Geology Reference
In-Depth Information
cently was thought to make its living only by decomposing dead wood.
Pleurotus
is
eaten by certain wood-dwelling nematodes who share our human predilection for its
savoury tissues. When the fungus senses the presence of the nematodes it secretes a
powerful substance that paralyses them in seconds. Specialised hyphae are then sent out
to find the stricken prey, which is digested in the time-honoured fungal fashion. Many
predatory, wood-decomposing fungi are also mycorrhizal, which evokes the slightly dis-
comforting realization that trees are carnivores, only indirectly. The reason is quite clear:
some of the nitrogen fed to the roots of trees and other plants by fungal hyphae must
have started out in once healthy nematodes, insects and bacteria (and even other fungi)
that have been strangled, paralysed or otherwise done to death by fungi in rotting logs
scattered about on the forest floor. By growing better with this extra nitrogen, trees
weather more rock.
But the fungi don't have it all their own way. Channels of communication, once
opened, can easily be taken advantage of. Various plants are able to break into fungal
pipelines to steal the sugars that they so deftly transport from plant to plant. An example
is the yellow bird's nest,
Monotropa hypopitys
, a plant which parasitizes the mycorrhiz-
al fungi which nourish beech trees (but also willow and pine) in Britain and beyond. For
a plant, yellow bird's nest has a distinctive Dracula-like feel— it has no need of chloro-
phyll and is thus a sickly waxy yellow rather than the usual green. Other plants that de-
pend on fungi are amongst the showiest, most exotic and most expensive plants in the
world: the orchids, all of which depend on fungi to complete their life cycles. Orchid
seeds are tiny, often microscopic, with no room to store nutrients. Once it germinates, an
orchid seed survives only if it has landed near a specific mycorrhizal species that helps
it to thrive by feeding it essential nutrients. Some orchids, such as
Gastrodia elata
,
lack
chlorophyll and gain all their sugars from parasitizing fungi such as
Armillaria
, the no-
torious root-rot fungus. But even these hyperparasites (parasite of parasites) may well
have beneficial impacts on their ecological communities by opening up ecological space
for species that might otherwise have been excluded. Hence they too could help to amp-
lify the rate of rock weathering.
Back to lichens
So far we have seen how fungi weather rocks indirectly by helping plant roots to grow
and by making soil out of dead bodies. But there are fungi that weather rocks dir-
ectly. Some are lichens. We know them as orange, grey, sometimes black patches on
rocks, trees and gravestones that often look like splashes of paint. These are the flat, or
crustose, lichens. Then there are the foliose lichens that look like lettuce leaves, and the
