Agriculture Reference
In-Depth Information
Chitinolytic fungi were approximately 20% in the first 6 months of decomposition and
after raised to 40%, staying at such value in the whole period with a little increase at 15
months of incubation when
Mortierella
spp reached the highest frequency. This suggests a
critical litter quality change at such a stage in which a relevant important fungal growth
occurred. When fungal biomass significantly increase, the dead hyphae, rich in chitin, became
a resource for chitinolytic fungi such as
Morteriella
. The role of chitin as a new substrate in
the litter has been also evidenced in beech litter (Kjøller and Struwe, 1990).
C
ONCLUSION
In the Mediterranean area the interactions among litter quality, environmental factors,
and microrganisms-fauna make more complex the decomposition process. However, its
understanding moves in the general paradigma that consider: a) the initial concentration of the
main components of litter, lignin, cellulose and hemicellulose, and nutrient content such as
nitrogen N, the controls the decomposition rate determining not only the resource availability
but also the palatability of organic matter, b) the degradation of lignin, cellulose and
hemicellulose is related to climatic conditions, c) neither group of litter compounds was
degraded independently, is a useful paradigma to understand such a process.
The dominant effect on litter decomposition in Mediterranean area was summer aridity
because it highly reduces the activity and growth of microorganisms, affecting also the
interactions with litter quality and soil organisms. The decomposition rate was positively
related to the Lang aridity index for all the studied litter even if no statistical significance was
evidenced.
The low moisture and the high temperature in the summer seasons strongly reduced
microbial activity, as indicated by the high decrease of soil respiration and activity of
cellulase and xylanase enzymes involved in the degradation of the main litter component.
Seasonal fluctuations were evident also for lignin degrading enzymes like peroxidases (not
laccases) in the studied litter, in agreement with the view that the overall microbial
community was affected. The overall laccase activity, that did not show significant seasonal
changes, was, however, dependent on multiple isoenzymes differently expressed along the
year.
Litter quality affected decomposition. Two phase of litter decay were generally
recognized in litter of tree species: the former in the first year occurred at high rate and the
latter, subsequently, at low rate. However, It was true for tree leaf litter but not for shrub litter
(
Myrtus
and
Cistus)
for which
the decomposition rate was higher in the second phase than the
first one. The plant habitus in the stand near the sea may account of significant changes of the
microclimatic conditions (temperature and moisture of the litter) under the shrubs.
The effect of nutrient on decomposition rate was in line with that reported for temperate
areas even if the influence of climatic conditions makes less evident the correlation. So
nitrogen content was positively related to the rate of the first phase of decomposition, while
initial lignin content was not positively related to the rate of second phase.
Most of the litter degraded lignin in the early stage of decomposition and appeared
negatively related the initial nitrogen content differently from what found in other areas.
