Decomposition of Cistus incanus leaf litter in a Mediterranean maquis ecosystem: mass loss, microbial enzyme activities and nutrient changes

The decomposition of leaf litter from the summer deciduous shrub, Cistus incanus, in a low Mediterranean maquis was followed for 18 months. Microbial activity in the decaying materials was evaluated by measuring respiration, as well as cellulase, xylanase, α- and β-amylase activities. Fungal biomass, pH, water soluble substances and nutrient content (N, S, P, Ca, K, Na, Mg, Mn) were also measured. Litter incubated in the field in autumn and in spring evidenced similar decay constants (ka=0.36±0.02 yr−1 and ks=0.32±0.03 yr−1, respectively). Mass loss rate was not affected by the dry summer. Microbial activity showed seasonal changes, with the highest values (150 μmol CO2 g−1 d.w. d−1) in autumn and winter and the lowest ones in summer (30 μmol CO2 g−1 d.w. d−1) when the litter water content was around 10% d.w.). Litter water content was strongly correlated to microbial respiration, cellulase and xylanase activities. The α-amylase and, to a lesser extent, β-amylase activities occurred at the highest level (0.78 and 0.35 μmol glucose g−1 d.w. h−1, respectively) during the initial stages of decomposition, when residual starch was still present in the litter, but rapidly declined. Total fungal biomass was significantly and positively correlated with mass loss throughout the experiment. Water soluble substances decreased in the first 4 months of decomposition and increased thereafter. The elements N, S, K, P, Ca, Na decreased, while Mg and Mn increased.