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

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