Photo courtesy of Agricultural Research Service
“Evidence now supports the vision that plants are living, breathing, communicating creatures,” wrote journalists Peter Tompkins and Christopher Bird in their 1973 seminal work, The Secret Life of Plants
. Though the book was a success and can now be found on the shelves of the New Age section of bookstores, it was not very popular among scientists.
Even today, characterizing any living organism that is without a nervous system as one exhibiting a ‘behavior’ must be done so with the utmost austerity. It is a word that took ecologist James Cahill and his colleagues at the University of Alberta a full two years to feel comfortable using when describing the actions of the annual plants that they were observing as part of their study published this past June.
Now that studies like Cahill’s are being conducted more frequently, the field of plant biology is changing. Scientists are no longer questioning whether or not plants can be said to exhibit behavior. The new question being asked now is how
Ecologist James Cahill in the field
How has the field of plant biology changed over the last few years?
Understanding plant biology has traditionally been about learning the physiology of plants and how they are broken down into their constituent parts, but in recent years many labs have moved more towards studying a plants’ sensory capacities. For example you don’t see many roots growing in the air. Why? Because plants can sense gravity. Traditionally the opinion of science has been that animals could express behavior but living organisms without nervous systems could not. What my lab and many other labs are starting to show is that it’s not that simple. Plants, we have learned, can express behaviors very similarly to the way animals express behavior.
Are scientists just discovering that plants can communicate or express a particular behavior for the first time?
In the 1970s and 1980s there were biologists who showed that trees could communicate. Unfortunately what happened then is that in their coverage of these studies the press ran headlines like, “The Talking Trees.” Between the headlines, a few flaws in some of the initial data, and some of the more unseemly realities of the field, like scientific jealousy, there was a fierce attack laid on these types of studies. The result was that studies about plant communication and behavior became a world that a scientist just couldn’t touch. What happened in the 90s is that scientists began collecting data that showed things like plants had the ability to grow their roots towards a source of nutrition; they don’t just grow them evenly through soil. Another study showed that plants try and grow their roots away from other plants to avoid competition. These behaviors, though at the outset we couldn’t call it behavior so we called it plasticity, became the grounds for the work that we did in our lab.
Why couldn’t you use the word behavior?
Scientific papers said so. There were other labs like ours studying plant behavior and the general consensus in the field was that it was not an appropriate term. But eventually it was clear that plants did exhibit behavior and the detractors just got worn down.
What was your study about and what did you find?
As I mentioned, there were studies that revealed that a plant could preferentially decide to grow their roots towards a source of nutrition, or away from a source of competition, so building on that we posed the question could plants go a step further and actually integrate those two pieces of information and behave accordingly? So what we did is we grew Abutilon theophrasti,
an annual plant, in experimental pods both with and without a neighbor, and we either spread resources throughout the soil or we put them between the plants. To track the movement of the roots we used a specialized camera to image them. What we found was that when the resources were spread evenly through the soil, the plants really avoided each other, but when the resources were placed between them, they grew their routes toward one another. This had not been shown before. It was previously thought that integrating information was too complex a behavior for a non-cognitive organism. But we found that plants could do it.
Roots of a potted plant in James Cahill's lab at the University
If it’s not appropriate to call plants ‘talking’ organisms what is a more appropriate name for plant communication?
What we are finding in our studies is the possibility of chemical communication; talking implies sound. We already know that plants communicate with insects using chemicals, and there is tons of evidence to support chemically based communication between plants, but we have yet to identify the chemicals themselves. But, it doesn’t matter. You can call it talking, you can call it chemically based interactions, you can call it Bob or Steve, what’s important is that we have clear evidence that there is information being passed.
Do insects and plants really communicate with one another?
Yeah, mostly plants communicate with insects. There is a reason that certain plants look and smell the way that they do. A plant will have its flowers look or smell a particular way in order to manipulate the decisions that a pollinating insect makes. This is communication to attract the insects it wants. Conversely plants have methods to repeal insects. Certain plants, when they get attacked by an insect, will purposefully alter their scent, and the alterations they make to their smell will actually attract the predator of the insect attacking it. It’s the old ‘the enemy of my enemy is my friend’ idea.
Were you Surprised by the results of your study?
Yes, I am a bit surprised that plants were able to do this. It’s just not the way I was brought up to believe the way the world works. I was raised to believe that plants are plants. You eat them, you grow them, and they look pretty, but this is suggesting that there is a lot more to them than just that. I really think that we’re at the cusp of a real paradigm shift and that people are going to be viewing plants very differently in the next ten years with a much more holistic view of what plants actually are. One of the great things about working in this area is that it’s new so there is so much to be explored.
What will you be studying next?
I’m moving on to investigate some behavioral predictions of the mimoso, which is a plant that closes its leaves very rapidly, and I’m also trying to find out if the way plants grow their roots is affected by the presence of earthworms in the soil. It’s a fun time for us in the lab now, because we are on the cusp of a whole new area. We can just think about behaviors plants might have and set up the lab to test for it.
Photo courtesy of Agricultural Research Service