Artificial light at night alters urban tree physiology, growth and BVOC emissions depending on tree species

Artificial light at night (ALAN) has been known to affect tree phenology since the mid-20th century, but despite recent studies, the topic remains largely underexplored. The present study aimed to analyse the possible disturbances of ALAN on plant physiology, BVOC emissions and growth in four urban tree species: Quercus ilex , Quercus cerris , Liquidambar styraciflua and Ginkgo biloba . The species were selected considering their different botanical families, phenology, and their potential distinct capacities to respond to ALAN. Across the seasons, stem growth, physiological traits (data collected at dawn, midday, and nighttime) and BVOCs were measured in night-illuminated and control trees. The results showed species-specific responses, with higher sensitivity of G. biloba in spring. Whereas, in summer, Q. ilex , Q. cerris , and L. styraciflua were more sensitive to ALAN than G. biloba , showing reduced Pn and gs at both dawn and midday, which also affected stem radial growth. Moreover, ALAN significantly increased nocturnal isoprene emissions in Q. ilex and L. styraciflua , while G. biloba showed no response. During autumn, in deciduous species, ALAN preserved leaf photosynthetic functionality (i.e., higher Pn, Fv/Fm, and Chlindex) compared to controls, with a parallel delay of leaf senescence except for G. biloba . In winter, ALAN altered physiological parameters in Q. ilex similarly to summer patterns. These species-specific responses underscore the need to develop species-specific sensitivity tables to ALAN. Such an approach would support informed tree selection and lighting design in urban environments, contributing to the resilience, functionality, and sustainability of urban ecosystems under increasing artificial nighttime illumination.