How artificial lighting makes tree leaves tougher and less appetizing to insects

A study reveals that night-time light pollution can harden tree leaves, making them less attractive to herbivorous insects: this phenomenon, observed in two tree species in Beijing, triggers a chain reaction that affects the entire ecosystem

Light pollution has long been recognized as a significant problem, with harmful effects on human health, wildlife, and plant life. A recent study published in Frontiers in Plant Science has uncovered a new adverse effect of nighttime artificial lighting: it makes tree leaves tougher and less appetizing to herbivorous insects.

Experts have speculated that exposure to high levels of artificial light could cause plants to allocate more energy to defense rather than growth. To test this hypothesis, researchers collected nearly 5,500 leaves in Beijing, focusing on two common species: Japanese acacia and green ash. If the plants were prioritizing growth, their leaves would have been larger. However, if they were channeling more resources into defense, the leaves would be tougher and contain higher levels of tannins and other chemical compounds.

Tougher leaves, less appealing: a vicious cycle

The results confirmed that both tree species, when exposed to intense artificial light, produced tougher leaves that showed fewer signs of damage from herbivorous insects. Artificial lighting appears to trigger a process that makes the leaves too difficult for insects to consume, reducing their feeding activity. However, the exact mechanism remains unclear. It is possible that prolonged exposure to light extends the duration of photosynthesis or prompts leaves to use more resources to produce structural fibers that toughen them.

The hardening of leaves sets off a chain reaction, leading to a decline in herbivorous insects, followed by a decrease in predatory insects and the birds that feed on them. This decline in insects, already a well-documented issue, is a complex and multifaceted problem. It is also possible that artificial light makes insects more visible to predators, further contributing to their decline. However, since the study was conducted in only one city and involved just two tree species, further research is essential to fully understand the impact of artificial lighting on urban ecosystems.

Source: Frontiers in Plant Science