Communication – only different
Fungal and plant communication is the most prevalent communication on Earth [4]!
Spending just a short period of time looking at plant/ fungi relationships and you will soon come across the term ‘Wood Wide Web’, a term coined by Dr. Suzanne Simard [15]. Dr Suzanne Simard and her team researched the chemical and electrical signals of fungal/ plant communication. They discovered signals travel faster through the mycelium network than from plant pheromones (which is the other way plants will communicate with each other).
Hyphae (the individual fungal cells) of an individual fungi grow and spread, much like plant roots. They seek out resources and nutrients. Communication is imperative for locating and distributing nutrients and environmental information to all parts of the hyphal network [20]. When the hyphae connect with each other (members of the same fungi), they fuse and combine, changing their cell wall and merging together. This helps to strengthen the fungi and establish a complex and dense network of mycelium [20].
Communication Facts
Fungi do not ‘talk’ to plants in the way we would recognise communication. They send chemical signals called volatile organic compounds (VOCs) between themselves and their plant partners. There could be multiple different fungi connected to the same plant [9].
This chemical communication is used to understand what resources the plant needs and for the plant to understand what the fungi needs [9]. This ensures the plant and fungi are compatible and the fungi is not a parasite to the plant.
The communication happens in stages, not unlike meeting someone for the first time.
Plant/ Fungal Stages
Initiation
The initial stage is like ‘getting to know each other’. Are these 2 species compatible? The hyphae will touch the root tips of the plant. The plant will release a chemical to prevent the fungi from producing spores[4], just incase the fungi is pathogenic.
Once the fungi and plant recognise each other as compatible, the hyphae grows and starts to envelope the root system. Covering 90% of the root [15]. The plant releases compounds (strigolactone (SL) (5-deoxy-strigol) which start the positive communication and encourages hyphal growth. These compounds aid in root structure to facilitate the communication [4]
First Touch
The fungi produce a special cell called an appressoria, when the roots touch. This facilitates penetration of the root hair cells and allows the fungal hyphae to push in to the plant cell walls [28].
This is known as ectomycorrhiza, meaning the fungal cells are inside the plant root cells. The hyphae grow until it is under the epidermal layer of cells. This is where the arbuscules are formed. The arbuscules are the nutrient transfer sites [4].
Signalling Stage
After 2 – 4 days, the arbuscules break down [4]. Although the exact mechanism is not fully understood, research indicates a signal for arbuscular disintegration comes from the fungi, allowing a new arbuscle to take its place [4].
When the arbuscle leaves, the cell is undamaged [28]. Compounds are released by the fungi to allow passage of the hyphae through the cell wall, which is in place to protect the plant cells from parasites [28].
Environment affecting communication
Fungal and plant communication can be affected by inorganic, chemical fertilisers used on the soil. These fertilisers diminish the chemical signals released by both plants and fungi, weakening the connection. Therefore, the plant and fungi do not receive the optimal nutrient and communication transfer [11]. This affects plant health, nutrient content of the food they produce and the pest protection offered by the fungi.
Trees are interconnected, research has discovered parent trees will receive a signal from struggling young trees to send them nutrients [43]. This communication happens significantly quicker through a mycelial network [15]. The signals are exchanged within hours through the mycelial network, as opposed to pheromones which can only travel 100 meters and disperse in the wind [43].
This happens with vascular plants too, like tomatoes. Tomato plants will release a pheromone when one is being eaten by an insect. This takes time to be detected by neighbouring plants. Therefore; use of fungi as a communicator allows for the signals to be received much quicker, protecting neighbouring plants from the invasion. Plants increase their pest resistance with the use of fungi and make themselves less edible to the pests [17] [2].
Image Credit: Hannah Zucker
