[Nitrogen uptake, distribution, and utilization in young bearing Huangguan pear trees under ¹⁵N-urea application in...

We investigated the characteristics of nitrogen uptake, distribution, and utilization in the three-year-old bearing Huangguan pear trees following ¹⁵N-urea application in early spring. The results showed that the growth of pear trees was mainly depended on vegetative organs such as shoots and leaves at the stage from budbreak to shoot growth arrest, but mainly on storage organs (roots) and supplemented by the formation of fruit yield and quality at the stage from shoot growth arrest stage to fruit harvest. Meanwhile, tree biomass, especially that storage organs, substantially increased. All organs, especially newly developed shoots and leaves, acquired more N in shoot growth arrest stage due to vigorous growth, with relatively higher N derived from fertilizer (Ndff). Ndff of each organ except for root was lower at fruit maturity stage than that at shoot growth stage. Most of the labeled nitrogen was distributed in the newly developed organs (shoots and leaves) from budbreak to shoot growth arrest stage, but in the storage organs during shoot growth arrest stage to fruit maturity stage. Labeled fertilizer nitrogen was mainly distributed in the storage organs, followed by the vegetative organs. Reproductive organs had the lowest allocation in the experimental stage. For the three-years-old pear trees, the ratio of absorbed N from fertilizer was responsible for 31.1% and 21.0% of total absorbed nitrogen from budbreak to shoot growth arrest stage and from shoot growth arrest stage to fruit maturity stage, respectively, with the remaining N (68.9% and 79.0% of total) being absorbed from soil N.