¹⁸O and ¹³C in Leaf Litter Versus Tree-ring Cellulose as Proxy Isotopic Indicators of Climate Change

Abstract

The Throughfall Displacement Experiment (TDE) has resulted in a number of arboreal responses, examples of which range from water potential differences in treatments (Gebre et al. 1998) to whole-tree mortality (Hanson et al. 2001). Many of these direct ecosystem adjustments have been readily measurable and are discussed in more detail throughout this volume. Nevertheless there are compelling reasons to measure more indirect physiological responses, such as stable-isotope ratios, within trees of this eastern North American deciduous forest subjected to a throughfall displacement disturbance. Stable-isotope ratios of plant organic material have been shown to have utility for integrating plant water status in the case of carbon isotopes [e.g., (2000)], and hydrogen and oxygen isotopes of organic matter also show potential for recording climatic variations (Edwards 1993; Farquhar et al. 1998). This has led to widespread interest in the climatic and physiological information that is potentially recorded in the isotopic composition (oxygen, carbon, and hydrogen) of organic matter in tree rings. However, interpreting isotope data from recent tree rings occurs in the context of industrial-era increases in CO₂, decreasing ¹³C/¹²C ratios in the atmospheric fraction of the gas, and incomplete or unavailable weather records for older tree-ring sequences. These complexities impair the use of isotopic variations for interpreting prehistoric and historic tree-ring records.