It’s easy to think of plants as just… well, plants. While we all know they are living organisms, we tend to think of them as fairly static, basic life forms that look nice when they are properly tended to. That’s about it.
The reality could not be more different. Plants are dynamic, vibrant and aggressive living organisms focused on survival and reproduction. As a farmer, I get to see what these amazing living creatures do every day; and there’s a lot more to them than you think. Incredibly, plants not only have the ability to recognize and respond to external threats, but they can also warn their neighbors about them. Yes – plants do actually have the ability to communicate. Not only will they look out for their neighbors, they will recognize and cooperate with their family. And, when threatened, plants will respond with full-blown chemical warfare.
As an example, think about a little soybean plant growing out in the field. Beside it, in the same row, you have a combination of unrelated neighbors and maybe, just maybe, a member of its kin. The soybean will grow more competitively with its unrelated neighbors than it will with its kin. Over eons of evolution, plants, just like animals, were more successful if they worked together.
Beside our little soybean plant, there is different competition. A weed. Based on the difference in light reflection between the bare ground and the weed, the soybean plant can sense that there is competition beside it. From the air, there may be other competition, such as a soybean aphid. Our soybean plant may release volatile organic compounds into the air to warn its neighbors, or it may instead secrete chemicals into the root zone (rhizosphere) for the same effect. Or, amazingly, it may instead use sounds to warn its neighbors, such as high-frequency clicking sounds (read more here).
What has been well-documented is that when threatened with competition from weeds, soybeans do not respond very well. As the soybeans send out and receive communication signals from other plants within the field, they “realize” they are competing with more aggressive plants. As a response, the soybean will try and grow as tall as possible, sacrificing root growth and it won’t grow the leaf mass it needs to produce high yields. With reduced root growth and smaller leaves, the soybean just won’t have the yield potential it would have had in the absence of competition. What our soybean is really trying to do is quite simple; its entire existence is predicated upon reproduction, and if it can keep itself from being shaded out, it can produce at least a few seeds to carry on its life cycle (source).
Wheat responds similarly to soybeans, trying to grow its leaves taller and longer to get ahead of its competition, sacrificing root growth and, therefore, yield as well. This is why weed control in our crops is so critical; if we allow weeds to compete, even if the crop outcompetes them, yields will be negatively affected.
It wasn’t very long ago that scientists were ridiculed for producing results like this. Plants can’t talk, right? Well, it seems that they can; and they may be capable of much more.
An Intelligent Shrub?
The European barberry is a species of shrub distributed throughout Europe. The tephritid fruit fly is a major pest for this plant, which punctures the berries produced by the shrub and lays its eggs inside, where the larvae will feed on the seeds. The barberry has the ability to abort its seeds if the fruit is infested with eggs, which would cause the death of any larvae. Interestingly, the seeds of the infested fruits are not always terminated; rather, it depends on the level of infestation. For example, if the infested fruit contains two seeds, it will almost always be aborted. However, if it only contains one seed, it is only rarely aborted. Giving up a fruit with only one seed causes the entire fruit to be lost, so the plant doesn’t want to do that unless it absolutely has to.
What is truly amazing about this whole process is that the fruit fly larvae are much more likely to die with only one seed to feed on, rather than two. So the barberry “speculates” that the larvae will die, holding onto that fruit for as long as it can. What does all this mean? The barberry is undergoing complex decision making, which has never before been imagined to be possible in plants. The barberry is anticipating future risks and weighing possible losses and gains (read more here).
Going to War
Evidence that trees talk to each other has grown in leaps and bounds over the past fifteen years. The question is why. In the case of the Sitka Willow, when under attack by Western Tent Caterpillars and Fall Webworms, the trees change the nutritional content of their leaves. Once the first tree’s leaves are chewed by these pests, it will release volatile organic compounds (VOCs) to warn its neighbors of the impending danger. The rest of the trees in the area will then change the nutritional content in their leaves to dissuade the insects from feeding, causing them to move on to other targets (source).
A more aggressive example of this signalling is in a more familiar plant – corn. When under attack, corn will release VOCs to attract parasitoids that attack the larvae feeding on the corn. Plant communication isn’t limited to plant-to-plant interactions; they talk to insects as well, when necessary. Some plants, after a warning from their neighbors, will even develop toxins in their leaves to ward off predators (read more here and here).
Applications for Agriculture
While I’m not going to go so far as to say plants are “intelligent” in any sense of the word, or, at least in our understanding of what intelligence is, I think the social community plants develop is absolutely fascinating. What’s more, it can be used for agriculture. Think about a whole field of wheat that “believes” it’s growing among its kin. Instead of competing against other wheat plants, they could actually work together as a whole to fight predators and weed competition. A signal plant could warn an entire field to produce defense mechanisms against a predator before it even enters the field. While all of this is a very long way away, improving our understanding of plant-to-plant interaction is critical to figure these things out.
Although a lot of this may sound very science-fiction, it has become quite accepted by the scientific community that despite a lack of eyes, ears or a nervous system, plants chatter with each other, with fungi, with insects, and countless microorganisms non-stop. Getting to experience this amazing community every day is something very special about being a farmer, and that’s why I had to share it with you. So next time you wander out in your yard, greenhouse or field, take a moment and think about what’s going on beneath your feet. There is far more going on that meets the eye.