Though not well-known to those outside
botany,
mycorrhizal
fungi exist as a critical part of
Earth's
ecosystem. These
microorganisms
form a symbiotic association with many plants,
allowing the plants access to more nutrients
than they could obtain from the soil directly.
In poor soil conditions, this can mean the
difference between a plant surviving or dying.
Additionally, the network they grow binds soil
particles together, significantly slowing the
effects of
erosion.
Before getting into the topic, a brief clarification
of terminology may aid the reader:
"Mycorrhizal fungi" or, plural, "Mycorrhizae",
refers to a colony of individual fungal cells,
similar to a
mushroom (though not for
reproductive purposes). It does not refer to
a particular species, but rather, to the
particular relationship these organisms have
with a plant.
"Hyphae" refers to individual fungal cells, in
the form of thread-like filaments that tangle
together in a larger multicellular mass (ie,
the mycorrhizae).
Conceptually, mycorrhizal fungi act like an extremely
fine terminal branching of the plant's own
root
systems, producing a microscopic web between and around
each individual soil particle.
The peripheral
hyphae, called the
soil network,
absorb
inorganic nutrients from the soil itself and
from decaying
organic matter in the soil, including
larger objects such as dead
insects. These nutrients
travel through channels between individual hyphae to
the
mantle, a small but visible fungal coating
around the roots of the plant. Finally, numerous
hyphae interface with the root cells themselves,
in structures called a
Hartig net. Here,
the mycorrhizae transfer inorganic nutrients to
a plant, and in return, the plant provides the
mycorrhizae with carbon in the form of simple
sugars, benefitting both the plant and the fungus.
According to Michael Miller, a US
Department of Energy
senior soil
scientist, "90 percent of the world's
vascular plants belong to families that have
symbiotic associations with mycorrhizal fungi".
Sources:
http://www.ucfv.bc.ca/biology/biol210/1999/Mutualism/Mycorr.htm
http://dmsylvia.ifas.ufl.edu/mycorrhiza.htm
http://www.planthealthcare.com/fungi.html
http://www.mastergardeners.org/newsletter/myco.html
http://www.consrv.ca.gov/OMR/smara/newsletter/winter2001.pdf