SUMMARY(1) 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.(2) 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 Sphagnumdominated bogs than in phanerogam-dominated fens.(3) Nand P mineralization were significantly faster in bogs with a Sphagnum cover than in phanerogam-dominated fens, and faster at 10 than at 25 cm.(4) 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.(5) The inverse relation between Nand 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 Nand P is immobilized in microbial tissues.(6) 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.
Abstract. A fertilization experiment was carried out in 3 mesotrophic fens to investigate whether plant growth in these systems is controlled by the availability of N, P or K. The fens are located in an area with high N inputs from precipitation. They are annually mown in the summer to prevent succession to woodland. Above-ground plant biomass increased significantly upon N fertilization in the two 'mid'-succession fens studied. In the 'late'-succession fen that had been mown for at least 60 years, however, plant biomass increased significantly upon P fertilization. The mowing regime depletes the P pool in the soil, while it keeps N inputs and outputs in balance. A long-term shift occurs from limitation of plant production by N toward limitation by P. Hence, mowing is a suitable management tool to conserve the mesothrophic character of the fens.
An experiment was carried out in two heathland ecosystems, one dominated by Calluna vulgaris and the other by Molinia caerulea, to analyse the effects of soil organic matter accumulation and nutrient mineralization on plant species dynamics during succession. The experiment included one treatment that received nutrient solution and two treatments where the rate of soil organic matter accumulation was reduced by removing litter or accelerated by adding litter. In a fourth treatment the C. vulgaris litter produced in the C. vulgaris-dominated plots was replaced by litter of M. caerulea and vice versa. Treatments were applied over 8 years. Addition of nutrient solution caused C. vulgaris to decline, and grass species to increase sharply, compared to the control plots. Addition of litter enhanced both N mineralization and the biomass of M. caerulea and Deschampsia flexuosa but reduced the biomass of C. vulgaris. The effects of replacing C. vulgaris litter by M. caerulea litter, or vice versa, on N mineralization and species dynamics could not be attributed to differences between the decomposability of the different litter materials that were transferred. The results confirm the hypothesis that increased litter inputs accelerate the rate of species replacement during succession.
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