Moderate salinity enhances nutritional quality but suppresses growth in spinach (Spinacia oleracea): A trade-off between stress adaptation and yield

Soil salinity is an increasing constraint to leafy vegetable production, often limiting crop yield while simultaneously altering nutritional composition. Understanding the balance between growth suppression and stress-induced nutritional enhancement is there­fore critical for sustainable spinach (Spinacia oleracea) cultivation in saline agroecosystems. This study investigated the growth and biochemical responses of spinach to incremental salinity stress (0-6 dS/m NaCl) under controlled conditions. The growth parameters (plant height, the number of leaves, and leaf area), proximate composition (moisture, ash, protein, carbohydrates, crude fat, and fibre), and mineral dynamics ( Ca² +, Fe² +, K+, Mg² +) were evaluated using a completely randomised design, supported by ANOVA and robust regression analyses. Salinity reduced vegetative performance overall, with the leaf number declining by approximately 50% at 6 dS/m and plant height showing a net reduction of 13% relative to the control at harvest, despite increases observed at intermediate salinity levels. Leaf expansion exhibited a hormetic response, with moderate salinity (2 dS/m) temporarily enhancing leaf area during the early growth stages. Bulk biochemical analysis revealed salinity-driven trade-offs, where ash (+33%) and protein (+42%) contents increased significantly (p < 0.001), while carbohydrate content declined by 17% ( R² = 0.946). Mineral composition displayed salinity-dependent shifts, with Fe² + peaking at 2 dS/m (20.63 mg/L) before declining at higher salinity, partial recovery of K+ uptake at 6 dS/m (59.91 mg/L), and relatively stable Ca² + and Mg² + concentrations. Moisture and crude fibre contents were not significantly affected (p > 0.05). Robust regression confirmed threshold-dependent responses, indicating that moderate salinity (2-4 dS/m) can enhance micronutrient availability without severely disrupting ionic homeostasis. These findings highlight a trade-off between nutritional quality enhancement and growth suppression under salinity stress and support precision irrigation and salinity-resilient breeding strategies to optimise spinach production in saline environments.