Graduation date: 2006

Graduation date: 1995

Thesis (M.Sc.)--Memorial University of Newfoundland, 2005. / Includes bibliographical references.

Le bilan carboné d'une rotation culturale de quatre ans a été établi entre 2004 et 2008 sur le site expérimental de Lonzée, Belgique. La région se caractérise par un climat tempéré océanique avec une température moyenne de l'air de 10°C et des précipitations annuelles de l'ordre de 800 mm. Le sol de la parcelle est un Luvisol. Les cultures composant la rotation sont des cultures de betterave, froment dhiver, pomme de terre et froment dhiver. Dans le but détablir un bilan carboné, des mesures ont été effectuées à différentes échelles spatiales et temporelles. Un système de mesure par eddy covariance fournit une estimation par demiheure de l'échange net en CO2 de l'écosystème (NEE). La qualité des procédures de sélection et de traitement des flux de NEE a été contrôlée. A partir de ces mesures, la productivité primaire brute (GPP) et la respiration totale de l'écosystème (TER) sont déduites. Plusieurs procédures basées sur les mesures diurnes ou nocturnes de NEE sont comparées. L'intérêt d'utiliser un court pas de temps dans ces procédures et la température du sol comme température de référence a été mis en avant, ainsi que la nécessité de déterminer une valeur seuil de la vitesse de friction (u*) pour chaque culture et les longues inter-cultures. Pour la culture de froment d'hiver 2005, une estimation de la GPP déduite des mesures d'eddy covariance est comparée à une estimation basée sur une modélisation de mesures réalisées, une fois par semaine, à l'échelle de la feuille. La conception initiale de l'appareil de mesure a permis de réaliser les mesures sur les feuilles uniquement. Les évolutions des deux estimations sont proches à l'échelle de la saison et à l'échelle journalière. La mise en oeuvre de la méthode basée sur les mesures à léchelle de la feuille a apporté dimportantes informations en termes de réponse de la GPP aux facteurs climatiques et non climatiques et a permis une validation de lestimation basée sur les mesures deddy covariance. Toutefois, dans le cadre de létablissement dun bilan carboné, la méthode basée sur les mesures d'eddy covariance est préférée. Des mesures de la respiration de sol, réalisées à l'échelle de la miniparcelle de sol, et des mesures du contenu en carbone des plantes sont aussi réalisées. Combinées aux mesures d'eddy covariance, ces mesures permettent de déduire les parts autoet hétérotrophiques de la respiration. Sur l'ensemble de la rotation, la parcelle apparait être une source significative de carbone de 0.17 (+/- 0.14) kg C m-2. Cela suggère que, durant la rotation, le contenu en carbone du sol a diminué. Ceci peut sexpliquer par labsence dapport de fertilisation organique durant les 10 dernières années ainsi que par la récolte systématique des pailles des céréales.

Abstract Målet för den naturvetenskapliga undervisningen är att ge eleverna kännedom om och förståelse för grundläggande begrepp och sammanhang. Fotosyntesen är en avgörande förutsättning för liv. För att förstå hur ekosystem hänger ihop krävs en förståelse för att atomer varken nybildas eller försvinner utan att alla processer innebär att atomerna är de byggstenar som används om och om igen. Denna insikt hos enskilda individer kan vara avgörande för hur mänskligheten lyckas hantera globala miljöproblem i ett större samhällsperspektiv.   Undersökningsgruppen består av 24 elever i årskurs 8. De fick inledningsvis formulera sig skriftligt om hur de tänker kring materiaomvandling i samband med fotosyntes och förbränning. Under 5 veckor fick de följa ett slutet kretslopp, samtidigt som de undervisades om materiaomvandling i samband med fotosyntesen. Eleverna deltog i en strukturerad halvklassdiskussion runt ett slutet kretslopp. Frågeställningarna behandlade vanliga vardagstankar och de baserades på några av de svårigheter som finns för fördjupad förståelse för fotosyntesen enligt NO-didaktikforskaren Björn Andersson. Undersökningen avslutades med att eleverna återigen fick formulera sina tankar skriftligt.   Undersökningens resultat verifierar övrig didaktisk forskning som pekat på svårigheter att förstå materiaomvandling. De undersökta eleverna visade inte upp det molekylbegrepp som innebär att samma atomer som ingår i en process återfinns som produkter efteråt.   Studien pekar också på att elevernas kvalitativa förståelse hänger samman med hur undervisningsstoffet presenteras. Varje individ lever i sin unika verklighet. Dessa elevers förståelse verkar fördjupas när de upplever en verkligt kvalitativ skillnad mellan förförståelsen och den undervisning som presenteras. I annat fall läggs nya fakta till gamla strukturer och eleven har lärt sig något annat än det som pedagogen avsåg att förmedla

Alternative oxidase (AOX) is a non-energy conserving branch of the mitochondrial electron transport chain (ETC) which has been hypothesized to modulate the level of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in plant mitochondria. The aim of the research presented herein is to provide direct evidence in support of this hypothesis and to explore the implications of this during plant-pathogen interactions in Nicotiana tabacum. We observed leaf levels of ROS and RNS in wild-type (Wt) tobacco and transgenic tobacco with altered AOX levels and we found that plants lacking AOX have increased levels of both NO and mitochondrial O2 - compared Wt plants. Based on the results we suggest that AOX respiration acts to reduce the generation of ROS and RNS in plant mitochondria by dampening the leak of electrons from the ETC to O2 or nitrite. We characterized multiple responses of tobacco to different pathovars of the bacterial pathogen Pseudomonas syringae. These included a compatible response associated with necrosis (pv tabaci), an incompatible response that included the hypersensitive response (HR) (pv maculicola) and an incompatible response that induced defenses (pv phaseolicola). We show that the HR is accompanied by an early mitochondrial O2 - burst prior to cell death. Also, we found iii that the appearance of HR and the appearance of the mitochondrial O2 - burst are delayed in transgenic plants lacking AOX. A similar delay is seen in transgenic plants treated with the complex III inhibitor antimycin A. In Wt plants, expression of Aox1a is suppressed during the HR response to pv maculicola despite the accumulation of signaling molecules known to induce Aox1a transcription. Also, MnSOD activity declined during the HR. We suggest that the mitochondrial ROS burst controlled by AOX and MnSOD is an important component for the induction and coordination of the HR during plant-pathogen interactions.

Plankton metabolic balance (PMBm) of the surface mixed layer was calculated as the ratio of areal rates of gross photosynthesis (AGP) to community respiration (AR), and estimated for four Laurentian Great Lakes coastal sites of contrasting physical, optical and nutrient regime: western Lake Ontario, Hamilton Harbour, Georgian Bay and Woods Bay. The applied methods were the oxygen light-and-dark bottle and 14C bottle methods as well as the oxygen stable isotope method (18O method). PMBm was net autotrophic in most of the cases (73% of the observations). Within- and inter-system variations in PMBm were heavily dependent on both a ratio of light-saturated photosynthesis to community respiration (Pmax/R) and a ratio of euphotic to mixing depths (Zeu/Zm). While short-term within-system variations in PMBm were driven by the interplay of chlorophyll a (Chl a), total phosphorus (TP) and Zeu/Zm ratio, its inter-lake long-term variability had a different behaviour. Average ratios of AGP/AR were dependent only on DOC or single physical parameters such as Zeu or Zm, while PMBm determined as the ratio between average AGP and AR was controlled by the joint effect of DOC, TP and Chl a. DOC affected average AGP/AR ratios primarily via its control over fluctuations of the physical environment and had a depressing effect on AGP rates but did not control rates of AR. Independent measurements of volumetric rates of photosynthesis (P) and community respiration (R) were made by 18O method adjusted for wind-driven gas exchange and compared against estimates from bottle estimates. The 18O method in Lake Ontario gave internally inconsistent results (e.g. negative absolute rates of P and R) and poor agreement with independent estimates of P, R and P/R despite superficially plausible estimates for P/R. The low productivity of Lake Ontario and frequent disturbances of water column masked the biological signal in both DO abundance and its isotopic signature, and thus invalidated the assumptions of steady state conditions. However, in Hamilton Harbour and some other relatively sheltered sites that were sampled occasionally, 18O method predicted absolute rates of P that were well correlated well with bottle estimates. Isotope model estimates for R and P/R in the harbour were not well correlated with bottle estimates but were of comparable magnitude on average, and differences were explicable in terms of physical forces and the different time scales of response for the two methods. The Hamilton Harbour hypolimnion presented an anomalous behavior in oxygen stable isotopes (18O depletion) where seasonal development of DO depletion was not accompanied by the progressive isotope enrichment expected from respiratory fractionation. The Lake Ontario and harbour hypolimnion results both appear to show that simple steady state models that assume literature values for fractionation processes and ignore physical dynamics are of limited applicability to lakes.

Plankton metabolic balance (PMBm) of the surface mixed layer was calculated as the ratio of areal rates of gross photosynthesis (AGP) to community respiration (AR), and estimated for four Laurentian Great Lakes coastal sites of contrasting physical, optical and nutrient regime: western Lake Ontario, Hamilton Harbour, Georgian Bay and Woods Bay. The applied methods were the oxygen light-and-dark bottle and 14C bottle methods as well as the oxygen stable isotope method (18O method). PMBm was net autotrophic in most of the cases (73% of the observations). Within- and inter-system variations in PMBm were heavily dependent on both a ratio of light-saturated photosynthesis to community respiration (Pmax/R) and a ratio of euphotic to mixing depths (Zeu/Zm). While short-term within-system variations in PMBm were driven by the interplay of chlorophyll a (Chl a), total phosphorus (TP) and Zeu/Zm ratio, its inter-lake long-term variability had a different behaviour. Average ratios of AGP/AR were dependent only on DOC or single physical parameters such as Zeu or Zm, while PMBm determined as the ratio between average AGP and AR was controlled by the joint effect of DOC, TP and Chl a. DOC affected average AGP/AR ratios primarily via its control over fluctuations of the physical environment and had a depressing effect on AGP rates but did not control rates of AR. Independent measurements of volumetric rates of photosynthesis (P) and community respiration (R) were made by 18O method adjusted for wind-driven gas exchange and compared against estimates from bottle estimates. The 18O method in Lake Ontario gave internally inconsistent results (e.g. negative absolute rates of P and R) and poor agreement with independent estimates of P, R and P/R despite superficially plausible estimates for P/R. The low productivity of Lake Ontario and frequent disturbances of water column masked the biological signal in both DO abundance and its isotopic signature, and thus invalidated the assumptions of steady state conditions. However, in Hamilton Harbour and some other relatively sheltered sites that were sampled occasionally, 18O method predicted absolute rates of P that were well correlated well with bottle estimates. Isotope model estimates for R and P/R in the harbour were not well correlated with bottle estimates but were of comparable magnitude on average, and differences were explicable in terms of physical forces and the different time scales of response for the two methods. The Hamilton Harbour hypolimnion presented an anomalous behavior in oxygen stable isotopes (18O depletion) where seasonal development of DO depletion was not accompanied by the progressive isotope enrichment expected from respiratory fractionation. The Lake Ontario and harbour hypolimnion results both appear to show that simple steady state models that assume literature values for fractionation processes and ignore physical dynamics are of limited applicability to lakes.

Thèse de doctorat : Rayonnement et imagerie en médecine : INPL : 2007. / Titre provenant de l'écran-titre. Bibliogr.

Thèse d'exercice : Chirurgie dentaire : Université de Nantes : 2007. / Bibliogr.