Effects of nitrogen nutrition on photosynthesis and fruit production in Japanese pear, apple and grape trees.

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The effects of nitrogen nutrition during the growth season on net photosynthesis, photosynthate accumulation, nitrogen absorption, yield and fruit quality in Japanese pear, apple and grapes were investigated. In this studies, <^(15)N> and <^(13)C> were used as tracer elements.Photosynthetic activities in the shoot growth period were higher at high N levels than that both medium N levels and none N levels. While, in the fruit growth period, it were highest at medium N levels.Most of the nitrogen which had been applied on early April, were absorbed and translocated into fine roots and buds. The nitrogen applied on mid June were mainly translocated into leves and shoots. On the other hand, the nitrogen absorbed on early September were mainly transelocated into older shoots and roots.In the fruit growth and mature periods, the amount of <^(13)C> translocated into fruit increased at both medium N levels and none N levels, and decreased at high N levels.The <^(13)C> incorporated into fruit increased mainly in the sugar fruction at medium N levels and none N levels, but did not increased in both organic acid and amino acid fructions. In high N levels, more <^(13)C> was found in the organic acid and amino acid fructions than in the sugar fruction.