Pollution,Pollination and the Sensitive Rules of Attraction
【The New York Times (Feburary 20, 2024)】
The damage that air pollution can do is wide-ranging and well known: The chemicals produced by human activities can trap heat in the atmosphere, change the chemistry of the oceans and harm human health in myriad ways. Now, a new study suggests that air pollution might also make flowers less attractive to pollinating insects. Compounds called nitrate radicals, which can be abundant in nighttime urban air, severely degrade the scent emitted by the pale evening primrose, reducing visits from pollinating hawk moths, researchers reported in Science this month.
The study focuses on the pale evening primrose, a plant with delicate flowers that open at night. Its key pollinators include hawk moths, which have exquisitely sensitive odor-detecting antennae(触角). A flower's scent is a complex olfactory bouquet that contains many chemical compounds. To identify the ingredients in the signature primrose scent, the scientists fastened plastic bags over the blooms, capturing samples of the fragrant air. When the team analyzed these samples in the lab, it identified 22 distinct chemical components.
The scientists then recorded the electrical activity of the moths' antennae when they were exposed to these scent compounds. They found that the moths were especially sensitive to a group of compounds called monoterpenes, which also help give conifers their fresh, evergreen smell.
The researchers used these attractive aromas to concoct their own simulated primrose scent. Then, they added ozone and nitrate radicals, both of which can form when pollutants produced by fossil-fuel combustion enter the atmosphere. Ozone, which forms in the presence of sunlight, is abundant during the day, whereas nitrate radicals, which are degraded by sunlight, are more dominant at night.
The scientists added ozone to the primrose scent first and observed some chemical degradation, with concentrations of two key monoterpenes dropping by roughly 30 percent.They next added nitrate radicals to the mix, which proved far more damaging, reducing these key moth attractants by as much as 84 percent compared with their original levels. They were"almost completely gone," Dr. Thornton, the leading researcher said.
The researchers believe that the problem extends far beyond the hawk moth and the primrose. Many pollinators are sensitive to monoterpenes, which are common in floral odors. Using computational modeling, the researchers calculated that in many cities around the world, pollution has reduced scent-detection distances by more than 75 percent since the preindustrial age.