Depth gradients of microbial and chemical properties in moder soils under beech and spruce

lIn five moder profiles under beech (Fagus sylvatica) and spruce (Picea abi es) in the Selling, Lower Saxony, respiration and four microbial biomass in dices were measured and related to pH and organic matter quality. In the L1 , L2 and F1 horizons of the beech sites, K2SO4 extractable C, respiration r ate, microbial biomass C by substrate-induced respiration (SIR) and by fumi gation-extraction (FE), biomass N and ergosterol markedly exceeded the corr esponding values of the spruce sites. In the H and A horizons, the differen ces between the sites were small. Kendall correlation coefficients by ranks between microbial properties and K2SO4 extractable C exceeded those betwee n microbial and the other soil properties. The biomass C/N ratio was on ave rage 9.9 and did not vary consistently between sites and horizons. Neither did the average biomass C-SIR/C-FE ratio vary between sites, but declined s trongly with soil depth from 1.4 in the L horizons, to 1.0 in the F horizon s, and to 0.4 in the H and A horizons. These horizon-specific differences b etween the biomass C estimates of SIR and FE are discussed and attributed t o changes in the fungal community structure. Ergosterol to biomass C ratios were generally high, indicating fungal dominance of decomposing microorgan isms. The horizon-specific ratio was at a maximum in the F (2.8 %, biomass C-FE) or in the H horizon (4.2 %, biomass C-SIR).