Flowers don’t just smell sweet to humans: Their delicious aromas attract bees and other pollinators. But, as Puneet Kollipara reports for Science, ozone could be changing that. New research shows that ozone pollution makes flowers smell different to bees.
Scientists have long known that ozone breaks down volatile organic compounds, or VOCs (the “volatile” means that they vaporize easily). Bacterial processes, plants and flowers all emit VOCs. In fact, VOCs are responsible for the intoxicating scents that attract both humans and bees. As Robert A. Raguso writes for Functional Ecology, there’s been a “growing realization among researchers” that plants use VOCs “to communicate with friends, enemies, neighbors and, indeed, themselves.”
A new study shows how ozone works against those sweet smells. Kollipara explains that researchers collected and grew black mustard plants, exposing them to different levels of ozone inside the lab. When they used a mass spectrometer to measure the scent molecules, writes Kollipara, they found that flowers exposed to 120 parts per billion of ozone had between 17 and 31 percent fewer scent molecules when measured from 4.5 meters away than flowers that hadn’t been exposed to ozone at all.
Next, researchers took bumblebees and watched how they reacted to flowers that had been exposed to ozone. They found that the bees spent more time in environments full of floral scents not exposed to ozone and landed on more artificial flowers associated with the scents of flowers that hadn’t been exposed to ozone.
While there is such thing as “good ozone” (the ozone in the upper atmosphere that protects Earth’s surface from the sun’s UV rays), ground-level ozone is a different story. As NASA notes, manmade pollution leads to more ozone on the surface, creating more volatile chemical reactions like the ones observed in flowers. Though the United States has managed to cut ozone production on the ground, rapidly-industrializing nations like China are contributing to growing ozone pollution, and air pollution can travel from continent to continent.
Given bees’ vital role in pollination (it’s thought that they’re responsible for a third of all crop production), their reactions to ozone-altered floral scents are yet another not-so-sweet consequence of polluted air.