Let’s not beat around the bush: Plants talk

August 24, 2018

There’s a “growing” school of thought that validates the communication systems of grasses, flowers, shrubs, and trees. It may have started back in 1986, when Britain’s Prince Charles, who is devoted to organic gardening and environmental issues, was widely ridiculed for saying, ”I just come and talk to the plants, really—very important to talk to them. They respond, I find.”

However, today, many scientists acknowledge that (to piggyback on another social movement) #GreenLivesMatter: Plants do lead anything but solitary and sedentary lives. In fact, James Cahill, a professor at the University of Alberta believes they “are smarter and much more interactive than we [had previously] thought.” His documentary, “What Plants Talk About,” ran on PBS in April 2013.

An article posted on Mental Floss in 2015 covers his research—outlining “five behaviors that show how active plants can be,” as follows:

  1. Plants can call for help: It’s sad to say, but when you inhale the fragrant smell of freshly mowed grass or cut flowers, what you actually are smelling is the plants’ distress call. Your lawn is trying to save itself from the injury it has just sustained. In fact, according to Cahill, who talked to Mental Floss, “Leafy plants release a number of volatile organic compounds called green leaf volatiles (GLVs). When the plants are injured—whether through animals grazing on them, you cutting or mowing them, or even just unintentionally rough handling—these emissions increase like crazy.” Some of the compounds stimulate the formation of new cells at the wound site, so it closes faster. Others act as antibiotics that prevent bacterial infection and inhibit fungal growth. A few spur the production of defensive compounds at un-wounded sites as a preemptive fortification.
  2. Plants can eavesdrop: In turn, nearby plants can “eavesdrop”—picking up those SOS calls and ramping up their own defenses in response. 2013 review led by Richard Karban, of the Department of Entomology at the University of California-Davis, found 48 studies that support the idea that plants increase their defenses after their neighbors are damaged. For instance, when wounded by a hornworm, sagebrush releases defensive proteins (called trypsin proteinase inhibitors [TPIs]), which prevent the insect from digesting protein and stunt its growth. When neighboring plants—even other species—are exposed to TPIs, they begin readying their defenses. Wild tobacco, scientists at New York’s Cornell University found, begins making TPIs when it senses a distress call from sagebrush, giving it a head start on defending itself if the caterpillar.
  3. Plants defend their own territory: Plants compete with each other for sunlight—truly “jostling for position” among their neighbors. They also can push out competition in other ways. The invasive knapweed plant—native to Eastern Europe but wreaking havoc on U.S. grasslands—has roots that release certain chemicals to help the plant absorb nutrients from the soil, Mental Floss reports. Those same chemicals also kill off native grasses. Thus, the knapweed ends up taking over large territories and killing off its competitors, much like some animals do. Interestingly enough, in self-defense, lupin roots secrete oxalic acid, which forms a protective barrier against the toxic chemicals given off by knapweed. Lupin even can protect other plants in its vicinity from falling prey to the invasive species.
  4. Plants recognize their siblings: Plants have “family pride,” tending to recognize and support their kin. Although the compete for sunlight with other species and grow more roots to compete for food, sibling plants are more “considerate” of each other’s needs. Experiments show that sibling plants recognize each other via chemical signals.
  5. Plants can communicate with mammals: Finally, while Prince Charles claimed that plants communicated with him, the most common example is the relationship between bats and the carnivorous pitcher plant that is native to Borneo. The plant has evolved to “hijack bat communication systems,” according to Cahill—helping the bats to locate its opening. Not only do the bats roost in the plant; they form a mutually beneficial relationship. The plants provide a comfy roost with few parasites and an ideal microclimate, and the bats poop in the plants. Bat guano is rich in nitrogen, a crucial plant nutrient.

Research contact: jc.cahill@ualberta.ca

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