Agriculture Reference
In-Depth Information
These data evidence changes in microbial succession during decomposition. It was
specifically supported by electrophoretic analyses of extracts from
Q. ilex
leaf litter (Di Nardo
et al., 2004). They were used to characterize laccase and peroxidase isoenzyme patterns. It
shows that the decomposer community can involve different microorganisms with similar
functional activity but expressing different isoenzymes (Sinsabaugh et al., 2002).
The main laccase and peroxidase isoenzymes, on decomposing
Q. ilex
leaves, occurred
during the wet autumn and winter (Figure 9) (Di Nardo et al., 2004). Others isoenzymes were
present in the dry spring and summer period when the lowest enzyme activity was recorded,
suggesting that such conditions had severely restricted microbial growth (Fioretto et al., 2000)
but enhanced diversity. However, the appearance of a new laccase isoforms in the second
year of decomposition suggested the blooming of microorganisms the litter, probably
favoured by the variations in physical and chemical composition of the litter. Changes in
laccase isoforms during decomposition of
Q. ilex
leaf litter have also been reported in other
Mediterranean areas (Criquet et al., 2000).
F
UNGAL
S
UCCESSION
During the decomposition of plant material the composition of fungal community
changes, evidencing a microbial succession (Frankland, 1998). This succession can be viewed
as changes in taxonomic diversity and, if the role of the fungal population is know, also as
functional diversity.
Fungal species distribution and successional changes occurring during the decomposition
process have been extensively investigated on several litter types of the European forests
(Dilly and Imler, 1998, Kjøller and Struwe, 1987, 1990, 2002; Rosenbrock et al., 1995) and
of Mediterranean ecosystems (Pasqualetti et al., 1999; Tempesta et al., 2003, 2005; Sadaka
and Ponge, 2003; Pasqualetti et al., 2006). Nevertheless, some of these studies only consider
the presence and the frequency of species, but did not try to relate the results to microbial
activity and litter quality changes.
Fungal colonization on needles litter of
P. pinea
,
P. laricio
and
P. sylvestris
, incubated in
the
P. pinea
wood on Terzigno (Vesuvius), and of
A. alba
, incubated in silver fir wood on
Monte Taburno, showed very similar pattern in all litter species (Virzo De Santo et al., 2002).
The invading fungi just after incubation (1-2 months) were the dematiaceous
hyphomycetes, with
Cladosporium
and
Altemaria
sp. pl. dominants in
P. pinea
and
P. laricio
.
In such litters the dematiaceous fungi were accompanied by the ascomycete
Lophodermium
, a
typical primary colonizer.
Cladosporium
and
Altemaria
may be considered chiefly external,
ubiquitous colonizers, able to utilize pectin, while their cellulolytic activity depend on species
and conditions (Domsch et al., 1993). In silver fir litter the dominant dematiaceous
hyphomycete was
Thysanophora penicilloides
.
Thysanophora
as well as
Lophodermium
are
internal colonizers restricted to specific hosts. The litter of
P. sylvestris
, was instead colonized
mainly by coelomycetes.
The frequency of the early stage dematiaceous hyphomycetes dropped significantly after
the four months of incubation, and in the later stages these fungi disappeared. From the sixth
month of incubation the frequency of other dematiaceous hyphomycetes, e.g.,
Polyscitalum
sp. pl., increased and became dominant, together with tuberculariaceous hyphomycetes.
