Using the bearing and non-bearing trees of the 3-year-old ‘Miyagawa-wase’ with which the annual net production (Δ
Pn) and gross production (Δ
Pg) were previously determined, seasonal changes of carbohydrate contents (percent of dry weight) in their various organs were studied.
During the growing season from July to September, sugar content in the main organs of both types of trees decreased to the lowest level. Then, it increased and reached to the highest level in January, but decreased again thereafter. Starch content in the main organs, especially old leaves and underground parts, of both types of trees decreased from April until July. After this period, although starch content became constant in both types of trees, that in the non-bearing trees was always higher than that in the bearing trees. After January it increased in both types of trees. In contrast, the content of acid hydrolizable polysaccharide in the main organs of both types of trees showed an increase to the highest level from July to September. Then, it decreased until January. After January, it began to increase again in both types of trees. No differences in the content between the bearing and the non-bearing trees in each period were observed.
Functional carbohydrate content, which is the sum of total sugar content, starch and acid hydrolizable polysaccharide, increased rapidly in the main organs of the non-bearing trees after thinning fruits, while that of the bearing trees increased rapidly after harvesting fruits.
Seasonal fluctuations of this carbohydrate content were divided into three phases:
In the first phase from April 5 (sprouting stage) to May 31 (arresting stage of current shoot elongation), new organs developed slowly depending partially on the conversion of carbohydrate reserved in the old organs. In other words, three percent of the total dry matter supplied in this phase was from carbohydrate reserved in such organs.
In the second phase from June 1 to January 11 (resting stage of the tree growth), production of dry matter was extremely great, and used mostly for growth and respiration, but saved very little for reserved carbohydrate, that is, the amount of accumulated carbohydrate was approximately 16% of Δ
Pg in the bearing trees and 10% in the non-bearing trees.
In the third phase from January 12 to February 25 (resting period of the tree growth), no growth occurred in both types of trees, but the reserved carbohydrate began to be consumed again.
Annual accumulation of reserved carbohydrate in each individual bearing tree was approximately 38g (12% of annual Δ
Pg), 9% of which was distributed to the leaves, 10% to the stems, 6% to the trunk, 18% to the underground parts, and 58% to the fruits. In contrast, annual accumulation of reserved carbohydrate in each individual non-bearing tree was approximately 28g (8% of annual Δ
Pq), 11% of which was distributed to the leaves, 22% to the stems, 11% to the trunk, 47% to the underground parts, and 9% to the fruits before thinning.
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