If you’re like me, you’ve managed to kill even the hardiest houseplants (yes, despite a PhD in plant biology). But imagine a world where your plants tell you exactly when they need water. This thought, it turns out, may not be so crazy after all.
You may be familiar with the growing body of work providing evidence that plants can sense sounds around them. Now, new research suggests they may also generate airborne sounds in response to stress (such as from drought or mowing).
A team led by experts from Tel Aviv University has shown that tomato and tobacco plants, among others, not only make noise, but loud enough for other creatures to hear. their findings, published today in Cell magazine, help us tune into the rich acoustic world of plants – a world that is all around us, but never quite within human hearing.
Plants can listen, but now they can talk!
Plants are “sessile” organisms. They cannot run from stressors such as herbivores or drought.
Instead, they have evolved complex biochemical reactions and the ability to dynamically alter their growth (and regrow body parts) in response to environmental signals such as light, gravity, temperature, touch, and volatile chemicals produced by surrounding organisms.
These signals help them maximize their growth and reproductive success, prepare for and resist stress, and form mutually beneficial relationships with other organisms such as fungi and bacteria.
2019, researchers showed the buzzing of bees can cause plants to produce sweeter nectar. Others have shown white noise played Arabidopsisa flowering plant in the mustard family, can cause a drought reaction.
Now a team led by Lilach Hadany, who also led the aforementioned bee nectar research, has recorded airborne sounds produced by tomato and tobacco plants and five other species (grapevine, henbit deadnettle, pincushion cactus, corn and wheat). These sounds were ultrasonic, in the range of 20-100 kilohertz, and therefore cannot be detected through human ears.
Stressed plants chatter more
To conduct their study, the team placed microphones 10 cm from plant stems that had been exposed to drought (less than 5% soil moisture) or had been cut off near the ground. They then compared the recorded sounds to those of non-stressed plants, as well as empty pots, and found that stressed plants emitted significantly more sounds than non-stressed plants.
As a cool addition to their paper, they also included a sound bite of a recording, downsampled to an audible range and sped up. The result is a clear “pop” sound.
The number of pops increased as drought stress increased (before starting to decrease as the plant dried up). In addition, the sounds could be detected at a distance of 3-5 meters, indicating long-distance communication capabilities.
But what actually causes these noises?
While this remains unconfirmed, the team’s findings suggest that “cavitation” may be at least partly responsible for the sounds. Cavitation is the process by which air bubbles expand and burst in a plant’s water-conducting tissue, or “xylem.” This explanation makes sense when we consider that drought stress and mowing both change water dynamics in a plant stem.
Regardless of the mechanism, it seems that the sounds produced by stressed plants were informative. Using machine learning algorithms, the researchers were able to distinguish not only which species produced the sound, but also what kind of stress it was suffering from.
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It remains to be seen if and how these sound signals can be involved in plant-to-plant or plant-to-environment communication.
The research has so far been unable to detect sounds from the woody stems of woody species (including many tree species), although they were able to detect sounds from non-woody parts of a vine (a woody species).
What could it mean for the ecology, and for us?
It’s tempting to speculate that these airborne sounds may help plants communicate their stress more broadly. Could this form of communication help plants, and perhaps broader ecosystems, better adapt to change?
Or perhaps the sounds are used by other organisms to detect a plant’s health status. Moths, for example, belong within the ultrasonic range and lay their eggs on leaves, as the researchers point out.
Then there is the question of whether such findings could help with future food production. The global demand because food will only rise. By tailoring water use to individual plants or parts of the field that make the most “noise”, we can intensify production more sustainably and minimize waste.
For me personally, if someone could give a microphone to my neglected vegetable patch and send the notifications to my phone, it would be greatly appreciated!
Read more: Rosemary on roundabouts, lemons over the fence: foraging safely, respectfully and smartly in the city
