Leaf Position-Specific Photosynthetic and Metabolic Adaptations Underpin Saline-Alkali Stress Tolerance in Oats (Avena sativa 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.