Last updated May 3, 2018 at 12:02 pm
Touching plants stresses them out, and they let their neighbours know about it.
Plants can communicate with each other through a huge range of complex mechanisms that we’re only just beginning to understand.
Sure, they can’t just up and run away, but they can change what types of anti-predator toxins they produce, change the shape of their leaves, or alter their growth in new directions.
Related: The secret (long) life of plants
Plants respond to touch
Mechanical stimulation, or touch, is a strong cue that can trigger a response from plants. “Canopy shyness” is a famous example of how plants respond to the touch of neighbours. It’s the term scientists use to describe why a tree canopy will grow outward and stop expanding when they touch canopies of the trees around them, to avoid them growing over each other.
We know from previous work that plants can most definitely respond to touch. For example scientists from the University of Western Australia showed in 2016 that liquid spray on leaves switched on a cascade of stress response genes in pea plants.
An underground communication network
A Swedish team have just published research in PLOS ONE on the impact of leaves touching on the underground communication between plants.
To test this out, experimenters simulated the type of touch plants might experience when wind causes leaves to brush past each other.
They did this by softly brushing the leaves of corn plants for just one minute a day from base to the top, using a soft squirrel hair make-up brush.
This light touch was all it took to set off the underground signaling process plants use to talk to their neighbours.
By secreting chemical signals from their roots, the touched corn plants were able to provoke changes in the ways their untouched neighbours grew. By sending out this signal, other plants get the message to “back off”, and they send their roots growing away from the crowded area, and change how much energy they put into growing shoots versus roots.
The researchers point out that plant scientists will need to take note of their results, not just for the fact that they reveal a new level of complexity in plant communication, but that scientists themselves will need try and limit how much they touch plants during experiments.