New research shows that plants grown in the bright light of artificial lighting, such as street lamps, have tougher leaves that are difficult for insects to eat.

This finding suggests that artificial light at night could pose a potential threat to urban biodiversity, study co-author Shuang Zhang, an ecologist at the Chinese Academy of Sciences, told Mongabay in an email.

On the illuminated streets of Beijing, Zhang and his colleagues observed something strange. The leaves of the trees on these streets showed little signs of insect infestation compared to the natural areas outside the city.

The researchers suspected that streetlights might play a role, so they selected 30 locations on Beijing’s streets, from which they collected nearly 5,500 leaves from 180 trees belonging to two species common in the city: the Japanese pagoda tree (Styphnolobium sylvestris) and green ash (Fraxinus pennsylvanica). The team calculated the amount of artificial light each site was exposed to at night and measured various aspects of the leaves, including their size, robustness, and signs of insect damage.

The study found that leaves collected from brightly lit locations were harder than those collected from relatively dimly lit locations. In addition, the harder the leaves were, the less insect damage they suffered. The leaves collected from the brightest locations showed no signs of insect damage.

Researchers don’t yet know why these patterns exist, but Zhang told Mongabay that one hypothesis is that trees exposed to artificial light at night could extend their photosynthesis period. The extra light could also change the way the plants use their resources, whether for the growth of the trees themselves or for producing tougher leaves that are difficult for herbivorous insects to eat.

“These leaves could allocate a larger proportion of resources to structural components such as fibers, which could lead to an increase in leaf toughness,” Zhang said in a statement.

Artificial light also produces a different kind of light than sunlight, moonlight or starlight, so the kind of light emitted by Beijing’s street lamps could also affect the leaves on trees, Ellen Cieraad said. National GeographicCieraad is a plant ecologist at the Nelson Marlborough Institute of Technology in New Zealand and was not involved in the study.

Artificial light doesn’t just affect the feeding preferences of insects. Light pollution can have devastating effects on wildlife in many ways. It disrupts the navigation of baby turtles, confuses migratory birds, affects the movement and feeding habits of bats, and is considered one of the main reasons for the decline in insect populations.

The impact of Beijing’s streetlights is not limited to tough leaves that make it difficult for insects to eat. Less food for insects also affects other urban animals higher up the food chain, the researchers write in the paper. This suggests that artificial light at night “could have far-reaching effects on the conservation of urban biodiversity and the functioning of ecosystems,” they add.

Banner image by Lamiot via Wikimedia Commons (CC BY-SA 4.0)