Latitudinal differences in induction of endodormancy in extratropical trees

In extratropical trees plant phenology is fundamentally constrained by the seasonal dormancy cycle. During autumn, buds are progressively induced into deep endodormancy until a peak dormancy depth is reached. While the dormancy phenomena of temperate and boreal tree species have been extensively studied, despite the high biodiversity and large carbon stocks of subtropical forests and their high sensitivity to climate warming, the timing and physiological regulation of dormancy in subtropical trees remain poorly characterized. To compare latitudinal differences in the timing of peak dormancy, we sampled multiple tree species across seven sites spanning the latitudinal gradient from 22° to 45° N in China and quantified dormancy depth by transferring plants collected at successive autumn and winter dates from natural conditions into a 25 °C growth chamber and measuring their time to budburst. We found a strong latitudinal gradient in the timing of peak dormancy, with trees at lower latitudes reaching their maximum dormancy significantly later than those at higher latitudes. Across species and sites, the day of year corresponding to peak dormancy advanced by approximately 2.2 days per degree of latitude, indicating a systematic delay of dormancy induction toward warmer regions. These results demonstrate that the timing of dormancy induction is not fixed across regions but varies systematically with latitude, providing a physiological basis for redefining the time when winter chilling accumulation should begin in different climate zones.