Real Girls: The surprising way plants show they're stressed


	October 25, 2024

Original photo by Prudence Earl/ Unsplash

Plants make sounds when they're stressed.

For those of us not blessed with a green thumb, it'd certainly be helpful if our plant friends could tell us when they need attention. Well, it turns out they do — we just can't hear them. In early 2023, scientists from Tel Aviv University revealed the results of an investigation into whether plants make sounds in ultrasonic frequencies. Previous studies had established that plants can hear sounds, despite not having ears, so it seemed possible that they could create sounds without mouths. After isolating plants in a soundproofed acoustic chamber and a greenhouse and then recording them, the researchers were able to train a machine learning algorithm to differentiate sounds among three disparate plant states: unstressed, cut, or dehydrated.

Unstressed plants made little noise and continued along in their usual happy routine of photosynthesizing, but cut and dehydrated plants let out frequent small pops and clicks in a range too high for humans to hear. Stressed plants produced up to 40 of these clicks per hour, while dehydrated plants increased clicks as they got more and more parched. Although tomato and tobacco plants were originally tested, other crops were found to produce similar noises. It's possible some animals that can hear in frequencies beyond human capabilities could respond to these noises. If a moth were trying to find a suitable plant to lay its eggs, for example, it might skip one that's popping in distress. But big mysteries remain: For one thing, scientists don't know how plants are making these sounds in the first place. All we know for sure is that the quiet lives of plants are not nearly as quiet as they seem.

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Trees can "talk" to one another.

Since the mid-19th century, naturalists have often regarded trees as solitary, monolithic figures, but recent research refutes this idea and suggests that trees are remarkably social. That's because trees in a forest can communicate via a symbiotic relationship known as mycorrhiza. The name, which is Greek for "fungus" and "root," essentially explains how it works. Fungal threads called mycelium provide nutrients to trees, which in turn deliver sugars generated from photosynthesis. Because mycelium is ubiquitous throughout a forest, it essentially networks trees together — in what some scientists refer to as a "wood-wide web." Trees can communicate when they are stressed, share information about potential threats, or deliver nutrients to struggling members of the web, especially if they're in the same family. One study analyzed six different 10,000-square-foot stands of Douglas fir in British Columbia and discovered that nearly all the trees were connected to each other by at most three degrees of separation. They also discovered that one "hub tree," an older specimen, was connected to at least 47 other trees (and likely many more), including cross-species trees such as the paper birch.