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.