Differential Ion Partitioning and Salinity Tolerance in Willow (Salix spp.) Clones under Semi-Arid Conditions

Salinity is a major abiotic stress that disrupts ion balance, reduces nutrient uptake, and limits plant growth. This study investigated differential ion partitioning and salinity tolerance in ten willow (Salix spp.) clones under semi-arid conditions. Seedlings were irrigated with four saline water regimes (4, 8, 12, and 16 dS/m) for up to 105 days, and sodium (Na⁺), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), and Na⁺: K⁺ ratios were quantified in leaves, stems, and roots. Sodium content increased progressively with salinity, with roots (0.60%) retaining more than stems (0.56%) and leaves (0.30%). In contrast, K⁺, Ca²⁺, and Mg²⁺ declined, while Na⁺: K⁺ ratios rose sharply, reflecting ionic imbalance. Genotypic differences were evident: clone 131/25 maintained higher K⁺ and lower Na⁺: K⁺ ratios across tissues, indicating superior ionic regulation, whereas PN731 was more sensitive. The results suggest that salinity tolerance in willow is closely linked to the capacity for differential ion partitioning, particularly the restriction of Na⁺ accumulation in metabolically active tissues. These findings highlight the potential of salt-tolerant willow clones for afforestation, biomass production, and rehabilitation of semi-arid saline lands, and provide physiological markers for breeding and selection.