Mitigating Severe Salinity Stress in Vicia faba L. via Exogenous Proline: A Climate Resilience Intervention

<title>Abstract</title> <p> Climate change and its impacts on soil salinization threaten faba bean ( <italic>Vicia faba</italic> L.) production in the Nile Delta. Although the osmotic benefits of exogenous osmoprotectants are well recognized, long-term, tissue-specific partitioning mechanisms of repeated foliar proline under unmitigated severe saline irrigation (12 dS m ^− 1 ) are poorly quantified. In the study, a holistic hydrochemical and agronomic approach was used to evaluate the efficacy of weekly foliar proline (500 mg L ^− 1 ) as an intervention for climate-resilience. The hydrochemical modeling confirmed severe irrigation constraints at 12 dS m ^− 1 , with a Sodium Adsorption Ratio (SAR) of 32.41 and positive Chloro-Alkaline indices, indicating strong reverse base-exchange phenomena. Pod counts where declined to 30 per plant under unmitigated saline irrigation (12 dS m ^− 1 ), and reproductive output collapsed. Weekly proline applications reprogrammed the stress response, with pod counts returning to 33.67 and 91.75% reproductive potential preserved. Under moderate salinity (6 dS m⁻¹), proline application recovered 70.91% of the yield potential lost due to osmotic stress. Metabolic recovery was governed by a coordinated N–K–protein trait axis, as indicated by a multivariate principal component analysis (97.47% of the variance explained). Critically, proline was not just allowing bulk sodium exclusion; it was altering tissue electrophysiology to preferentially maintain leaf potassium (2.01% vs. 1.56%) and protect nitrogen assimilation. Thus, the leaf crude protein increased to 21.84%, and the harvested seeds showed a high protein fraction of 23.90%. The study offers a robust data-driven framework to transform hazardous saline water into an agricultural input and a scalable climate-adaptation approach aligned with SDGs 2, 6, and 13. </p>