The Stable Hydrogen Isotopic Signature: From Source Water to Tree Rings

Abstract

The hydrogen isotopic signature (δ2H) of water in trees contains information on plant functional responses to climatic changes and on the origin of the water. This is also true for the non-exchangeable hydrogen isotopic signature (δ2HNE) of plant organic matter, which contains additional physiological and biochemical information that can be dated to specific years if extracted from annual rings of trees. Despite this potential for gaining unique insights from δ2HNEof tree-ring cellulose (δ2HTRC), it has not been widely used compared to other isotope signals, likely due to challenging methodological constraints and interpretations of these isotopic signals. In this chapter, we first summarize hydrogen isotope (2H-) fractionation that occurs between source water and tree rings and review methods (e.g. nitration, equilibration, position-specific applications) and calculations to determine δ2HNE in tree material. Building upon a summary of the current state of knowledge, this chapter also provides an exhaustive synthesis of δ2HTRC papers, applications, and associated data from approximately 180 sites across the globe (paired with modelled precipitation δ2H values and climate data). The data allow us to investigate the hydrological-climatic effects driving δ2HTRC pattern on a global scale, the relationship of hydrogen with oxygen isotopes in the same tree-ring material, as well as the influence of physiological-biochemical effects (e.g., species differences, tree growth) that appear to be more important on local or temporal scales than on a large spatial scales. Thus, when local hydro-climatic influences on source water δ2H can be isolated, δ2HTRC gives novel insights on tree physiological responses to abiotic and biotic stresses. We conclude that the growing constellation of tree-ring metrics, including advancements in 2H-processing (i.e., equilibration techniques allowing rapid determinations of δ2HNE) and further refinements to the understanding of post-photosynthetic 2H-fractionations will together provide many new opportunities to understand past climates and ecophysiology by using δ2H in tree rings.

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

“…As primary sugars are synthesised in leaves, sugars and by extension plant cellulose should theoretically show similar δ 18 O–δ 2 H covariation as plant water due to the incorporation of O and H sourced both directly and indirectly from water during compound biosynthesis. Across large spatial scales, this appears to be a reasonable assumption (Lehmann et al ., 2022). However, at the local scale, analysing temporal variation in tree‐ring chronologies, weak relationships between δ 2 H and δ 18 O are often observed (Nabeshima et al ., 2018; Nakatsuka et al ., 2020; Vitali et al ., 2022).…”

“…Also, position‐specific intramolecular δ 2 H analysis has suggested different fractionation factors for individual H‐atom positions, which respond to environmental conditions (Schleucher et al ., 1999; Augusti et al ., 2006; Wieloch et al ., 2022a,b). Variation in the isotopic offset between cellulose δ 2 H and plant water pools also supports the view that fractionation factors can change with species and growth conditions (Sternberg & Deniro, 1983; Cormier et al ., 2018, 2019; Baan et al ., 2022, 2023; Lehmann et al ., 2022).…”

Hydrogen isotope fractionation in carbohydrates of leaves and xylem tissues follows distinct phylogenetic patterns: a common garden experiment with 73 tree and shrub species

“…However, the actual 2 H fractionation processes influencing the δ 2 H ne of sugars and cellulose in autotropic and heterotrophic tissues remain elusive (Badea et al ., 2021; Schönbeck & Santiago, 2022). Recent studies have highlighted that the transfer of the 2 H signal from leaf sugars to leaf cellulose (Holloway‐Phillips et al ., 2022) or from source water to tree‐ring cellulose (Arosio et al ., 2020b; Lehmann et al ., 2022; Vitali et al ., 2022) varies both within and among species and is also dynamic over time. However, systematic studies on potential phylogenetic effects on δ 2 H ne in trees are still missing.…”

“…Furthermore, various heterotrophic 2 H fractionation processes occur during plant metabolism (Augusti et al ., 2008), altering the initial δ 2 H ne of the fresh assimilates (e.g. nonstructural carbohydrates (NSCs) in the form of sugar and starch) in the pathway to tree‐ring cellulose formation (Kagawa & Battipaglia, 2022; Lehmann et al ., 2022). At the leaf level, heterotrophic 2 H fractionation processes within a species seem to be relatively constant under stable climatic conditions, and the δ 2 H ne of leaf sucrose can explain more than the half of the δ 2 H ne variation in leaf cellulose (Holloway‐Phillips et al ., 2022).…”

“…Furthermore, recent findings suggest that fundamental plant traits, such as seasonal leaf shedding behavior, significantly impact the δ 2 H ne of tree‐ring cellulose (Arosio et al ., 2020b). Such effects may be caused by differences in 2 H fractionation processes (Lehmann et al ., 2022), but the mechanistic basis of these processes is not yet known. Several biochemical pathways probably influence the apparent autotrophic and heterotrophic 2 H fractionation, and they can be summarized as ε HA (autotrophic 2 H fractionation, between leaf water and sugar) and ε HE (heterotrophic 2 H fractionation, between sugars and cellulose).…”