Taking the Temperature of a Tree: Novel Insights on Tree-leaf Temperature via the Oxygen Isotope Ratio of Tree Rings

温度是树木生产力的基本控制因素，但人们对树木生长季节过程中树叶的原位温度与碳吸收的关系知之甚少。本项目的目的是进一步发展一种通过分析树轮的氧同位素比值来解析树冠叶温的方法。初步结果表明，在50°纬度的39个树种中，碳汇过程中的树叶温度保持稳定。将在四个地点进一步测试同位素方法和动态平衡假说，这四个地点将最大限度地扩大气候和物种差异，同时也最大限度地利用公共资助的气象和生态系统碳交换数据。在每个田间地点，根据同位素得出的树叶温度将与完全独立的光合作用加权冠层温度估计值进行比较。所有的温度估计将在三个生长季节的年际基础上进行比较，并进行多年综合。吸收本科生学习并帮助实现该项目的目标是一个持续的主要目标--培养一名研究生和一名博士后以及雇用一名技术员。这项研究的最终成果将为平均气候和年际天气变化对树木生态和生理的影响提供新的见解。这些结果有可能影响我们目前对植物生物学许多方面的理解--对树木分布的控制、森林碳和水交换的生态系统模型、对气候变化的生理反应、气候作为一种选择性压力--以及巩固氧同位素的新用途，该用途将适用于所有植物。

Temperature is a fundamental control on tree productivity, yet little is known about the in situ temperature of tree leaves in relation to carbon uptake during the course of the growing season. The aims of this project are to further develop a method to resolve tree-canopy leaf temperature by analyzing the oxygen isotope ratio of tree-rings. Initial results showed a leaf temperature homeostasis during carbon gain in 39 tree species across 50° of latitude. The isotopic method and the homeostasis hypothesis will be further tested in the field at four sites which maximize climatic and species differences, while also maximizing the overall use of publicly-funded meteorological and ecosystem carbon exchange data. At each field site, the isotope-derived leaf temperatures will be compared with completely independent estimates of photosynthesis-weighted canopy temperatures. All of the temperature estimates will be compared on an interannual basis over three growing seasons as well as a multi-year integration. The inclusion of undergraduate students to both learn from and help with the aims of this project is a continuing and primary objective - as is the training of a graduate student and a post-doctoral student and the employment of a technician. The final product of this research will give novel insight into the effects of mean climate and inter-annual weather variation on tree ecology and physiology. These results have the potential to impact our current understanding of many aspects of plant biology - the controls on tree distribution, ecosystem models of forest carbon and water exchange, physiological responses to climate change, climate as a selective pressure - as well as solidify a new use of oxygen isotopes that will be applicable to all plants.