EGU21-8918
https://doi.org/10.5194/egusphere-egu21-8918
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Measurements of leaf sucrose to explain variability in hydrogen isotope composition of leaf cellulose

Meisha Holloway-Philips1, Jochem Baan1, Daniel Nelson1, Guillaume Tcherkez2, and Ansgar Kahmen1
Meisha Holloway-Philips et al.
  • 1University of Basel, Department of Environmental Sciences - Botany, Basel, Switzerland (m.holloway-phillips@unibas.ch)
  • 2Research School of Biology, College of Science, Australian National University, 2601 Canberra, ACT, Australia

The hydrogen isotope composition (δ2H) of cellulose has been used to assess ecohydrological processes and carries metabolic information, adding new understanding to how plants respond to environmental change. However, experimental approaches to isolate drivers of δ2H variation is limited to the Yakir & DeNiro model (1990), which is difficult to implement and largely unvalidated. Notably, the two biosynthetic fractionation factors in the model, associated with photosynthetic (εA) and post-photosynthetic (εH) processes are currently accepted as constants, and the third parameter – the extent to which organic molecules exchange hydrogen (fH) with local water – is usually tuned in order to resolve the difference between modelled and observed cellulose δ2H values. Thus, by virtue, the metabolically interpretable parameter is only fH, whilst from theory, metabolic flux rates will also impact on the apparent fractionations. To overcome part of this limitation, we measured the δ2H of extracted leaf sucrose from fully-expanded leaves of seven species and a phosphoglucomutase ‘starchless’ mutant of tobacco to estimate the isotopic offset between sucrose and leaf water (εsucrose). Sucrose δ2H explained ~60% of the δ2H variation observed in cellulose. In general, εsucrose was higher (range: -203‰ to -114‰; mean: -151 ± 21‰) than the currently accepted value of -171‰ (εA) reflecting 2H-enrichment downstream of triose-phosphate export from the chloroplast, with statistical differences in εsucrose observed between species estimates. The remaining δ2H variation in cellulose was explained by species differences in f(estimated by assuming εH = +158‰). We also tested possible links between model parameters and plant metabolism. εsucrose was positively related to dark respiration (R2=0.27) suggesting an important branch point influencing sugar δ2H. In addition, fH was positively related to the turnover time (τ) of water-soluble carbohydrates (R2=0.38), but only when estimated using fixed εA = -171‰. To decipher and isolate the “metabolic” information contained within δ2H values of cellulose it will be important to assess δ2H values of non-structural carbohydrates so that hydrogen isotope fractionation during sugar metabolism can be better understood. This study provides the first attempt at such measurements showing species differences in both source and sink processes are important in understanding δ2H variation of cellulose.

How to cite: Holloway-Philips, M., Baan, J., Nelson, D., Tcherkez, G., and Kahmen, A.: Measurements of leaf sucrose to explain variability in hydrogen isotope composition of leaf cellulose, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8918, https://doi.org/10.5194/egusphere-egu21-8918, 2021.

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