Biomass responses of widely and less-widely naturalized alien plants to artificial light at night.
Artificial light at night has rapidly increased during the last century, and could potentially affect many ecological processes, from individuals via communities to entire ecosystems. Recent research has shown that artificial light at night may not only affect the behaviour of animals but also growth of plants and vegetation composition. However, it is not known yet whether artificial light at night may also affect other global change components such as plant invasions. Here, we tested how naturalized alien plants respond to artificial light at night, and particularly whether widely naturalized species differ from less-widely naturalized species in their response to artificial light at night. We grew nine taxonomically related pairs of widely naturalized and less-widely naturalized species alone and in competition, with native plants with and without artificial light at night. We found that in the competition treatment, artificial light at night significantly increased the total biomass production per pot, but not the biomass ratio between the naturalized alien plants and the native competitors. Interestingly, although the less-widely naturalized species produced overall significantly less biomass than the widely naturalized species, there was a trend that the less-widely naturalized species increased their biomass more strongly in response to artificial light at night than the widely naturalized species did (p = 0.07). Synthesis. Our study shows that although widely naturalized plants produce more biomass than less-widely naturalized plants across different environmental conditions, they took less advantage of artificial light at night. This suggests that artificial light at night might lead to increased spread of currently less-widely naturalized species, at least when artificial light at night continues to increase.