EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Identifying sources of hydrogen isotope fractionation in plant carbohydrates and lipids under low carbohydrate supply

Meisha Holloway-Phillips1, Anina Wacker1, Günter Hoch1, Daniel B. Nelson1, Marco Lehmann2, and Ansgar Kahmen1
Meisha Holloway-Phillips et al.
  • 1University of Basel, Department of Environmental Sciences - Botany, Basel, Switzerland (
  • 2Swiss Federal Institute for Forest, Snow and Landscape Research, Birmendsorf, Switzerland

Appreciation for the influence of plant metabolism on the hydrogen isotope composition (δ2H) of plant compounds has increased in recent years, adding new opportunities to understand how plants respond to environmental change. In general, where carbon supply is limited (e.g. at the beginning of the growth season, in darkness, under low CO2), the resulting δ2H of newly produced plant compounds tends to be 2H-enriched. The source of the 2H-enrichment has yet to be identified but hypotheses include: 1) a direct effect of reduced photosynthesis; 2) change in the partitioning of photoassimilates to sucrose/transitory starch; 3) use of longer-term starch reserves; and/or, 4) increased isotopic exchange with water suggesting increased metabolite cycling. To test these ideas, we utilised samples collected from a study which grew tree saplings under 100% and 6% of ambient sunlight in the field (Weber et al. 2018, New Phytologist, 222: 171-182).  In general, relative growth rate was attenuated by a species-specific amount that ensured homeostasis of non-structural carbohydrate (NSC) concentrations; however, not before an initial two-fold reduction in NSC levels – the time period the current study focussed on. Cellulose was purified and n-alkanes extracted from leaves of six deciduous species (Betula pendula, Carpinus betulus, Fagus sylvatica, Prunus avium, Quercus petraea and Tilia platyphyllos) in July 2016, around one year after the shade treatment began. The isotopic difference of cellulose between shaded and full sunlit grown leaves (εshade-sun) was significantly different from zero, with species-specific offsets ranging between 20 to 70‰. In comparison, the treatment effect was minimal for the C-chain length concentration weighted δ2H values of n-alkanes, ranging between -7 to +10‰. To narrow down the source of 2H-enrichment in leaf cellulose, the δ2H of sucrose and starch are currently being analysed in samples collected from stem wood (without bark) before bud-break in March 2016, and in leaf and stem material sampled after leaf-out in July 2016. An increase in sucrose δ2H values from shade leaves relative to controls would support Hypothesis 1 and 2; 2H-enriched storage starch relative to leaf sucrose would support Hypothesis 3; and an increase in the δ2H of sucrose in stem wood relative to storage starch (before bud-break), would support Hypothesis 4. Our study has important implications for interpreting 2H-enrichment of plant compounds with respect to reduced C supply.

How to cite: Holloway-Phillips, M., Wacker, A., Hoch, G., Nelson, D. B., Lehmann, M., and Kahmen, A.: Identifying sources of hydrogen isotope fractionation in plant carbohydrates and lipids under low carbohydrate supply, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9401,, 2023.