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

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.

[Effects of different phosphorus application rates on growth, 15N-urea absorption, and utilization characteristics of pear rootstocks.] / ä¾›ç£·æ°´å¹³å¯¹æ¢¨ç §æœ¨ç”Ÿé•¿å’Œ15N-å°¿ç´ å¸æ”¶åˆ©ç”¨ç‰¹æ€§çš„å½±å“.

Three kinds of potted one-year-old pear rootstocks (Pyrus calleryana, P. pashia, and P. xerophila) and 15N trace technique were used to examine the effects of different phosphorus application rates (P0, P1, P2, P3 and P4 equivalent to 0, 50, 100, 150 and 200 kg·hm-2 P2O5, respectively) on plant growth and the characteristics of 15N-urea absorption and utilization. The results showed that, with the increases of phosphorus levels, plant height, ground diameter, dry mass, root surface area, root length, number of root tips, root activity, root respiration rate, Ndff values, and nitrogen use efficiency of rootstocks first increased and then decreased. However, the range of rise and fall of different rootstocks were distinct, and each index reached the highest level at different phosphorus levels. The plant height, diameter, dry mass of P. xerophila were the highest under the same phosphorus level, followed by P. pashia, and P. calleryana was the lowest. The root architecture parameters and root respiration rate showed the same trend, but Ndff values and nitrogen use efficiency performed different. Under different phosphorus levels, each index of P. xerophila reached the highest level at P3, but those of P. pashia and P. calleryana appeared at P2 and P1 rates, respectively. The Ndff values in stem were the highest among different organs of rootstocks at diffe-rent phosphorus levels, and the highest nitrogen use efficiency of P. xerophila, P. pashia and P. calleryana was 9.6%, 8.9% and 8.3%, respectively. The variations of plant growth and N absorption and utilization of different pear rootstocks across different phosphorus levels indicated that phosphorus fertilizer should be carry out reasonably in practice and give full consideration of phosphorus demands of plants.