Plant Behavior: Do Plants Have Perceptions of their Environment?

By now, everyone has probably heard Ivan Pavlov’s name in a Psychology class when discussing classical conditioning. His experiment with his dogs was revolutionary. What if this experiment was carried out with plants— and they responded the same way that the dogs did? Would this be evidence that plants can perceive and react to the environments around them – or even have a conscience? 

Plant Behavior 

One of the first “instances” of plant behavior was by Cleve Backster, a former Central Intelligence Agency (CIA) agent (Tompkins, 1973 in Pollan, 2013). In 1966, he decided to hook up a galvanometer to the leaf of a plant, and just by imagining the plant on fire, found an increase in electrical activity in the plant. This increase of electrical activity on the polygraph machine suggested that the plant was stressed out by Backster’s thoughts (Tompkins, 1973 in Pollan, 2013). After discovering this, Backster decided to test it on many plants such as lettuce, onions, oranges, and even bananas. During the duration of the experiment, he saw that the plants were reacting to positive and negative thoughts of individuals who were close to them (Tompkins, 1973 in Pollan, 2013). Plant scientists who tried to replicate these experiments were unsuccessful, so the research was discredited. But this illustrates how some “research” gains attention but can be misconstrued in our attempt to make sense of everything around us. 

Although there are may examples of discredited research, there is also reproducible research on plant behavior. Much of that research comes from Monica Gagliano, a research associate professor in evolutionary ecology at the Biological Intelligence Lab at Southern Cross University, who has done a significant amount of research focusing on plant cognition, plant communication, and marine ecology. In one study, Gagliano examined whether plants could perceive changes in the environment and respond to to classical conditioning. Classical conditioning is learning that happens unconsciously (Elmer, 2020). The best example of classical conditioning is with Ivan Pavlov’s dogs. Pavlov observed that dogs would salivate when they were about to receive their dinner. Over time, he would ring the bell when he gave the dogs their dinner, and they would associate the ringing of the bell with being fed. The dogs learned the relationship between the bell and their meal and would salivate in anticipation of being fed when the bell rang. 

Gagliano did the same thing with plants but changed the variables. She knew that blue light is food for plants, triggering a positive phototropic response where plants would start to bend towards the light (Monica Gagliano – Plant Intelligence and the Importance of Imagination In Science | Bioneers, 2018). For her neutral stimulus, the bell in Pavlov’s experiment, she used a tiny fan. She would turn on the fan and the blue light, and after time, when presenting just the fan, the plant would bend towards it. The plant would anticipate where the light was, even when the light was not there. It had the perception that it was there because of the classical conditioning that it underwent, proving that plants can learn and even have a perception of their surroundings (Monica Gagliano – Plant Intelligence and the Importance of Imagination In Science | Bioneers, 2018). Although it may seem like plants have a mind of their own, scientists today view intelligence in plants more like insect colonies, working together in a network (Pollan, 2013). 

Plant Signaling

Heidi Appel, a chemical ecologist at the University of Missouri, found that when she played a recording of a caterpillar biting a leaf to plants, the plant would generate defense chemicals (Appel, 2014 in Pollan, 2013). This observation is not the only instance of plants having defense mechanisms. Because plants can not physically dodge potential dangers and competition, they “signal distress, deter or poison enemies, and recruit animals to perform various services for them” (Appel, 2014 in Pollan, 2013).

Plants can also recognize when they are closely related versus if another plant is a “stranger.” For example, Rick Karban, a U.C. Davis ecologist has shown that when plant leaves are clipped to simulate an insect attack, the trimmed plant and its neighbors suffer fewer insect damage over the season. Karban believes that the plant is notifying its neighbors, who then prepare themselves for the attack so it affects them less (Karban, 2006 in Pollan, 2013). It was noted that the more similar the plants were, the more they responded to the chemical signal, ensuring that similar genes would continue to survive (Karban, 2006 in Pollan, 2013). 

Plant Bioacoustics

Relative to plant signaling, research on plant bioacoustics is now helping researchers determine how plants respond to their environment through specific frequencies. Plant bioacoustics is “the ability of plants to respond to sound waves or vibrations in their environment” (Gagliano, 2013). Because plants can exhibit frequency-selective sensitivity, animals have evolved to match this frequency. For example, bees use buzz pollination. Buzz pollination is when the pollen is released from flowers when bees vibrate their flight muscles at the correct frequency (Gagliano, 2013).  You can see how this happens in the video below (especially from 1:30)!

Just because plants and some animals do not have outer ears like humans does not mean that they cannot collect airborne vibrations. For example, snakes do not have both ears and eardrums, yet their jawbones can pick up vibrations from the ground and process the information (Gagliano, 2012). Plant scientists are recognizing plants as “highly sensitive organisms that perceive, access, interact, and even facilitate each other’s life by actively acquiring information from their environment” (Gagliano, 2012). So what does this mean if plants make up 80% of the Earth’s biomass? (Thode, 2019). 

How does it affect us?

Although more research needs to be conducted, current studies have proven that plants can learn and have a perception of their surroundings. So how does this affect us? First, it allows us to have a better understanding and appreciation of how interconnected the world is. Next time you go outside, be sure to think about all of the plant signaling and behavior that is going on around you. Even if you can not see it, it still brings significance to how we view being outdoors. Second, we should ask ourselves what we can learn from plants and from being in nature as a whole. Plants can lose up to “ninety percent of its body without being killed.” (Mancuso in Pollan, 2013). Talk about adaptability and resilience! How can you use the knowledge you learned about plants through this article and apply it to your own life? In what ways are you as resilient and adaptable as plants are?

Sources: 

Appel, H. M., & Cocroft, R. B. (2014). Plants respond to leaf vibrations caused by insect herbivore chewing. Oecologia, 175(4), 1257-1266.

Elmer, J. (2020, January 8). Classical Conditioning and How It Relates to Pavlov’s Dog. Healthline. https://www.healthline.com/health/classical-conditioning

Gagliano, M., Mancuso, S., & Robert, D. (2012). Towards understanding plant bioacoustics. Trends in plant science, 17(6), 323-325.

Gagliano, M. (2013). The flowering of plant bioacoustics: how and why. Behavioral Ecology, 24(4), 800-801.

Karban, R., Shiojiri, K., Huntzinger, M., & McCall, A. C. (2006). Damage‐induced resistance in sagebrush: volatiles are key to intra‐and interplant communication. Ecology, 87(4), 922-930.

Monica Gagliano – Plant Intelligence and the Importance of Imagination In Science | Bioneers. (2018, November 27). [Video]. YouTube. https://www.youtube.com/watch?v=90BUQoLu_Hg

Phototropism & photoperiodism (article). (n.d.). Khan Academy. Retrieved October 6, 2021, from https://www.khanacademy.org/science/biology/plant-biology/plant-responses-to-light-cues/a/phototropism-photoperiodism

This Vibrating Bumblebee Unlocks a Flower’s Hidden Treasure | Deep Look. (2016, July 19). [Video]. YouTube. https://www.youtube.com/watch?v=SZrTndD1H10

Thode, A. M. (2019). Bearing Fruit: Plant Bioacoustics is Blossoming. Acoust. Today, 15(4), 47-54.

Tompkins, P., & Bird, C. (1973). The Secret Life of Plants (1st Printing ed.). Harper & Row, Publishers.

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