A high‐temperature water vapor equilibration method to determine non‐exchangeable hydrogen isotope ratios of sugar, starch and cellulose

Schuler, Philipp; Cormier, Marc-André; Werner, Roland A.; Buchmann, Nina; Geßler, Arthur; Vitali, Valentina; Saurer, Matthias; Lehmann, Marco M.

doi:10.1111/pce.14193

Cited by 31 publications

(49 citation statements)

References 74 publications

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“…Isotopic exchange occurs between the plant organics and water. Seventy percent of hydrogen in cellulose, the main component of xylem, is bound to carbon and isotopically nonexchangeable, whereas the remaining 30% is bound to oxygen in hydroxyl groups and is easily exchangeable in an aqueous medium (Sauer et al., 2009; Schimmelmann et al., 2006; Schuler et al., 2021). On one hand, the xylem water becomes progressively more enriched in 2 H during CVE due to progressive evaporation from the sample.…”

Section: Discussionmentioning

confidence: 99%

Causes and Factors of Cryogenic Extraction Biases on Isotopes of Xylem Water

Wen

Dong

et al. 2022

Water Resources Research

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Plant transpiration is the largest contributor to continental water flux (Jasechko, 2018;Jasechko et al., 2013). Understanding the sources of transpiration water is important for predicting the effects of global change on water security and ecosystem services. Stable isotope tracing is one of the most useful tools for the aforementioned purpose (Evaristo et al., 2015;Sprenger et al., 2016). A central assumption in the use of stable isotopes to investigate plant water sources is that, excluding leaf-evaporative effects, the stable isotopes 2 H and 18 O act as conservative tracers. Therefore, the isotopic composition of xylem water effectively reflects that of source water (Ehleringer & Dawson, 1992). This requires that there is no occurrence of significant isotopic fractionation during root water uptake and the subsequent water transport in plant organs (Ehleringer & Dawson, 1992;Washburn & Smith, 1934;Zimmermann et al., 1968); and sampling and isotopic analysis of plant water do not introduce errors (Brunel et al., 1995).However, recent studies have shown that isotopic signatures of the extracted xylem water do not always match those of the water source(s), thus creating isotopic offsets between stem water and the water source. Isotopic offsets, usually depleted in 2 H, of stem water relative to the water source, have now been reported in ecologically diverse plant species (de la Casa et al., 2021). Lin and Sternberg (1993) and Ellsworth and Williams (2007) first reported that fractionation, associated with transmembrane water transport at the root-soil interface, results in the depletion of stem water for drought-tolerant and salinity-tolerant plants. Zhao et al. (2016) did not find evidence for deuterium fractionation during water uptake; they attributed the observed soil-stem water isotopic offsets as a putative discrimination during water transport and redistribution within the plant. Other alternative explanations for the isotopic offsets of stem water have also been hypothesized, such as soil pore-scale isotopic heterogeneity (Lin & Horita, 2016;Oerter & Bowen, 2019;Oerter et al., 2014), vapor transport and condensation on the root tips (Vargas et al., 2017), and a mixture of sap and tissue water (Barbeta et al., 2022). However, a recent study by Chen et al. (2020) proved that little isotopic fractionation occurs during water uptake and transport among diverse habitats/species, and the offsets in δ 2 H are artifacts of cryogenic vacuum extraction (CVE).

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Section: Discussionmentioning

confidence: 99%

Causes and Factors of Cryogenic Extraction Biases on Isotopes of Xylem Water

Wen

Dong

et al. 2022

Water Resources Research

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“…Another nonexclusive possibility is disequilibrium between de novo sucrose and sucrose derived from transitory stores of starch, which may be exacerbated by differences in diel growth patterns between species. When triose‐phosphate is directed to starch synthesis, a large 2 H‐depletion in starch relative to sucrose has been observed in C 3 plants (Schuler et al, 2021), owing to disequilibrium of chloroplastic PGI, which 2 H‐depletes glucose‐6‐phosphate relative to fructose‐6‐phosphate (Schleucher et al, 1999). Our point‐in‐time measurements of the isotopic composition of leaf water and sucrose assume sugars that supply cellulose synthesis carry the isotopic composition of daytime conditions, despite sucrose export and cellulose deposition not being limited to the day.…”

Section: Discussionmentioning

confidence: 99%

“…For the determination of carbon-bound δ 2 H, samples were prepared as pairs and each individual equilibrated with one of two waters of known δ 2 H value, as per the method of Schuler et al (2021). Precision of cellulose δ 2 H measurements was on average 2‰ (average of standard deviations for cellulose measurements in table 1 of Schuler et al, 2021) 2.5 | Sugar δ 2 H analysis Carbon-bound hydrogen δ 2 H of sucrose was analysed by gas chromatography-isotope ratio mass spectrometry (GC-IRMS). This required that the sucrose be derived, both to make the compound amenable to analysis by gas chromatography, and to replace hydroxyl hydrogen with hydrogen of known δ 2 H to then calculate the carbon-bound hydrogen δ 2 H from the measured whole molecule value.…”

Section: Cellulose δ 2 H and δ 18 O Analysesmentioning

confidence: 99%

Section: Cellulose δ 2 H and δ 18 O Analysesmentioning

confidence: 99%

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Species variation in the hydrogen isotope composition of leaf cellulose is mostly driven by isotopic variation in leaf sucrose

Holloway‐Phillips

Baan

Nelson

et al. 2022

Plant Cell & Environment

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Experimental approaches to isolate drivers of variation in the carbon‐bound hydrogen isotope composition (δ2H) of plant cellulose are rare and current models are limited in their application. This is in part due to a lack in understanding of how 2H‐fractionations in carbohydrates differ between species. We analysed, for the first time, the δ2H of leaf sucrose along with the δ2H and δ18O of leaf cellulose and leaf and xylem water across seven herbaceous species and a starchless mutant of tobacco. The δ2H of sucrose explained 66% of the δ2H variation in cellulose (R2 = 0.66), which was associated with species differences in the 2H enrichment of sucrose above leaf water ( ε sucrose ${\unicode{x003B5}}_{sucrose}$ : −126% to −192‰) rather than by variation in leaf water δ2H itself. ε sucrose ${\unicode{x003B5}}_{sucrose}$ was positively related to dark respiration (R2 = 0.27), and isotopic exchange of hydrogen in sugars was positively related to the turnover time of carbohydrates (R2 = 0.38), but only when normalε sucrose ${\unicode{x003B5}}_{sucrose}$ was fixed to the literature accepted value of − 171 $\unicode{x02212} 171$ ‰. No relation was found between isotopic exchange of hydrogen and oxygen, suggesting large differences in the processes shaping post‐photosynthetic fractionation between elements. Our results strongly advocate that for robust applications of the leaf cellulose hydrogen isotope model, parameterization utilizing δ2H of sugars is needed.

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“…In woody tissue, oxygen-bound H atoms can exchange with those in surrounding liquid water and water vapour. Theoretically, about 30 % to 50 % of the H atoms of cellulose and its precursors are exchangeable (Schuler et al, 2022;Filot et al, 2006). If the CVD extraction disturbs the previously established isotopic equilibration between organic tissue and tissue water because of the gradually isotopically enriched tissue water during extraction, the potential H exchange would affect ecohydrological interpretations of 2 H (Barbeta et al, 2020;De La Casa et al, 2022).…”

Section: Introductionmentioning

confidence: 99%

Technical note: On uncertainties in plant water isotopic composition following extraction by cryogenic vacuum distillation

Diao

Schuler

Goldsmith

et al. 2022

Hydrol. Earth Syst. Sci.

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Abstract. Recent studies have challenged the interpretation of plant water isotopes obtained through cryogenic vacuum distillation (CVD) based on observations of a large 2H fractionation. These studies have hypothesized the existence of an H-atom exchange between water and organic tissue during CVD extraction with the magnitude of H exchange related to relative water content of the sample; however, clear evidence is lacking. Here, we systematically tested the uncertainties in the isotopic composition of CVD-extracted water by conducting a series of incubation and rehydration experiments using isotopically depleted water, water at natural isotope abundance, woody materials with exchangeable H, and organic materials without exchangeable H (cellulose triacetate and caffeine). We show that the offsets between hydrogen and oxygen isotope ratios and expected reference values (Δ2H and Δ18O) have inversely proportional relationships with the absolute amount of water being extracted, i.e. the lower the water amount, the higher the Δ2H and Δ18O. However, neither Δ2H nor Δ18O values, were related to sample relative water content. The Δ2H pattern was more pronounced for materials with exchangeable H atoms than with non-exchangeable H atoms. This is caused by the combined effect of H exchange during the incubation of materials in water and isotopic enrichments during evaporation and sublimation that depend on absolute water amount. The H exchange during CVD extraction itself was negligible. Despite these technical issues, we observed that the water amount-dependent patterns were much less pronounced for samples at natural isotope abundance and particularly low when sufficiently high amounts of water were extracted (>600 µL). Our study provides new insights into the mechanisms causing isotope fractionation during CVD extraction of water. The methodological uncertainties can be controlled if large samples of natural isotope abundance are used in ecohydrological studies.

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A high‐temperature water vapor equilibration method to determine non‐exchangeable hydrogen isotope ratios of sugar, starch and cellulose

Cited by 31 publications

References 74 publications

Causes and Factors of Cryogenic Extraction Biases on Isotopes of Xylem Water

Causes and Factors of Cryogenic Extraction Biases on Isotopes of Xylem Water

Species variation in the hydrogen isotope composition of leaf cellulose is mostly driven by isotopic variation in leaf sucrose

Technical note: On uncertainties in plant water isotopic composition following extraction by cryogenic vacuum distillation

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