The underground social network between trees

When I picked up Peter Wohlleben’s book The Hidden Life of Trees, I expected to read about interactions between fungi and plant life. And indeed, the fascinating relationships between these diverse life forms were discussed at great depths. Together, tree roots and fungi form the mycorrhiza which some have referred to as the Wood Wide Web. Fungi are fundamental to the underground social networks that trees use to communicate to one another, to warm others of danger, and to transport nutrients and water.

This symbiotic Wood Wide Web provides nutrients to the tree and the fungi. Trees that cooperate with fungi take in about twice as much nitrogen and phosphorus than plants that tap the soil alone. Fungi also filter out heavy metals and guard the tree against destructive bacteria or fungi. For their help, the fungi get something in return. Nearly a third of the tree’s total food production is shuttled to the fungi.

Every tree has multiple fungal partners and fungi can form networks between trees of different species. A single tree may have hundreds of fungi colonizing different niches on its roots. This diversity is beneficial in changing environments: if some fungal species die, the tree still has several others fungal symbionts.

Though many fungi form mutualistic relationships with their plant partners, some fungi come to the aid of tree predators. Take the bark beetle for example. Bark beetles drill holes into trees in search of sugars and minerals. Healthy tree can kill beetles by producing chemicals toxic to the beetles. But if the beetle has a fungal symbiont that destroys the chemicals, it can then invade the tree. Because the fungus spreads through the tree quicker than the beetle can drill holes, they disarm the tree’s defenses before the beetle comes into contact with the toxins.

Aside from its microscopic form, fungi also form large multicellular structures that we know as the mushroom. Like it’s microscopic counterparts, mushrooms can form cooperative or antagonistic relationships with trees.

In the case of the pine tree, its partner fungi (Lacaria bicolor) help the pair in times of need. In nitrogen-starved conditions, the fungus secretes a toxin to kill soil-dwelling insects. These dead insects soon become nitrogen sources for the tree and the fungus. How’s that for carnivores in disguise?

Unlike this carnivorous pair, the honey fungus embodies the parasitic type of fungal-tree relationship. The honey fungus forces its way into the roots of firs, beeches, and oaks and eventually grows up right beneath the bark. It buries deeper and deeper into the tree searching for nutrients. The tree rots and ultimately dies. You may have heard of the honey fungus before as it forms one of the largest living organisms on this earth to date. One such example spans 2000 acres in Oregon and is estimated to be 2400 years old and weight 660 tons.

Fungi participate in interconnected webs of cooperation and antagonism with plants and their predators. Without the intimate Wood Wide Web, our forests would not be like they are today.

CC BY-NC-ND 4.0 The underground social network between trees by Jennifer Tsang is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

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