Reduced leaf size enhances photosynthetic acclimation to high-light under heat stress by enhancing hydraulic conductance in rice

• Reduced leaf area enhances rice photosynthesis under combined high light and heat stress by increasing xylem hydraulic conductance, which sustains stomatal conductance and mitigates water potential decline. This study establishes a direct link between leaf size and hydraulic regulation, offering a new strategy for improving crop photosynthetic adaptability. Improving the adaptability of rice leaves to high-light under heat stress is essential for maximizing photosynthetic efficiency. This study examined the responses of leaf gas exchange and hydraulic parameters to intense light under heat stress (40 °C) in wild type ( Nipponbare ) and four genetically modified rice varieties ( NAL1-K, NAL1-O, Ghd7.1-K, and Ghd7.1-O ) that exhibited significant differences in leaf area ( LA ). When measured irradiance increased from 1000 to 2000 μmol m -2 s -1 under heat stress, the changes of photosynthetic rate ( A 2000 -A 1000 ) ranged from -2.8 μmol m -2 s -1 in NAL1-O to 14.9 μmol m -2 s -1 in NAL1-K . A negative correlation between A 2000 -A 1000 and LA was observed. The varying responses of A to high-light were primarily associated with stomatal conductance ( g s ). Enhanced leaf hydraulic conductance ( K leaf ) facilitated the g s response to high-light under heat stress conditions. Furthermore, this study revealed that, under high-light and heat stress conditions, K leaf is predominantly regulated by leaf hydraulic conductance inside the xylem ( K x ), and reduced LA can significantly improve K x . These findings demonstrate that reducing LA can enhance K leaf , thereby improving the response of A to high-light under heat stress.