Abstract
The relation between new shoot growth and the utilization of stored assimilates (nitrogen and carbon) was investigated. A one-year-old apple tree (‘Fuji’ on Malus prunifolia (Willd.) Borkh.), after pruning, was treated with 15N and 13C in the year prior to the experiment. The trees were examined early (in May), at mid-term (June) and when mature (September). Shoot growth stages and nitrogen and carbon status were analyzed at each harvesting. The shoot length did not relate with its position and difference in the length of the shoots was small in May, but thereafter the upper shoots grew longer than the lower shoots. There was no relationship between the length of the shoot and the 15N excess% of the shoot at each stage, but the value of the 15N excess% of the shoots in September was much lower than that in either May or June. The 13C excess% decreased during the period from May to June, and a limited inverse correlation was found with the length of the shoot. There was a significant positive correlation between the lengths of the shoot and 15N or 13C distribution in the shoot. It was suggested that, as they grew, the longer shoots absorbed higher amounts of stored assimilates than the shorter shoots. Although the degree to which stored versus current absorbed assimilates contributes to new shoot growth might be the same in all shoots, stored nitrogen plays an important role in new shoot growth.
