Use of stored carbon for new organ development in apple saplings in early spring for two consecutive years after 13C labelling.

The use of stored carbon is essential for new organ development in deciduous trees during early spring. However, the contribution of carbon to the development of new organs in early spring of subsequent years is not well understood. Using a ¹³C labelling approach, we investigated the reallocation of assimilated carbon into new aboveground organs on apple (Malus domestica) saplings in the following two years. Eight three-year-old potted saplings were exposed to ¹³CO₂ in an exposure chamber on each of eight different dates during the growth season. Some of the trees were harvested in the late autumn of the same year. The remaining trees were transferred to a field and cultivated during the two following growing seasons. We directly showed that the assimilated ¹³C was used to develop terminal and flower buds for two consecutive years after labelling. The proportions of the concentration of ¹³C remobilized to the terminal and flower buds in the second year were 5 and 24% of those in the first year after labelling, respectively. The concentration of assimilated ¹³C was higher in the terminal buds than in the flower buds in the first year after the labelling, while opposite results were found in the second year. This study demonstrates that the stored carbon used for the development of new organs was a mixture of recent- and old-stored carbon and indicates that recently-stored carbon was preferentially used to develop new organs. We also indicated that the stored carbon was remobilized to flower buds during development.