Plants have long been known to be responsive to airborne sound – at least to playback of human generated sounds, which can alter plant growth in multiple ways. However, only recently have researchers begun to ask whether plants respond adaptively to any of the natural sound sources in their environment.

 

Because plants do not have ears, “sound” (airborne pressure waves) can only be relevant to plants when it is transformed into vibration. And indeed, plant leaves absorb sound, and each leaf or flower petal provides a clear vibrational copy of the airborne sounds in its environment.

 

In our work, we focus on vibration - the ‘native language’ of plants. In particular, when caterpillars or other chewing herbivores feed on a leaf, they produce little to no airborne sound. However, they do produce characteristic high-amplitude, broadband vibrations. When we reproduce these vibrations in the absence of the caterpillar itself, this primes Arabidopsis plants to produce more of their herbivore-deterring glucosinolates when subsequently attacked (Appel and Cocroft 2014). In other words, Arabidopsis plants respond to an ecologically meaningful acoustic stimulus, in an ecologically relevant way!

 

Building on this work, we found that feeding vibrations not only cause the release of plant stress hormones, but also trigger changes in the release of the airborne volatiles that can warn other parts of the plant and attract natural enemies of the herbivores (Body et al 2019 a,b). It turns out that feeding vibrations are very similar, regardless of the kind of caterpillar or plant; and indeed, Arabidopsis plants responded in the same way to playback of feeding vibrations of two different caterpillar species (Kollasch 2020).

 

Furthermore, triggering of anti-caterpillar defenses by feeding vibrations occurs not only in Arabidopsis, but also in domesticated tobacco (Pinto et al 2019). It is likely that vibration-based herbivore detection occurs widely in plants.

 

More recently we have begun to move this research from the lab to the field, with the goal of characterizing natural plant vibroscapes in the field (Appel and Cocroft 2023). Furthermore, we know from prior work (Appel and Cocroft 2014) that the responses of Arabidopsis are at least somewhat selective, being triggered by feeding vibrations but not by wind vibrations or leafhopper song. Now we would like to know just how specific the plants’ defense responses are to a particular kind of stimulus, within the context of a natural acoustic environment.