Nitrogen and Phosphorus Mineralization in Fens and Bogs

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Abstract
The release of inorganic nitrogen and phosphorus in ten mires in The Netherlands with different vegetation and hydrology was measured by incubating soil in situ in polyethylene bottles at depths of 10 and 25 cm. At the same time, cellulose decomposition was estimated by means of tensile strength loss of in-situ cotton strips. The size of the inorganic N pool was not related to depth, mire type or the presence of a Sphagnum cover. The labile inorganic P pool was significantly larger in Sphagnum-dominated bogs than in phanerogam-dominated fens. N and P mineralization were significantly faster in bogs with a Sphagnum cover than in phanerogam-dominated fens, and faster at 10 than at 25 cm. Cellulose decomposition rates were significantly higher in phanerogam-dominated fens than in Sphagnum-dominated bogs. The depth patterns of the decomposition rates also showed a difference between these mire types: in fens, the rates were relatively low at the surface but increased to a sustained higher value at 10 cm and below; in bogs, the rates were highest at the surface but decreased steeply to very low values. The inverse relation between N and P mineralization and decomposition is probably due to the chemical properties of Sphagnum litter predominant in bogs. The N- and P-rich protoplasm breaks down and releases nutrients quickly, whereas the bulk of cell walls is decomposed so slowly that not much N and P is immobilized in microbial tissues. Comparison of N mineralization measured in Dutch bogs with values from other regions found in the literature revealed no indications of an enhanced rate under the conditions of high atmospheric N deposition prevailing in The Netherlands.