The onset of autumnal leaf senescence (T) plays a crucial role in understanding and modeling how plants prepare for winter dormancy, but it has remained under-explored. Previous research, based on limited in situ observations, have proposed that the year-to-year invariant photoperiod is the primary trigger of T, indicating potential insensitivity to climate change. This study verifies this hypothesis using high spatial resolution satellite data and ground-based observations throughout the European continent. Surprisingly, our findings reveal a widespread delay in T during 2001–2019 (approximately 73 %, significant in 19 % of the continent, < 0.05), closely aligned with delayed leaf senescence end (T) as reported in previous studies. Moreover, as the delaying trend was larger for T than for T, it is apparent that climate change does not only postpone the onset of the leaf senescence process but also shortens its duration across the continent. This finding indicates that a reduced duration for plants to get ready for dormancy could potentially undermine their resilience to cold and other winter stresses. Contrary to the hypothesized photoperiodic control, T exhibited opposing inter-annual temporal trends along temperature gradients, despite similar daylengths. Ground based observations failed to support photoperiodic influence either, highlighting the substantial spatial variation in T responses to climate change. Intriguingly, complex climate-T interactions were observed, with radiation dominating T changes in 37.0 % of the study area. This analysis underscores the necessity of considering multiple variables to comprehend the patterns of T at continental and vegetation scales.

中文翻译：

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光周期本身并不能解释整个欧洲叶片衰老开始的变化


秋季叶片衰老（T）的开始在理解和模拟植物如何准备冬季休眠方面发挥着至关重要的作用，但它仍未得到充分探索。先前的研究基于有限的现场观测，提出逐年不变的光周期是 T 的主要触发因素，表明对气候变化的潜在不敏感性。这项研究利用高空间分辨率卫星数据和整个欧洲大陆的地面观测验证了这一假设。令人惊讶的是，我们的研究结果揭示了 2001 年至 2019 年 T 的广泛延迟（约 73％，在非洲大陆的 19％ 中显着，< 0.05），与先前研究中报告的叶片衰老结束（T）延迟密切相关。此外，由于T的延迟趋势比T更大，很明显，气候变化不仅推迟了叶子衰老过程的开始，而且缩短了整个大陆的持续时间。这一发现表明，植物准备休眠的时间缩短可能会削弱它们对寒冷和其他冬季胁迫的抵抗力。与假设的光周期控制相反，尽管日长相似，T 沿着温度梯度表现出相反的年际时间趋势。地面观测也未能支持光周期影响，凸显了 T 对气候变化响应的巨大空间变化。有趣的是，我们观察到了复杂的气候与气温的相互作用，在 37.0% 的研究区域中，辐射主导了气温的变化。该分析强调了考虑多个变量以理解大陆和植被尺度上 T 模式的必要性。