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，尤其是树木，是如何随着时间和景观的变化而适应环境变化的。在这方面，本建议侧重于三个主题：叶片内二氧化碳（CO2）传导变化的原因；2. 日长敏感性的发展及其对长高期的影响；和3。植物天然氮同位素组成变化的生理机制。第一点很重要，因为叶片的内部导度（gm）可能会像气孔导度一样限制二氧化碳的扩散。然而，与气孔导度不同，增加转基因对叶片水分流失没有影响。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。氮和水往往是自然和农业生态系统中最有限的两种资源。我们已经描述了在加拿大各地的苦杨中转基因的显著纬度差异，并利用三种不同的技术来评估这种差异的基础。这些数据直接提供给加拿大的杨树育种计划。第二个主题与高度生长的物候学有关，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，夏末的短日照会导致高度生长停止和芽休眠。然而，从适应性上讲，重要的是，新生长的植物不会对春天同样短的日照做出反应。我们已经证明，在春天花蕾花期之后，苦杨的芽对白昼长度（光周期）有几个星期不敏感，阻止它们在一年中过早发芽（除非它们种植在错误的地方；或者，也许在未来，如果春天到来得太早）。本研究旨在利用基因组工具（转录组测序和全基因组关联）阐明黑棉杨和光周期敏感性的功能基础，并描述这些物种和其他物种之间和光周期敏感性的发展变化。最后，我们引入了一个简单的模型来解释植物及其部分（即根、茎和叶）N同位素组成的变化。正如本文所提出的那样，该模型需要进一步的开发和验证，但在筛选影响产量和氮利用效率的一系列性状的树木和作物方面具有重大潜力。

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.