[Characteristics of absorption, utilization, and distribution of ¹⁵N-urea for Korla fragrant pear in spring.]

Six-year-old Korla fragrant pear trees were fertilized with ¹⁵N-labelled urea before early bud stage to examine the absorption, distribution, and utilization of urea. Results showed that there was a significant difference of ¹⁵N distribution rate in organs at different growth stages. ¹⁵N was pre-ferentially distributed in the roots , with Ndff (¹⁵N amount absorbed from the fertilizer contribution rate of the total nitrogen organ) being the highest in roots following by new shoots at full-bloom stage. During new shoot growing and fruit expanding stages, ¹⁵N absorbed in roots preferentially moved to new organs (leaves and new shoots), with ¹⁵N distribution rate to roots being continuously decreased. Fruits became the new distribution center with highest Ndff at harvest stage. The amounts of absorbed ¹⁵N in fruits accounted for 19.8% of total absorbed ¹⁵N in the tree. The utilization rate of ¹⁵N-labelled urea at current season increased gradually with the growth stages. The maximum value of utilization rate was 18.5%, which was observed at harvest stage.