Mycorrhizal network sustains diversity in a forest by transporting nutrients and water.

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In a Douglas-fir and pine forest in North America there are trees of all ages, ranging from tiny seedlings to giants that are hundreds of years old. Hidden in the soil is a vast network made up of millions of miles of thin threads called mycelium. Most of the mycelium spread throughout this forest are mycorrhizal fungi. These are fungi that live in a mutualistic partnership with trees and other plants. The mycelium acts like an internet network but instead of moving electronic information around, they transport water and chemicals to keep the trees alive and communicating with each other. This network has been called the “Wood Wide Web”.

On the internet, nodes are individual computers and the network moves information among them. Hubs are places that connect lots of nodes together and have a lot of information traveling through them, such as Google. The nodes of the Wood Wide Web are all the individual trees in the forest. The oldest trees, which are often also the tallest and largest, are the ‘hubs’ because they have the most connections running through them. 

Mycelia form the connections between all the nodes in the Wood Wide Web. The mycelia wrap around the fine roots of the hub tree and other vegetation, snuggling so close that water, nutrients, and other chemicals can move between the cells of the roots and fungi. A hub tree has more access to sunlight than smaller trees because of its size. Sometimes that results in it producing too much sugar through photosynthesis. When this happens, it sends the sugar out through the mycelium network to be used by its own seedlings and even other species of trees. The fungi take some of the sugar as it passes between trees and use it for themselves.  

Water is also shared among the fungi and plants in the network. The water and nutrients increase seedling growth and help other trees survive. At another time, if the hub tree is stressed and needs water or nutrients, the mycelium and other trees can send them back to the hub tree. 

But this isn’t just about one hub tree. It’s about a hub tree connected to a seedling connected to a sapling, connected to another hub tree, and so on. Researchers at a study site in Canada discovered that one tree was connected to 47 others through this network. Sixty percent of the tree species in the world are associated with these mycorrhizal fungi. Most trees form symbioses with a wide variety of fungal species (there are more than 5000 of them) and each species of fungus can have relationships with a wide variety of trees.

Besides sharing nutrients and water, the network also sends warnings. If a tree is attacked by a bark beetle, it sends out a chemical signal, called a defense signal. The mycelium passes this signal along to other nearby trees. When they get the signal, they reinforce their chemical defenses, which makes it easier for them to fight off an attack when it comes.

The Wood Wide Web can show us the value of sharing resources, efficient ways to move them, and the importance of forming close partnerships. We also can learn how to better manage our forests to maintain this underground network that provides mutual support to all partners.

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Watch Suzanne Simard’s 2016 TED Talk.

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References

“Adaptive behaviour of plants, including rapid changes in physiology, gene regulation and defence response, can be altered when linked to neighbouring plants by a mycorrhizal network (MN). Mechanisms underlying the behavioural changes include mycorrhizal fungal colonization by the MN or interplant communication via transfer of nutrients, defence signals or allelochemicals…We have found that the behavioural changes in ectomycorrhizal plants depend on environmental cues, the identity of the plant neighbour and the characteristics of the MN. The hierarchical integration of this phenomenon with other biological networks at broader scales in forest ecosystems, and the consequences we have observed when it is interrupted, indicate that underground ‘tree talk’ is a foundational process in the complex adaptive nature of forest ecosystems.” (Gorzelak et al. 2015:1)

Journal article
Gorzelak MA, Asay AK, Pickles BJ, Simard SW. 2015. Inter-plant communication through mycorrhizal networks mediates complex adaptive behaviour in plant communities. AoB PLANTS 7: plv050 AoB PlantsGorzelak MA, Asay AK, Pickles BJ, Simard SW

Journal article
Beiler KJ, Durall DM, Simard SW, Maxwell SA, Kretzer AM. 2009. Architecture of the wood‐wide web: Rhizopogon spp. genets link multiple Douglas‐fir cohorts. New Phytologist 185(2):543-553New PhytologistBeiler KJ, Durall DM, Simard SW, Maxwell SA, Kretzer AM

Journal article
Song YY, Simard SW, Carroll A, Mohn WW, Zeng RS. 2015. Defoliation of interior Douglas-fir elicits carbon transfer and stress signalling to ponderosa pine neighbors through ectomycorrhizal networks. Scientific Reports 5 (8495).Scientific ReportsSong YY, Simard SW, Carroll A, Mohn WW, Zeng RS

Book section
Simard SW. 2018 Mycorrhizal networks facilitate tree communication, learning, and memory. Pages 191-213 In: Baluska F, Gagliano M, Witzany G. (eds) Memory and Learning in Plants. Signaling and Communication in Plants. Springer, ChamMemory and Learning in PlantsSimard SW

Book
Stamets P. 2005. Mycelium running: How mushrooms can help save the world. Ten Speed Press, New York.Mycelium RunningStamets P

Magazine article
Simard, SW. 2015. Conversations in the forest: The roots of Nature’s equanimity. SGI Quarterly. 79: 8-9.SGI QuarterlySimard SW

Magazine article
Young, E. 2016. The Wood Wide Web. The Atlantic.The AtlanticYoung E

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