Fróðskaparrit - 01.01.2002, Síða 128

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THE MYCORRRHIZAL STATUS
IN MOUNTAINOUS VEGETATION IN THE FAROE ISLANDS
Ectomycorrhiza
Most of the fungal partners in this mycor-
rhiza belong to the basidiomycetes. Com-
pared with the few fungal species forming
arbuscular mycorrhiza, the ecto-mycor-
rhizal fungal species are numerous, approx.
5,000. Ectomycorrhiza provides the plant
mainly with nitrogen, from both inorganic
and, dependent on the fungal species, or-
ganic nitrogen sources (Smith and Read,
1997).
The ectomycorrhizal plant species in this
vegetation study were Salix herbacea and
Polygonum viviparum.
Ericoid mycorrhiza
Calluna vulgaris, Empetrum nigrum and
Vaccinium myrtillus were the only plant
species likely to form ericoid mycorrhiza
found in this vegetation survey. Ericoid
mycorrhiza dominates in the heath commu-
nity. The fungal partner in this mycorrhiza
belongs to the ascomycetes. This type of
mycorrhiza usually occurs in environments
where nutrients are extremely unavailable.
In addition to organic sources such as
proteins the ericoid mycorrhizal fungi are
able to use chitin as a sole nitrogen source
(Finlay et al., 1992).
Orchid mycorrhiza
Orchid mycorrhiza provides the plant with
carbohydrates, nitrogen and phosphorus,
and the fungus apparently gets nothing in
return. Most of the basidiomycetes which
form orchid symbiosis, are reiatively fast-
growing saprophytes, while other are
known as parasites (Smith and Read,
1997).
In addition to saprophytic sources there
is mounting evidence of mycelial links be-
tween orchids and ectomycorrhizal plant
species (Smith and Read, 1997). With such
a link it is possible for both orchid and fun-
gus to acieve carbohydrates, produced by a
ectomycorrhizal plant.
Dactylorhiza maculata and Listera cor-
data were the only plant species found in
this study which form orchid mycorrhiza.
Listera cordata was only represented by a
single specimen.
There could be objections that orchid
mycorrhiza is not a mutualistic symbiosis,
but rather that the plant is a parasite on the
fungus. However, when the plant dies, the
fungus is ready to utilise the plant in a
saprophytic way. Further it is known that if
the host plant is unable to restrict the fungal
colonisation, then the plant is killed by the
fungus (Smith and Read, 1997).
Non-mycorrhizal species and
species with no mycorrhizal record
Eight plant species known to be non-myc-
orrhizal were found in the survey described
here. In addition nine plant species are esti-
mated to be non-mycorrhizal (Table 2). Of
these Koenigia islandica is the most fre-
quent.
In this vegetation survey the mycorrhizal
status is unknown for six plant species, ac-
counting for 0.3 per cent of the total sum of
plant frequencies (Table 3). In addition, 10
species are considered as arbuscular myc-
orrhizal plant species, by looking at their
relatives (Table 1).