Climate Signals in Stable Isotope Tree-Ring Records

Abstract

In this chapter we introduce the climate signal in stable isotope tree-ring records, with the emphasis on temperate forests. The development of the subdiscipline is recapped followed by an exploration of isotope dendroclimatic records by geography and, broadly, by isotopic species. Whilst there are still questions to be answered around signal strength and age-related effects in different environments and in different species, the proxy is now contributing to palaeoclimatology in a far greater way than in the days of the first hints of ‘isotope tree thermometers’. We include two summary tables. Table 19.1 exemplifies the range of climate information available from stable carbon isotope time series and Table 19.2 explores oxygen isotope proxy signals. Due to the greater complexity seen in stable carbon isotope interpretations we explore response groupings with example references given for each category of proxy response. Finally, we summarize the state of the art in isotope dendroclimatology and discuss possible future directions.

New insights into the mechanisms of plant isotope fractionation from combined analysis of intramolecular13C and deuterium abundances inPinus nigratree-ring glucose

“…Combined analysis of Δ i ’ and ε met provided new insights into plant isotope fractionation. First, isotope fractionation beyond leaves is usually considered to be constant for any given species (Roden et al ., 2000; Gagen et al ., 2022). Our results suggest, however, that a significant part of the carbon and hydrogen isotope variation in tree-ring glucose originates in stems from processes affecting Δ 1 ’, Δ 2 ’, and ε met simultaneously.…”

Shining a New Light on the Classical Concepts of Carbon-Isotope Dendrochronology

“…2 extracted from tree rings to preclude error due to variation in wood composition (arguments given below apply to cellulose but not necessarily to wood) (6). Tree-ring cellulose 13 C/ 12 C data are commonly expressed in terms of 13 C discrimination, Δtrc, denoting carbon isotope changes caused by physiological processes (9).…”

“…Tree-ring cellulose 13 C/ 12 C data are commonly expressed in terms of 13 C discrimination, Δtrc, denoting carbon isotope changes caused by physiological processes (9). Current data interpretations invoke a simple mechanistic model accounting for 13 C discrimination accompanying two processes: CO2 diffusion from ambient air into leaf intercellular air spaces (or chloroplasts) and carbon assimilation by rubisco (6,10,11), collectively termed diffusion-rubisco (DR) discrimination (12). Carbon assimilated by leaf phosphoenolpyruvate carboxylase (PEPC) is thought to not enter cellulose biosynthesis or significantly affect its isotope composition (13).…”

“…Intercellular CO2 concentration, in turn, varies with the rate of CO2 supply through leaf stomata and the rate of CO2 assimilatory demand. Since stomata respond to moisture conditions, Δtrc correlations with humidity parameters are thought to derive from CO2-supply-side effects on DR discrimination (6). By contrast, CO2 assimilation responds to air temperature and solar radiation, and corresponding Δtrc correlations are thought to derive form CO2-demand-side effects on DR discrimination (6).…”

Contrasting patterns of water use efficiency and annual radial growth among European beech forests along the Italian peninsula

“…Long-term changes in intrinsic water use efficiency ( i WUE), i.e. the cost of fixing carbon per unit of water loss (Seibt et al ., 2008; Gagen et al ., 2022), can be assessed by measuring carbon isotope composition in tree rings (δ 13 C). Tree-ring δ 13 C is equivalent to the ratio between photosynthesis ( A ) and stomatal conductance ( g s ) and this can vary, since both affect the ratio between CO 2 partial pressure in leaf intercellular space and in the atmosphere (Farquhar et al ., 1982; Battipaglia & Cherubini, 2022).…”