The Hydrogen Isotope Composition δ2H Reflects Plant Performance

The stable carbon (delta C-13) and oxygen (delta O-18) isotope compositions in plant matter reflect photosynthetic and transpirative conditions in plants, respectively. However, the nature of hydrogen isotope composition (delta H-2) and what it reflects of plant performance is poorly understood. Using durum wheat (Triticum turgidum var durum), this study evaluated the effect of different water and nitrogen growing field conditions on transpiration and how this effect influenced the performance of delta H-2 in autotrophic (flag leaf), mixotrophic (ears), and heterotrophic (grains and roots) organs. Moreover, delta H-2 was compared with the delta C-13 and delta O-18 in the same organs. Isotope compositions were analyzed in dry matter, the water-soluble fraction, and in water from different tissues of a set of genotypes. Similar to delta C-13, the delta H-2 correlated negatively with stomatal conductance, whereas no correlation was observed for delta O-18. Moreover, d2H was not only affected by changes in transpiration but also by photosynthetic reactions, probably as a consequence of NADPH formation in autotrophic organs. Compared with the delta H-2 of stem water, plant delta H-2 was strongly diminished in photosynthetic organs such as the flag leaves, whereas it strongly increased in heterotrophic organs such as grains and roots. In heterotrophic organs, delta H-2 was associated with postphotosynthetic effects because there are several processes that lead to H-2-enrichment of carbohydrates. In summary, delta H-2 exhibited specific features that inform about the water conditions of the wheat crop, together with the photosynthetic characteristics of the plant part considered. Moreover, correlations of delta H-2 with grain yield illustrate that this isotope can be used to assess plant performance under different growing conditions.