Effects of Trunk Covering and Airflow Treatment on Sap Flux and Bud Burst During the Dormant Stage in ‘Fuji’ Apples

The effects of recent climate change, including warm winters and repeated temperature fluctuations during dormancy, can lead to freezing injuries that result in significant economic losses in the fruit industry. This study aimed to examine the physiological responses of ‘Fuji’/M9 apple trees to trunk covering and continuous airflow treatments over 30 days, providing insights into mitigating freezing damage. The temperature difference between the sunlit and shaded sides of the trunk was lower in the whitewashed and foam insulation-covered treatments compared to those covered with newspaper, rice straw, or left uncovered. Under airflow treatment, the temperature difference in the uncovered control was 2.2 °C lower than in the non-airflow group, while no significant difference was observed in the whitewash treatment. Sap flow initiation was observed the earliest in the foam insulation-covered treatment and the latest in the whitewashed treatment. The timing of bud burst followed the order of foam insulation, rice straw, whitewash, newspaper, and the uncovered control. Furthermore, sap flow initiation and the bud burst period were delayed under airflow treatment compared to non-airflow conditions. This study provides fundamental insights into the effects of covering materials and airflow on apple tree physiology during dormancy, offering valuable information to guide future research in this field.