Abstract: Using ¹³C pulsed labeling technique, we examined the biomass and carbon accumulation of different organs as well as the distribution characteristics of ¹³C assimilate of 6-year-old Korla fragrant pear trees under three nitrogen application levels, i.e., 150, 300, and 450 kg N·hm^-2 (marked as N₁, N₂, and N₃, respectively). Results showed that the biomass, carbon accumulation, ¹³C fixation and leaf assimilation capacity of the whole pear tree increased while root to shoot ratio decreased with increasing nitrogen application. Both biomass and carbon accumulation amount of reproductive organs (i.e., fruits) were the highest under N₂ treatment. The ¹³C content and distribution rate of each organ changed dynamically along with increasing nitrogen application. At the new shoot growing stage, leaves and roots had stronger competitive abilities for photosynthate, with ¹³C distribution rates being the highest under N₁ treatment. During fruit swelling and mature stages, leaves and fruits were more competitive, with ¹³C content and distribution rate in leaves being the highest under N₃ treatment and those in fruits being the highest under N₂ treatment. According to the absorption and distribution characteristics of carbon assimilate across organs under the three nitrogen application levels, the optimal nitrogen application level for achieving high fruit yield in the 6-year-old Korla fragrant pear tree orchard is recommended as 300 kg·hm^-2 .

Key words: Korla fragrant pear, nitrogen application level, photosynthate, distribution