The science that observes and studies in what ways and how many ways plants communicate with each other is called Plant Neurobiology and is based on a fundamental observation: plants have various perceptive abilities that in many cases have proven to be even superior to those of animals. The best-known abilities are those of being able to intercept light and shadow; they are able to change their apical arrangement in relation to the plants they are near, sometimes almost embracing each other, other times moving branches away. They can detect subtle differences in nutrients and molecules present in the soil, as well as those emitted by other plants, and can perceive gases emitted from the soil, fungi, or other plants and are able to create consequent reactions.
A tree in a forest forms relationships with various types of fungi, each connected to multiple other trees, creating a mycorrhizal network that acts as a transmitter of information, explains Cathie Aime, professor of mycology at Purdue University (research program supported by the National Science Foundation).
The most receptive part of the plant, in this case, is the roots; when they encounter fungi, an exchange of RNA fragments occurs between the two, altering the genetic expression in the other organism.
If the fungus is an ally, it communicates a positive message that the plant receives and the fungus, in its saprophytic activity, helps the plant to grow. If the fungus is a parasite, the transmitted RNA fragment serves to destroy the plant's defense genes so it can be attacked more easily.
If several trees are connected to each other through a fungus, they can share resources.
The path of carbon from one plant to another has been traced, and it was observed how its journey, starting from an old nurse tree, passing through fungal networks, reached a young tree, too small to reach a sufficient light source to perform photosynthesis, thus ensuring its survival and growth.
Many fungi can extend and reach nutrients, passing them to the plant in exchange for the sugars it produces through photosynthesis.
Underground, plants also communicate with microbes: like fungi, these are attracted to the roots and attach themselves, forming a sort of biofilm. Growth-promoting bacteria, for example, can stimulate the plant's defenses, increasing its resistance to diseases.
However, research on the underground microbiome of plants is still in its early stages, but it is extremely important to obtain the necessary information to help restore organic substances in the soil.
In a study published in the journal Nature Communications, researchers from Saitama University in Japan revealed how plants emit a series of signaling compounds in response to wounds and herbivore attacks. The author of the research, Dr. Masatsugu Toyota, states that these signaling compounds, known as volatile organic compounds (VOCs), exert multiple protective effects such as directly repelling a threat or attracting the natural enemies of herbivores to defend themselves. Nearby intact plants perceive these VOCs as danger signals to trigger defense responses or prepare to respond promptly to incoming stresses.
The researchers were able to verify how communications between plants trigger calcium (Ca2+)-dependent defensive responses against future threats.
It is known that calcium ions play an important role in signaling stress responses within plants. What the researchers discovered is that these signals are first detected by the stomata of the leaves, highlighting how the latter act as a "nose" for the plant to capture external signals from neighboring plants. "In addition to providing fascinating insights into the inner workings of our natural world, these results could pave the way for the development of more effective pest controls in agriculture and global food production," said Toyota.
Andrea Clavijo McCorminck, head of Research at the Faculty of Agriculture and Environment at Massey University, together with her team, discovered that with special microphones designed to detect bat calls, it is also possible to "listen" to plants. Several plant species, under stress conditions, emit sounds at the ultrasonic level audible to insects such as moths and mammals such as bats and mice. The researchers studied these sounds to try to identify new diagnostic methods.
Plants also, through volatile compounds such as gases, can recognize their own kind, changing their behavior toward the neighboring plant. It has been observed that in some way they recognize their own offspring, helping them to grow instead of competing with them, says Dr. McCorminck.
These studies have important repercussions; understanding the ways in which plants communicate could help us better safeguard their Bio-Habitat on a rapidly changing planet due to climate change, and would help us better integrate them with each other, optimizing cultivated areas to meet the growing demand for food.
All this ethically places us before a new awareness of the nature of plants and their ability to interact with each other and with us humans.