How light pollution can affect spring development of urban trees and shrubs

While artificial light at night (ALAN) is gaining more attention in view of its proven negative effect on animals, including humans, it remains a little-known matter when it comes to plants. Street lamps emit light that can be perceived by plants, and therefore disturb their natural photoperiod. In the present work we examine two different light treatments considered as low intensity (L-LP) and medium intensity (M-LP) light pollution (1 μmol·m−2·s−1 and 30 μmol·m−2·s−1 during the night, respectively) both comparable to different street lamps parameters (based on own field measurements). We have studied the influence of those LP treatments on the spring phenology and physiology of 4 tree species and 4 shrub species. The experiment involved species commonly used in European urban areas: Tilia tomentosa, Betula pendula, Fagus sylvatica, Acer campestre, Cornus alba, Lonicera pileata, Kerria japonica and Spiraea ×cinerea. All the investigated species were influenced by ALAN and developed buds faster than the control group. However, the changes were visible at different stages of bud development depending on species. The light pollution treatments resulted in a reduction of soluble sugars, measured in apical twigs of T. tomentosa, S. ×cinerea, K. japonica and A. campestre. In contrast, the soluble sugar content increased in branches of light-polluted L. pileata and C. alba when compared to the control group. These results prove, that light pollution affects the spring phenology and physiology of deciduous species. Long-term consequences of such reactions require more detailed studies.