Study on the Relationships Between Calcium Accumulation in Fruits and Calcium Dynamics in Fruit Stalks During the Development and Ripening of Cerasus humilis Fruit

Cerasus humilis is a unique fruit tree renowned for its exceptional calcium content. To investigate the relationship between calcium absorption and accumulation in the fruit, as well as the dynamic changes in calcium within the fruit stalks during development and maturation, this study examined the content and proportion of different forms of calcium in the fruits and fruit stalks under different Cerasus humilis types and 2,4-D treatment. Additionally, the characteristics of the calcium concentration difference ratio between the fruit stalks and fruits were analyzed. Given that the study is based on a single year of data, this preliminary research explores the calcium transport relationship between the fruit stalks and fruits, providing a foundation for more extensive future research. The results revealed that the content and proportion of water-soluble calcium in fruits and fruit stalks gradually increased during development. In contrast, the content and proportion of other calcium forms, such as calcium oxalate and calcium phosphate, showed a downward trend. This decline was more pronounced in the fruits than in the fruit stalks. Treatment with 2,4-D significantly increased the content of all calcium components in the fruits, reduced the proportion of calcium oxalate and calcium phosphate in the fruit stalks, and increased their proportion in the fruits. The changes in calcium forms between the fruits and fruit stalks were closely interrelated, with 2,4-D treatment enhancing the correlation between the contents of calcium phosphate and calcium oxalate in both tissues. The calcium concentration in the fruit stalks is significantly higher than in the fruits, showing a noticeable calcium concentration difference ratio, with water-soluble calcium exhibiting the smallest difference and calcium oxalate and calcium phosphate displaying the largest. Treatment with 2,4-D significantly reduced the calcium concentration difference ratio between the fruit stalks and the fruits. In conclusion, the periods from the young fruit stage to the hard seed stage and from the hard-ripe stage to the fully ripe stage are critical for calcium transformation, transport, and accumulation. Different calcium forms in the fruits and fruit stalks can interconvert, with water-soluble calcium being more readily transported to the fruits. In contrast, calcium oxalate and calcium phosphate tend to accumulate in the fruit stalks. Calcium pectin behaves differently in the two types of Cerasus humilis. In MY-2, it is more readily transported to the fruit, while in MY-9, it tends to accumulate in the fruit stalks. Treatment with 2,4-D facilitates the transport of calcium from the fruit stalks to the fruits, enhances calcium content in the fruits, and optimizes calcium distribution.