Artificial nighttime light amplifies urban-rural difference in spring phenology in cold cities but narrows in warm cities

Increasing artificial nighttime light (NTL) profoundly influences spring phenology. However, this has been found under idealized laboratory conditions, without considering the complexities of natural urban conditions. Therefore, disentangling the impact of NTL on plant dynamics in complex urban environments remains challenging. Here, by employing a structural equation model on each urbanization intensity (UI) gradient across 152 China's cities, we revealed that reducing the accumulation period of growing degree days (GDD) is the primary mechanism that NTL advanced spring phenology within majority cities. Notably, in high-latitude regions where spring temperatures are relatively low, NTL led to greater reductions in GDD along the UI gradients with a standardized coefficient of −0.43 ± 0.03, widening the urban-rural difference in spring phenology. Conversely, in low-latitude regions with relatively high spring temperatures, NTL induced fewer GDD reductions and even caused an increase in GDD enhancement alongside UI with a standardized coefficient of 0.07 ± 0.01, narrowing the urban-rural difference in spring phenology. Therefore, our study provides compelling evidence for considering the important role of artificial nighttime light on urban vegetation spring phenology. It is crucial to understand the impacts of future urbanization on vegetation and future sustainable urban development.