Plant communication: Secrets underground and messages in the air
Plants, often considered passive and silent organisms, hide a surprisingly active and sophisticated communication network. Although they lack a nervous system, they have developed mechanisms to exchange vital information through volatile compounds and subway networks. This article explores two of the main communication systems among plants: volatile organic compounds (VOCs) and mycorrhizal networks.
Messages in the air: volatile organic compounds
Volatile organic compounds (VOCs) are chemical molecules emitted by plants into the environment. These substances play a key role (described since 1983) in plant-plant communication by alerting neighbors of potential threats, such as herbivores or pathogens. For example, when a plant is attacked by insects, it releases VOCs that can be detected by other nearby plants, preparing them to activate their defense mechanisms before being attacked. The VOCs emitted are a mixture of different substances that can vary both quantitatively and qualitatively depending on the triggering stimulus.
An emblematic case is that of maize (Zea mays). When damaged by caterpillars, it emits a specific mixture of VOCs that not only activates defense genes in neighboring plants, but also attracts natural predators of the caterpillars, such as parasitoid wasps. This “chemical alarm” system not only improves the survival of the emitting plant, but also that of the entire plant community.
The range and accuracy of VOCs vary depending on factors such as species, type of threat and environmental conditions (but can reach several hundred meters in some cases). In addition, recent research has shown that genetically related plants respond more effectively to chemical signals from their relatives, suggesting a specific level of recognition within the plant community.
Finally, we must not lose sight of the fact that in addition to plants, these VOCs can be synthesized by other organisms in their environment (such as microorganisms).
Chemically speaking, these VOCs can be synthesized from several metabolic pathways and belong to different classes among which we can mention: terpenoids, benzenoids, phenylpropanoids or molecules derived from fatty acids among others.
Hidden networks: communication through mycorrhizae
Beneath the soil, a vast and complex system of fungal interconnections, known as a mycorrhizal network, connects the roots of different plants. These symbiotic associations between fungi and roots allow plants to exchange nutrients, water and, most surprisingly, information. In previous posts of this blog we have developed the topic of mycorrhizae in more depth.
Mycorrhizal fungi act as “biological wires” that carry chemical signals from one plant to another. For example, when a plant suffers an attack by pathogens or herbivores, it can send signals through the mycorrhizal network to warn its neighbors. These recipient plants can then activate their own defense mechanisms in a preemptive manner.
A notable example has been observed in legumes, where plants connected by mycorrhizal networks show greater resistance to insect attacks compared to non-connected plants. Moreover, recent studies have revealed that mycorrhizal networks not only facilitate the transfer of danger signals, but also of beneficial compounds, such as antioxidants or key nutrients, promoting cooperation in the plant community.
The interaction between VOCs and mycorrhizae
Although VOCs and mycorrhizal networks are distinct mechanisms, in many cases they work in a complementary manner. For example, a plant that emits VOCs when attacked may also send signals through the mycorrhizal network, maximizing the reach of its “message”. This type of interaction multiplies the likelihood that neighboring plants will quickly detect and respond to the threat.
In addition, environmental conditions and ecological context can influence which communication system predominates. In dense ecosystems where mycorrhizal networks are well developed, mycorrhizal networks are often the primary means of communication. However, in open or less connected environments, VOCs play a more prominent role.
Ecological implications and future research
Communication between plants is essential for ecosystem stability. Understanding how plants exchange information could have important applications in agriculture, such as the development of crops that are more resilient to pests or the design of strategies to improve cooperation between species.
Ultimately, plants are much more than immobile beings. Their ability to communicate through VOCs and mycorrhizal networks reveals a collective intelligence that makes them active participants in ecosystems. These systems not only reinforce their ability to survive, but also underline the complexity of plant life.
Supplementary material: list of VOCs (extracted from Brosset & Blande, 2021)
Bibliography
- “Mycorrhizal Networks: Common Goods of Plants Shared under Unequal Terms of Trade”. Walder et al., 2012. www.plantphysiol.org/cgi/doi/10.1104/pp.112.195727
- “The role of volatiles in plant communication”. Bouwmeester et al., 2019. https://doi.org/10.1111/tpj.14496
- “Volatile-mediated plant–plant interactions: volatile organic compounds as modulators of receiver plant defence, growth, and reproduction”. Brosset & Blande, 2021. https://doi.org/10.1093/jxb/erab487
- “Volatile-mediated plant–plant communication and higher-level ecological dynamics”. Kessler et al., 2023. https://doi.org/10.1016/j.cub.2023.04.025
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