Comparative physiology of plant adaptation: nitrogen isotope discrimination, mesophyll conductance, and competency to perceive photoperiod in trees

点击翻译按钮获取中文摘要

My long-term objective is to understand how plants, particularly trees, are adapted to environmental variation over time and across the landscape. Within this context, the present proposal focuses on three themes: 1. Causes of variation in carbon dioxide (CO2) conduction within leaves; 2. The development of sensitivity to day length and its influence on height growth duration; and 3. Physiological mechanisms responsible for variation in the natural nitrogen isotope composition of plants. The first of these is important because the internal conductance (gm) of leaves may restrict CO2 diffusion just as much as stomatal conductance does. However, unlike stomatal conductance, increased gm has no impact on water loss from leaves. Hence gm is an important target for increasing photosynthesis in trees and crops, while simultaneously maintaining or improving their efficiencies of water and nitrogen use. Nitrogen and water are often the two most limiting resources in natural and agricultural ecosystems. We have described significant latitudinal variation in gm within balsam poplar from across Canada, and are utilizing three different techniques to assess the basis for this variation within this and other native tree species. These data feed directly into Canada's poplar breeding program. The second theme relates to the phenology of height growth, which largely determines variation in the total growth per year seen in trees from different latitudes. In most temperate species, height growth cessation and bud dormancy are induced by short days during late summer. Adaptively, however, it is important for new growth not to respond to similarly short days in spring. We have demonstrated that following bud flush in the spring, shoots of balsam poplar are insensitive to day length (photoperiod) for several weeks, preventing them from setting bud too early in the year (unless they're planted in the wrong place; or, perhaps in the future, if spring arrives too early). The present proposal aims to elucidate the functional basis for this phenomenon using genomic tools (transcriptome sequencing and genome-wide association), in both black cottonwood and balsam poplar, and describe how the development of sensitivity to photoperiod varies both within and between these and other species. Finally, we have introduced a simple model to account for variation in the N isotopic composition of plants and their parts (ie roots, stems and leaves). This model requires further development and validation, as proposed here, but has significant potential for screening trees and crops for a range of traits that impact production and the efficiency of nitrogen use.