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，是如何适应随时间和整个景观的环境变化的。在此背景下，本提案集中于三个主题：1.叶片内二氧化碳(CO2)传导变化的原因；2.对日长的敏感性及其对高度生长持续时间的影响；以及3.植物天然氮同位素组成变化的生理机制。其中第一点很重要，因为叶片的内部电导(Gm)可能和气孔电导一样限制二氧化碳的扩散。然而，与气孔导度不同的是，增加Gm对叶片失水没有影响。因此，转基因是提高树木和作物光合作用的重要目标，同时保持或提高它们的水和氮利用效率。氮和水往往是自然和农业生态系统中最有限的两种资源。我们已经描述了来自加拿大各地的苦瓜杨在转基因方面的显著纬度差异，并正在利用三种不同的技术来评估这种差异在该树种和其他本地树种中的基础。这些数据直接提供给加拿大的杨树育种计划。第二个主题涉及高度生长的物候学，这在很大程度上决定了不同纬度树木每年的总生长量的变化。在大多数温带植物中，夏末的短日照会导致高度生长停止和花蕾休眠。然而，在适应性方面，对于新生的植物来说，重要的是不要对春季类似的短日数做出反应。我们已经证明，在春季萌芽后，苦瓜杨树的嫩枝在几周内对日长(光周期)不敏感，防止它们在一年中过早落蕾(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)。本提案旨在利用基因组工具(转录组测序和全基因组关联)，在黑杨和苦瓜杨中阐明这种现象的功能基础，并描述这些物种和其他物种内部和之间对光周期的敏感性发展是如何变化的。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。该模型需要进一步的开发和验证，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特征方面具有很大的潜力。

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.