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Plants communicate between plants of the same species, other plant species, animals, insects, fungi, and soil microbes in a variety of different ways. The three main forms of plant communication are electrical signaling, common mycorrhizal root networks, and emitted volatile organic compounds. Plant communication can be inudced in response to a variety of environmental cues, mainly ones of predation. Examples of these cues are herbivory, infestation, parasitism, mechanical damage, insect feeding, lack of nutrients, among many others (Heil and Karban 2011).

Volatile Organic Compounds:

In Runyon et al 2006, the researchers demonstrate how the parasitic plant Cuscuta pentagona (dodder weed) uses VOCs to interact with various hosts and determine locations. Dodder seedlings show direct growth toward tomato plants (Lycopersicon esculentum) and specifically elicited tomato plant volatiles. This was tested by growing a dodder weed seedling in a contained environment, connected to two different chambers. One chamber contained tomato VOC’s while the other had artificial tomato plants. After 4 days of growth, the dodder weed seedling showed a significant growth towards the direction of the chamber with tomato VOC’s. Their experiments also showed that the dodder weed seedlings could distinguish between wheat (Triticum aestivum) VOCs and tomato plant volatiles. As when one chamber was filled with each of the two different VOCs, dodder weeds grew towards tomato plants as one of the wheat VOC’s is repellent. These findings show evidence that volatile organic compounds determine ecological interactions between plant species and show statistical significance that the dodder weed can distinguish between different plant species by sensing elicited volatile organic compounds (Runyon et al. 2006).

Tomato plant to plant communication is further examined in Zebelo et al 2012. Here, him and fellow researchers test how tomato plants respond to herbivory. Upon herbivory by Spodoptera littoralis, tomato plants emit VOCs that are released into the atmosphere and induce responses in neighboring tomato plants. When the herbivory-induced VOCs bind to receptors on other nearby tomato plants, responses occur within seconds. The neighboring plants experience a rapid depolarization in cell potential and increase in cytosolic calcium. These emitted volatiles were measured by GC-MS and the most notable were 2-hexenal and 3-hexenal acetate. It was found that depolarization increased with increasing green leaf volatile concentrations. These results indicate that tomato plants communicate with one another via airborne volatile cues, and when these VOC’s are perceived by receptor plants, responses such as depolarization and calcium influx occur within seconds (Zebelo 2012).

Electrical Signaling:

As mentioned above, plants also communicate via electrical signals, which is explored in Calvo et al. 2017. These electrical signals are mediated by cytosolic Ca2+ ions. Cytosolic calcium signals are mediated by hundreds of protein and protein kinases, and many of the signals also induce action potentials in plants. The phloem of the plant serves as the pathway for electrical communication, and as the plant grows and learns from its past, the phloem becomes increasingly cross linked. Plants respond to various environmental cues and elicit electrical responses internally to alter the function of the plant body. This can range from avoiding predation, releasing defense mechanisms, responding to changing temperature, changing growth direction, and sharing nutrients in the soil. This form of memory stored in the plant’s phloem allows it to better respond to similar stimuli in the future and shows how electrical signaling allows a plant to communicate with itself and alter its’ own physiology to better suit certain environmental cues (Calvo et al. 2017).

Root Networks and Common Mycorrhizal Networks:

Another form of plant communication occurs through their complex root networks. Through roots, plants can share many different resources including nitrogen, fungi, nutrients, microbes, and carbon. This transfer of below ground carbon is examined in Philip et al. 2011. The goals of this paper were to test if carbon transfer was bi-directional, if one species had a net gain in Carbon, and if more Carbon was transferred through the soil pathway or common mycorrhizal network (CMN). CMNs occur when fungal mycelia link roots of plants together (Philip et al. 2011). To test this, the researchers followed seedlings of paper birch and Douglas-fir in a greenhouse for 8 months, where hyphal linkages that crossed their roots were either severed or left intact. The experiment measured amounts of CO2 in both seedlings. It was discovered that there was indeed a bi-directional sharing of CO2 between the two trees, with the Douglas-fir receiving a slight net gain in CO2. Also, the Carbon was transferred through both soil and the CMN pathways, as transfer occurred when the CMN linkages were interrupted, but much more transfer occurred when the CMN’s were left unbroken. This experiment showed that through fungal mycelia linkage of the roots of two plants, plants are able to communicate with one another and transfer nutrients as well as other resources through below ground root networks (Philip et al. 2011). Further studies go on to argue that this underground “tree talk” is crucial in the adaptation of forest ecosystems. Plant genotypes have shown that mycorrhizal fungal traits are heritable and play a role in plant behavior. These relationships with fungal networks can be mutualistic, commensal, or even parasitic. It has been shown that plants can rapidly change behavior such as root growth, shoot growth, photosynthetic rate, and defense mechanisms in response to mycorrhizal colonization (Gorzelak et al. 2015). Through root systems and common mycorrhizal networks, plants are able to communicate with one another below ground and alter behaviors or even share nutrients depending on different environmental cues.

Plants ability to communicate with themselves and their surroundings allows them to adapt and alter their behaviors rapidly in response to environmental cues. Through pathways such as volatile organic compounds, electrical signaling, and common mycorrhizal root networks, plants can respond to threats of predation by altering their body processes to best suit there given environment. This is seen in studies of the dodder weed growing specifically towards tomato plant VOCs, rapid calcium influx and membrane depolarization in neighboring plants responding to herbivory emitted VOCs, and the sharing of nutrients between plants through connected root networks.

References:

Calvo et al. 2017. “Plant, Cell, & Environment. Are Plants Sentient?”

Gorzelak et al. 2015. “Inter-plant communication through mycorrhizal networks mediates complex adaptive behaviour in plant communities.”

Martin Heli and Richard Karban. 2010. “Explaining evolution of plant communication by airborne signals.”

Phillip et al. 2011 “Pathways for below ground carbon transfer between paper birch and Douglas-fir seedlings”

Runyon et al. 2006 “Volatile Chemical Cues Guide Host Location and Host Selection by Parasitic Plants.”

Zebelo et al. 2012. “Plasma membrane potential depolarization and cytosolic calcium flux are early events involved in tomato (Solanum lycopersicon) plant-to-plant communication”.