![]() The chemical compounds hydrogen peroxide and malondialdehyde are indicators of stress in plants and both were found at much higher levels in the specimens exposed to the traffic noise. Analysis of their leaves revealed that all of them were suffering. None of the plants exposed to the traffic noise did well. After 15 days had passed, samples were taken from the youngest fully expanded leaves on every plant in the experiment and studied. The other group was left to grow in silence. One group was exposed to 73 decibels of traffic noise recorded from a busy motorway in Tehran for 16 hours a day. The plants were grown from seed and allowed to mature for two months in the same space before they were divided into two groups. Working with a team of colleagues, Dr Ghotbi-Ravandi grew two species in his lab that are commonly found in urban environments-French marigolds and scarlet sage. To this end, Dr Ghotbi-Ravandi decided to set up an experiment to study precisely this question. Yet blasting plants with ultrasound is not the same as growing them in the presence of actual traffic noise. A number of experiments have confirmed this in recent years-plants bombarded with ultrasound in the lab have shown a range of adverse responses including the expression of stress-related genes, stunted growth and reduced germination of seeds. ![]() Scientists have previously hypothesised that plants may be able to sense these waves as they are struck by them. Sounds are concussive pressure waves transmitted through gases, liquids and solids. ![]()
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