Environmental, Physiological and Biochemical Processes Determining the Oxygen Isotope Ratio of Tree-Ring Cellulose

Abstract

Analysis of the oxygen isotope ratioof tree-ring cellulose (δ18Ocell) is a promising tool for reconstructingpast climatic variations and their influence on terrestrial ecosystems, but control mechanisms of δ18Ocell are multi-faceted, involving a number of fractionation steps along the oxygen transfer pathway from precipitation water to the site of cellulose formation. The goal of the current chapter is to provide an overview of the current knowledge concerning fractionation mechanisms related to δ18Ocell. The review is organized by using the currently widely-used δ18Ocell model as a reference context, and is focused on three main determinants of δ18Ocell: source water isotope ratio (δ18Osw), leaf water isotope enrichment (Δ18Olw), and biochemical fractionations downstream of Δ18Olw. For each component, we summarize environmental, physiological, and/or biochemical processes underlying 18O fractionations, and provide explanations of how these processes are critically relevant for linking δ18Ocell to climatic factors in real-world scenarios. We identify knowledge gaps in mechanistic controls of δ18Ocell, and highlight opportunities for more research to improve upon the existing model.

Covariation between oxygen and hydrogen stable isotopes declines along the path from xylem water to wood cellulose across an aridity gradient

“…For modelling the δ 18 O value in cellulose, f O (also referred to as p ex in the literature) is assumed to be c . 0.4 (Song et al ., 2022). We use 0.39 based on studies that also measured f H (Table S1).…”

“…However, recent studies have challenged this assumption. For example, the incorporation and exchange of oxygen from water in organic matter, which is an equilibrium isotope process, is thought to vary with temperature (Sternberg & Ellsworth, 2011), and the extent to which isotopic exchange occurs with water during sink cell metabolism has been shown to exhibit considerable variation, particularly in response to the environment (reviewed in Song et al ., 2022).…”

Updating the dual C and O isotope – gas exchange model: A concept to understand plant responses to the environment and its implications for tree rings

“…The variability of the δ 18 O values in leaf organic matter is predominantly determined by the extent of leaf H 2 O gas exchange during photosynthesis. Cernusak et al, (2016) and Song et al, (2022) with literature therein provide a summarizing overview of the various aspects of leaf water enrichment. Therefore, we cover only briefly the most important aspects on leaf water enrichment.…”

Inter-annual and intra-annual tree-ring oxygen isotope signals in response to monsoon rainfall in northwestern Thailand

“…Oxygen isotope ratios in tree-ring cellulose are influenced by the isotopic signature of the source water (i.e. the isotopic signature of rainfall infiltrating the soil, which can be modified by evaporation), the fractionation processes in the leaf during transpiration, biochemical fractionation during biosynthesis of cellulose, and the 18 O/ 16 O exchange between xylem water and phloem water (Roden et al, 2000; Song et al, 2022).…”