Ion homeostasis coordinates oxidative defense and photosynthesis to sustain rice yield under high-salinity stress

Soil salinization severely constrains global agricultural productivity. Identifying salt-tolerant germplasm and elucidating regulatory mechanisms are crucial for utilizing saline–alkali lands. This two-year field study evaluated the salt-tolerant hybrid rice Jingliangyou 3261 (JLY3261) against three reference cultivars (Yuxiangyouzhan (YXYZ), Shuangliangyou91 (SLY91), and Jingyou007 (JY007)) under 0‰ and 5‰ salinity using a split-plot design with three replicates, in which salinity treatment was assigned as the main plot factor and cultivar as the subplot factor. Salt stress at 5‰ was initiated 10 d after transplanting and maintained through regular EC monitoring and drainage–irrigation adjustment. Integrating agronomic, physiological, and molecular data using principal component analysis (PCA) and partial least squares structural equation modeling (PLS-SEM) revealed that ion homeostasis functioned as an upstream regulatory module, sustaining yield by alleviating oxidative stress and preserving photosynthetic performance. Compared to other reference cultivars, JLY3261 maintained superior yield stability, relatively high K + concentrations, and relatively high K + /Na + ratio under 5‰ salt stress. OsSOS1 expression was significantly higher in JLY3261 than in SLY91 under salt stress, suggesting enhanced potential for Na + exclusion. Furthermore, JLY3261 maintained stronger antioxidant capacity and higher expression of photosynthesis-related genes, particularly psbA and rbcL , thereby helping protect photosystem II and sustain carbon assimilation. These findings indicate that salt-tolerant rice cultivars can sustain yield under high-salinity stress through stronger ion homeostasis that coordinates oxidative defense and photosynthetic maintenance.