Litter decomposition of Scirpus maritimus L. in a Mediterranean coastal marsh: Importance of the meiofauna during the initial phases of detached leaves decomposition

Growth, senescence and decomposition rates of Scirpus maritimus were studied in a Mediterranean brackish wetland. Plant tussocks were tagged in March, 2002 and were totally dead by September, 2002. Decomposition rates were determined over 360 days using litter bag technique and mass loss, nutrient dynamics fungal biomass, meiofauna and macroorganisms were determined. Decomposition rate of detached S. maritimus litter was 0.00196 (k, day(-1)) with a 54% of mass lost observed in 1 year. The pattern of mass loss was characterized by an initial phase of fast loss of organic matter with high density of meiofauna and a decrease of oxygen content, followed by two slower phases, with no significant losses from 50 to 180 days and with 21% of mass lost from 180 to 360 days. Nitrogen (N) and phosphorus (P) content of plant litter increased during decomposition process whereas atomic C:N and C: P ratios decreased suggesting a nutrient immobilization on plant detritus. Fungal biomass measured as ergosterol content decreased after submersion of leaves, indicating that their importance in litter decomoposition decreases in submerged leaves during the first days of decomposition. An inverse relationship (r=-0.79, P < 0.005) was observed between ergosterol content and nematodes density on S. maritimus litter. Our results suggest that in Mediterranean brackish marshes, where large amounts of dead organic matter is accumulated over the sediment surface, decomposition process is greatly affected by extremely high temperatures in summer that, if water is available, accelerates microbial activity decreasing oxygen content thus slowing decomposition.