The Hydrogen Isotope Composition δ 2 H Reflects Plant Performance.

The stable carbon (δ ¹³ C) and oxygen (δ ¹⁸ O) isotope compositions in plant matter reflect photosynthetic and transpirative conditions in plants, respectively. However, the nature of hydrogen isotope composition (δ ² H) 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 δ ² H in autotrophic (flag leaf), mixotrophic (ears), and heterotrophic (grains and roots) organs. Moreover, δ ² H was compared with the δ ¹³ C and δ ¹⁸ O 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 δ ¹³ C, the δ ² H correlated negatively with stomatal conductance, whereas no correlation was observed for δ ¹⁸ O. Moreover, δ ² H 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 δ ² H of stem water, plant δ ² H 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, δ ² H was associated with postphotosynthetic effects because there are several processes that lead to ² H-enrichment of carbohydrates. In summary, δ ² H 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 δ ² H with grain yield illustrate that this isotope can be used to assess plant performance under different growing conditions.
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