Litter Decomposition Rates in a Post-mined Peatland: Determining Factors Studied in Litterbag Experiments

The litter decomposition process is one of the keys to restoring wetlands after peat mining, because litter decomposition largely determines peat regeneration. We monitored the process on a post-mined peatland in northern Japan from 2020 to 2021 with litter species and the environments (surface temperature, shade and moisture). Litterbag experiments were conducted by two litter species, Moliniopsis japonica and Sphagnum papillosum because the succession was replaced from M. japonica grassland (MJ) to Sphagnum mat (SP). Three environments were developed: unshaded control, black shear net and white net. %C, %N, δ¹³C and δ¹⁵N in the litter were measured with litter mass remaining. Black nets showed lower mean temperatures with smaller variations than white nets. SP showed lower water level and peat moisture than MJ. Litter decomposition was faster in the black nets than in the white nets. These results indicated that litter decomposition was regulated by temperature fluctuation and its related factors, rather than mean temperature. Sphagnum showed a home-field advantage in decomposition, whereas M. japonica did not. δ¹³C and δ¹⁵N were lower and higher in Sphagnum litter than in M. japonica litter, respectively, showing that N and C components differed between litter species. The high δ¹⁵N in Sphagnum litter indicated that intracellular N₂ fixers contributed to N in the litter. In conclusion, litter decomposition was not faster at higher temperatures and was determined primarily by litter species.