Plants Talk — We Just Cannot Hear Them

Plants undergoing stress, such as drought or insect damage, use various tactics to defend themselves and warn others of danger. Some release strong scents, while others change color and shape. A recent study found that stressed plants even produce popping or clicking sounds. However, humans cannot hear them because they are at frequencies beyond our hearing range.

For their research, Dr. Lilach Hadany and her team at Israel's Tel Aviv University selected tomato and tobacco plants. They stressed some plants by either not watering them for a few days or cutting their stems. The team then used special microphones to record the sounds, first in a soundproof room and later in a noisier greenhouse.

An analysis using a special algorithm found that the unstressed plants made little to no sound. However, the stressed plants were much noisier. They emitted up to 40 clicks and pops per hour, depending on the species.

Interestingly, the water-deprived plants began making noise before any visible signs of dehydration. The sounds increased as the plant became drier, but stopped completely once it dried out. The scientists suspect the noises may be due to air bubbles forming and bursting in the plant’s vascular system.

"Unstressed plants emitted less than one sound per hour, on average," said Hadany. The stressed plants – both dehydrated and injured – emitted dozens of sounds every hour."

Hadany believes these clicking sounds may warn nearby plants of danger. She speculates that animals with ultrasonic hearing might also use them to their advantage.

“For example, a moth that intends to lay eggs on a plant or an animal that intends to eat a plant could use the sounds to help guide their decision,” she explains.

The scientists believe their discovery could be very beneficial to farmers. With climate change causing unpredictable droughts, they could use sound-detecting devices to identify when crops need water or extra care.

Resources: Sciencealert.com, CBSnews.com, eurekalert.org