Plants Emit High-Pitched Sounds When They Get Cut, or Stressed by Drought, a New Study Shows

Image via Wiki­me­dia Com­mons

Are plants sen­tient? We know they sense their envi­ron­ments to a sig­nif­i­cant degree; like ani­mals, they can “see” light, as a New Sci­en­tist fea­ture explains. They “live in a very tac­tile world,” have a sense of smell, respond to sound, and use taste to “sense dan­ger and drought and even to rec­og­nize rel­a­tives.” We’ve pre­vi­ous­ly high­light­ed research here on how trees talk to each oth­er with chem­i­cal sig­nals and form social bonds and fam­i­lies. The idea sets the imag­i­na­tion run­ning and might even cause a lit­tle para­noia. What are they say­ing? Are they talk­ing about us?

Maybe we deserve to feel a lit­tle uneasy around plant life, giv­en how ruth­less­ly our con­sumer economies exploit the nat­ur­al world. Now imag­ine we could hear the sounds plants make when they’re stressed out. In addi­tion to releas­ing volatile chem­i­cals and show­ing “altered phe­no­types, includ­ing changes in col­or, smell, and shape,” write the authors of a new study pub­lished at bioRx­iv, it’s pos­si­ble that plants “emit air­borne sounds [their empha­sis] when stressed—similarly to many ani­mals.”

The researchers who test­ed this hypoth­e­sis at Tel Aviv Uni­ver­si­ty “found that toma­to and tobac­co plants made sounds at fre­quen­cies humans can­not hear,” New Sci­en­tist reports. “Micro­phones placed 10 cen­time­tres from the plants picked up sounds in the ultra­son­ic range of 20 to 100 kilo­hertz, which the team say insects and some mam­mals would be capa­ble of hear­ing and respond­ing to from as far as 5 metres away.”

The plants made these sounds when stressed by lack of water or when their stems were cut. Toma­to plants stressed by drought made an aver­age of 35 sounds per hour. Tobac­co plants, on aver­age, made 11. Unstressed plants, by con­trast, “pro­duced few­er than one sound per hour.” The sci­en­tists used machine learn­ing to dis­tin­guish between dif­fer­ent kinds of dis­tress calls, as it were, and dif­fer­ent kinds of plants, “cor­rect­ly iden­ti­fy­ing in most cas­es whether the stress was caused by dry­ness or a cut,” and they con­duct­ed the exper­i­ments in both closed acoustic cham­bers and a green­house.

Plants do not, of course, have vocal cords or audi­to­ry sys­tems. But they do expe­ri­ence a process known as “cav­i­ta­tion,” in which “air bub­bles form, expand and explode in the xylem, caus­ing vibra­tions,” the paper explains. These vibra­tions have been record­ed in the past by direct, con­tact-based meth­ods. This new study, which has yet to pass peer review, might be the first to show how plants might use sound to com­mu­ni­cate with each oth­er and with oth­er liv­ing organ­isms, sug­gest­ing “a new modal­i­ty of sig­nal­ing.”

The pos­si­bil­i­ties for future research are fas­ci­nat­ing. We might learn, for exam­ple, that “if plants emit sounds in response to a cater­pil­lar attack, preda­tors such as bats could use these sounds to detect attacked plants and prey on the her­bi­vores, thus assist­ing the plant.” And just as trees are able to respond to each oth­er’s dis­tress when they’re con­nect­ed in a for­est, “plants could poten­tial­ly hear their drought stressed or injured neigh­bors and react accordingly”—however that might be.

Much remains to be learned about the sen­so­ry lives of plants. Whether their active calls and respons­es to the stim­uli around them are indica­tive of a kind of con­scious­ness seems like a philo­soph­i­cal as much as a bio­log­i­cal ques­tion. But “even if the emis­sion of the sounds is entire­ly invol­un­tary,” the researchers write (seem­ing to leave room for plant voli­tion), it’s a phe­nom­e­non that counts as a form of com­mu­ni­ca­tion: maybe even what we might some­day call plant lan­guage, dif­fer­ent from species to species and, per­haps, between indi­vid­ual plants them­selves.

Relat­ed Con­tent:

The Secret Lan­guage of Trees: A Charm­ing Ani­mat­ed Les­son Explains How Trees Share Infor­ma­tion with Each Oth­er

The Social Lives of Trees: Sci­ence Reveals How Trees Mys­te­ri­ous­ly Talk to Each Oth­er, Work Togeth­er & Form Nur­tur­ing Fam­i­lies

Graph­ic Shows the House Plants That Nat­u­ral­ly Clean the Air in Your Home, Accord­ing to a NASA Study

Josh Jones is a writer and musi­cian based in Durham, NC. Fol­low him at @jdmagness