Abstract
In this work, the challenges and progression in stable isotope investigation, from the analytical tools and technical sample preparation procedures to the dendroclimatological experiments, were reviewed in terms of their use to assess tree physiological responses to environmental changes. Since the isotope signature of whole wood is not always a reliable tool in studying the climate changes, cellulose is often preferred as the study material in paleoclimatic studies. Nevertheless, the isotope analysis of cellulose is challenging due to the difficulty to remove the other wood components (extractives, lignin, pectin, and hemicelluloses). Additionally, in the case of hydrogen isotope analysis, about 30% of the hydrogen atoms of cellulose are exchanged with the surrounding water, which complicates the isotope analysis. In recent years, more automated isotope analysis methods were developed based on high temperature pyrolysis of cellulose, followed by the chromatographic separation of H2 from CO and by their individual isotope analysis using isotope ratio mass spectrometry. When used to investigate climate factors, the combined isotope analysis δ13C and δ18O appears to be the most promising isotope tool. In contrast, the role of δ2H values is yet to be elucidated, together with the development of new methods for hydrogen isotope analysis.
Highlights
Ecosystems and biodiversity are already being influenced by climate change, as well as a wide range of physical and biological processes in many regions of the world, with available observational evidence being indicated in the forest biomes [1]
Given the need for careful evaluations of stable isotopes as climate proxies for different regional environments and tree species, this overview of the up-to-date information on tree rings isotopic composition aims at: (1) describing the main extraction techniques and stable isotope analysis methods recently developed for the tree rings cellulose, and (2) reviewing research avenues to identify their correlation with climate changes
For α-cellulose extraction from wood samples, there are currently over 10 different methods and procedures presented in the literature, including variants of the main three methods: (i) diglyme-HCl methods [21], (ii) Brendel type [22], and (iii) Jayme-Wise type [11,23,24] methods
Summary
Ecosystems and biodiversity are already being influenced by climate change, as well as a wide range of physical and biological processes in many regions of the world, with available observational evidence being indicated in the forest biomes [1]. Additional contribution of hydrogen, carbon, and oxygen isotopes might be given by extractives (alkaloids, polyphenols, fatty acids, essential oils, proteins, terpenes, pectins, waxes, resins, gums, starch, glycosides, saponins, etc.) which show a wide range of δ-values, since they are produced in the secondary plant metabolism [13]. They can have a minor impact on the total 13 C value of wood, especially if these extractives only account for an insignificant fraction and/or their values are mostly in the cellulose and lignin isotope variability. Given the need for careful evaluations of stable isotopes as climate proxies for different regional environments and tree species, this overview of the up-to-date information on tree rings isotopic composition aims at: (1) describing the main extraction techniques and stable isotope analysis methods recently developed for the tree rings cellulose, and (2) reviewing research avenues to identify their correlation with climate changes
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