Probing Tree Physiology Using the Dual-Isotope Approach

Abstract

AbstractThe environmental and physiological interpretation of stable isotope variation in organic matter is affected by many different and interacting factors. This is especially true when considering isotope variation in tree rings, which are influenced not only by leaf-level photosynthetic gas exchange processes but also by post-photosynthetic fractionation. It has been proposed that measuring multiple isotopes on the same sample may constrain such interpretations if one isotope provides independent information about important fractionation events that cause variation in another isotope. Here we describe one such “dual-isotope approach” where oxygen isotope variation (δ18O) is used to probe the effects of stomatal conductance on carbon isotope (δ13C) variation for the same sample. This chapter describes the development of this conceptual model, constraints on model applicability, particularly with respect to tree rings, and how it has been utilized to explore aspects of tree physiology.