Optimized Leaf Morphology and Delayed Senescence Boost Rice Yield via Enhanced Leaf and Canopy Photosynthesis

Four modern hybrid and four japonica rice varieties differing in biomass, yield, and daily biomass production rate during the grain-filling period (DBPGF), were used to reveal the eco-physiological photosynthetic characteristics of high-yield and high-efficiency rice. Varietal differences were analyzed in leaf and canopy photosynthetic parameters, associated leaf morphological and anatomical traits (e.g., stomatal density, vein density, mesophyll cell arrangement), as well as differences in canopy light interception and leaf area index, and their effects on yield and biomass accumulation. Hybrid rice with yield higher than 11.0 t/hm2 and DBPGF higher than 200 kg/(hm2·d), and japonica rice with yield higher than 9.0 t/hm2 and DBPGF higher than 200 kg/(hm2·d), were classified as high-yield and high-efficiency varieties; other varieties were considered general types. Based on this criterion, two hybrid (Yongyou 2640 and Shanyou 63) and two japonica varieties (Huaidao 5 and Nangeng 5718) were categorized as high-yield and high-efficiency types, while the remaining two hybrid (Liangyoupeijiu and C Liangyou 513) and two japonica varieties (Suxiu 867 and Yangnongdao 1) were classified as general types. Results indicated that high-yield and high-efficiency varieties generally have higher leaf and canopy photosynthesis, superior leaf stomatal, vascular, and mesophyll structures that facilitate CO2 diffusion and hydraulic transport, higher canopy light transmittance, and slower leaf area attenuation. Rice yield and biomass were positively correlated with photosynthetic parameters and closely linked to associated photosynthetic traits. Efficient rice production was attributed to coordinated improvements in leaf structure, canopy architecture, and delayed leaf area attenuation. This study provides important theoretical guidance for breeding high-efficiency rice varieties.