Salinity stress severely limits barley production by disrupting physiological and biochemical processes critical for growth and yield. Although numerous studies have examined individual physiological or antioxidant responses to salinity, an integrated multivariate understanding of how these mechanisms collectively contribute to yield stability at the flowering stage remains limited. This study aimed to elucidate the integrated antioxidant and physiological mechanisms underlying salinity tolerance in barley genotypes during flowering. Barley plants were subjected to controlled salinity treatments, and a comprehensive set of phenolic compounds, antioxidant capacity indices, physiological traits, and yield components were measured. Multivariate analyses, including redundancy analysis (RDA) and partial least squares regression (PLSR), identified key traits contributing to yield stability under salinity. Multivariate analyses revealed also genotype-specific physiological strategies underlying contrasting salinity tolerance levels. Antioxidant defenses, such as total phenolics, DPPH and ABTS radical scavenging activities, and α-tocopherol, along with osmotic regulators like proline and soluble sugars, were closely associated with improved water status and reduced oxidative damage. These coordinated responses correlated strongly with yield components, including thousand-grain weight and main spike seed number. Notably, this study provides new insights into the predictive relevance of selected biochemical and physiological markers for yield performance under salt stress using PLSR at the flowering stage. PLSR further demonstrated the high predictive power of a limited subset of biochemical and physiological markers for yield traits under salt stress. Collectively, these findings reveal that the interplay between antioxidant machinery and osmotic adjustment at flowering is critical for barley resilience to salinity, providing valuable physiological markers to inform breeding strategies aimed at improving salt tolerance.

Treated wastewater (TWW) may still contain residual pollutants and chemicals that can accumulate in plant tissues and seeds, potentially disrupting plant m