Linkage between seasonal photosynthesis and hydraulic acclimation of different paper birch populations in Canada

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Paper birch (Betula papyrifera Marsh.) is one of the commercially most important hardwood species in Canada's boreal forests. Its economic importance may increase in the future as it is used to produce value-added wood products such as veneer and furniture. It is also an ecologically important component of boreal broadleaf-conifer mixture. There are considerable genetic variations among birch populations for growth, morphology and drought tolerance. However, few studies have focused on the variability within a single species over a broad range of environmental conditions. For example, genetic plasticity of water transporting mechanism would be a factor that permits the species adaptation to drier habitats. As predicted by experts around the world, our boreal climate will become warmer and drier. This climatic change will definitely affect our forest ecosystem, such as the relationship between deciduous and evergreen conifers. Understanding the responses of paper birch trees to increased air temperature, prolonged growing season and a drier environment can strengthen our ability to predict how paper birch will respond to climate change. Hydraulic properties, or the capabilities of plants to transport water from soil to leaves, are important both in determining how plants respond to water availability and in setting maximum rate of gas exchange. In the proposed project I will use a common garden experiment planting paper birch trees from different habitats mainly along a moisture gradient to examine water relationships of different birch populations. At the same time I will use a greenhouse experiment by controlling soil moisture and atmospheric CO2 concentration to examine how different birch populations respond to water stress and increased CO2. In both field and greenhouse experiments I will measure birch stem hydraulic conductivity, leaf photosynthetic rate throughout the growing season. In silvicultural practice, the knowledge will provide a guide for the better management of paper birch/conifer mixed-species forests in the Canadian boreal and deciduous regions.