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

纸桦树（Betula papyrifera Marsh.）是加拿大北方森林中最具商业价值的硬木树种之一。它的经济重要性在未来可能会增加，因为它被用来生产增值木制品，如贴面和家具。它也是北方阔叶针叶树混合物的重要生态组成部分。桦树种群在生长、形态和耐旱性方面存在相当大的遗传变异。然而，很少有研究关注单一物种在广泛的环境条件下的变异性。例如，水分输送机制的遗传可塑性可能是物种适应干旱栖息地的一个因素。正如世界各地专家预测的那样，我们的北方气候将变得更加温暖和干燥。这种气候变化肯定会影响我们的森林生态系统，比如落叶针叶树和常绿针叶树的关系。了解纸桦树对气温升高、生长季节延长和干燥环境的反应可以增强我们预测纸桦树如何应对气候变化的能力。水力特性，或植物将水分从土壤输送到叶片的能力，在确定植物如何响应水分可用性和设置最大气体交换速率方面都很重要。在提议的项目中，我将使用一个普通的花园实验，主要沿着湿度梯度种植不同栖息地的纸桦树，以研究不同桦树种群的水关系。同时，我将通过控制土壤湿度和大气二氧化碳浓度的温室实验来研究不同桦树种群对水分压力和增加的二氧化碳的反应。在田间和温室试验中，我将测量整个生长季节桦树的茎导水性和叶片光合速率。在造林实践中，这些知识将为更好地管理加拿大寒带和落叶地区的纸桦树/针叶树混交林提供指导。

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.