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Seasonal priorities for the use of current photosynthate were studied in the leaves of Betula glandulosa Michx. and Ledum groenlandicum Oeder from northern Quebec. A sequential extraction scheme was developed to separate ('14)C-labelled leaf tissues into several classes of organic compounds. Data were analysed in terms of carbon use priority (CUP) defined as the ('14)C activity in a compound category as percentage of the total activity in the leaf. / Developing leaves represented the strongest sink for current photosynthate among evergreen leaf age classes. In both species the priorities for structural components, leaf protection and metabolic components decreased while the importance of cellular lipids and storage carbohydrates increased with leaf age. The deciduous leaves had higher overall carbon use priorities for metabolic components, cellular lipids and storage carbohydrates. The priorities for structural components and leaf protection were higher in the evergreen leaves. Leaf protection was an important consideration in both species. Both B. glandulosa and L. groenlandicum leaves (1) allocated photosynthate to antiherbivore compounds when leaf succeptibility was highest, (2) used both quantitative and qualitative type defenses, and (3) reduced carbon use for quantitative type defenses during active growth.

Mémoire (B.Sc.)--Université du Québec à Chicoutimi, 1990. / Document électronique également accessible en format PDF. CaQCU

On the territory of the Czech Switzerland National Park took place during the Holocene significant changes in vegetation cover to the form is most enrolled medium Holocene climatic optimum when broadleaf deciduous forests expanded into Central Europe. These transformations are caused by climatic changes. However, it started the process of soil acidification to this day that caused the other variations of the vegetation composition, even the extinction a variety of species especially in sandstone areas. In addition, in the last few centuries the human impact is graduating, which more or less of the original forests changes due to agricultural and economic reasons to breed-specific and the same-aged plantations which supports the already declining species diversity and relative abundance of the undergrowth species. This work focuses on a single species, evergreen undergrowth shrub Ledum palustre which is characterized by strong demands on its habitat and indicates the specific habitat type. It grows on the upper north-facing edges of rocks with plenty of light and humidity. At these locations stores organic material thanks the favourable hydrology. This makes possible to study the use of pollen and macroremains the paleoecology of the species. On the basis of recent occurrences and the relationships...