Urban is regarded as the ideal natural laboratory for predicting vegetation growth response to future warming, as urban warming promotes the growth of urban vegetation and advances spring phenology. However, the effects of daytime and nighttime warming on the spring phenology of natural vegetation remain unclear under global warming. Here, we used urbanization intensity (UI) as a proxy for future warming, then investigated the start dates of the growing season (SOS) response to daytime and nighttime warming across different levels of UI. We found both nighttime and daytime temperature sensitivities increased significantly from rural to urban centers in cold cities, decreasing in warm cities. It indicated that the advancement in spring phenology of urban vegetation accelerates along with UI in cold cities but slows down in warm cities. Because in cold cities, urban warming and increased humidity accelerate vegetation growth, while in warm cities urban warming and decreased humidity decelerate growth. Therefore, in future we should consider not only the asymmetrical responses of urban vegetation spring phenology to daytime and nighttime warming, but also the disparate responses in different background climate regions under future warming.

中文翻译：

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城市变暖对寒冷城市春季物候影响加速，但温暖城市春季物候影响减弱


城市被认为是预测植被生长对未来变暖的反应的理想天然实验室，因为城市变暖促进了城市植被的生长并推动了春季物候学的发展。然而，在全球变暖下，昼夜变暖对自然植被春季物候的影响仍不清楚。在这里，我们使用城市化强度 （UI） 作为未来变暖的代理，然后研究了不同级别的 UI 中生长季 （SOS） 对白天和夜间变暖的响应的开始日期。我们发现，在寒冷的城市，夜间和白天的温度敏感性从农村到城市中心都显著增加，而在温暖的城市则下降。结果表明，在寒冷城市，城市植被春季物候的进展与 UI 一起加速，但在温暖城市则放缓。因为在寒冷的城市，城市变暖和湿度增加会加速植被生长，而在温暖的城市，城市变暖和湿度降低会减缓生长。因此，未来不仅要考虑城市植被春季物候对昼夜变暖的不对称响应，还要考虑未来变暖下不同背景气候区的不同响应。