Distribution of assimilated carbon in the system Phragmites australis-waterlogged peat soil after carbon-14 pulse labelling

Short-term (3-6 days) and long-term (27 days) laboratory experiments were carried out to determine the distribution of assimilated C in the system Phragmites australis (common reed)-waterlogged fen soil after C-14 pulse labelling. The investigated system of fen plants and anaerobic organic soil showed different patterns of assimilated C-14 distribution when compared to systems with cultivated plants and aerobic mineral soil. Between 90% and 95% of the C-14 in the system was found in the reed plants. A maximum of 2% of the assimilated plant C-14 was released from the fen soil as CO2 and about 5-9% remained in the soil. The C-14 remaining in the waterlogged fen soil of the reed plant had the same amount as that of a cultivated plant in mineral soil, despite lower C-14-release (i.e. rhizodeposition and root respiration) from reed roots. Assuming that root respiration of fen plants is low, this indicates that microbial C turnover in waterlogged fen soil is much slower than in mineral soil. The estimated quantity of the assimilated C remaining in the soil was of an ecologically relevant order of magnitude.