Organic matter dynamics were investigated in the surface peat layer (acrotelm) in study sites traversing three raised ombrotrophic peat deposits, containing up to 3, 6 and 12 m, respectively, of peat located on the east coast of Sumatra, Indonesia. The three deposits were uniform in climate, topography, surficial geology and were under continuous forest cover. Increased peat depth and distance from the edge of the deposit was associated with important changes in species composition, structure

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... d morphology. To account for the differences in peat depth, I hypothesized that the relative importance of: 1) peat age, 2) organic matter decomposition and 3) litter additions, in controlling peat accumulation varies among the three deposits. Age differences, using 1 4C dating, did not account for variable peat accumulation. Peat at the clay-peat interface was approximately 4000 to 4500 years old in each study site, while acrotelm peat ranged from 45 to 660 years old. The relatively recent age of the acrotelm layer suggested that peat accumulation in the study sites was either at steady state or expanding. Older peat in this layer would have indicated surface degradation of the raised peat deposits. Small roots and root fragments in the acrotelm of the deep peat deposit were considerably younger than the matrix of amorphous peat. Samples of acrotelm peat were incubated under aerobic conditions for 30-day periods in glass jars. There were no significant differences in peat respiration rates between samples at different moisture levels. Significantly higher respiration rates, however, were measured in acrotelm peat from the 12 m deposit compared with the same layer in the 9 and 6 m sites in the same deposit and in the sites on the 3 and 6 m deposits. Buried cotton strips disappeared at the same rate at all study sites. However, the disappearance of leaf litter from mesh bags was most rapid in the 3 m site and slowest in the 12 m site. Decay rates were mainly controlled by varying organic matter quality du [...]