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

University Of Pennsylvania, Philadelphia PA

Investigators

Abstract

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.