A study on the movement of reserve nutrients in Japanese pear.

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In order to clarify the relationships between the reserve nutrients in Japanese pear tree and the tree vigor and fruit production, carbohydrate and nitrogen contents in the whole tree of young (3 years-old), abult (17 years-old) and old tree (62 years-old) of 'Nijisseiki' were investigated.1. The main reserve nutrients in pear tree are carbohydrate and nitrogen. The carbohydrate was constituted by starch and 4 soluble sugars of sorbitol, fructose, glucose and sucrose, and the main reserve substances were starch and sorbitol. The nitrogen was constituted by protein and soluble nitrogen, amino acids in which arginine was major.2. Younger branch contained more carbohydrate and nitrogen contents in any trees. Most of these reserve nutrients were stored in shoot and main root in youg tree, in primary scaffold limb from 10 to 15 years old and main root in adult tree, and in less than 30 years old limb and main root in old tree.3. In the branch starch content increased in Autumn and thereafter markedly decreased in May because of new growth. Sugar contents markedly increased in Winter and then decreased in Spring. In the roots both starch and sugar contents in Autum, then decreased followed by new growth. Amino acid contents decreased in Winter, then markedly increased from late February to early April.4. In adult tree all part of tree serve as storage organs so that many starch and nitrogen were stored as the suplus nutrients even after the untrient diversion period in May. It was found that in old tree the xylem more than 30 years old lost the ability of storage, so reserve nutrients were few in the whole tree and the suplus nutrients after May also decreased. It was suggested that these few suplus nutrient causes a decline of tree vigor in old tree.