Light intensity modulates phosphorus adaptation strategies in contrasting rice cultivars through photosynthetic...

Phosphorus (P) availability in soils is often limited, but rice (Oryza sativa L.)cultivars can adapt by altering physiological traits. Our hypothesis is that enhanced light intensity alleviates P deficiency stress in rice by promoting root growth through improved photosynthetic carbon assimilation. This study investigated how light intensity (high vs. low) and P supply (sufficient vs. deficient) affect dry matter accumulation, root morphology, photosynthesis, and P absorption in two rice cultivars: P-tolerant "Dalixiang" and P-sensitive "Meixiangzhan". Key findings include: (1) High light significantly enhanced dry matter accumulation, especially under P-deficient (DP), with "Dalixiang" showing an 88.6 % increase in root biomass. (2) Photosynthetic traits were light-dependent, with "Dalixiang" outperforming in efficiency. (3) "Dalixiang" optimized carbon allocation to roots (123.1 % higher root-to-shoot ratio) under DP, linked to elevated acid phosphatase (ACP) activity and Adenosine triphosphate (ATP) levels. (4) "Meixiangzhan" allocated more P to shoots but exhibited weaker DP adaptation, likely due to upregulated stem phosphate transporters (PT, 32.5 %) but limited root P activation. In summary, P-deficiency tolerant rice cultivars adapt to P deficiency by optimizing carbon allocation, enhancing root morphological plasticity, and improving P activation capacity, while light intensity significantly influences this adaptive strategy by regulating photosynthetic carbon supply. This study provides a theoretical basis for breeding P-efficient rice cultivars and determining optimal planting densities in P-deficient paddy fields.