A new study is upsetting many vegans and vegetarians as it shows that plants do feel as animals do when dying. For the first time, researchers have discovered that plants make sounds when stressed. Many people may not think of plants as capable of hearing or smelling; however these airborne vibrations could open up a new field in precision agriculture where farmers listen for water-starved crops to determine how they can best help them grow.
A team of researchers at Tel Aviv University in Israel found that tomato and tobacco plants made sounds, which humans cannot hear when stressed by a lack of water or when their stem is cut.
When water is lacking the tomatoes and tobacco plants emit sounds that are inaudible to humans. This was discovered by Itzhak Khait of Tel Aviv University when he noticed his tomato plant made noises during its daily cycle of wilting on hot days, then reviving at nightfall. The frequencies range from 50 Hz for smaller species like petunias or carnations down to 20 kHz for larger ones such as chili peppers or maize (corn). Other plants could even hear the other plants squealing in pain as well.
“These findings can alter the way we think about the plant kingdom, which has been considered to be almost silent until now,” they write in their study, which has not yet been published in a journal.
Previously, scientists have recorded the vibrations caused by bubbles forming and imploding inside xylem tubes which are used for water transport. This new study is the first time that sounds from plants have been measured at a distance.
Drought-stressed tomato plants made an average of 35 sounds per hour, while tobacco plants only produced 11. When plant stems were cut, tomato and the unstressed group both averaged less than one sound in the following hour.
It is even possible to distinguish between the plants’ sounds and noise in order to determine what kind of stress they are under. Researchers trained a machine-learning model, successfully identifying dryness versus cut damage most of the time based on intensity and frequency. Water-hungry tobacco appears to make louder sounds than cut tobacco, for example.
Even though Khait and his colleagues only looked at tomato and tobacco plants, they believe other plants may also make sounds when stressed. In a preliminary study, they recorded ultrasonic sounds from spiny pincushion cactus (Mammillaria spinosissima) as well as the weed henbit dead-nettle (Lamium amplexicaule). Cavitation is a possible explanation for how these plant generate sound which could be useful in future acoustic engineering applications to modify structures such as ship propellers or wind turbines by changing cavitating flows of water around them so that loud noises are reduced over time.
Allowing farmers to listen for water-stressed plants could “open a new direction in the field of precision agriculture”, the researchers suggest. They add that such an ability will be increasingly important with water shortages worldwide.
“The suggestion that the sounds that drought-stressed plants make could be used in precision agriculture seems feasible if it is not too costly to set up the recording in a field situation,” says Anne Visscher at the Royal Botanic Gardens, Kew, in the UK.
The results of this study cannot yet be extrapolated to other factors such as salt and temperature because we don’t know if moths can hear these sounds. This is speculation for now, but it would really interesting if the idea could work in practice with animals too!
Plants may be making noises when they are stressed, but it doesn’t sound like the plants know what’s happening. They emit a popping noise that scientists think is made because of bubbles in water moving around under pressure called cavitation. One scientist says “cavitation would explain the sounds”, but other experts doubt this since there need to be more controls and experiments done on these findings before anything can come out about them being accurate or not.”
Farmer adds that the idea moths might be listening to plants and shunning stressed ones is a “little too speculative”, and there are already plenty of explanations for why insects avoid some plants and not others.