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This paper studies the effect of large- and small-scale changes of soil temperature and humidity on soil microbial biomass C and N, ergosterol, carbon utilization potential, organic and inorganic N and rate of C and N mineralization at 25°C. Large-scale variations are identified with seasonal changes in temperature and humidity. To simulate small-scale changes, soil temperature and humidity were manipulated in the field. The treatment resulted in damping of temperature fluctuations and a decrease of soil humidity.The majority of the studied variables exhibit pronounced seasonality, showing a clear-cut distinction between summer (July–August) and winter (December). In summer, C mineralization rate and carbon utilization potential was high but microbial and fungal biomass (ergosterol) was low.C and N mineralization rate and microbial and fungal biomass were only affected by sampling date, demonstrating that gross parameters of biomass and activity of microorganisms are not affected by small-scale changes in temperature and humidity. In contrast, variables relating to N availability (organic N, NH4+ and NO3-, microbial biomass N) and carbon utilization potential of the microbial community were highly affected by small-scale changes in soil abiotic conditions. The results suggest that changes in N dynamics induced by small-scale changes of temperature and humidity are caused by shifts in the structure of the microbial community rather than by variations in microbial biomass. [Copyright &y& Elsevier]