Trees can’t chase their food, so they must count on resources harvested from their immediate area. Through the process of photosynthesis, they can feed themselves directly from the atmosphere using sunlight and carbon dioxide. But this chemical process also requires plenty of water … and for many trees, a consistent source is not always a given.
From the fungal point of view, water is not a problem. Fungi have the ability to draw water from the most grudging of sources, even from the air itself. They also break down molecules into simpler nutrients that can be absorbed by tree roots. But they are not capable of creating their own food because they do not photosynthesize. Trees and fungi are meant for each other!
It’s a lovely, romantic idea. But how exactly do these two very different species get together? How does the two-way transfer of water and nutrients work?
In my last post, we saw that a fresh seed root soon introduces itself to the massive fungal network in the top layer of the forest floor. The root tip exudes a natural hormone that awakens fungal spores or strands nearby. In a process called colonization, the alerted fungal strands pierce their way through the epidermis (skin) of the roots. (If this sounds like a terrifying Body Snatcher situation, remember that our own bodies are walking zoos: we have at least ten times as many bacteria, not including yeasts and fungi, as we have human cells.)
Once inside, the fungal strands colonize the root in one of two ways, depending on the species:
1) Arbuscular fungi start growing INSIDE root cells along the central core of the root. They are called Arbuscular because once inside the cells, they form tiny tree-like structures: trees inside trees! The large surface area created by their dense canopies is an efficient way to transfer water and nutrients.
2) Ectomycorrhizal fungi spread their strands AROUND root cells, forming a 3-D spongy structure called the Hartig net. The tip of the root becomes enveloped with a pale mantle, easily seen with the naked eye.
Some fungi are specific to particular trees – for example, Arbutus and Maple trees have their own favourite fungal species. But many fungi are non-specific and will colonize trees, grasses and many other plant species. Also, one tree may host several types of fungi at once. The established fungi maintain the flow of water and nutrients through fungal strands that connect their specialized inner root structures with the outer soil network, visible to us in the form of mushrooms and truffles.
But the best view of all is under the microscope. When tree rootlets are thinly sliced, treated with special dyes and magnified, it becomes possible to see exactly where and how the two species, tree and fungus, meet and mate. Electron microscope photographs are bizarre and beautiful, and these are no exception: a gold mine of ideas and eye candy. Below is one of many that drew my attention.
And the quilted panel that it inspired:
In this piece my intention was to stay true to the photo so I could learn to manipulate line and shape, but while working on it I began to see great potential for design and content. More adventures ahead in future posts!