The Hydrogen Isotope Composition δ2H Reflects Plant Performance.

The stable carbon (δ13C) and oxygen (δ18O) isotope compositions in plant matter reflect photosynthetic and transpirative conditions in plants, respectively. However, the nature of hydrogen isotope composition (δ2H) 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 δ2H in autotrophic (flag leaf), mixotrophic (ears), and heterotrophic (grains and roots) organs. Moreover, δ2H was compared with the δ13C and δ18O 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 δ13C, the δ2H correlated negatively with stomatal conductance, whereas no correlation was observed for δ18O. Moreover, δ2H 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 δ2H of stem water, plant δ2H 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, δ2H was associated with postphotosynthetic effects because there are several processes that lead to 2H-enrichment of carbohydrates. In summary, δ2H 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 δ2H with grain yield illustrate that this isotope can be used to assess plant performance under different growing conditions.