ECOTRI · Ecophysiological Aspects of Tree Ring Isotopes

Understanding biosphere-climate interactions is essential for reliable assessments of ecosystem responses under a changing climate. A potentially rich source of information on vegetation climate responses across large scales of space and time exists in the natural archives of tree-rings. In particular, the isotopic composition (d13C and d18O) of tree-ring cellulose may yield valuable information due to climate-related fractionation effects at the leaf. However, incomplete understanding of the relationship between the isotopic composition of photo-assimilate and that of tree-ring cellulose currently compromises the use of tree-ring isotopes in developing reliable climate proxies. A number of potential physiological processes may operate to modify the isotopic composition of carbohydrates post-fixation, such as respiration, mixing with remobilized stores, isotopic exchange between xylem and phloem water and cellulose synthesis. Therefore this project aims to advance our understanding of the relationship between the environmentally mediated leaf level isotopic signals and tree ring isotope composition. The proposed research is a multidisciplinary study involving ecophysiology, isotope ecology and dendroclimatology. The research will focus on the processes affecting tree-ring d13C and d18O in response to seasonally and climatically driven physiological and phenological influences through controlled environment and field experiments using isotope tracer and labeling methods. The results will be applied to an integrated multi-isotope tree ring model in order to both assist with model development and enhance interpretation of the results. The outcomes of this research will thus advance our process-level understanding of ecosystem-climate responses and therefore assist in making informed decisions relating to strategies under future climate scenarios.