Using stable isotope natural abundances (δ15N and δ13C) to integrate the stress responses of wild barley (Hordeum spontaneum C. Koch.) genotypes

To integrate the complex physiological responses of plants to stress, natural abundances (δ) of the stable isotope pairs 15N/14N and 13C/12C were measured in 30 genotypes of wild barley (Hordeum spontaneum C. Koch.). These accessions, originating from ecologically diverse sites, were grown in a controlled environment and subjected to mild, short‐term drought or N‐starvation. Increases in total dry weight were paralleled by less negative δ13C in shoots and, in unstressed and droughted plants, by less negative whole‐plant δ13C. Root δ15N was correlated negatively with total dry weight, whereas shoot and whole‐plant δ15N were not correlated with dry weight. The difference in δ15N between shoot and root varied with stress in all genotypes. Shoot–root δ15N may be a more sensitive indicator of stress response than shoot, root or whole‐plant δ15N alone. Among the potentially most productive genotypes, the most stress‐tolerant had the most negative whole‐plant δ15N, whether the stress was drought or N‐starvation. In common, controlled experiments, genotypic differences in whole‐plant δ15N may reflect the extent to which N can be retained within plants when stressed.