Uptake and Allocation of Newly Absorbed Nitrogen in Young Pear Trees Grafted onto Vigorous Rootstocks (Pyrus betulifolia)

Abstract

Nitrogen is one of the essential elements for fruit tree growth. Therefore, a 15N tracing experiment was conducted to investigate the characteristics of nitrogen uptake and distribution in young pear trees. The experiment included: groups A and B, fertilized with 15 g unlabeled and 5 g labeled N per tree in the spring of 2017; and group C, fertilized with 20 g unlabeled N per tree in the spring of 2017 and 25 g unlabeled and 5 g labeled N per tree in the spring of 2018. Results indicated that new organs grew vigorously before June, and about 50% of the fertilizer nitrogen was concentrated in leaves. From June to November, the growth rate of storage organs was faster than that of new organs, and fertilizer nitrogen was mainly stored in the shoots, trunk, and roots. During the defoliation period, about 84% of the leaf fertilizer nitrogen was mobilized to the shoots, trunk, and roots. There was significant correlation between current fertilizer nitrogen and the dry mass weight of each organ after the completion of the nitrogen cycling of a whole year; the correlation coefficient was 0.98. Fertilizer nitrogen use efficiency increased with the ages of the pear trees. Therefore, nitrogen fertilizer rate should be formulated according to the tree growth characteristics and increased with the ages of the young pear trees; topdressing fertilizer should be applied in summer to ensure trunk and root development.