Rhizobial Symbiosis Enhances Salinity Tolerance in Legumes Through Coordinated Physiological and Molecular Responses:...

Soil salinisation severely constrains crop production. Legumes rely on rhizobial symbiosis for sustainable nitrogen acquisition. Although salinity is known to impair nodulation and nitrogen fixation, how symbiosis influences plant tolerance to salt stress remains unclear. In this study, we integrate physiological, biochemical, transcriptomic, ionomic, and metabolomic analyses to investigate the role of rhizobial symbiosis in salinity tolerance in Vicia sativa (common vetch) and Pisum sativum (pea). In both species, nodulated plants exhibited markedly enhanced survival and grain production under prolonged salt stress compared with nitrogen-fertilised (N-fed) controls. Under moderate salinity, nodulation helped maintain water status and stomatal conductance, reduced Na⁺ accumulation while improving K⁺ retention, and attenuated osmotic and oxidative stress, as evidenced by lower proline and malondialdehyde levels. Transcriptomic profiles in vetch revealed that symbiosis is associated with changes in the plant responses toward growth and microbial signalling, reducing the strong activation of stress pathways that typically occurs in non-nodulated plants. Ionomic and metabolomic data further showed that nodulated plants preserve nutrient balance and maintain a more stable carbon-nitrogen metabolism under salinity. These findings highlight the potential of Rhizobium inoculation to enhance crop resilience in salt-affected agroecosystems and demonstrate that symbiosis correlates with a more efficient and physiologically moderated acclimation to salinity in legumes.