The word "truffle" for the majority of readers is probably associated
with either some sophisticated and very expensive dish about which A.
S. Pushkin wrote in "Evgeniy Onegin": "...the luxury of young age,
best blossoming of French cuisine... " or with chocolate candy. We
wish however to tell about truffles themselves - truffle mushrooms
(Tuberales) - because it is their fruit bodies that the sophisticated
dishes are cooked from, and because it is the shape of these mushrooms
that reminds everybody about the well-known candy.
Truffle mushrooms can be found in relatively warm regions of temperate
zones of both hemispheres. They belong to the group of so called
underground (hypogean) Ascomycetes, a specific character of which is
underground fruit bodies. Their shape is round or tuber-like,
consistency is fleshy or gelatinous, size - from a pea to a large
potato tuber and even larger, and their weight can sometimes reach 1
kg.
All fruit bodies have external leathery layer - smooth, cracked or
covered with warts, which is called peridium, and spores-containing
tissue located inside, which, when cut, has a typical marble pattern
made of light and dark veins. Fruit bodies of several kinds of
truffles can be yellow, pink, purple, orange, green, black, blue...
Why do they need such diversity of colors if most of the time they are
hidden under the ground or forest litter? This is still a mystery.
Like many other soil mushrooms, most truffles form mycorrhiza -
symbiotic connections with the roots of forest trees and bushes.
Mycelium covers young soft roots of the host plant, thin mushroom
threads penetrate surrounding soil and act as extension of the root
system of the host, obtaining minerals and water for it. Mushrooms
also guard the plant's root system from germs contained in the soil,
for example, Phytophthora.
The host plant, in its turn, provides the truffle with energy stored
in carbohydrates.
So-called black truffles (Tuber melanosporum, T.aestivum) are
symbiotic with oak, beech, hornbeam, hazelnut; white truffles
(T.magnatum, Choiromyces meandriformis) - with birch, poplar, elm,
basswood, willow, ash, hawthorn. Sometimes truffles form mycorrhiza
with coniferous trees, too.
Studies of recent years have shown that there is a wide variety of
truffles in the forests of Australia, where trees are mostly of the
Eucalyptus genus. These forests have no analogues in the world in
quantity of truffle kinds, and the list of mushrooms growing there
continues to expand as new areas are being explored.
The mushrooms fruit bodies of which develop on the surface distribute
their spores by means of wind and water. But fruit bodies of truffles
are located underground, and for them it is impossible; also for the
spores it is rather difficult to get released from the fruit body
covered with a thick skin.
The role of spore distributors for these mushrooms is performed by
several animals who seek and eat truffles. Spores located inside the
fruit body pass through their bowels intact and are disseminated all
over the forest together with feces. Later they find their way
underground together with rain water or with the help of dung beetles
who dig animal excrements in the soil, storing them for their larvae.
If the conditions happen to be favorable, spores germinate and create
mycorrhiza with a host plant. In Australian forests at least 40 kinds
of mammals play the role of truffle distributors. The most specialized
of them belong to the family of kangaroo rats (Potoroidae) whose
nutrition almost completely consists of truffles. Among them - rare
and endangered Potorous longipes. This night animal of the size of a
hare devotes most of its active time to sniffing out truffles. In some
places potorouses feed on more than 50 kinds of truffles!
Many other Australian animals hunt for truffles as well - for
example,
bandicoots (marsupial badgers), but they don't do it so purposefully,
eating a significant proportion of other foods.
In coniferous forests of Pacific coast of USA truffle spores are
disseminated mostly by rodents, for example, Californian red vole.
These creatures spend a considerable part of their life under the
ground - close to truffles, their beloved food. Another species of
American mammals, northern flying squirrel (Glaucomus sabrinus),
spends the daytime inside hollow trees while performing very far raids
at night, coming down to earth in the search of truffles. Rodents are
the main truffle consumers and distributors in other regions of Earth
(South America and Europe) as well.
So, how do the animals find truffles? By smell - mature mushrooms
emit distinctive aroma, often pungent or fragrant. Various kinds of
truffles have various smells: some of them are pleasant for humans,
others are not (for example, the smell of rotten onions, freshly laid
road asphalt or even feces). But obviously the animals don't care
about the smell of mushrooms. In Spain, Italy and France farmers use
trained dogs and even pigs for sniffing out mature black truffles,
which are loved by gourmets and known for its wonderful aroma and
delicate flavor. Until 1960s of XIX century even trained bears were
used for gathering truffles around Moscow.
Besides attractive smell and edible flesh, some truffles have other
accommodations for distributing their spores by animals. For example,
Mesophellia - an endemic genus of Australian truffles - has a fruit
body consisting of three different layers. The first one - hard outer
skin - is a combination of mushroom tissues and plant roots. There is
the second layer under it which consists of a multitude of
grayish-green spores. And the third layer is a jelly-like core, which
attracts animals with its taste - it is sterile and doesn't have any
other obvious function except being a food reward for an animal that
finds the mushroom.
Long-nosed bandicoot - truffle lover
It is very interesting to observe animals eating truffle fruit bodies
which happened to survive in the sites of forest fires. For example,
at the island of Tasmania after a forest fire bettongs experience
something like truffle fever, devoting all their time to mushroom
hunting. The same behavior was observed with potorouses and bandicoots
in Australia. At the fire sites truffles are much more fragrant than
in neighboring unburned areas. One can suggest that fire causes
changes in the smell of truffles that make them even more attractive
for animals or enhance animals' appetite. Of course confirmation of
this hypothesis requires special research, but we can say with
confidence that, by eating truffles in burnt forest areas and then
disseminating their spores, mycophagous animals largely help the
recovery of truffle populations. And therefore - the recovery of
normal conditions for growth of mycorrhiza-forming trees weakened by
the fire.
So, truffles are not only a gastronomic product but also an important
link in the chain of interacting components of the forest.
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