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Lehmann MM, Diao H, Ouyang S, Gessler A. Different responses of oxygen and hydrogen isotopes in leaf and tree-ring organic matter to lethal soil drought. TREE PHYSIOLOGY 2024; 44:tpae043. [PMID: 38618738 DOI: 10.1093/treephys/tpae043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Revised: 03/02/2024] [Accepted: 03/23/2024] [Indexed: 04/16/2024]
Abstract
The oxygen and hydrogen isotopic composition (δ18O, δ2H) of plant tissues are key tools for the reconstruction of hydrological and plant physiological processes and may therefore be used to disentangle the reasons for tree mortality. However, how both elements respond to soil drought conditions before death has rarely been investigated. To test this, we performed a greenhouse study and determined predisposing fertilization and lethal soil drought effects on δ18O and δ2H values of organic matter in leaves and tree rings of living and dead saplings of five European tree species. For mechanistic insights, we additionally measured isotopic (i.e. δ18O and δ2H values of leaf and twig water), physiological (i.e. leaf water potential and gas-exchange) and metabolic traits (i.e. leaf and stem non-structural carbohydrate concentration, carbon-to-nitrogen ratios). Across all species, lethal soil drought generally caused a homogenous 2H-enrichment in leaf and tree-ring organic matter, but a low and heterogenous δ18O response in the same tissues. Unlike δ18O values, δ2H values of tree-ring organic matter were correlated with those of leaf and twig water and with plant physiological traits across treatments and species. The 2H-enrichment in plant organic matter also went along with a decrease in stem starch concentrations under soil drought compared with well-watered conditions. In contrast, the predisposing fertilization had generally no significant effect on any tested isotopic, physiological and metabolic traits. We propose that the 2H-enrichment in the dead trees is related to (i) the plant water isotopic composition, (ii) metabolic processes shaping leaf non-structural carbohydrates, (iii) the use of carbon reserves for growth and (iv) species-specific physiological adjustments. The homogenous stress imprint on δ2H but not on δ18O suggests that the former could be used as a proxy to reconstruct soil droughts and underlying processes of tree mortality.
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Affiliation(s)
- Marco M Lehmann
- Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland
- Forest Soils and Biogeochemistry, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland
| | - Haoyu Diao
- Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland
| | - Shengnan Ouyang
- Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland
- Institute for Forest Resources and Environment of Guizhou, Guizhou University, Jiaxiu South Road, Huaxi District, Guiyang 550025, China
| | - Arthur Gessler
- Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zürcherstrasse 111, 8903 Birmensdorf, Switzerland
- Institute of Terrestrial Ecosystems, ETH Zurich, Universitätstrasse 16, 8092 Zurich, Switzerland
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Pan Y, Li F, Lin W, Zhou Y, Song X. Quantifying isotope parameters associated with carbonyl-water oxygen exchange during sucrose translocation in tree phloem. THE NEW PHYTOLOGIST 2024; 242:975-987. [PMID: 38439696 DOI: 10.1111/nph.19654] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Accepted: 02/19/2024] [Indexed: 03/06/2024]
Abstract
Stable oxygen isotope ratio of tree-ring α-cellulose (δ18Ocel) yields valuable information on many aspects of tree-climate interactions. However, our current understanding of the mechanistic controls on δ18Ocel is incomplete, with a knowledge gap existent regarding the fractionation effect characterizing carbonyl-water oxygen exchange during sucrose translocation from leaf to phloem. To address this insufficiency, we set up an experimental system integrating a vapor 18O-labeling feature to manipulate leaf-level isotopic signatures in tree saplings enclosed within whole-canopy gas-exchange cuvettes. We applied this experimental system to three different tree species to determine their respective relationships between 18O enrichment of sucrose in leaf lamina (Δ18Ol_suc) and petiole phloem (Δ18Ophl_suc) under environmentally/physiologically stable conditions. Based on the determined Δ18Ophl_suc-Δ18Ol_suc relationships, we estimated that on average, at least 25% of the oxygen atoms in sucrose undergo isotopic exchange with water along the leaf-to-phloem translocation path and that the biochemical fractionation factor accounting for such exchange is c. 34‰, markedly higher than the conventionally assumed value of 27‰. Our study represents a significant step toward quantitative elucidation of the oxygen isotope dynamics during sucrose translocation in trees. This has important implications with respect to improving the δ18Ocel model and its related applications in paleoclimatic and ecophysiological contexts.
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Affiliation(s)
- Yonghui Pan
- Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, 511458, China
- College of Life Sciences and Oceanography, Shenzhen University, Shenzhen, 518060, China
| | - Fang Li
- College of Life Sciences and Oceanography, Shenzhen University, Shenzhen, 518060, China
- Huzhou Vocational & Technical College, Huzhou, 313000, China
| | - Wen Lin
- State Key Laboratory of Herbage Improvement and Grassland Agro-ecosystems, College of Pastoral Agriculture Science and Technology, Lanzhou University, Lanzhou, 730000, China
| | - Youping Zhou
- Department of Marine Science and Technology, Southern University of Science and Technology, Shenzhen, 518055, China
| | - Xin Song
- College of Life Sciences and Oceanography, Shenzhen University, Shenzhen, 518060, China
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Rani A, Zhao Y, Yan Q, Wang Y, Ma R, Zhu Z, Wang B, Li T, Zhou X, Hocart CH, Zhou Y. On the Chemical Purity and Oxygen Isotopic Composition of α-Cellulose Extractable from Higher Plants and the Implications for Climate, Metabolic, and Physiological Studies. Anal Chem 2023; 95:4871-4879. [PMID: 36878693 DOI: 10.1021/acs.analchem.2c04384] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/08/2023]
Abstract
The 18O/16O ratio of α-cellulose in land plants has proved of interest for climate, environmental, physiological, and metabolic studies. Reliable application of such a ratio may be compromised by the presence of hemicellulose impurities in the α-cellulose product obtainable with current extraction methods, as the impurities are known to be isotopically different from that of the α-cellulose. We first compared the quality of hydrolysates of "α-cellulose products" obtained with four representative extraction methods (Jayme and Wise; Brendel; Zhou; Loader) and quantified the hemicellulose-derived non-glucose sugars in the α-cellulose products from 40 land grass species using gas chromatography-mass spectrometry (GC/MS). Second, we performed compound-specific isotope analysis of the hydrolysates using GC/Pyrolysis/IRMS. These results were then compared with the bulk isotope analysis using EA/Pyrolysis/IRMS of the α-cellulose products. We found that overall, the Zhou method afforded the highest purity α-cellulose as judged by the minimal presence of lignin and the second-lowest presence of non-glucose sugars. Isotopic analysis then showed that the O-2-O-6 of the α-cellulose glucosyl units were all depleted in 18O by 0.0-4.3 mUr (average, 1.9 mUr) in a species-dependent manner relative to the α-cellulose products. The positive isotopic bias of using the α-cellulose product instead of the glucosyl units stems mainly from the fact that the pentoses that dominate hemicellulose contamination in the α-cellulose product are relatively enriched in 18O (compared to hexoses) as they inherit only the relatively 18O-enriched O-2-O-5 moiety of sucrose, the common precursor of pentoses and hexoses in cellulose, and are further enriched in 18O by the (incomplete) hydrolysis.
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Affiliation(s)
- Andleeb Rani
- Isotopomics in Chemical Biology (ICB), School of Chemistry and Chemical Engineering, Shaanxi University of Science and Technology, Xi'an 710021, China
| | - Yu Zhao
- Isotopomics in Chemical Biology (ICB), School of Chemistry and Chemical Engineering, Shaanxi University of Science and Technology, Xi'an 710021, China
| | - Qiulin Yan
- Isotopomics in Chemical Biology (ICB), School of Chemistry and Chemical Engineering, Shaanxi University of Science and Technology, Xi'an 710021, China
| | - Ying Wang
- Isotopomics in Chemical Biology (ICB), School of Chemistry and Chemical Engineering, Shaanxi University of Science and Technology, Xi'an 710021, China
| | - Ran Ma
- Isotopomics in Chemical Biology (ICB), School of Chemistry and Chemical Engineering, Shaanxi University of Science and Technology, Xi'an 710021, China
| | - Zhenyu Zhu
- Isotopomics in Chemical Biology (ICB), School of Chemistry and Chemical Engineering, Shaanxi University of Science and Technology, Xi'an 710021, China
| | - Bo Wang
- Isotopomics in Chemical Biology (ICB), School of Chemistry and Chemical Engineering, Shaanxi University of Science and Technology, Xi'an 710021, China
| | - Ting Li
- College of Science and Engineering, ARC Centre of Excellence for Australian Biodiversity and Heritage, Centre for Tropical Environmental and Sustainability Science, James Cook University, Cairns 4878, Australia
| | - Xiuwen Zhou
- Isotopomics in Chemical & Biological Oceanography (ICBO), Department of Ocean Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China
| | - Charles H Hocart
- Isotopomics in Chemical Biology (ICB), School of Chemistry and Chemical Engineering, Shaanxi University of Science and Technology, Xi'an 710021, China
- Research School of Biology, Australian National University, Acton 2601, Australian Capital Territory, Australia
| | - Youping Zhou
- Isotopomics in Chemical Biology (ICB), School of Chemistry and Chemical Engineering, Shaanxi University of Science and Technology, Xi'an 710021, China
- Isotopomics in Chemical & Biological Oceanography (ICBO), Department of Ocean Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China
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