Effects of Artificial Light at Night on Photosynthesis and Respiration of Two Urban Vascular Plants

The widespread use of artificial light at night (ALAN) due to urbanization and infrastructure development has raised concerns about its potential impacts on plant physiology. To explore the effects of ALAN with different light intensities on the photosynthesis and respiration of two urban vascular plants, Euonymus japonicus Thunb and Rosa hybrida E.H.L.Krause, under continuous and non-continuous-light conditions, respectively, a field experiment was conducted. Our findings indicate that continuous ALAN significantly inhibited the photosynthesis and respiration of the two plants, disrupting the carbon-balance pattern of their leaves during the day, but this effect is influenced by the intensity of ALAN and plant species. Euonymus japonicus Thunb is more susceptible to continuous ALAN than Rosa hybrida E.H.L.Kraus. Non-continuous ALAN did not significantly affect the photosynthesis and respiration of two species during the day. Furthermore, we observed that high light intensity at night could also impact the value of the net photosynthetic rate (Pn) of Euonymus japonicus Thunb during the night. Turning off light sources at night, reducing the light intensity, and cultivating ALAN-tolerant plants are effective measures to reduce the negative effects of ALAN on plants and maintain plants’ normal carbon-balance mode. Future studies should explore the effects of different types of artificial-light sources combined with other environmental conditions on the photosynthesis and respiration of plants at the canopy scale.