Phylogenetic studies on the leaf unfolding date are expected to improve understanding of phenological change. However, it remains unclear whether the response of leaf unfolding date to temperature is phylogenetically conserved among close relatives across differential and harsh habitats. Meanwhile, the phenological mechanism underlying the role of phylogenetic relationship on plant phenology remains unclear. We used Blomberg's K to assess phylogenetic signal in leaf unfolding date, its sensitivities to daily mean, minimum and maximum temperatures, in growing-degree-days and average level of each of daily mean, minimum and maximum temperatures experienced by plants over a given period prior to leaf unfolding date for eighteen species at seventeen sites in the Tibetan Plateau. We showed that leaf unfolding date and its sensitivities to daily mean, minimum and maximum temperatures did not exhibit overall significant phylogenetic signals. Moreover, the sensitivity of leaf unfolding date to daily minimum temperature exhibited phylogenetic antisignal at species level, which indicated the trait difference among close relatives exceed that among distantly related lineages. However, there were overall significant phylogenetic signals in growing-degree-days and the average level of each of daily mean, minimum and maximum temperatures experienced by plants before leaf unfolding date. The signals were stronger for the growing-degree-days and the average level of each of daily mean, minimum and maximum temperatures in the period closer to leaf unfolding date. Our results imply that close relatives trace similar heat requirements for leaf unfolding date in the harsh and spatially heterogeneous environment of the Tibetan Plateau. However, the time when these lineage-specific heat requirements are met varies spatially depending on local conditions, thereby resulting in phylogenetic non-conservatism of leaf unfolding date and its temperature sensitivities. This provides a phenological explanation, for the first time, for phylogenetic non-conservatism in plant leafing phenology.

对叶片展开日期的系统发育研究有望增进对物候变化的理解。然而，尚不清楚在不同和恶劣的生境中的近亲中，叶片展开日期对温度的反应是否在系统发育上是保守的。同时，系统发生关系对植物物候的作用的物候机制仍不清楚。我们用了Blomberg的K评估叶片展开日期的系统发育信号，其对日平均，最低和最高温度的敏感性，生长度天数以及叶片展开前给定时期内植物所经历的每日平均，最低和最高温度的平均水平在青藏高原的十七处发现了十八种。我们表明，叶片展开的日期及其对日均温度，最低和最高温度的敏感性未显示出总体上显着的系统发生信号。此外，叶片展开日期对日最低温度的敏感性在种水平上表现出系统发生的抗信号作用，这表明近亲之间的性状差异超过了远亲谱系之间的差异。然而，在生长度日中，总体上存在显着的系统发育信号，并且在叶片展开日期之前，植物所经历的每日平均，最低和最高温度的平均水平。在接近叶片展开日期的时期中，信号对于生长日数和每日平均，最低和最高温度的平均水平均较强。我们的结果表明，在青藏高原恶劣且空间上异质的环境中，近亲对叶片展开日期的热量需求相似。但是，满足这些谱系特定热量要求的时间在空间上根据局部条件而变化，从而导致叶片展开日期的系统发育非保守性及其温度敏感性。这是第一次提供了物候解释。