Synergistic root-photosynthesis responses to phosphorus rates optimise grain appearance quality in phosphorus‑efficient rice cultivars

Combining phosphorus management with phosphorus-efficient cultivars is an effective strategy for improving rice quality. To investigate their effects on root characteristics and photosynthetic traits, a pot experiment was conducted with two rice cultivars differing in phosphorus efficient: Liangeng 7 (weakly efficient) and Yongyou 2640 (highly efficient). Four phosphorus rates (0, 0.44, 0.88, and 1.32 g/pot, designated as P0, P1, P2, and P3, respectively) were applied. A significant cultivar-phosphorus interaction was observed. Most root traits (the length, dry weight, volume, total absorption area, active absorption area, oxidation activity, and acid phosphatase activity) and photosynthetic traits (photosynthetic rate, transpiration rate, and stomatal conductance) initially increased and then decreased with increasing phosphorus rates, while the leaf intercellular CO₂ concentration showed the opposite trend. Liangeng 7 performed optimally under P2, whereas Yongyou 2640 reached its peak under P1. Compared with Liangeng 7, Yongyou 2640 exhibited better appearance quality, root traits, and photosynthetic parameters. Correlation analysis showed that root length, root physiological activity and leaf photosynthetic parameters (except intercellular CO₂ concentration) were significantly negatively correlated with chalkiness degree. These findings demonstrate that matching phosphorus supply to cultivar‑specific efficiency optimises root‑photosynthesis synergy, leading to superior grain appearance quality with less phosphorus input.