The initiation of spring leaf-out is a critical determinant of the growing season in trees, affecting primary production and species interactions in forest ecosystems. Variations in the timing of leaf-out among tree species are linked to their differential progression of bud dormancy. However, identifying reliable markers for bud dormancy has been challenging, leaving the connection between the timing of autumn leaf senescence, bud dormancy and spring leaf-out unclear. To test whether species initiating dormancy release earlier also exhibit earlier leaf senescence in autumn and earlier leaf-out in spring, we estimated the dates of peak dormancy depth (PDD), senescence timing and spring leaf-out across various species, locations and experimental conditions in Central Europe. PDD was defined as the date when the maximum thermal sum was required for leaf-out, whereas leaf senescence was assessed through the decrease in leaf greenness. Our findings reveal that PDD timing is a more accurate predictor of species-level differences in spring leaf-out dates than the timing of leaf senescence, the latter being a poor proxy for PDD. The observed temporal asynchrony between PDD and senescence was linked to dormancy induction showing species-specific sensitivity to temperature variations. Conversely, the timing of leaf senescence showed a consistent reaction to temperature changes across all species. These findings suggest that the physiological processes within buds and leaves during autumn are governed by distinct environmental cues, with the bud dormancy process serving as a more reliable predictor of spring phenological differences among forest tree species than does autumn leaf senescence.

中文翻译：

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春天的发条：芽休眠时间是温带落叶树春天落叶的驱动因素

春季落叶的开始是树木生长季节的关键决定因素，影响森林生态系统中的初级生产和物种相互作用。树种之间落叶时间的差异与其芽休眠进程的差异有关。然而，确定芽休眠的可靠标记一直具有挑战性，导致秋季叶子衰老、芽休眠和春季落叶时间之间的联系尚不清楚。为了测试较早开始休眠解除的物种是否也表现出较早的秋季叶片衰老和较早的春季落叶，我们估计了不同物种、地点和实验条件下的峰值休眠深度（PDD）、衰老时间和春季落叶的日期在中欧。 PDD被定义为落叶所需最大热和的日期，而叶片衰老则通过叶片绿度的降低来评估。我们的研究结果表明，与叶片衰老时间相比，PDD 时间能够更准确地预测春季落叶日期的物种水平差异，后者不能很好地代表 PDD。观察到的 PDD 和衰老之间的时间异步性与休眠诱导有关，显示出物种对温度变化的特异性敏感性。相反，所有物种的叶子衰老时间都显示出对温度变化的一致反应。这些发现表明，秋季芽和叶内的生理过程受到不同环境因素的控制，芽休眠过程比秋季叶衰老更能预测森林树种之间的春季物候差异。