Abstract: Clarifying the appropriate application rates of N, P, and K fertilizers and the physiological mechanisms of wheat under water-saving recharge irrigation in the North China Plain would provide a theoretical basis for formulating reasonable fertilization plans for high-yield and high-efficiency wheat production. We established four treatments with different amounts of nitrogen (N), phosphorus (P₂O₅), and potassium (K₂O) application: 0, 0, and 0 kg·hm^-2 (F₀), 180, 75, and 60 kg·hm^-2 (F₁), 225, 120, and 105 kg·hm^-2 (F₂), and 270, 165, and 150 kg·hm^-2 (F₃). During the jointing and anthesis stages of wheat, the relative water content of each treatment in the 0-40 cm soil layer was replenished to 70%, to investigate the differences in wheat flag leaf photosynthetic characteristics, distribution of ¹³C assimilates, grain starch accumulation, and fertilizer utilization. The results showed that the relative chlorophyll content of flag leaves, photosynthetic and chlorophyll fluorescence parameters, ¹³C assimilate allocation in each organ, enzyme activities involved in starch synthesis, and starch accumulation in the F₁ treatment were significantly higher than that in F₀ treatment, which was an important physiological basis for the 20.9% increase in grain yield. The above parameters and yield in the F₂ and F₃ treatments showed no significant increase compared to F₁ treatment, while fertilizer productivity and agronomic efficiency of N, P, and K decreased by 17.5%-58.4% and 12.7%-50.7%, respectively. Therefore, F₁ could promote flag leaf photosynthetic assimilate production and grain starch accumulation under water-saving supplementary irrigation conditions, resulting in higher grain yield and fertilizer utilization efficiency.

Key words: wheat, application rate of N, P, K fertilizers, ¹³C assimilate distribution, starch accumulation, ferti-lizer utilization