Severe droughts are expected to become more frequent and persistent. However, their effect on autumn leaf senescence, a key process for deciduous trees and ecosystem functioning, is currently unclear. We hypothesized that (I) severe drought advances the onset of autumn leaf senescence in temperate deciduous trees and (II) tree species show different dynamics of autumn leaf senescence under drought.We tested these hypotheses using a manipulative experiment on beech saplings and 3 years of monitoring mature beech, birch and oak trees in Belgium. The autumn leaf senescence was derived from the seasonal pattern of the chlorophyll content index and the loss of canopy greenness using generalized additive models and piecewise linear regressions.Drought and associated heat stress and increased atmospheric aridity did not affect the onset of autumn leaf senescence in both saplings and mature trees, even if the saplings showed a high mortality and the mature trees an advanced loss of canopy greenness. We did not observe major differences among species.To synthesize, the timing of autumn leaf senescence appears conservative across years and species and even independent of drought, heat and increased atmospheric aridity. Therefore, to study autumn senescence and avoid confusion among studies, seasonal chlorophyll dynamics and loss of canopy greenness should be considered separately.

中文翻译：

---

干旱是否会促进温带落叶林树木秋季叶片衰老的开始？

预计严重干旱将变得更加频繁和持久。然而，它们对秋叶衰老（落叶树和生态系统功能的关键过程）的影响目前尚不清楚。我们假设 (I) 严重干旱促进了温带落叶树秋叶衰老的开始，以及 (II) 树种在干旱条件下表现出不同的秋叶衰老动态。我们使用山毛榉树苗的操纵实验和 3 年的监测比利时成熟的山毛榉、桦树和橡树。使用广义加性模型和分段线性回归，从叶绿素含量指数的季节性模式和冠层绿度的损失中推导出秋季叶片衰老。干旱和相关的热应激以及大气干旱的增加不会影响树苗和成熟树木秋季叶子衰老的开始，即使树苗表现出高死亡率并且成熟树木的冠层绿色度提前丧失。我们没有观察到物种之间的重大差异。总而言之，秋叶衰老的时间在不同年份和物种之间似乎是保守的，甚至与干旱、炎热和增加的大气干旱无关。因此，为了研究秋季衰老并避免研究之间的混淆，应分别考虑季节性叶绿素动态和冠层绿度损失。秋叶衰老的时间在不同年份和物种中显得保守，甚至不受干旱、炎热和大气干旱加剧的影响。因此，为了研究秋季衰老并避免研究之间的混淆，应分别考虑季节性叶绿素动态和冠层绿度损失。秋叶衰老的时间在不同年份和物种中显得保守，甚至不受干旱、炎热和大气干旱加剧的影响。因此，为了研究秋季衰老并避免研究之间的混淆，应分别考虑季节性叶绿素动态和冠层绿度损失。