April 28, 2022
Fun Fact: Plants hate being stuck in traffic.
It’s easy to understand the ecological damage animals suffer as a result of noise pollution, but it has been less clear how it affects plants…until now. The indirect effects are obvious. Flowering species depend on pollinators and fruit-bearing species need animals to disperse their seeds. If the noise is a problem for their animal partners, botanical counterparts will also suffer. A recent study by Dr. Ghotbi-Ravandi, a botanist at Shahid Beheshti University in Tehran, has shown that plants are also directly affected by noise.
A number of experiments have shown that plants can sense ultrasound waves as they are struck by them, but this isn’t quite the same as urban noise pollution. In their lab, Dr. Ghotbi-Ravandi and his team grew two species that are commonly found in urban environments: French marigolds (Tagetes patula) and scarlet sage (Salvia splendens). Once mature, the plants were divided into two groups. One was exposed to 73 decibels of traffic noise for 16 hours a day, and the other was left to grow in silence. After just 15 days all of the plants in the noisy group were suffering. Two chemical compounds (hydrogen peroxide and malondialdehyde) that are indicators of stress in plants were found at much higher levels (2 to 3 times) in the group exposed to the traffic noise. Two stress hormones (jasmonic acid and abscisic acid) which are normally produced to fend off insect attacks and deal with harsh environmental conditions, were also elevated, and a range of hormones normally associated with healthy growth and development were present at significantly reduced levels in the plants exposed to the noise.
The vibrations generated by traffic noise bothered the plants in the study enough to trigger stress responses that are not much different than if they had been exposed to drought, high salinity, or heavy metals in their soil. . I guess we’ll have to call it “road sage” now…
If you’re interested in more reading, see their paper: Z.H. Kafash, Khoramnejadian S., Ghotbi-Ravandi A.A., Dehghan S.F. 2022. Traffic noise induces oxidative stress and phytohormone imbalance in two urban plant species. Basic and Applied Ecology. Volume 60. Pages 1-12.