SPECIES AND SITE DIFFERENCES IN THE DECOMPOSITION OF LITTERS AND ROOTS FROM WET HEATHLANDS

The decomposition of litter and roots from a site dominated by Erica t etralix and a site dominated by Molinia caerulea was measured using me sh bags. Leaf litter and roots of each species were incubated on both sites. The experiments lasted up to 3 years. The weighted decompositio n constant was 0.23 per year for Molinia litter, and 0. 10 per year fo r Erica litter; the decomposition constants for roots were 0.29 per ye ar for Molinia but only 0.03 per year for Erica. The decomposition rat es of leaf litters and roots were similar on both sites, and the chemi cal composition of the materials determined the decomposition rate. Li tters and roots with high lignin concentrations decomposed slowly. Dur ing the experiments, most materials showed a net retention of N and P. Large net N releases were measured only for Molinia roots and basal i nternodes, and a large net P release was measured only for Molinia roo ts. It was concluded that the rate of accumulation of soil organic mat ter per gram of plant debris is slower on die site dominated by Molini a than on the site dominated by Erica. In the long term, N and P are p robably released faster from Molinia than from Erica plant debris.