We don't want to alarm you but plants have been shown to have Pavlovian responses, able to learn to associate a stimulus with what they want and adapt their behavior appropriately. We might not be facing a Day of the Triffids scenario just yet, but given what humanity is doing to the planet's largest plants their associations with us may not be favorable.
Dr Monica Gagliano of the University of Western Australia has made a career of showing that plants have a more interesting capacity than most scientists expect, attracting considerable controversy in the process. Her latest study may be the most ground-breaking yet.
Gagliano grew pea seedlings in a Y-shaped maze. A fan was operated in one arm of the maze for periods of 90 minutes, the last half hour of which overlapped with an hour of pea-friendly blue light. For half the peas the fan and light were in the same arm, while the other half had fan and light in opposite arms. The process was repeated three times, with the location of the light and fan varying between arms.
Naturally, the seedlings grew towards the light. However, in her study published in Scientific Reports, Gagliano revealed that when the “trained” peas were exposed to the fan on its own, they anticipated a new dose of light. Sixty-two percent of seedlings that were used to having the fan in the same arm as the light reached towards it. Sixty-nine percent of seedlings that experienced the fans and light in opposition grew towards the other arm. A control group, which had not experienced the fan, mostly grew towards whichever arm of the Y had most recently contained the light.
The peas had come to associate breezes with the arrival of their energy source, just as Pavlov's dogs learned that a bell meant food was on its way, a process known as associative learning.
Associative learning has been considered unique to animals.
Proving plants are even more like humans, Gagliano explained to IFLScience how she experimented on some plants in ways she compared to waking someone up in the middle of the night to give them a test, or asking them to perform while jetlagged. Lacking even the comfort of a pre-test coffee, the peas failed to perform under these circumstances.
Gagliano told IFLScience she chose pea plants for the experiment, not only because they grow in an easy to study manner, but as a nod to Gregor Mendel's studies that gave birth to the science of genetics. “It's like they are saying 'don't just look at our genes, look at the organism as a whole,'” she said.
Although her work has overthrown centuries of botanical thinking, Gagliano considers it unsurprising. She argues that plants, lacking animals' capacity to get away from danger, have needed to learn to preempt threats, which pattern recognition can do.
How the associative learning works is unclear, although the paper notes: “Modifications of the patterns of interactions between molecules and communication between cells can be stored in a way rather similar to neural networks.”
Gagliano told IFLScience she is not keen to see her work used to encourage crops to grow more quickly in monocultures, but she “hopes it will instill more respect, encourage ways to help plants grow in more diverse and respectful ways.”