Last week I talked about music and how plants respond to bird songs, symphonies, and sound vibrations. This week, I will discuss whether or not our beloved plants respond to the sound of our voice or the gentle touch of our hand. However, the answers to these questions are not a simple yes or no. Scientists now realize plant physiology and plant “behaviors” are far more complex – and sophisticated – than initially thought.
Many plants do seem to exhibit enhanced growth rates and increased chlorophyll production when humans talk to them. But some plant species appear to be more responsive to human speech than others, and the number of additional confounding variables which may also affect study results prohibit a definitive conclusion. What we do know is that plants seem to respond more favorably to female voices than male voices, probably due to gender associated voice vibration frequencies. As we discussed last week, sound vibrations can promote or inhibit plant stomata responses, so the human voice may function in a similar way as music.
Now, while the jury may still be out regarding whether or not our plants enjoy our voices, those of us who do love to talk to our plants can continue to take heart. Every time we speak to our beloved spider plant (Chlorophytum comosum) or Chinese evergreen (Aglaonema), we nourish them with CO2 from our breath. As the plant metabolizes CO2, it releases O2. So, talk away. And if anyone askes you why you’re talking to your plants, tell them it’s for your health, their health, your plant’s health, and for cleaner air for our environment.
Which brings us to the next question, which is, do plants enjoy being touched? Well, once again, the answer is mixed and complex. Recent studies have shown that some plants, like those in the thistle family, appear to be unaffected by human touch. On the other hand, Potentilla recta and Butter and Eggs (Linaria vulgaris) seem to thrive when gently stroked by human hands and actually develop stronger resistance to insect infestations. However, if you are growing Indian hemp (Apocynum cannabinum) for making rope or for medicinal purposes, studies have shown human touch can decrease harvest yields and can even make the plant susceptible to a variety of diseases.
Why does this happen? Touch a Sensitive Plant (Mimosa pudica) and you will immediately see its fan-like leaves gracefully fold and close. Utilizing a process called thigmomorphogenesis, (I dare you to say this word 3 times as fast as you can), the Sensitive Plant’s response to touch (technically referred to as thigmonastic movement) is quick and obvious. While other plants may not show such obvious changes, they nevertheless still undergo similar dramatic hormone and gene alterations whenever they are touched by humans, animals, insects, or even the wind.
Dr. Jim Whelan, a biologist at La Trobe University in Australia, noted that within 30 minutes of being touched, at least 10% of a plant’s genome is altered. Think of this as being similar to our fight or flight response. Plants obviously can’t run away or physically fight a perceived threat, but each plant carries within it a unique biochemical cascade which functions to protect it in some way from its external environment.
In addition to thigmomorphogenesis and thigmonastic movement, fascinating new evidence also appears to suggest plants behave purposefully in a quasi-cognitive manner.
For example, in one study, scientists repeatedly tested the response rate of a Venus flytrap’s (Diaonaea muscipula) food capture using various stimuli and time intervals. The results demonstrated the flytrap eventually only attempted to trap an insect if its potential prey landed at least twice on the plant within a 20 second period. Researchers deduced the plant had “learned” to preserve precious energy by not responding to random stimuli at random time intervals if there is no “expectation” for reward (food).
While plants do not have a brain in the sense that humans do, they nevertheless exhibit defensive and offensive responses, they can acquire and express a memory for a response to stimuli, and they are even able to communicate with other plants.
Wait, did I just write that plants talk with each other. Yes, I did. And boy, do they love to talk. In fact, they are downright chatty.
And that will be the topic of next week’s post:
Gabby Gardens and Wordy Woodlands: It Seems Plants Have a Lot to Say
Have a wonderful week.
