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Effects of soil type and microclimate on winter decomposition of maize (Zea mays L) leaf litter and microbial carbon use efficiency (CUE) were investigated, using a reciprocal soil transplantation experiment. The clay site DEP is located at an elevated plateau on limestone, the silt site NEB at a broad valley on loess. At DEP, the mean soil temperature was 0.4 degrees C higher than at NEB. Mean CO2 efflux was 62.8 g C m(-2) 130 d(-1) at NEB, more than 4 times higher than that of 15.1 g C m(-2) 130 d(-1) at DEP. At both sites, no differences in CO2 efflux were observed between soil type and maize leaf litter treatments. The alkaline clay and the calcareous bedrock at DEP apparently trapped all CO2 evolved below 4 cm depth. Microbial biomass C (MBC) content was about 50% lower in the silt than in the clay at 0-4 cm depth. The ergosterol to MBC ratio was 13% higher in the clay than in the silt. Maize leaf litter application increased MBC as well as the MB-C/N ratio from 7.9 to 9.7 but decreased the ergosterol to MBC ratio by 9%. Total recovery of maize leaf litter C was 65%, i.e. the sum of MBC (10%), microbial residue C (32%) and particulate organic matter C (23%), while the remaining 35% must have been lost as CO2. From these data, a CUE of 0.55 was calculated for maize leaf litter in the field, which was not affected by soil type and site conditions.