关键词: 香榧, 树形调整, 光照强度, 内源激素, 成花坐果

Abstract:

Objective: In this study, the number and opening angle adjustment of Torreya grandis cv. Merrillii skeleton branches were performed in order to explore their effects on the formation of mixed bud and fruit setting, so as to provide a scientific basis for tree cultivation of T. grandis cv. Merrillii young forest and to promote early fruiting and high yield. Method: Single factor and interactive experiments with the number and opening angle of skeleton branches were conducted to investigate the development of flowers and fruits, proportion of mixed buds, and fruit setting rate. Light intensity, endogenous hormone content, photosynthetic carbon assimilate content, carbon nitrogen ratio and other indicators were determined. Result: The number adjustment of skeleton branches had a great effect on the light transmission ability, and 3 skeleton branches (N3) and 4 skeleton branches (N4) significantly increased the light intensity in the central and lower layers of T. grandis cv. Merrillii canopy, which was conducive to improving the utilization of light energy and promoting flowering and fruit setting. Treatment with an opening angle of 60° (A60°) significantly reduced the contents of auxin (IAA), gibberellin (GA₁ and GA₃) in mixed buds, increased the ratio of ABA/IAA, ABA/GA₁₊₃, CTKs/IAA and CTKs/GA₁₊₃, and significantly increased the contents of sucrose and starch, and C/N ratio in mixed buds. The proportion of mixed buds in a tree significantly increased. The interactive treatment with the number and opening angle of skeleton branches effectively improved the light intensity and the net photosynthetic rate. Under the treatments of N3-A60° and N4-A60°, the light intensity of the central layer reached 25 000–27 000 lux, and that of the lower layer reached 11 000–14 000 lux, and the net photosynthetic rate reached 9.07 and 9.70 μmol CO₂·m^?2 s^?1, respectively. In addition, N3-A60° and N4-A60° also significantly increased the contents of GAs and some cytokinins in young fruits, significantly promoted the accumulation of sucrose and total soluble sugars in fruits, and improved the fruit setting rate. Conclusion: Both the number and opening angle of skeleton branches can promote the flowering and fruit setting of T. grandis cv. Merrillii young forest, and the interaction between 3 and 4 skeleton branches with opening angle of 60° has the best promotion effect.

Key words: Torreya grandis cv. Merrillii, tree management, light intensity, endogenous hormone, flowering and fruit setting