Root Structural and Metabolic Plasticity Confers Tolerance to Salinity in Wild Barley Species Grown Under Waterlogging.

Salinity combined with waterlogging is a major abiotic stress that severely limits crop growth and yield. We investigated species-specific adaptations to salinity under constant waterlogging conditions in the wild halophytic barleys Hordeum marinum and H. glaucum, compared with the cultivated H. vulgare. Using magnetic resonance imaging, fluorescence scanning microscopy, ¹³C-based carbon fixation analysis, and ion and metabolite profiling, we identified key anatomical and physiological traits underlying differential salinity responses. H. marinum exhibited the highest tolerance under saline waterlogging, maintaining water status, metabolic activity, and high carbon fixation rates. This species accumulated the lowest concentrations of Na⁺ and Cl⁻ while retaining the highest levels of K⁺ in both roots and shoots. H. glaucum showed intermediate tolerance associated with reduced water content, whereas H. vulgare failed to survive under these conditions. We propose that salinity tolerance in H. marinum is mediated by an integrated root-based mechanism in which intact aerenchyma sustains internal oxygen transport. At the same time, salt-induced enhancement of lateral root branching promotes sequestration of excess Na⁺ within the lateral root cortex, thereby limiting its translocation to photosynthetically active tissues. This aeration-sequestration system stabilizes root function under salinity and waterlogging, and promotes whole-plant resilience in wild barleys, but is only weakly maintained in cultivated H. vulgare.