δ2H, δ18O, and δ13C behave differently when assessing transpirative and photosynthetic performance of wheat under contrasting VPD conditions
2025
Fatima Zahra Rezzouk | Maria Dolors Serret | José Luis Araus | Rut Sanchez Bragado
Carbon (δ13C) and oxygen (δ18O) isotope compositions are considered indicators of the effect of water conditions on plant photosynthesis (δ13C) and transpiration (δ18O). Hydrogen isotope composition (δ2H), tracks transpiration like δ18O, while also affected by the organ trophism. Such dual behaviour, together with its highly exchangeable nature have hindered the use of δ2H to assess plant performance. We compared the effect of contrasting water pressure deficit (VPD) on the signatures of the three isotopes across different durum wheat parts. Plants were hydroponically grown under conditions, differing in VPD and the isotopic labelling of the nutrient solution (natural abundance versus δ2H and δ18O-enriched) and isotopic signatures analysed at mid-grain filling. Higher VPD increased plant-matter δ13C, δ2H, and δ18O, in accordance with atmospheric drought decreasing stomatal conductance and transpiration. Moreover, positive correlations within and across organs between δ2H and δ18O of organic-matter and water further supported a similar source of variation related to evaporation. However, δ2H was depleted in photoautotrophic (leaves and glumes), enriched in mixotrophic (peduncle and awns) and even more in heterotrophic (grains) organs. This study highlights the similarities and differences in mechanisms determining δ2H, δ18O, and δ13C through the interactions of these isotopes with VPD and plant organs.
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