Leaf Position-Specific Photosynthetic and Metabolic Adaptations Underpin Saline-Alkali Stress Tolerance in Oats ( <i>Avena sativa</i> L.)

Saline-alkali stress is a major abiotic constraint limiting cereal productivity on global marginal lands. This study integrated multiomics and physiological phenotyping analyses to characterize leaf position-specific stress responses in contrasting oat cultivars. Leaf excision experiments confirmed upper third leaf (L3) retention is the critical determinant of oat survival under stress: L3-excised plants all died within 13 days post-treatment, while first leaf (L1)-excised plants maintained survival rates comparable to intact controls. All tested oats showed consistent position-dependent resilience patterns: although tolerant lines have higher overall tolerance, all cultivars exhibit far milder functional impairment in L3 than L1, with multiomics data confirming position-specific regulation of photosynthesis, AsA-GSH and TCA cycle pathways underpins this difference. These findings reveal a novel tissue-specific tolerance regulatory mechanism, guiding saline-alkali tolerant crop breeding.