Nutrient and carbon dynamics in peat from rich fens and Sphagnum-fens during different gradations of drought

Our results show that under anaerobic, waterlogged conditions, net N-mineralization rates per mass dry peat soil and per microbial C mass were much higher (on average 10 times) in the Sphagnum-peat than in peat from rich fens, probably caused by higher microbial N-demand and N-immobilization in rich fens. The response upon aeration differed greatly between rich fen peat and Sphagnum-peat. Whereas aeration led to increased carbon loss and net N-mineralization rates in the rich fen peat, these rates did not change for Sphagnum-peat. The absence of aeration effects in Sphagnum-dominated fens suggests that decomposition rates are more strongly determined by litter quality than by oxygen intrusion. Upon further desiccation, both net P-release and DOC production, which remained unchanged upon aeration, increased significantly in both fen types. This may be due to microbial mortality and/or a change in microbial composition. The low anaerobic net N-mineralization rates and the strong response to aeration in rich fens compared to Sphagnum-fens, as well as the strong increase in P-availability upon further desiccation in both fen types, have important implications for peatland management in relation to drought.