Plants emit high frequency "screams" when under stress, says study

Tel Aviv: Plants are now suspected to emit a high-frequency scream when they are faced with stressors like draught or being cut. This 'scream' is not audible to humans but new studies strongly hint at airborne sounds.

Researchers at Tel Aviv University studied tomato and tobacco plants and found that these sounds are loud enough for other creatures to hear. The team led by Lilach Hadany has recorded these ultrasonic sounds in the range of 20-100 kilohertz.

After downsampling to an audible range and being sped up, the recording provides a "distinguishable" pop sound that humans can hear. As the researchers increased the drought stress, the number of pops went up. As the plant dried up, the number of pops started declining.

Experts also found that these sounds could be detected from a distance of 3-5 metres which suggests that plants have the potential for long-range communication.

The study also suggests that these 'screams' are part of the biochemical responses that help plants form mutually beneficial relationships with other organisms like fungi and bacteria.

Plants cannot run away from stressors like drought or herbivores. So, they have evolved a set of complex biochemical responses. These are linked to the ability to alter their growth in response to environmental signals like light, gravity, temperature, touch, and volatile chemicals produced by other organisms. These influence the growth and reproductive success of plants.

An earlier study found that the buzzing of bees causes plants to produce sweeter nectar. Another study found that a flowering plant in the mustard family had a drought response to white noise.

Many have criticised that these pop sounds are just results of the air bubble expanding and bursting inside the plant's water-conducting tissue. Scientists at Tel Aviv agree that this process, known as cavitation, is at least partially responsible for the sounds. Both drought and cutting alter the water dynamics in the plant stem.

However, sounds produced by stressed plants are very likely used for communication and are informative in nature. Machine learning algorithms have helped researchers to distinguish which species of plants produced a certain sound and what type of stress it was suffering from.