Attention plant killers: new research shows that your plants may be silently screaming at you


If you're like me, you've managed to kill even the hardiest indoor plants (yes, despite a PhD in plant biology). But imagine a world where your plants actually told you exactly when they needed watering. This thought, as it turns out, might not be so stupid after all.

You may be familiar with the growing body of work that provides evidence for plants that can sense sounds around them. Now new research suggests they can also generate airborne sounds in response to stress (such as from drought or cuts).

A team led by experts at Tel Aviv University has shown that tomato and tobacco plants, among others, not only make sounds, but make them loud enough for other creatures to hear. Their results, published today in the journal Cell, helps us tune into the rich acoustic world of plants—a world that unfolds all around us, yet never quite within human earshot.

Plants can listen, but now they can talk!

Plants are “sedentary” organisms. They cannot escape from stressors such as herbivores or drought.

Instead, they have evolved complex biochemical reactions and the ability to dynamically alter their growth (and regrowth of body parts) in response to environmental cues including light, gravity, temperature, touch, and volatile chemicals produced by surrounding organisms.

These signals help them maximize their growth and reproductive success, prepare for and withstand stress, and form mutually beneficial relationships with other organisms such as fungi and bacteria.

During 2019, researchers showed the buzzing of bees can cause plants to produce sweeter nectar. Other have shown white noise played Arabidopsisa flowering plant in the mustard family, can trigger a drought response.

Now, a team led by Lilach Hadany, who also led the aforementioned bee nectar study, has recorded airborne sounds produced by tomato and tobacco plants and five other species (grapevine, henbit deadnettle, needle cactus, corn and wheat). These sounds were ultrasonic, in the range of 20-100 kilohertz, and therefore cannot be detected of human ears.

Stressed plants chatter more

To conduct their research, the team placed microphones 10 cm from plant stems that were either exposed to drought (less than 5% soil moisture) or had been cut close to the soil. They then compared the recorded sounds to those of unstressed plants, as well as empty pots, and found that stressed plants emitted significantly more sounds than unstressed plants.

As a cool addition to their paper, they also included a soundbite from a recording, downsampled to an audible range and sped up. The result is a distinct “pop” sound.

The number of poppers increased as drought stress increased (before beginning to decrease as the plant dried). In addition, the sounds could be detected at a distance of 3-5 meters – indicating the potential for long-distance communication.

But what actually causes these sounds?

While this remains unconfirmed, the team's findings suggest that “cavitation” may be at least partially responsible for the sounds. Cavitation is the process by which air bubbles expand and burst inside a plant's water-conducting tissue, or “xylem.” This explanation makes sense if we consider that drought stress and cutting will both change the water dynamics of a plant stem.

Regardless of the mechanism, it appears that the sounds produced by stressed plants were informative. Using machine learning algorithms, the researchers were able to discern not only which species produced the sound, but also the type of stress it was suffering from.

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We now have the first research evidence that plants can make airborne sounds, heard up to a few meters away.

It remains to be seen whether and how these audio signals may be involved in plant-to-plant or plant-to-environment communication.

The research has so far failed to detect any sounds from woody trunks of woody species (which includes 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 us?

It is tempting to speculate that these airborne sounds may help plants communicate their stress more widely. Could this form of communication help plants, and perhaps wider ecosystems, to better adapt to changes?

Or the sounds may be used by other organisms to detect a plant's health status. Moths, for example, hear in the ultrasonic range and lay their eggs on leaves, as the researchers point out.

Then there is the question of whether such findings can help with future food production. The global demand because the food will only rise. Tailoring water use to target individual plants or parts of the field that make the most “noise” can help us more sustainably intensify production and minimize waste.

For me personally, if someone could put a mic on my neglected vegetable patch and get the messages sent to my phone, it would be greatly appreciated!

Read more:
Rosemary in roundabouts, lemons over the fence: how to forage in cities safely, respectfully and smartly

The conversation

Alice Hayward receives funding from The Australian Research Council Linkage Scheme and various industry partners. Her salary is paid by The Queensland Alliance for Agriculture and Food Innovation (a partnership between the University of Queensland and the Department of Agriculture and Fisheries, Queensland). Previously, she has received funding from The Queensland Government, The Australian Government, The Chinese Academy of Sciences, UQ and Hort Innovation Australia. She is a member of Native Plants Queensland and The Australian Branch of the International Association of Plant Biotechnology.

Originally published in The conversation.

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