Microbial activities in forest floor layers under silver birch, Norway spruce and Scots pine

The aim of this study was to compare microbial activities in the litter (L), fermentation (F) and humified (H) layers of the forest floor under silver birch (Betula pendula Roth), Norway spruce (Picea abies (L.) Karst) and Scots pine (Pinus sylvestris L.). Soil pH, C-to-N ratio, respiration rates, concentration of NH4-N, net N mineralization and nitrification rates, gross NH4+ production and consumption rates and amounts of C (Cmic) and N (Nmic) in the microbial biomass were determined from samples taken from the L, F and H layers under silver birch, Norway spruce and Scots pine. The forest floors under birch and spruce were more active than that under pine, having higher respiration and net N mineralization rates, and higher Cmic and Nmic values than pine forest floor. Differences between tree species were smaller in the H layer than in the L and F layers. The L layer had the highest rates of respiration for all tree species, while rates of net N mineralization were highest in the F layer for birch and spruce. Pine showed negligible net N mineralization in all layers. Concentration of NH4-N was the best predictor of rate of net N mineralization (r=0.748r=0.748). In general, Cmic and Nmic were higher in the L and F layers than in the H layer, as were their relative proportions of total C (Ctot) and N (Ntot), respectively. Cmic correlated positively with soil respiration (r=0.980r=0.980) and Nmic with concentration of NH4-N (r=0.915r=0.915).