Effect of rice leaf color-changing patterns and nitrogen application on stem non-structural carbohydrate translocation during grain filling

• Rice variety with slow leaf color change exhibited lower stem NSC remobilization efficiency than fast leaf color change variety. • Stem NSC translocation efficiency was negatively correlated with leaf color change onset time while positively correlated with the leaf color change rate. • N application postponed the onset of leaf color change and enhanced yield while reducing NSC translocation and its contribution to grain filling. To elucidate the relationship between leaf color-changing and stem NSC translocation during grain filling and their impact on yield formation, two indica-japonica hybrid varieties with distinct leaf color change patterns were planted under three N fertilizer dosages (LN 0 kg ha −1 ; MN 150 kg ha −1 ; HN 300 kg ha −1 ). Leaf color change characteristics, photosynthetic productivity, stem NSC translocation, yield and harvest index were analyzed. The results showed that CY927 (slow leaf color change) achieved 10.45%−21.81% higher yields than YY1540 (fast leaf color change) under high-temperature conditions. Compared to YY1540, CY927 delayed the onset of leaf color-changing (T 0 ) by 2.1−4.1 d, enhanced the final leaf color indicator at maturation (CI f ) by 16.79−52.25%, contributing to 10.56−42.77% greater aboveground biomass accumulation through higher photosynthetic capacity, but significantly limited stem NSC remobilization, reduced total NSC translocation by 23.78−33.19% and NSC translocation ratio by 14.65−22.19%, resulting in a 2.66−8.43% lower harvest index. N application increased rice yield via a delay in leaf color-changing onset (T 0 ), a reduced color-changing rate (R m ), a shortened color-changing duration (T 100 ), and an improved final color index (CI f ). This retardation of senescence enhanced photosynthetic capacity, which was associated with elevated sucrose content and sucrose synthase activity. However, N reduced stem α-amylase activity (14.83−62.07%) and NSC translocation ratio (5.44−16.30%) in both varieties. Correlation analysis revealed significant positive relationships between T 0 and aboveground biomass ( P