Characteristics of bud endodormancy and physiology in Quercus acutissima seedlings growing in an environment with low chill availability

Global warming is expected to hamper bud endodormancy. Understanding endodormancy in low chill availability environments helps to predict endodormancy in future winters. The objective of this study was to elucidate characteristics of endodormancy and physiology in Quercus acutissima seedlings in a nursery under a vinyl sheet in the southern part of the warm-temperate zone. Endodormancy was evaluated by examining leaf phenology of seedlings in the nursery, and bud break of shoot cuttings in growth promoting conditions from October to March. Water content (WC), relative water content (RWC), respiration rate, concentrations of starch, and sugars (glucose, fructose, and sucrose) were measured in twigs and buds of current-year shoots. As leaves decolorized towards December, bud break rates increased. Complete leaf browning paralleled low bud break rates in January and February indicating endodormancy. Compared to species in high chill availability environments which typically enter endodormancy in autumn and release in mid-winter, our results suggested delays in the onset and release of endodormancy, providing time for buds to develop before endodormancy onset. Decreased respiration rates and starch concentrations in twigs and buds coincided with the endodormancy period. These were accompanied by high concentrations of glucose and fructose, suggesting changes in the respiratory mechanism, and occurrence of starch to sugar conversion. Increased WC in twigs at endodormancy onset was speculated as a response to the environment, related to endodormancy regulation and/or freezing tolerance. A prominent phenomenon in buds was the elevated RWC irrespective of hydration at endodormancy onset, suggesting a decline in water holding capacity.