Abstract:

Objective: This study aims to provide a theoretical basis for the construction of chestnut canopy productivity and proper bud retention, by investigating the effects of fruit loading in different canopy layers on photosynthetic characteristics, growth and development and fruit quality. Method: Three main branches with the opening angle greater than 60° of Chinese chestnut variety 'Yanshan Zaofeng' were targeted, and the branches with one (F1), two (F2) and 3 (F3) fruit loads were selected from different directions in the upper, middle and lower canopy layers, respectively. The leaf area, specific leaf area and photosynthetic indexes were measured in July. The fruits were collected at the fruit ripening stage in September, and the single fruit weight, transverse and vertical diameters and related contents were determined. The differences of leaf and fruit indexes under different bulb loadings were analyzed, and the optimal fruit loading suitable for each canopy layer was explored based on both economic benefits and fruit quality. Result: 1) There were differences in leaf photosynthesis and growth and development indexes under different fruit loads (P < 0.05). With the increase of bulb load, the net photosynthetic rate, instantaneous water use efficiency, leaf area and relative chlorophyll content all decreased significantly, while the transpiration rate and intercellular CO₂ concentration increased significantly. The starch content of leaves decreased in all canopy layers, and the soluble sugar content of leaves decreased in the middle and lower parts of the canopy, but increased in the upper part of the canopy. 2) There were to some degrees differences in fruit indexes under different fruit loads (P < 0.05). With the increase of fruit load, the single-fruit weight, total nitrogen content, starch content and soluble sugar content of fruits decreased in all canopy layers, but the empty bud rate increased. The single fruit weight, fruiting percentage, and starch and soluble sugar contents of fruits were the lowest in the F3 treatment; Due to weak light in the lower part of the canopy, the F3 treatment had higher empty bud rate, and the horizontal and vertical diameters of the fruit were smaller, and the ripening stage was delayed. Conclusion: The fruit loading has a significant effect on the leaf photosynthesis and fruit quality of chestnut. It is suggested that in the actual production of chestnut, the fruit loading of each fruiting branch in the upper, middle and lower canopy layers should be controlled at 3, 2~3, and 1~2, respectively.

Key words: chestnut, fruitload, photosynthetic characteristics, fruit quality, growth and developent