Shedding light on the effects of LED streetlamps on trees in urban areas: Friends or foes?

Streetlamp illumination disturbs the natural physiological processes and circadian rhythms of living organisms, including photosynthesizing “citizens”. The light-emitting diode (LED) technology has replaced high-pressure sodium lamps. Therefore, the effects of LED streetlamps on urban trees need to be elucidated as these new lamps have a different light spectrum (with a peak in the blue and red regions of the spectrum, i.e., highly efficient wavebands for photosynthesis) compared to older technologies. To address the above-mentioned issue, two widely utilised tree species in the urban environment, including Platanus × acerifolia (P) and Tilia platyphyllos (T), were grown with or without the effect of LED streetlamps using two realistic illumination intensities (300 and 700 μmol m−2 s−1). Gas exchanges and biochemical features (starch, soluble sugar, and chlorophyll content) of illuminated vs non-illuminated trees were compared during the whole vegetative season. Our results showed that both tree species were strongly influenced by LED streetlamps at physiological and biochemical levels. Specifically, the mature leaves of P and T streetlamp-illuminated trees had a lower CO2 assimilation rate at dawn and had higher chlorophyll content, with lower starch content than controls. Our results showed that the differences between the effects of the two selected light intensities on the physiochemical attributes of P and T trees were not statistically significant, suggesting the absence of a dose-dependent effect. The most significant difference between T and P trees concerning the LED-triggered species-specific effect was that the delay in winter dormancy occurred only in P individuals. This study provided insights into the extent of LED streetlamp disturbance on trees. Our findings might raise awareness of the necessity to provide less impacting solutions to improve the wellness of trees in the urban environment.