Improved photosynthesis from leaf to canopy scale drives yield progress in super hybrid rice

Super hybrid rice (SHR) plays a crucial role in achieving global food security by boosting grain yields. However, the physiological mechanisms underpinning yield gains—particularly from the leaf to canopy scale—under different nitrogen (N) regimes remain insufficiently understood. This study explores the physiological drivers of yield enhancement by examining biomass production, photosynthetic characteristics, radiation use efficiency (RUE), and yield components across varying nitrogen application rates. A three-year field experiment (2021–2023) assessed three representative SHR varieties—Liangyoupeijiu (LYPJ), Y-liangyou 1 (YLY1), and Y-liangyou 900 (YLY900)—released between 1999 and 2015, under four N treatments (0, 90, 180, and 270 kg N ha⁻¹). Among them, YLY900 achieved the highest average grain yield (9.78 Mg ha⁻¹), which was 9.1 % higher than that of LYPJ and YLY1, primarily owing to a 21.2 % increase in spikelets per panicle and a 12.6 % increase in total biomass. Its yield advantage was associated with enhanced RUE (2.91 g MJ⁻¹), 12.8 % higher than that of LYPJ, owing to sustained photosynthetic capacity under high N input. Unlike earlier varieties that depended mainly on intercepted photosynthetically active radiation (IPAR), YLY900 exhibited superior RUE through higher net photosynthetic rate, stomatal conductance, and photochemical quenching, together with lower non-photochemical quenching. Elevated Rubisco and phosphoenolpyruvate carboxylase activities supported efficient carbon assimilation. Overall, recent SHR breeding advances indicate a shift from maximizing light interception to enhancing photosynthetic efficiency and RUE, providing a physiological basis for future breeding and N management strategies aimed at sustainable yield improvement. • YLY900 showed 12.6% biomass increase and 8.6% yield advantage due to enhanced radiation use efficiency. • YLY900 excelled in leaf-to-canopy photosynthesis under high nitrogen, with higher enzymatic activity and chlorophyll. • Recent super hybrid rice lines shifted yield traits from radiation interception to improved photosynthetic efficiency.