The Sink–Source Relationship Regulated Camellia oleifera Flower Bud Differentiation by Influencing Endogenous Hormones and Photosynthetic Characteristics

To explore the reasons for the differences in flower bud differentiation in Camellia oleifera under different sink&ndash:source relationships, different types of new shoots (T1 and T2) were selected to represent different sink&ndash:source relationships (new shoots with one fruit borne alongside at the bottom of the new shoots-T1: new shoots without one fruit borne alongside at the bottom of the new shoots-T2), and the flower bud differentiation rate, endogenous hormones and photosynthetic characteristics were determined. With the increase in the sink, the flower differentiation rate decreased significantly and the IAA and GA3 content in the leaves and ABA content in the buds increased significantly, while the GA3 and ZT content in the buds decreased significantly, which were significantly and positively correlated with the flower differentiation rate, with correlation coefficients of 0.777 and 0.817, respectively. Furthermore, an increase in the number of sinks contributed significantly to the increase in soluble sugar and starch content in leaves, while the soluble sugar and starch content in flower buds decreased significantly with the increase in sinks, with maximum differences of 3.45 mg&middot:g&minus:1 (soluble sugar in leaves), 4.09 mg&middot:g&minus:1 (soluble sugar in flower buds), 7.08 mg&middot:g&minus:1 (starch in leaves) and 4.87 mg&middot:g&minus:1 (starch in flower buds), and the high soluble sugar and starch content in flower buds at preflower bud differentiation with correlation coefficients of 0.854 and 0.837, respectively. The chlorophyll content and net photosynthetic rate increased with increasing sinks. In the presence of fruit at the base of the new shoot, more 13C assimilates were allocated to fruit and less to flower buds, resulting in a decrease in the rate of flower bud differentiation. The 13C assimilate allocated to the flower buds of T1 (6.71 mg&middot:g&minus:1) was significantly lower than the 13C assimilate allocated to the flower buds of T2 (10.26 mg&middot:g&minus:1) during late bud differentiation, and the difference between T1 and T2 was greatest during this period. Our work demonstrated that the sink&ndash:source relationship regulated Camellia oleifera flower bud differentiation by influencing endogenous hormones and photosynthetic characteristics. To achieve stable production of Camellia oleifera in successive years in the future, the ratio of the number of new shoots of the two types in relation to the different sink&ndash:source relationships should be reasonable.