Species-specific responses of three dominant urban tree species to artificial light at night: Phenological shifts, trait trade-offs and implications for urban forest management

Abstract

Rapid global urbanization has driven the widespread expansion of artificial light at night (ALAN), a pervasive anthropogenic disturbance that alters nocturnal ecosystem dynamics. Urban trees are continuously exposed to ALAN, yet species-specific adaptive strategies underlying phenological shifts and leaf functional trait coordination remain poorly characterized. This study selected three dominant urban tree species (Platanus × acerifolia (Aiton) Willd., Prunus serrulata var. lannesiana (Carri.) Makino, and Ginkgo biloba L.) and combined in-situ field monitoring with laboratory physiological analyses to investigate the effects of long-term ALAN exposure in Qingdao, a coastal city in northern China. Results showed that ALAN significantly advanced spring bud break and floral bloom across all three species. In autumn, leaf senescence was delayed in P. × acerifolia and P. serrulata but markedly accelerated in the relict species G. biloba. P. × acerifolia employed a high light-use efficiency strategy, with elevated chlorophyll content and increased leaf mass per area (LMA). P. serrulata relied on morphological adjustment via enlarged leaf area, with no detectable change in chlorophyll levels. In contrast, G. biloba exhibited physiological–phenological decoupling: chlorophyll content increased passively, but leaf senescence occurred prematurely. ALAN induced divergent trait coordination patterns and distinct tolerance thresholds among the three species. These findings confirm that ALAN does not universally benefit urban trees, and reveal notable trade-offs between ecological effects and management risks. They provide actionable, species-specific guidance for urban forest planning, lighting design, and vegetation maintenance, supporting a balance between human lighting demands and urban ecosystem health.