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 c arried out to determine the distribution of assimilated C in the system Phr agmites australis (common reed)-waterlogged fen soil after C-14 pulse label ling. The investigated system of fen plants and anaerobic organic soil show ed different patterns of assimilated C-14 distribution when compared to sys tems with cultivated plants and aerobic mineral soil. Between 90% and 95% o f the C-14 in the system was found in the reed plants. A maximum of 2% of t he 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 minera l soil, despite lower C-14-release (i.e. rhizodeposition and root respirati on) from reed roots. Assuming that root respiration of fen plants is low, t his indicates that microbial C turnover in waterlogged fen soil is much slo wer than in mineral soil. The estimated quantity of the assimilated C remai ning in the soil was of an ecologically relevant order of magnitude.