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Do plants respond to sound?

This might seem like something from a science fiction story. But there is actually strong evidence that plants respond to sound.


In one intriguing study, researchers recorded the sound of a caterpillar eating the leaves of a potted plant (species Arabidopsis thaliana). Then they played the recording back to other plants of the same species and measured changes in the chemical composition of the leaves.


Compared to plants in a control group, plants subjected to the sound recordings subsequently produced elevated levels of chemical defenses in their leaves -- chemicals that deter predation by caterpillars and other natural leaf predators.


The researchers also tested the effects of other vibrations -- (1) the vibration produced by the wind (recreated by aiming a fan at the plants), and (2) the "vibrational mating song of a leafhopper" (presented via audio playbacks).


The scientists matched the amplitude of these alternative vibrations so they overlapped with that of the chomping caterpillar sounds. Thus, they vibrated the plants with a similar intensity. But the plants didn't respond to these alternative vibrations in the same way. They did not show the same increase in defensive chemical compounds.


Obviously, plants don't have ears. But these experiments indicate that they aren't merely responding in a general way to any vibrations that wiggle their leaves. As the study authors note, they can "distinguish the vibrations that signal herbivore feeding from the many environmental vibrations that do not."


How do they do it?


The researchers point out that the plants could, in theory, use differences in frequency to distinguish the caterpillar chewing noises from the vibrations of the wind. But that wouldn't have worked for the leafhopper song. It had the same frequency as the caterpillar chewing noises. The plants must have used some other cue to tell these apart. One possibility is that the plants detected differences in temporal pattern. Over time, the chewing sounds unfolded in repeated, short bursts. By contrast, the leafhopper sound was a more persistent, uninterrupted sound. The researchers conclude that the plants are probably sensitive to multiple cues.


Results like these have been replicated many times by researchers in other labs.  Experiments have shown that sound can alter plant development and physiology in many ways, affecting for example


  • growth

  • seed germination

  • photosynthesis, and

  • disease resistance.

And researchers are studying applications in agriculture. As Ratnesh Mishra and colleagues note in a recent review:


"[Sound vibrations] have been shown to increase the yields of several crops and strengthen plant immunity against pathogens. These vibrations can also prime the plants so as to make them more tolerant to impending drought." 


References


Appel HM and Cocroft RB. 2014. Plants respond to leaf vibrations caused by insect herbivore chewing. Oecologia. 175(4):1257-66.


Mishra RC, Ghosh R, and Bae H. 2016. Plant acoustics: in the search of a sound mechanism for sound signaling in plants. J Exp Bot. 67(15):4483-94.

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