Whole-Cycle Responses of Photosynthetic Capacity, Biomass Accumulation, and Grain Yield Across an Additive Blue-Light Supplementation Gradient in Two Rice Genotypes

Rice is central to global food security, and plant factories enable precise control of lighting conditions. However, genotype-specific responses to supplemental blue light across the full crop cycle remain poorly understood. Here, Nipponbare and CP511 were grown from transplanting to maturity under a green, red, and far-red background supplemented with 0, 50, 100, 150, or 300 μmol m−2 s−1 blue light (B0–B300). In both genotypes, increasing supplementation reduced plant height, increased tillering and biomass, advanced flowering by 9–13 d, and enhanced pigment content and photosynthetic capacity. Nipponbare maintained photosynthetic improvements at higher supplementation levels, whereas CP511 plateaued earlier. In Nipponbare, grain yield increased from 1.46 g plant−1 at B0 to 5.09 g plant−1 at B100 but did not increase significantly thereafter, despite enhanced photosynthesis and sucrose metabolism. At B300, seed setting declined to 54%, with reduced dry-matter allocation to panicles. In CP511, higher supplementation increased total panicle production but not effective panicle formation, seed setting, or grain yield, which changed from 3.29 g plant−1 at B150 to 2.49 g plant−1 at B300. Thus, the most favorable treatment depended on coordination between source capacity and effective reproductive sink formation rather than maximal photosynthesis or panicle production alone.