What do plants hear?

            Plants and trees are seldom considered to have acute senses – at least not like those of many mammals. But scientists at the University of Western Australia discovered that plants have far more complex senses than previously believed, and they can even detect and respond to the sound of moving water.

            In a study led by Associate Professor Monica Gagliano, pea plants sensed sound vibrations from running water moving through pipes or in the soil, and the plant’s roots responded to that sound by moving toward the source of water. The study also revealed that plants avoid other sounds by moving away from them.

            The researchers put pea plants into containers with two tubes at the base, giving them a choice of directions for their roots to grow. They then exposed the plants to a series of sounds beneath each tube, including white noise, running water, and a recording of running water.  They found that the plants could tell where the source of the water was and their roots grew toward the water.

            “It was surprising and extraordinary to see that the plant could actually tell when the sound of running water was a recording and when it was real, and that the plant did not like the recorded sound,” said Gagliano, adding that when moisture was readily available in the soil, the plants did not respond to the sound of running water.

How the plants accomplish this feat is unknown. “The detection of acoustic vibrations, which are vibrations of mechanical nature, is likely to involve the same sensory systems plants use to detect touch – and they’re really good at that,” she said. “If correct, this would possibly involve touch genes and mechanoreceptors because sound is a touch-at-a-distance kind of phenomenon.”

These findings may explain how and why tree roots invade sewer pipes and could lead to the development of soundproof materials for pipelines.

“This would not only improve the sewer systems but reduce exorbitant repair and maintenance costs to municipalities worldwide and make the use of toxic chemicals currently used to clear the roots from the sewer system unnecessary, hence reducing environmental pollution and contamination,” Gagliano said.

The study also raises questions about the implications of noise pollution on plants. Might the increasingly noisy environment be drowning out the ability of plants to hear moving water? Gagliano calls that an open question that should be investigated.

“In animal communities, both in terrestrial and marine environments, these kinds of questions have been raised and the current available studies are showing that these effects are indeed serious and detrimental,” she said. “Based on our findings, it is reasonable to expect that this would be the case for plants, too. Acoustic pollution could mask important acoustic information and make life and survival for plants more difficult. And we have no idea of the long-term consequences of this form of anthropogenic disturbance to plant life.” 

This article first appeared in the fall 2017 issue of Northern Woodlands magazine.