Munns' two-phase model: Phase 1 — osmotic effect (immediate, similar to drought): high external salt lowers soil water potential, reducing water uptake; Phase 2 — ion-specific toxicity (gradual, days-weeks): Na⁺ and Cl⁻ accumulate in transpiring leaves exceeding compartmentation capacity, damaging photosynthetic machinery, enzymes, and membranes. Salt-tolerant crops manage both phases through osmotic adjustment and ion exclusion/compartmentation.