions. Under limiting light, the activity of the CCM generally decreases, causing an increase in leakiness, (Φ), the ratio of CO2 retrodiffusing from the BS relative to C4 carboxylation processes. This increase in Φ had been theoretically associated with a decrease in biochemical operating efficiency (expressed as ATP cost of gross assimilation, ATP / GA) under low light and, because a proportion of canopy photosynthesis is carried out by shaded leaves, to potential productivity losses at field scale. In C4 leaves, because of the concentric anatomy, light reaches M cells before the deeper BS (Evans et al., 2007), and could alter the energetic partitioning balance between BS and M and potentially cause efficiency losses. In this experimental programme I investigated strategies deployed by C4 plants to adjust operating efficiency under different illumination conditions. Firstly, maize plants were grown under high and low light regimes (respectively HL, 600 vs LL, 100 μE m-2 s-1). Short term acclimation of Φ was compared from isotopic discrimination (Δ), gas exchange and photochemistry using an improved modelling approach which does not suffer from elements of circularity. Long term acclimation to low light intensities brought about physiological changes which could potentially increase the operating efficiency under limiting ATP supplies. Secondly, profiles of light penetration across a leaf were used to derive the potential ATP supply for M and BS cells induced by changing light quality. Empirical measurements of net CO2 uptake, ATP production rate and carbon isotope discrimination were made on plants under a low light intensity. The overall conversion efficiency was not affected by light quality. A comprehensive metabolic model highlighted the importance of both CO2 delivery pathways in maize. Further, metabolic plasticity allowed the balancing of ATP and NADPH requirements between BS and M. Finally, I tested the hypothesis that plants can modify their physiology so as to reach a status of higher operating efficiency when exposed to high light and then to low light, so as to mimic the transition which leaves undergo when shaded by newly emerging leaves in a crop canopy. Plants were grown under high light and low light for three weeks, then, HL plants were transferred to low light for a further three weeks. Re-acclimation was very effective in reducing ATP cost of net assimilation under low light intensities. In addition, the hyperbolic leakiness increase observed under low light intensities was not associated to operating efficiency loss. Overall, in the three experimental Chapters I showed compelling theoretical and empirical evidence proving the hypothesis that C4 plants deal with low light conditions and with different light qualities without losing operating efficiency.

This thesis deals with the image object detection using Contour cues. The text describes methods how to train and test object detector. The main contribution of this thesis consists in creation Feature extractor for creation object detector in Java programming. The functionality of object detector was demonstrated on medical images.