Abstract:

Objective: This study aims to explore the corresponding relationship between external morphological changes and anatomical structures in the differentiation process of Choerospondias axillaris flower buds, and reveal the relationship between the dynamic changes of nutrients in leaves and the differentiation process of flower buds. Method: The paraffin section method was used to observe the flower buds of C. axillaris, and the contents of soluble protein, soluble starch, soluble sugar, total phosphorus, total nitrogen, total potassium, and organic matter in the leaves near the bud were determined at key differentiation stages. Result: 1) The flower type of C. axillaris was thyrse or solitary, with the male flower as inflorescence, and the female flower as inflorescence or solitary. Most of the flower buds of C. axillaris were mixed buds, with a sprouting rate of 99% for adult male trees and 70% for female trees. 2) The differentiation of C. axillaris flower buds can be divided into 9 stages: undifferentiated stage, physiological differentiation stage, bract formation stage, sepal formation stage, inflorescence formation stage, petal formation stage, stamen formation stage, pistil formation stage, and lateral inflorescence developing stage. The differentiation of C. axillaris flower buds started at the end of March. After bud sprouts in late February, it took about 40 days to enter the physiological differentiation stage. The mid to late June was the peak period for the differentiation of the female and male primordia of flower buds. In early March of the following year, lateral inflorescences of both female and male flowers were fully developed. 3) The growth of horizontal and vertical diameters of flower buds showed a trend of first fast and then obviously slow. The horizontal diameter of female and male flower buds in the physiological differentiation stage increased by 211.36% and 231.11%, respectively, compared to the undifferentiated stage, and the size of flower buds was rapidly rising. Transverse diameters of female and male flower buds in the inflorescence formation stage increased by 5.43% and 10.00%, respectively, compared to the sepal formation stage, suggesting that growth rate slowed down. 4) The soluble protein contents in leaves on the bud base dropped to its lowest in inflorescence primordia differentiation stage, while the contents of soluble protein and soluble starch in female and male leaves reached their peeks in inflorescence primordia differentiation stage, with the values of 2.29 and 2.51, 25.43 and 21.50 mg·g^?1, respectively. During the inflorescence formation stage, the nitrogen content in female and male leaves decreased significantly, with a decrease of 22.88% and 32.51%, respectively, compared to the undifferentiated stage. The total nitrogen contents decreased by 25.35% and 34.09%, and the total phosphorus contents decreased by 41.07% and 39.67%, the total potassium contents decreased by 23.94% and 22.52%, respectively, compared to the undifferentiated stage. The carbon nitrogen ratio of female flower bud leaves ranged from 21.01 to 26.52, while male flower bud leaves ranged from 21.14 to 28.90. Conclusion: It takes about 4 months from the sprouting of the buds to the initial differentiation of pistil and stamen primordia of C. axillaris, and inflorescences are fully developed at the following year of March. The physiological differentiation process of female flowers is about 10 days later than that of male flowers. The nutrients in the leaves proximate to flower bud have great changes in physiological differentiation period. The high contents of nitrogen, phosphorus and potassium in the leaves are conducive to the physiological differentiation of flower buds, and higher carbon-nitrogen ratio can regulate the morphological differentiation process of C. axillaris. During the inflorescence formation period, the leaves need to accumulate more soluble sugar and soluble starch. The physiological differentiation stage (in late April) and inflorescence differentiation stage (in early June) are the most critical periods, when a special attention should paid to effcient irrigation and fertilization management and fruit yield regulation of C. axillaris.

Key words: Choerospondias axillaris, flower bud differentiation, leaf physiology, nutritional composition