The hydrogren 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, baseline information on hydrogen isotope composition (δ2H) and what it can tell us about plant performance is uneven and scarce. Using durum wheat, this study evaluates the effect of different water and nitrogen growing field conditions on transpiration and how this influences the performance of δ2H in autotrophic (flag leaf), mixotrophic (ears) and heterotrophic (grains and roots) organs compared to the δ13C and δ18O in the same organs. Isotope composition was 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 in the case of δ18O there was no correlation. 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 to the δ2H of stem water, plant δ2H was strongly diminished in photosynthetic organs like the flag leaves, whereas it strongly increased in heterotrophic organs such as grains and roots. In heterotrophic organs, δ2H was associated with post-photosynthetic effects as there are several processes that lead to 2H-enrichment of carbohydrates. Summarizing, δ2H exhibited specific features that inform about the water conditions of the crop, together with the photosynthetic characteristics of the plant part considered. Moreover, correlations of δ2H with grain yield enable consideration of this isotope in assessing plant performance under different growing conditions.