LEAF LITTER DECOMPOSITION DYNAMICS IN MEDITERRANEAN AREA - Soil Ecology Research Developments - page 43

P and K had the highest content in the litter of P. laricio (Table 4) while the lowest ones in
the P. sylvestris (0.23 mg g -1 ; 1.32 mg g -1 , respectively). Among the micronutrients, Mn, Zn
and Cu were high in the P. sylvestris (1026 μg g -1 ; 49μg g -1 ; 5.5 μg g -1 ) while, as said before,
P. pinea litter contained the lowest Mn amount (Table 4). As concern the lignin content, P.
pinea showed the highest value compared to that of P. laricio (Table 4) and P. sylvestris
(37%) ones.
The different litter quality caused different rate and pattern of mass loss (Fioretto et al.,
1998; Virzo De Santo et al., 1993).
In the P. laricio wood, P. pinea showed a delay in the start of decomposition and a low
decomposition rate throughout the whole study period (2.5 y). It resulted in a mass loss of
18% of the initial mass as compared to 33%-34% of P. sylvestris and P. laricio , respectively,
(Table 6) after 2.5 years of incubation, in spite of the highest initial N concentration that
normally stimulate the decomposition rate (Witkamp, 1966). Probably, as suggested by Berg
(1986) the high N content associated to high lignin content determined the synthesis of new
recalcitrant N compounds in the litter that inhibited the decomposition. Moreover, P. pinea
exhibited the lowest Mn initial content and it is probable that this concentration was limiting
for microbial activity. The Mn dynamics in this litter evidenced an increase of absolute
amount during decomposition (Fioretto et al., 2001a). The decay started at the end of the first
year of exposure when the Mn immobilized reached 86 μg g -1 , value probably sufficient to
sustain decomposition, that in the second year had a rate higher than that of the other two
litters (Table 6). By comparing the lignin decay dynamics, it emerges that in P. laricio and P.
pinea only 10% of the initial lignin was degraded during about 2 years of decomposition.
However, in P. sylvestris no lignin was degraded in the same period (data not shown).

Table 6. Decay constant ( K ) of needle litter of P. laricio ,
P. pinea , P. sylvestris calculated by the formula X / X 0 = e -kt
(X = mass remaining at time t, X 0 = initial mass) (Olson, 1963)

First year
( K y -1 )

Second year
( K y -1 )

Total period (2 y)
( K y -1 )

P. laricio 0.18 0.22 0.17

P. pinea 0.004 0.26 0.08

P. sylvestirs 0.21 0.22 0.16

In the P. pinea stand, the native needle litter, had in the early stage of decomposition a
mass-loss dynamics similar to those of P. laricio and P. sylvestris litters (Virzo De Santo et
al., 1993), suggesting that the initial low Mn content did not influence negatively the
decomposition rate in the native stand probably because of microflora specialized to work at
low Mn level or of a translocation of the element from soil.

E NVIRONMENTAL E FFECT ON D ECOMPOSITION R ATE

The influence of environment on decomposition rate and pattern was tested incubating a
same litter type in different woods.