CAREX LITTER DECOMPOSITION AND NUTRIENT RELEASE IN MIRES WITH DIFFERENT WATER CHEMISTRY

Losses of dry weight, nitrogen, phosphorus and potassium from shoot litter of Carex diandra Schrank and Carex acutiformis Ehrh. were studied in a 2-year litter bag experiment in two fens, each dominated by one of these species. Weight losses over time showed negative exponential curves during Year 1, with k values of 0.0018 and 0.0009 day-1 for Carex diandra and Carex acutiformis, respectively. Total weight loss during Year 1 equalled that during Year 2, and amounted to 45% and 27% of the initial weight for Carex diandra and Carex acutiformis, respectively. Total nitrogen in the litter bags remained approximately constant throughout the 2-year-period for Carex acutiformis, whereas it remained constant during Year 1 and then dropped to 23% of the initial value during Year 2 for Carex diandra. Total phosphorus showed a similar pattern: no changes for Carex acutiformis, and a substantial decrease to 15% of the initial value during Year 2 for Carex diandra. A study of cotton strip tensile strength loss showed that conditions for cellulose decay are much more suitable in the groundwater fed (base-rich) fen dominated by Carex diandra than in the rain-water fed (base-poor) fen with Carex acutiformis, which is in accordance with the results of the litter bag study. The slower nutrient release from Carex acutiformis litter does not lead to a lower mineralization rate of soil organic matter in the fen dominated by this species. The high release rates of inorganic nitrogen and phosphorus in this fen are probably because of the presence of Sphagnum-derived organic matter.