Thesis (Ph. D.)--Johns Hopkins University, 1910. / Vita. Required type-written copy.

Thesis (Ph. D.)--Johns Hopkins University. / Biographical note. Reprinted from the "Botanical gazette," vol. 50, 1910. Published also as Contributions from the Botanical laboratory of the Johns Hopkins university no. 14. Literature cited: p. 371.

Thesis (M.S.)--University of Wisconsin--Madison, 1962. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 62-63).

Les relations entre l'activité de la source et l'activité du puits contrôlent en grande partie la croissance des plantes. Ces activités varient au cours du développement, mais aussi en réponse à des changements des conditions environnementales. Notre étude avait pour but d'identifier le rôle du métabolisme carboné dans la réponse de la croissance d'E. americanum à la modulation des activités de la source et du puits. Dans une première partie, l'activité du puits est modulée par la température de croissance. Aux fortes températures, l'activité du puits est plus élevée, alors que sa capacité est réduite. Ces effets, dus à la modulation du métabolisme du saccharose, mènent à une saturation précoce en amidon des bulbes à forte température. Par la suite, la baisse de la demande en carbone du puits induit un rétrocontrôle négatif de l'activité photosynthétique et finalement, la sénescence foliaire. À l'inverse, l'activité du puits à faible température est en rythme avec l'accroissement de la capacité, menant à une biomasse supérieure du bulbe en fin de croissance épigée. Dans une seconde partie, l'activité de la source est modulée en changeant la concentration en CO2 et en O3. Malgré la stimulation de la source sous fort CO2 et son inhibition sous fort O3, l'accumulation d'amidon et la biomasse du bulbe ne sont pas affectées. En effet, le surplus de carbone parvenant au puits est brûlé par la voie alternative de la respiration, celle-ci étant stimulée par l'activité de l'enzyme malique. La voie alternative de la respiration évite ainsi une saturation hâtive en amidon et éventuellement, une sénescence foliaire précoce. Dans une dernière partie, l'activité de la source est modulée par l'irradiance et la photopériode. L'accumulation d'amidon varie en fonction de la photopériode alors que l'irradiance n'a aucun effet. De plus, l'activité photosynthétique est inhibée très précocement sous longue photopériode. Cette inhibition semble due à un déséquilibre entre la quantité totale de carbone fixé par jour et son utilisation suite à son transfert au sein du bulbe. Nous pouvons donc conclure que les régulations du métabolisme carboné permettent d'ajuster l'activité du puits à la capacité de celui-ci chez l’E. americanum / Relationships between source and sink activities largely control the growth of plants. Both activities vary during development as well as in response to changes in environmental conditions. The aim of our study was to identify the role carbon metabolism plays in the response of E. americanum growth to changes in source and sink activities. Firstly, sink activity is modulated by changing growth temperature. Sink activity is higher at higher temperatures, whereas sink capacity is more restricted. These effects, due to the modulation of sucrose metabolism, lead to an earlier starch saturation of bulbs at higher temperature. Thereafter, the reduction in carbon sink demand induces a feedback inhibition of photosynthetic activity and finally, leaf senescence. In contrast, sink activity at low temperature is more in rhythm with the increasing sink capacity, leading to larger bulbs at the end of the epigeous growth season. Secondly, source activity is modulated by changing CO2 and O3 concentrations. Despite a stimulation of the source activity under high CO2 and its inhibition under high O3, neither plant growth nor starch accumulation was affected. Indeed, excess carbon translocated within the sink is burned by the alternative respiratory pathway. This pathway is stimulated by malic enzyme. Alternative respiratory pathway thus avoids an early starch saturation of the bulb and eventually, an early leaf senescence. Finally, source activity is also modulated by changing irradiance and photoperiod regimes. Starch accumulation changes in response to photoperiod but not to irradiance. Furthermore, photosynthetic activity is inhibited early in the season under long photoperiod. This inhibition seems due to an imbalance between the total amount of carbon fixed per day and its utilisation following translocation to the bulb. We can thus conclude that regulation of carbon metabolism allow to adjust sink activity to sink capacity in E. americanum.

No description available.

There is concern that climate change may cause mismatches between timing of flowering and activity of pollinators (phenology). However, concluding that mismatches will occur, and have serious consequences for pollination services, requires assumptions that have not yet been tested. I begin by discussing a set of these assumptions, bringing past research into the context of mismatch. Briefly, the assumptions are that 1) dates of first-flowering or emergence (DFFE) correctly describe phenology (and therefore mismatch); 2) differences in DFFE represent the magnitude of mismatch; 3) advancement of DFFE will be the primary phenological change; 4) shifts will be random and independent for each species; 5) populations of plants and pollinators are “bottom-up” regulated by their mutualistic interactions; 6) all interactions are of similar strength and importance; 7) dispersal, and the spatial context of phenological mismatches can be ignored; and ecological processes including 8) phenotypic plasticity and adaptive evolution of phenology, 9) competition and facilitation, and 10) emergence of novel interactions, will not affect mismatches. I then describe novel experiments, which could help to account for some of these assumptions, clarifying the existence and impacts of mismatches. Next, I present an original field experiment on factors affecting seed set in an alpine meadow in the Coast Range of British Columbia, Canada. I found evidence contradicting the assumption that seed set is primarily limited by pollination. My data highlight the roles of phenology, temperature (degree-days above 15°C, and frost hours), and interactions with pollinators (mutualists) and seed-predators (floral antagonists) in driving patterns of seed set. Seed set of early and late-flowering species responded differently to a 400m elevation gradient, which might be explained by phenology of bumble bees. My data suggest that the consequences of mismatch may be smallest for plants that are fly-pollinated and self-fertile. Non-selfing, bee-pollinated species might be more prone to reproductive limitation through mismatch (affected by snowmelt and cumulative degree-days). Plants that are limited by seed-predators might be negatively affected by warming temperatures with fewer frost hours, and extreme events such as late-season frosts and hail storms can prevent plants from setting seed entirely. Overall, my work emphasizes the importance of complementing theory, data-driven simulations, and meta-analyses with experiments carried out in the field. / Graduate