Photosynthate partitioning in damaged satsuma mandarin trees caused by briny wind disaster

The distribution characteristics of ¹³C-labeled photosynthate and sink strength of each organ in damaged satsuma mandarin (Citrus unshiu Marc.) trees, caused by briny wind of Typhoon No. 19, November 1991, were studied during the recovering stage using naturally and artificially damaged trees. The damaged trees were separated into 3 groups, according to the degree of defoliation after the storm, that is, severe (70-80% of defoliation rate), modest (30-50%) and light damage (10-20%). The more severe, briny wind-damage the trees experienced, the more defoliation and root decay occurred. The most severely damaged trees had the highest shoot/root ratio, 2.0 the following season. Nine months after the natural damage (July, 1992), about 60 % of ¹³C-labeled photosynthate was partitioned into fine and small roots in the most severely damaged and fruit-thinned trees. It is supposed that the photosynthate was mostly consumed to accelerate rooting and for elongation of fine and small roots. Half a month after incurring artificial damage by fruit-thinned trees in October, spring flush leaves, 2-and 3-year-old twigs, roots, and old leaves accumulated most of the photosynthates, whereas in fruit-bearing trees, regardless of defoliation rate, the crop amassed 40-50 % of the dry matter and absorbed much of the ¹³C administered. These results indicate that the fruit which has a very high sink strength diverted photosynthates necessary for growth and respiration of fine roots. Thus, fruit-bearing is an important factor in the recovery of damaged trees.