Results
Within the six weeks of the decomposition experiment, the EM fungal
species lost on average 53.7% of the necromass, ranging from a minimum
of 30.6% (L. deliciosus ) to a maximum of 68.1% (S.
verrucosum ). The differences in decomposition were highly significant
both between species and between weeks, but there was no significant
effect of their interaction (Species: F value= 6.55, p
value<0.001; Week: F value= 60.08, p value< 0.001;
Species*Week: F value= 1.29, p value= 0.22). This is visible from the
similar trends in mass loss, with an average loss of around 38% of the
initial mass during the first week, followed by a slower degradation
during the last five weeks (Figure 1). L. deliciosus was the only
species which decomposition was significantly lower than the others.
The six species showed different initial concentrations of glucans in
their necromass, where L. bicolor , L. deliciosus andP. involutus had significantly higher concentrations compared toH. hiemale , S. verrucosum and I. rimosa . On the
other hand, melanin and chitin initial concentrations did not show any
significant difference among species (Figure 2).
After six weeks,
concentrations
of glucans and melanin did not differ between species, while chitin
concentration of H. hiemale was higher than in the rest of the
species, suggesting that the loss of glucans and chitin differed among
species (Figure 3). The analysis of covariance (Table 1) confirmed this
supposition and provided more detailed insights. The dynamics of
compounds loss differed among fungal species: glucans concentration
increased over time in I. rimosa and L. bicolor , while it
decreased for the other species (Figure 3. B); chitin concentration
tended to increase over time in every species besides P.
involutus (Figure 3. C).
The initial concentrations of the secondary compounds within fungal
species biomass was not a good predictor of decomposition (melanin:
R2= 0.015, p= 0.281; chitin: R2=
0.007, p=0.542; glucans: R2=0.003, p= 0.32) and
therefore could not explain the difference in decomposition betweenL. deliciosus and the other species. However, the change in
concentrations of cell-wall compounds during the decomposition process
was related to biomass loss. Specifically, the chitin concentration in
the necromass was negatively related to the weekly mass loss (F
value=6.34, df=53, P value=0.0149, Figure 4), while for melanin and
glucans this was not the case (melanin: F value=0.398, df=52, P
value=0.531; glucans: F value=2.75, df=42, P value=0.104)
Interestingly, we found that the relationship between chitin
concentration in the samples and the weekly mass loss changed over time
(Figure 4): in the first week, the effect of chitin concentration on
weekly mass loss was positive, while for the rest of the decomposition
period it was negative.