Today’s take home message: watch what you say or do out in the buckwheat patch. Plants aren’t exactly seeing, but they could be listening and they are definitely communicating.
That’s what Jack Schutlz, a biologist and zoologist at the University of Missouri, whose business card describes him as a chemical ecologist, tells me anyway. Schultz admits when he gives a talk, he is a bit of a novelty act at farm conference. But who knew there was actually research into if, when and how plants communicate?
But when you consider all the remarkable natural defence mechanisms animals and plants developed through evolution, why not plants in canola, wheat, pea and corn crops communicating with each other?
Since I retired from my active three-day farming career about 50 years ago I can’t claim to have much first hand exposure to this. But I do know if you cut a hay crop there is definitely an aroma. In Jack Schultz’s research that’s plant communication.
“Plants communicate very effectively with each other both above and below ground,” says Schultz. “By understanding these mechanisms it can help farmers understand how crop production practices might affect these natural defence systems.”
How plants communicate
All plants produce odours, says Schultz and when they are attacked or damaged by a pest they produce a specific volatile odour. His research over the years shows that if one plant is attacked by a pest it emits an odour, which will soon trigger a defence mechanism in the plant next to it, even though the next-door plant isn’t being attacked itself. The next-door plant senses the odour change and takes action. And the odour emitted by the attacked plant will vary depending on which pest is attacking — a different volatile odour for each pest.
Wheat, for example, has a natural defence system. The wheat midge begins feeding on wheat, and the plant emits a volatile odour, which in turn can be sensed by parasitic wasps that feed on wheat midge.
“The parasitic wasp can be very effective in controlling wheat midge, but it is very tiny,” says Schultz. “If there is a wheat midge in a field of wheat how does that little wasp find the pest? The wasp senses the odour being produced by the wheat plant and is attracted to the plant and attacks the wheat midge.”
As well as above ground odours, plants also send signals through their roots into the soil, says Schultz. Experiments showed if an attacked plant was covered with a jar so its odour was contained, neighbouring plants with root connections to the covered plant would still respond to the threat. The signal is carried through the intertwined roots, and perhaps even by the bacteria (mycorrhiza) in the soil.
How else do plants communicate and what other defence mechanisms do they have? With brassicae plants such as canola, for example, when plant leaves fall on the ground and decompose they produce a natural fungicide in the soil, which helps control certain fungi.
Humans are very familiar with other chemistry processes plants use as defence mechanisms. Plants such as tobacco, coffee and hot peppers, for example, produce chemicals, which humans have capitalized on for components in food and consumer products. Cigarettes and cigars, a cup of coffee and hot pepper sauce are all consumer products.
“Why would a plant develop nicotine, or caffeine or some other chemistry we sense as burning or hot?” says Schultz. “They don’t do it for humans to enjoy. These are all natural insecticides. Nicotine or caffeine or that hot pepper spice were all developed through evolution by plants to act as a natural defence against some type of pest or threat.” A damaged or attacked plant will produce higher levels of these compounds.
Now that you know most plant communication is limited to detecting odours, that doesn’t mean you can frolic naked in the barley field with total impunity. A neighbour or some passer-by with a cellphone camera will be watching and your romp will be featured on Facebook, YouTube or maybe even the six o’clock news before you get home. Try explaining your way out of that one.