Root decomposition and soil nutrient and carbon cycling in two temperate fen ecosystems

Although root litter contributes to a large extent to soil organic matter accumulation in peatlands, decomposition of root litter is often neglected in studies on litter decomposition and carbon and nutrient cycling in these ecosystems. In this study, decomposition of root and rhizome litter of Carex diandra and Carex lasiocarpa was determined in two temperate fens, one dominated by Sphagnum species (Sphagnum, fen; soil pH = 4.4) and one without a Sphagnum cover Carex fen: soil pH = 5.7. One-year mass loss increased in the order: roots Carex diandra < roots Carex lasiocarpa < rhizomes Carex lasiocarpa. This ranking was in agreement with the generally established relationships between decomposition rate and litter chemistry, since rhizome litter had the lowest concentration of lignin and the highest nitrogen (N) and phosphorus (P) concentrations. The decomposition constants (k-values) varied from 0.10 to 0.30 yr(-1), which is at the low end of the range found for above-ground litter of Carex species in other studies. Decomposition rates of root litter were lower in the Sphagnum site than in the Carex site, probably as a result of a lower pH and a lower nutrient status in the Sphragnum site. At both sites, N and P content of the litter decreased rapidly in the first three months indicating fast nutrient leaching and mineralization. Nutrient release per unit initial litter mass in the Carex site did not differ from that in the Sphagnum site. Estimated first year losses of N and P from Carex diandra roots in the Carex site were 2.31 g N m(-2) and 0.20 g P m(-2) First-pear nutrient losses From leaf litter of this species, as determined in another study, were only 0.06 g N m(-2) and 0.02 g P m(-2). These results show that roots do indeed play a major role in the cycling of carbon and nutrients in temperate fen ecosystems.