Fróðskaparrit - 01.01.2002, Síða 131

SOPPARÓT f FØROYSKUM FJALLAVØKSTRI
129
Type of mycorrhiza Correlation Phos. Nitr. Probability (rs) Phos. Nitr.
Arbuscular 0.102 0.236 0.000 0.000
Ecto 0.152 0.143 0.000 0.001
Ericoid -0.076 0.052 0.078 0.232
Table 10. The different mycorrhizas correlated with
phosphorus and nitrogen. While both arbuscular
and ecto mycorrhizal plants as a group seem to be
correlated to the nutrients at a significiant level,
ericoid mycorrhizal plants are not.
The fact that ecto- and ericoid mycor-
rhizal plants do not grow together, has been
noticed before. Robinson (1972) describes
how the endophyte in Calluna vulgaris is
eradicated by applying fertilisers, and after
the endophyte is eradicated, the plant is
vulnerable for fungal pathogenic infec-
tions. Further Robinson concludes from ex-
periments that it is likely that the ericoid
fungal symbiont is responsible for this by
excreting fungicides into the soil. Apart
from preventing pathogenic infections, it
also seems to be a growth inhibitor for ecto-
mycorrhizal fungi.
Robinson conducted only experiments
with Calluna heath. However, it is likely
that the same is valid for Empetrum ni-
grum, but not for Vaccinium myrtillus. Only
once does Calluna vulgaris get a score in a
plot where ecto-mycorrhizal plant species
are identilled. This occurs twice for Em-
petrum, but Vaccinium achieves 88 scores
together with ecto-mycorrhizal species.
The only nutrients with good correla-
tions to the vegetation were phosphorus
and nitrogen. The correlations with some of
the mycorrhizal groups are presented in
Table 9.
Conclusion
Arbuscular mycorrhiza is the most wide-
spread type of mycorrhiza. However, de-
spite of few species forming ericoid and ec-
tomycorrhiza, they are much more wide-
spread than would be expected, if only the
number of species was to account for their
distribution. Both ecto- and ericoid mycor-
rhizal fungi are able to degrade organic
compounds and thus provide the plants
with nutrients from organic sources. The
Faroese soils are poor in available phos-
phorus, and probably also ip inorganic ni-
trogen (humus and total nitrogen in soil
samples are extremely well correlated, r =
0.95). Further the teinperature is low, so
mineralisation of organic material is slow.
At such conditions ectomycorrhizas can
be more competitive than arbuscular myc-
orrhizas (Moyersoen et al., 1998). Howev-
er, other findings indicate, that ectomycor-
rhizal species impose a greater carbon drain
on their host than do arbuscular mycor-
rhizas, owing to the greater biomass of as-
sociated fungi (Moyersoen et ai, 1998).
Ericoid mycorrhizal fungi can be more
efficient than ectomycorrhizal as decom-
posers. On the other hand there seems to be
a limited number of plant species capable
to coexist with ericoid mycorrhizal fungi.
Arbuscular mycorrhiza is the most wide-
spread. This is probably because it is the
type which is “cheapest” for the system.
However, it is not as efficient as decompos-
er as the olher types of mycorrhiza, and that
could be why other types of mycorrhiza,
despite their association with very few
plant species, are so successful.
The connection between sorne arbuscu-