While many consider plants to be passive organisms, the reality is quite the opposite. Plants are in constant motion, moving with purpose to detect and respond to their fluctuating environmental conditions. Not only do plants transmit hormonal signals, known as phytohormones, from root to leaf, but they communicate with their neighbors, too. New research in plant physiology aims to introduce plants as complex, interconnected communities rather than competing individuals. With a future hinged on a changing climate, scientists are more eager than ever to uncover the secret lives of plants.
Scientists Ian Baldwin and Jack Schultz were among the first to study plant communication in the late twentieth century. Their research suggests that environmental stressors lead to biogeochemical changes in plants, which could somehow be “spread” to others in close proximity. Although Baldwin and Schultz were met with criticism, studies now are expanding upon the conclusions found decades earlier.
Current research shows that plants can communicate using sophisticated methods, demonstrating forms of alertness and sociability. Forests, in particular, form codependent relationships and alliances amongst trees of all species. Despite lacking a brain, this network is often compared to that of an insect colony. As it turns out, “talking trees” may not be a myth, after all. Beyond the human eye, trees are connected through their underground root systems, aided by microscopic fungal threads known as mycelia. In exchange for about 30% of sugars produced by photosynthesis, mycelia offer trees nutrients and water molecules absorbed from the surrounding soil. This symbiotic relationship, collectively called mycorrhiza, provides the vital link through which trees share resources and communicative signals with one another.
These underground channels are the reason why saplings without adequate light or nutrients survive to become mature trees. Older and taller neighbors have better access to the sunlight required to perform photosynthesis. Sensing a tree restricted by a lack of resources, the latter is able to share its abundance with the disadvantaged sapling. Birch and Douglas-fir trees, infamously known as enemies in the forestry world, exemplify communication using the underground mycorrhizal network. Although birch trees often outcompete the nearby conifers for sunlight, beneath the surface they share resources accordingly. In fact, birch trees will transfer carbon through the root system relative to the extent that they shade the neighboring Douglas-firs. On a seasonal basis, these trees exchange nutrients as needed. When birches lose their leaves in the fall, Douglas-firs offer their photosynthetic sugars. When Douglas-firs become shaded in the summer, birches reciprocate the gesture.
Another fundamental aspect of plant communication is the use of volatile organic compounds (VOCs). VOCs encompass the various chemicals released by a plant, via air or root, to signal danger or distress. As the released VOCs reach the unharmed plant, it can respond to potential predators even before they are noticeable. On the savannas of Australia and Africa, acacia trees communicate the threat of hungry giraffes. While being consumed by the herbivores, acacias emit ethylene gas, an airborne VOC which warns nearby trees of the presence of predators. As a result, acacia trees bring large concentrations of poisonous tannins into their leaves. In other biomes, elms and pines emit VOCs to attract parasitic wasps onto predatory caterpillars. Maples will introduce poor-tasting chemicals to their leaves in response to the presence of deer saliva.
Scientists even believe that plants can communicate through sound. Cellular vibrations produce sound at frequencies undetectable to the human ear, thought to influence a species growth direction and compatibility with other plants. A 2013 study conducted in Australia suggested that basil plant vibrations positively affected chili seedling growth, while fennel plants had the opposite outcome. This phenomenon provides evidence for what many gardeners have discovered themselves through trial and error: some plants just do not get along.
Observed methods of communication in plants are evolutionary responses to stimuli. Whether sharing resources or relaying danger, the reasoning behind these actions is relatively simple. Communication emphasizes the importance of connection and biodiversity to overall ecosystem resilience. Expansive mycorrhizal networks improve forest health and the ability to bounce back from potential disturbances. Therefore, although each plant’s actions may be individually motivated, together they benefit entire ecosystems.
Peter Wohlleben, a German forester and author, is passionate about sharing the secrets of plant communication. In his 2015 book, The Hidden Life of Trees: What They Feel, How They Communicate, Wohlleben reveals some of his formative experiences as a longtime caretaker of a forested nature reserve near Hümmel, Germany. With his vivid use of language, Wohlleben depicts trees as seemingly conscious beings. Despite what his critics argue, however, Wohlleben does not deny the science of plant physiology. Rather, in personifying trees, Wohlleben hopes to protect forests by inspiring interest in these sophisticated ecosystems. In response to publishing his book, Wohlleben says that his most outspoken challenger has been the commercial logging industry.
Driving current research behind plant communication is Dr. Suzanne Simard, a professor of forest ecology at the University of British Columbia, and her team of graduate students. By conducting research on the mycorrhizal networks of Canadian forests, Dr. Simard introduced the concept of hub, or mother, trees as a vital component of the underground communication system. Mother trees are the oldest, tallest trees in a forest whose access to resources leads them to share water or nutrients with surrounding individuals. Dr. Simard’s group found that a single mother tree could be connected to hundreds of younger trees in the forest, even having the ability to recognize and favor the roots of their kin. When mother trees were removed, its absence had significant impacts on overall forest health, as many saplings had formed a dependence on the hub. Summarizing her decades-long work, Dr. Simard humorously coined the term “wood-wide web” to describe the complexity of tree relationships.
Although scientists have proven the existence of plant relationships, they have yet to understand the exact nature of these communications. Future research is concerned with how plants will respond and adapt to a warming climate. With the goal of developing resilience to changing temperatures, scientists hope that by fully understanding plant communication, they can genetically engineer plants and crops in the years to come. While tree canopies have long captivated audiences, the world is just coming to realize the wonders that lie below the surface.
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