Physiological responses of typical subtropical landscape shrubs to artificial light at night.

Artificial light at night is rapidly spreading and has become an important component of global change. Although numerous studies have focused on its potential ecological impacts, the physiological response mechanisms of landscape plants to artificial light at night have rarely been quantified. With common landscape shrubs in subtropical regions of China, , and , as test materials, we exa-mined the responses of antioxidant enzyme system and biomass in the light environment at night under different light quality (yellow light, white light) with different light intensities (20, 40, 60 lx) . The results showed that artificial light at night significantly increased the membrane peroxidation, stimulated plant antioxidant protection systems and raised the antioxidant enzyme activities of the three species. The effects of light quality on plant antioxidant enzymes varied across dspecies. The peroxidase (POD) and catalase (CAT) activities of under white light were 1.5 and 1.3 times as that under yellow light, respectively. Both enzyme activities of were 1.1 times as that under white light than under yellow light. The activities of two enzymes in under white light were 88.6% and 99.5% of those under yellow light, respectively. The antioxidant enzyme activities of the three species increased with increasing light intensity at night, whereas the contents of malondialdehyde increased rapidly and the antioxidant enzyme activities decreased when beyond a certain light intensity threshold (at 120 d, the threshold was about 40 lx). The protective enzymes that played the major role under nighttime light stress were different among the three species. For , POD and CAT complemented each other to resist stress-induced oxidative damage, while the main enzyme of was POD. The biomass of the three species increased significantly under artificial light at night. was the most sensitive to nighttime light stress, while had the strongest resistance to the stress. The deciduous shrub could tolerate the white night light lower than 40 lx, while the evergreen shrubs and could tolerate the yellow night light lower than 40 lx.