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

我的长期目标是了解植物，特别是树木，如何适应随着时间的推移和整个景观的环境变化。在这一背景下，本提案侧重于三个主题：1.叶片内二氧化碳（CO2）传导变化的原因; 2。光长敏感性的发展及其对高生长持续期的影响; 3.植物天然氮同位素组成变化的生理机制。其中第一个是重要的，因为叶片的内部电导（gm）可能会限制CO2扩散一样多的气孔导度。然而，与气孔导度不同，gm的增加对叶片失水没有影响。因此，转基因是增加树木和作物光合作用的重要目标，同时保持或提高它们对水和氮的利用效率。氮和水通常是自然和农业生态系统中最具限制性的两种资源。我们已经描述了加拿大各地香脂白杨转基因的显着纬度变化，并正在利用三种不同的技术来评估这种和其他本土树种中这种变化的基础。这些数据直接输入加拿大的白杨育种计划。第二个主题涉及高度生长的物候，这在很大程度上决定了不同纬度树木每年总生长量的变化。在大多数温带物种中，高生长停止和芽休眠是由夏末的短日照引起的。然而，从适应性的角度来看，新的增长不对春季同样短的天数做出反应是很重要的。我们已经证明，在春天的芽冲洗之后，香脂白杨的芽对日照长度（光周期）不敏感几个星期，防止它们在一年中过早地发芽（除非它们种植在错误的地方;或者，也许在未来，如果春天来得太早）。本提案的目的是阐明这种现象的功能基础，使用基因组工具（转录组测序和全基因组关联），在黑棉白杨和香脂白杨，并描述如何发展的光周期的敏感性变化内和这些和其他物种之间。最后，我们介绍了一个简单的模型来解释植物及其部分（即根，茎和叶）的N同位素组成的变化。该模型需要进一步开发和验证，如本文所述，但在筛选树木和作物的一系列影响产量和氮素利用效率的性状方面具有重要潜力。

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.