Artificial light at night alters morphology, phenology, and reproductive capacity in an annual herb

The rapid global expansion of artificial light at night (ALAN) has spurred growing interest in its ecological impact on plant life. However, the effects of low-intensity ALAN on plants in their natural habitats remain largely unexplored, particularly concerning the influence of morphological and phenological responses on the overall fitness of these plants. We conducted a field experiment using the annual herbaceous plant Elsholtzia densa as a model species to assess the effects of ALAN on plant morphology, reproductive phenology, and reproductive capacity. The results indicate that ALAN increased the specific leaf area and elongated the top inflorescences, but it resulted in a reduction of secondary branches and a decrease in the proportion of individuals with undeveloped top inflorescences. Additionally, ALAN induced a shift in biomass allocation toward the aboveground parts of plants. It also accelerated the onset of budding, blooming, fruiting, and seed maturity by 3.4 to 6.2 days and caused a decrease in the number of fruity inflorescences. This study suggests that ALAN can significantly affect plant morphology, reproductive timing, and potentially the fitness of plants. While ALAN induces potentially adaptive changes in leaf area and biomass allocation, it may also disrupt plant-pollinator interactions and negatively impact plant reproductive capacity.