Leonard Kelley holds a bachelor's in physics with a minor in mathematics. He loves the academic world and strives to constantly explore it.
One of the reasons I enjoy science so much is the surprising facts it uncovers about our world. Mycorrhizal networks, or wood wide webs, are one of these amazing facets of our lives that is underneath our feet, making incredible things happen both on a micro and macro scale. But just how does it work, and how does it impact you and me?
It’s been known for some time that fungi can exist in many conditions unsuitable for other living things, but Suzanne Simard was one of the first to uncover their potential for resource management. In 1997, she published her Ph.D. thesis on mycorrhizae networks, where plants and fungi interact with each other and the greater environment. Simply put, fungi can interact with a plant’s root system either by proximity or penetration and give/send elements based on the plant and the surrounding conditions (Hooper 40, Yih 5).
This alone is amazing, but over the years it has been shown that more than one plant can be connected to the same fungal grouping and also that more than one fungi grouping can be associated at any given point. This leads scientists to compare this network much like the world wide web, with many interconnecting and layering elements to it, hence the wood wide web (Ibid).
She came to this conclusion after a study she and Susan Dudley conducted with conifers. Parent trees were given radioactive CO2 (in this case, carbon-13) after their seedlings had taken root. Later, the surrounding area was measured for the radioactive carbon, and much to everyone’s surprise the parents and seedlings had it but nothing else. Somehow, the conifers knew their kids and shared resources with them only. No strange plants had it. Somehow, the mycorrhizal networks facilitated this transfer but how exactly isn’t quite clear (Hooper 41).
The fungi are able to access resources that are otherwise outside a plants ability to reach, and the plant can give the fungi elements it doesn’t have access to in return. Fungi can give water, phosphorous, nitrogen, zinc, and copper to plant roots, while the roots provide carbohydrates that were left over from photosynthesis to the fungi. This allows plants to divert more resources to growing upward rather than outward (Hooper 40, Yih 2, MacFarlane, Marcel 1407).
Types of Mycorrhizal Fungi
While there are several types of fungi that facilitate these networks, the big two are arbuscular mycorrhizal fungi (AM fungi) and ectomycorrhizal fungi (EM fungi). AM fungi get their name from the shape the fungi make around the roots of a plant, essentially like a mini tree in appearance. They gather around a plant when the first carbohydrates are detected, and within a few days the roots can be surrounded and penetrated, building a mycorrhiza (Yih 2-4, Marcel 1408).
Some AM fungi end up being Arum-type, where they grow between the rows of cells and thus never penetrate a cell’s plasma membrane but instead become enveloped by them. Other AM fungi end up being Paris-type, with a coiling structure that weaves in and out of many cells. Based on fossil record, it’s possible that these fungi first appeared about 410 million years ago, and may have been the bridge between aquatic and land plants. AM fungi facilitate mycorrhizal networks with herbs, grasses, and many trees, with up to 200,000 plants belonging to one network (Ibid).
EM fungi are a more recent development, having first appeared about 50 million years ago. They account for mainly wood plants and don’t penetrate the roots but instead form a sheath around them. They stay outside, hence the ecto prefix in the name. This sheath has many fungal hyphae extending from it, forming a Hartig net which grows between the outer layers of the root cells. EM fungi driven mycorrhizal networks are mainly amongst shrubs and temperate trees, and can up to 6000 plants per network (Yih 4, Marcel 1408).
Two minor fungi that deserve to be mentioned are orchid mycorrhizal fungi and ericoid mycorrhizal fungi, which facilitate the planets mentioned in their name. Altogether, about 90% of all plant life on Earth participates in some mycorrhizal network, with 74% being with AM fungi, 2% with EM fungi, 9% with orchid fungi, and about 1% with ericoid fungi. Some plant species can have both AM and EM present at once, making the distinctions between networks challenging (Yih 2, Marcel 1408).
Experiments and observations have shown that 10 to 20% of a plant’s photosynthetic products go to AM fungi, with up to 50% being sent to EM fungi or ericoid fungi. Based on how prevalent the type of fungi is for a given network, the carbon being transferred can clearly fluctuate greatly. Things that can detriment this sharing includes heavily tilled land, non-fungal interacting crops, and fertilizers. Work by Christian Korner and Tamir Klein showed that for roughly every 100,000 square feet of forest, about 280 kilograms of carbon can be transferred a year! This was based on radioactive CO2 (again, the carbon-13 being the choice isotope) being piped to 5 conifers and tracking their amounts to their seedlings. For those trees, about 40% of that carbon was in their fine roots and only 4% a result of photosynthesis byproducts (Marcel 1410-2, Yong).
Nitrogen and Phosphorus Impacts
Experiments and observations have shown that AM fungi can give up to 90% of the phosphorus a plant intakes, but nitrogen contributions suffer and are usually suppressed by soil acidity, water saturation, and soil composition. For EM fungi and ericoid fungi, they can give up to 80% of both their nitrogen and phosphorous to plants. Keep in mind though that these values may fluctuate as better observations and more refined experiments pipe down, and occasionally mycorrhizal fungi can prevent N and P loss which normally happens to plants via leeching effects. We could be overplaying the transference and underplaying the maintenance (Marcel 1410).
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Mapping It Out
Recent work by Thomas Crowther and Kabir Peay using machine learning and select sampling of 28,000 trees over 70 countries has led to a wood wide web map for EM fungi and AM fungi. They looked at correlations between EM and AM fungi with their trees and how local factors such as temperature, precipitation, soil chemistry, and topography impacted the networks, then fed that into a machine learning program to help extrapolate probably fungal locations (Marshall, Popkin).
It found that EM fungi prefer cool and dry climates while AM fungi prefer wet and hot. This is very important, because EM fungi store carbon better than AM fungi, and right now up to 60% of trees are in EM fungi networks. If global temperatures increase as predicted, then by 2100 it will be about 50-50 instead, furthering climate change. We can therefore use this map to best determine optimal EM fungi locations and the tree species we should use to facilitate our networks, helping to curb climate change (Ibid).
Connections to Us?
Further research into these networks shows many parallels to brain networks, which use neurotransmitters to communicate across different brain lobes. Mycorrhizal networks operate similarly, and interestingly enough glutamate is both a common neurotransmitter and a resource sent along the wood wide web. Also being revealed is plant paternal instincts, with the offspring of plants benefiting from sharing in the network (Hooper 40-2, MacFarlane).
This all is challenging tot the traditional notion of solitary, discrete plants and instead now paints cooperative (and sometimes competitive) networks of living things. This could even challenge the dividing line between species, and even hint at plant intelligence. It has been shown that trees in these networks release carbon to help dying trees, something that isn’t strictly a benefit to said tree. Tree disturbances and how the network reacts to them point to better awareness than we usually give them (Ibid)
But people were not on board with this idea at first, and it still isn’t universally accepted. As Simard speculates, it could be because “it comes back to the fact that there had been this separation of humanity from nature, mind from body, spirit from intellect, and that we had moved away from this more holistic, spiritual way of seeing the world.” It is my hope that this article maybe makes you too reconsider if we need to reconsider our approach to the world, and maybe in the process find even further things to be left in wonder (Hooper 41)
Hooper, Rowan. “The Wisdom of the Woods.” New Scientist. New Scientist, 01 May 2021. Print. 40-2.
MacFarlane, Robert. “The Secrets of the Wood Wide Web.” Newyorker.com. The New Yorker, 07 Aug. 2016. Web. 16 Dec. 2021.
Marcel G.A. van der Heijden et al. “Mycorrhizal ecology and evolution: the past, the present, and the future.” The New Phycologist, Vol. 205, No. 4, Ecology and evolution of mycorrhizas (March 2015), pp. 1407-8, 1410-2.
Marshall, Claire. “Wood Wide Web: Trees’ Social Networks Are Mapped.” Bbc.com. BBC, 15 May 2019. Web. 03 Jan. 2022.
Popkin, Gabriel. “’Wood Wide Web’ – The Underground Network of Microbes That Connects Trees – Mapped for First Time.” Sciencemag.org. Science, 15 May 2019. Web. 03 Jan. 2022.
Yih, David. “Food, Poison, and Espionage: Mycorrhizal Networks in Action.” Asnoldia, 2017, Vol. 75, No. 2 (2017), pp 2-5.
Yong, Ed. “The Wood Wide Web.” Theatlantic.com. The Atlantic, 14 Apr. 2016. Web. 03 Jan. 2022.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2022 Leonard Kelley