Do you talk to your plants? Do your plants talk back? They might, according to new research. Two new papers from Tel-Aviv University may suggest that plants are in fact capable of responding to sounds, and may even be able to communicate their physical condition by giving off ultrasound waves of their own. Researchers say that these ultrasound waves could be heard meters away by not only other plants but animals as well. So if you are one of those folks that talks to their plants, you're still crazy, but you might not be wrong.
The two studies were published on bioRxiv, a pre-publishing platform for scientific papers awaiting peer review, so this research is still too new to be treated as completely airtight. That said, the findings are still very interesting. The first study looked at how primrose flowers respond to the sounds of approaching bees. Researchers found that primrose flowers will produce sweeter nectar within three minutes of hearing the sound of an approaching pollinator. They found that the response was the same to both a recorded bee sound as well as a synthesized sound in the same frequency range. Sounds at higher frequencies had no effect, suggesting that it is a specific response. According to the paper's abstract:
We found that the flowers vibrated mechanically in response to these sounds, suggesting a plausible mechanism where the flower serves as the plant's auditory sensory organ.
Sensitivity of plants to pollinator sound can affect plant-pollinator interactions in a wide range of ways: Plants could allocate their resources more adequately, focusing on the time of pollinator activity; pollinators would then be better rewarded per time unit; flower shape may be selected for its effect on hearing ability, and not only on signaling; and pollinators may evolve to make sounds that the flowers can hear.
Responding to sounds is all well and good, but the second paper suggests that plants may be able to communicate information via sound as well. According to the paper, researchers recorded ultrasonic waves emitted by tomato and tobacco plants that seem to change based on the physical condition of the plant, whether healthy, dry, or cut. The ultrasounds they recorded hovered around 55 kHz, which is above the range of human hearing but well within the hearing range of other animals. It's not quiet either. According to the paper, the recorded ultrasounds were approximately 65 dB SPL— decibel sound pressure level—at 10 cm. That's louder than a normal conversation, and only slightly quieter than a vacuum cleaner.
Researchers also trained a machine learning program to listen to the ultrasounds produced by the tomato and tobacco plants and then accurately determine if the plant was healthy or stressed, either through drying or cutting, suggesting that the differences in the ultrasounds produced were not a one time coincidence. They also found that the stressed plants produced louder sounds. From the paper:
We successfully classified the plant's condition - dry, cut, or intact - based on its emitted sounds. Our results suggest
that animals, and possibly even other plants, could use sounds emitted by plants to gain information about the plant's condition.
It remains to be seen if these papers will pass peer review, but if they do it could completely change the way we think of plants. Taking a stroll through the woods becomes a totally different experience when you know all those plants are both listening to and yelling at you.