Influence of forest floor type on rates of litter decomposition in microcosms

Rates of mass loss of leaf litter of paper birch were measured during a 70 wk laboratory incubation in microcosms containing forest floor material from red alder (C-to-N ratio = 27), Douglas fir (C-to-N, 32), and lodgepole pine (C-to-N, 59) forests. Mass loss from leaf litter was fastest in alder forest floors and slowest in pine, and so was related to the C-to-N ratio of the forest floors. The decomposition rate was related to the amount of KCl-extractable NH4+N and NO3−N in each microcosm, but not to the concentrations of extractable N (mg g−1), which were greater in Douglas fir forest floors than in alder for most of the incubation. There were larger amounts of faecal material from soil fauna in the litter incubated in the alder forest floors, indicating greater faunal activity in these floors. The relationship between rates of decomposition and N concentrations may be due to the influence of soil fauna activity on both factors, rather than to a direct influence of N availability on rates of litter decomposition.