Geology Reference
In-Depth Information
icate, ubiquitous tracery of tightly interlinking hollow fungal tubes. Mycelia can grow
at prodigious speed and explore space with phenomenal density. They can extend sev-
eral centimetres in a day and can infuse a mere gram of soil with over a kilometre of
their intensely networked pipe-like cells. In some habitats such as forest soils, fungal
biomass often reaches 90% of the combined biomass of microorganisms (such as bacter-
ia) and mesoorganisms (small animals, including worms and nematodes). A fungal bio-
mass equivalent to about 15 sheep lives under each football pitch sized piece of English
permanent organic pasture. Thus, despite being microscopic, the biomass of mycelia in
these grasslands matches and possibly outweighs that of animals.
Some mycelia can be massive in both age and size. Perhaps the largest organism on
earth is a 2,200-year-old
Armillaria
root-rot fungus that grows in 2,400 acres of forest
soil in eastern Oregon—a veritable behemoth that periodically kills the forest, produ-
cing deep rich soil in which taller trees can grow before their turn comes to be felled by
their fungal recycler. The biomass of these fungal networks is immense: several tonnes
of mycelium can exist is one hectare of Swedish forests. Other fungi are tiny, such as
the unicellular yeast,
Saccharomyces cerevisiae,
without whose help there would be no
baking or brewing.
A mycelium feeds in a manner very different from the way we animals go about
it. Animals ingest: we push food into a long, highly sensitive tube within our bodies.
This is the gut. Food enters the tube via our mouths and then passes into our stomachs,
where digestive juices dismantle it into nutritious molecular components for subsequent
absorption by the small intestine. Wastes are excreted out of the other end of the tube.
From our point of view, the mycelium makes use of a peculiarly inverse digestive logic:
it doesn't bother with a gut at all—or, rather it uses its 'skin', its cell wall and membrane
as a kind of outward-facing gut. So, when hungry, mycelia sense the presence of fresh
food and grow towards it in wave-like surgings of their pipelines. Simple foods such as
sugar molecules are merely absorbed through openings in the chitin walls, but complex
organic molecules such as protein and wood are dealt with by releasing digestive juices
into the surroundings that break the food down into simple molecules for subsequent ab-
sorption.
When ready to reproduce, previously invisible mycelia gather some of their hyphae
together to form fruiting bodies such as the mushrooms and moulds that sprout into the
air—and into our consciousness, when we are sufficiently tuned in to detecting them.
They can emerge quickly because the underlying mycelium is immensely effective at
supplying concentrated hydraulic power to a specific point in the network at very short
notice. Fungal fruiting bodies release spores tiny enough to ride on swirling currents of
air, and thus they find new places fit for colonisation. Vast numbers of spores are pro-
