Plants that grow under the glare of artificial lighting like streetlights have tougher leaves that insects find hard to eat, new research has found.
This finding suggests that artificial light at night could be 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 lit-up streets of Beijing, Zhang and his colleagues observed something peculiar. Tree leaves on these streets showed little sign of insect damage compared to natural areas outside the city.
The researchers suspected the streetlights could have a role to play. So they chose 30 sites on Beijing’s streets from where they collected nearly 5,500 leaves from 180 trees, belonging to two common species in the city: Japanese pagoda (Styphnolobium japonicum) and green ash trees (Fraxinus pennsylvanica). The team calculated the amount of night-time artificial light each site was exposed to and measured various aspects of the leaves, including their size, toughness, and signs of insects chomping on them.
The study found that leaves collected from brightly lit-up spots had tougher leaves than those picked up from relatively low-light sites. Moreover, the tougher the leaves, the less insect damage they had. Leaves collected from the brightest spots had no sign of insects feeding.
The researchers don’t yet know why these patterns exist. However, Zhang told Mongabay one hypothesis is that trees exposed to artificial lights at night may be extending their photosynthesis period. The additional light could also be altering where the plants allocate their resources, whether toward growth of the trees themselves, or to create tougher leaves that herbivorous insects find hard to eat.
“These leaves might allocate a greater proportion of resources to structural compounds, such as fibers, which could lead to an increase in leaf toughness,” Zhang said in a statement.
Artificial light also introduces a different type of light than sunlight, moonlight or starlight. So the type of light emitted by Beijing’s streetlights could also be influencing the tree leaves, Ellen Cieraad told National Geographic. Cieraad is a plant ecologist at New Zealand’s Nelson Marlborough Institute of Technology and wasn’t involved in the study.
It’s not just insect food preferences that are affected by artificial lights. Light pollution can wreak havoc on wildlife in many ways. It messes up turtle hatchling navigation, confuses migratory birds, interferes with how bats move and feed, and is thought to be a major driver of insect population declines.
The effects of Beijing’s streetlights don’t end with tough leaves that insects find hard to munch on. Less food for insects also affects other urban animals up the food chain, the researchers write in the paper. This suggests that nighttime artificial light “may have far-reaching effects on the maintenance of urban biodiversity and ecosystem functioning,” they add.
Banner image by Lamiot via Wikimedia Commons (CC BY-SA 4.0)
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