Linking osmotic adjustment and stomatal characteristics with salinity stress tolerance in contrasting barley accessions

Salinity tolerance is a complex trait – both physiologically and genetically – and the issue of which mechanism or trait has bigger contribution towards the overall plant performance is still hotly discussed in the literature. In this work, a broad range of barley (Hordeum vulgare L. and Hordeum spontaneum L.) genotypes contrasting in salinity stress tolerance were used to investigate the causal link between plant stomatal characteristics, tissue ion relations, and salinity tolerance. In total, 46 genotypes (including two wild barleys) were grown under glasshouse conditions and exposed to moderate salinity stress (200 mM NaCl) for 5 weeks. The overall salinity tolerance correlated positively with stomata density, leaf K⁺ concentration and the relative contribution of inorganic ions towards osmotic adjustment in the shoot. At the same time, no correlation between salinity tolerance and stomatal conductance or leaf Na⁺ content in the shoot was found. Taken together, these results indicate the importance of increasing stomata density as an adaptive tool to optimise efficiency of CO₂ assimilation under moderate saline conditions, as well as benefits of the predominant use of inorganic osmolytes for osmotic adjustment in barley. Another finding of note was that wild barleys showed rather different strategies dealing with salinity, as compared with cultivated varieties.