the Wood Wide Web
A guest post by Merlin Sheldrake
In the rainforests of Central America lives a small gentian flower, Voyria tenella. Their flowers are a vivid blue, and their stalks pale white. These ghost plants have no leaves, nor any trace of green. In the place of branching, exploratory root systems they have clusters of fleshy fingers that sit like small fists in the shallow soil. With no leaves and no green pigment, Voyria plants are unable to eat light and carbon dioxide in the process of photosynthesis. Their stubby rootlets are ill-suited to absorb water or nutrients from the soil. How, then, can Voyria survive?
I study the relationships that form between plants and symbiotic fungi that live in their roots, known as mycorrhizal fungi (from the Greek mykes, meaning fungus, and rhiza, meaning root). More than ninety percent of plants depend on these partnerships. They are a more fundamental part of planthood than flowers, fruit, leaves, wood, or roots, and lie at the base of the food chains that sustain nearly all terrestrial life. Fine threads of tubular fungal cells — known as mycelium — emanate from plant roots into the surrounding soil. These networks can link different plants in shared networks, sometimes referred to as the ‘Wood Wide Web’. This is how Voyria are able to make a living. Through shared fungal networks, nutrients and energy-containing sugars pass into Voyria from neighbouring plants. But unlike their green plant neighbours, Voyria don’t seem to give anything back to the fungi, making them, in a sense, hackers of the fungal web.
Thinking about fungi makes the world look different. The longer I’ve studied their behaviours and remarkable abilities, the more fungi have loosened the grip of my certainties about how the world works. Over time, many of the well-worn concepts that I use to organise my experience — including notions of identity, autonomy and individuality — have become questions rather than answers known in advance. Voyria has helped me pursue some of these questions. In Panama, I wanted to find out more about how mycorrhizal networks behaved, and spent weeks scrambling through the jungle searching for these charismatic flowers in the hope that they might tell me something about what was taking place underground.
Symbiosis — the intimate associations formed between unrelated organisms — is a fundamental feature of life and enables new biological possibilities. Mycorrhizal fungi are some of the more striking examples. These ancient alliances gave rise to one of the pivotal transitions in the history of the planet: the movement of plants’ ancestors out of the water and onto the land. Early land plants had no roots and were ill-equipped to scavenge for water and nutrients in the open air. They struck up a relationship with fungi, which are accomplished foragers and could serve as plant root systems for tens of millions of years until plants could evolve their own roots. This makes mycorrhizal associations the foundation of all recognisable life on land.
The symbiotic networks formed between plants and fungi comprise an ancient life support system that easily qualifies as one of the wonders of the living world. To this day, plants’ fungal partners help them cope with drought, heat and the many stresses that life on land has presented since the beginning. Plants supply their fungal associates with as much as thirty percent of the energy they produce in photosynthesis. Mycorrhizal fungi supply their plant partners with nutrients, such as phosphorus and nitrogen – much of the phosphorus that makes up the structure of your DNA will have passed through a mycorrhizal fungus at some point – and defend plants from disease. Plants and fungi engage in sophisticated trading strategies, striking compromises and resolving dizzyingly complex trade-offs. The influence of these quadrillions of microscopic trading decisions spills out over whole continents. Mycorrhizal relationships are so prolific that between a third and a half of the living mass of soils is made up of mycorrhizal fungi, their networks form a living seam that helps to hold the soil together. Globally, the total length of mycorrhizal mycelium in the top ten centimeters of soil is around half the width of our galaxy. In 1845, Alexander von Humboldt described the ‘living whole’ of the natural world using the metaphor of a ‘net-like, entangled fabric’. Mycorrhizal fungi make the net and fabric real.
Ecology is the study of the relationships between organisms. Networks of mycorrhizal fungi embody these relationships and help to lead us out of reductive stories featuring neatly-bounded individuals locked in competition for resources. I like to imagine the bewilderment of an extraterrestrial anthropologist who discovered only yesterday, after several decades of studying modern humanity, that we had something called the Internet. It’s a bit like that for contemporary ecologists, grappling with the many ways that mycorrhizal fungi change our understanding of how organisms interact. As Voyria demonstrate, nutrients can move between plants via shared fungal connections. They are not exceptions. ‘Normal’ green plants in the shaded understory might be sustained by resources acquired from their more amply provided neighbours. It isn’t only nutrients that pass through these networks. A plant attacked by aphids can release signals that alert neighbouring plants to the imminent threat. Bacteria use fungal networks as highways to travel through the bustling obstacle course of the soil. Even if plants don’t share the very same network, mycorrhizal fungi regulate plant co-existence, in some cases intensifying the competition between plants and in some cases relaxing it.
Whether in agriculture, forestry, or in our attempts to restore degraded ecosystems, we depend entirely on the healthy functioning of mycorrhizal relationships. But they are hard for us to see, hidden within plant roots and buried underground. To create this collection of symbiotic rootscapes, I used a novel technique that provides an extraordinary view of the fungal relationships that underlie all life on land; an entangled flourishing that underlies our past, present and future.
All of these images are scans of non-photosynthetic ‘ghost’ plants, whether the blue-flowered Voyria tenella or Gymnosiphon suaveolens, which I collected in tropical rainforests in Panama. To produce these scans, I first stained roots with two fluorescent dyes: one of which selectively stains plant tissue and the other fungal tissue. I then mounted the specimens in resin and imaged them with a Leica confocal laser scanning microscope. The microscope scans hundreds of ‘slices’ of the sample, producing image stacks that I digitally render as three-dimensional projections. By using different coloured lasers I am able to capture the plant and fungi data on separate channels, making it possible to display them in different colours and at different levels of translucency. In all the images, plant tissue is coloured in blue-green, and fungal tissue in red. Some of the pieces consist of two or three panels showing the same section of root with the plant tissue made increasingly transparent.