Abstract
Three-year-old 'Nijisseiki' pear (Pyrus pyrifolia Nakai) trees were treated twice with 13CO2 in October (fall). The distribution of labeled 13C within the tree during dormancy and remobilization in the following season were determined. After leaf-fall, about 63% of the total 13C recovered from the tree was distributed in the roots. At anthesis the 13C content from the previous season's organs showed a significant decrease : the aerial organs decreased by about 53% and the roots by nearly 60%. About 35% of the total 13C recovered from the trees after leaf-fall was consumed by respiration until anthesis. New shoot, flower, and root growth accounted for 8.5%, 9.9%, and 3.9% of the total 13C recovered from the tree after leaf-fall, respectively. One month after anthesis, the 13C remaining in the previous season's organs, had further decreased, having been exported to the new leaves and current shoots. The 13C remaining in the fruitlets dramatically decreased because of the abscission of sepals, petals, stamens, and partial pistils (style and stigma). New roots had the highest concentration of 13C among all new organs. These data suggest that root systems play a special role in the storage of carbohydrates in young pear trees. All organs depend on carbohydrate reserves for spring growth, especially new roots which seem to depend on reserves for a longer time.
