Land use-induced changes in activity and biomass of microorganisms in raised bog peats at different depths

We examined peat from six raised bogs (0–60 cm depth) in northern Lower Saxony, developed from similar Sphagnum species under similar climatic conditions, but differing widely in the actual vegetation and intensity of land use for activity and biomass of soil microorganisms. Two sites were virtually undisturbed, two sites had been converted to grassland and two to woodland. Biomass and activity of soil microorganisms were characterized by the CO 2 production rate, substrate-induced respiration (SIR) for biomass C and fumigation-extraction for biomass C and biomass P (FE). Activity and biomass of microorganisms were much greater in the oxic horizons (litter layer, root-felt, earthic peat) than in the anoxic bottom horizons (intermittent and wet peat), and these microbial indices increased also under grassland use compared to fallow and woodland. Biomass C FE exceeded biomass C SIR, although both indices were closely correlated ( r=0.84). In the oxic horizons, the ratio of biomass P-to-total P was on average 32%, indicating the importance of microorganisms for the turnover of P in organic soils with very low concentrations of total P.