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 Sax ony, developed from similar Sphagnum species under similar climatic conditi ons, but differing widely in the actual vegetation and intensity of land us e 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 CO2 production rate, substrate-induced respiration (SIR) for biomass C and fum igation-extraction for biomass C and biomass P (FE). Activity and biomass o f microorganisms were much greater in the oxic horizons (litter layer, root -felt, earthic peat) than in the anoxic bottom horizons (intermittent and w et peat), and these microbial indices increased also under grassland use co mpared to fallow and woodland. Biomass C-FE exceeded biomass C-SIR, althoug h both indices were closely correlated (r = 0.84). In the oxic horizons, th e ratio of biomass P-to-total P was on average 32%, indicating the importan ce of microorganisms for the turnover of P in organic soils with very low c oncentrations of total P. (C) 1999 Elsevier Science Ltd. All rights reserve d.