Are Plants Social Creatures?

Unremarkable and largely unnoticed by the many hikers that passed it on their way to higher peaks, there is a half-rotted remnant of a Kauri tree (Agathis australis) that fell to the earth decades ago in a New Zealand forest. Unnoticed, that is, until Professor Sebastian Leuzinger of the Auckland University of Technology passed by, and realised it was not dead at all.

This unassuming trunk has remained alive decades after it fell and Professor Leuzinger quickly found the live wood was functional and showed definite water flows. How could this be possible, when the stump had had no leaves and none of the normal equipment a tree would need to draw water through its stems and leaves?

This Kauri remained grafted and connected through its roots to other Kauri trees in the surrounding forest, whose own activity provided the water flows and nourishment the stump needed to remain alive. By supporting each other, these trees form a resilient colony that works together, genetically unique as individuals but linked together through the roots.

“This is different from how normal trees operate, where the water flow is driven by the water potential of the atmosphere,” Professor Leuzinger says. “The stump has to follow what the rest of the trees do because since it lacks transpiring leaves, it escapes the atmospheric pull.”

So are plants social creatures?

Social organisms are groups of individuals that form social structures to enhance their survival in the world – just as you and I live in societies and form communities to better specialise and provide mutual support in our lives.

There is increasing evidence that plants of all kinds do exactly this: working together to develop specialisations, mutualisms and cooperative structures that enhance their survival.



The Hidden Lives of Trees

In Peter Wohlleben’s now-famous book, The Hidden Life Of Trees, it describes how umbrella thorn acacias react to feeding by giraffes. Very shortly after the trees detected feeding damage they produce a chemical that turns the leaves bitter and inedible, and the giraffes no longer find them palatable. However, this isn’t just in the trees the giraffes fed on – it influences the surrounding trees, up to about 100 metres away. These trees are communicating and it turns out the chemical exchange is through ethylene, the same gas that ripens your bananas and damages cut flowers.

Other plants can tell when insects have begun chewing on them, and mount a chemical communication that readies their neighbours for the coming attack. Research from ETH in Switzerland found that Brassicas infested with herbivore eggs induced a chemical response that caused surrounding brassicas to turn on their defence mechanisms, even before they had eggs on them. In turn, these plants produced more flowers and more seed much faster than they would have, as a proactive means of ensuring the transfer of their genes and ongoing survival.

This strategy of working together to share information and mount a defence is a clever evolutionary response to the enduring threats posed by insect damage and almost looks like an ‘arms race’ as insects and plants react and respond. Chemicals such as jasmonic acid influence the responses of surrounding plants and induce chemical or hormonal reactions that prepare their colleagues for an imminent attack.

 

 

Professor Stephan Mancuso is a scientist at the University of Florence who believes that the parts of a plant are, in effect, much like a giant brain. A plant needs to be able to communicate across its whole structure as well as through the environment that surrounds it, using a combination of electrical, biological, physical and chemical stimuli. This, he says, poses the question of awareness and consciousness in plants.

How aware are plants of their own existence?

“Consciousness is a little bit tricky in both our languages. Let’s talk about awareness. Plants are perfectly aware of themselves. A simple example is when one plant overshadows another – the shaded plant will grow faster to reach the light. But when you look into the crown of a tree, all the shoots are heavily shaded. They do not grow fast because they know that they are shaded by part of themselves. So they have a perfect image of themselves and of the outside,” says Professor Mancuso.

Mancuso says that plants are excellent at detecting vibrations, especially around the 200 to 300 hertz frequency because that is close to the vibrations that running water makes. This kind of stimulus-response helps the plant’s roots to orient toward the water source, hidden from light in the damp earth.

As horticulturists and plant professionals, we let the plants do the talking. But if you look a little closer, you may just find they are doing a lot more talking than any of us ever realised.

 

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