Physiological Resilience, Ionic Homeostasis and Stress-Adaptive Responses Underlying Salinity Tolerance in Citrus Cultivars

Salt stress severely restricts citrus productivity in arid and semi-arid regions by disturbing ionic balance, water relations, and physiological functioning. The present study investigated salinity-induced changes in growth, ionic composition, physiological traits, and stress-responsive metabolites in four commercially important citrus cultivars, namely sweet orange (Blood Red), grapefruit (Star Ruby), kinnow mandarin, and lemon (Baramasi). Plants were exposed to five salinity levels ranging from 0.12 to 7.0 dS m−1 under controlled pot conditions using a completely randomized design with five replications. Increasing salinity progressively reduced plant growth, chlorophyll stability, biomass accumulation, tissue hydration, and leaf health, while membrane injury increased markedly under severe stress. Salinity also disrupted ionic homeostasis through enhanced accumulation of Na+ and SO42− ions coupled with depletion of Ca2+, Mg2+, and K+ in leaves and roots. Accumulation of anthocyanins and flavonoids increased under saline conditions, suggesting activation of stress-responsive biochemical protection mechanisms. Marked cultivar-specific differences were observed in salinity tolerance. Sweet orange and kinnow maintained lower Na+ accumulation, better K+/Na+ balance, higher chlorophyll stability, improved relative water content, and greater biomass retention under stress conditions. In contrast, grapefruit and lemon exhibited greater ionic imbalance, membrane injury, and physiological disruption. The findings indicate that maintenance of ionic homeostasis, chlorophyll stability, and adaptive biochemical modulation plays an important role in salinity tolerance in citrus cultivars. Among the cultivars evaluated, sweet orange and kinnow exhibited comparatively stronger adaptive resilience under progressive salinity stress.