1987 Volume 55 Issue 4 Pages 434-444
In this experiment 15N and 13C were used as tracer elements. With an increase of flowering load, percentage fruit setting and the number of shoots of spring flush decreased. The percentage fruit setting was particularly lowered by an increase of leafless inflorescences.
In trees where the ratio of leaf to flower number was less than 10, the total amount of nitrogen contained in the dropped flowers was more than 10% of the nitrogen in all the fruit harvested in autumn.
The percentage fruit setting of leafy inflorescences was higher and the ovary growth during 4 to 5 days of preflowering stage was greater than that of leafless inflorescences. It was also confirmed that the nitrogen which had been applied on April 20, was absorbed and translocated to new shoots as well as to flowers at anthesis. Thus it seems that the nitrogen promoted photosynthesis and increased the fruit setting. On the other hand, nitrogen which had been applied on May 8, had almost no effect on fruit setting but contributed to the development new shoots after anthesis. Most of the nitrogen which was applied on September 1, was steadily absorbed until mid November. 15N content in the leaves remained almost constant until the following February. Throughout the period from March to May, 15N content of shoots, leaves and fibrous root decreased, while that of the new leaves and flower organs increased. 15N which was applied on April 20 as well as on September 1 was uniformly distributed to plant parts such as flower organs and new shoots. Dropped flower organs contained a considerable amount of the 15N. This shows that much of the nitrogen in the flower organs was lost through flower dropping.
Although a lot of 13C-photosynthates was translocated to leafy inflorescences, the total amount of 13C in the dropped flowers was greater. Among the plant parts, 13C content was highest in the new leaves through anthesis. 13C content in the old leaves decreased rapidly while that of flower organs increased.
