| Abstract: | The activity and biomass of soil microorganisms were determined in samples at 0—140 cm depth taken from an arable site, where the soil has been developed by erosion and colluvial deposition overlaying a black earth at 70—110 cm depth. The central aim was to get an insight into the breakdown of increasingly old and thus recalcitrant soil organic matter down the profile, effects on the availability of C to microorganisms and the microbial community structure. From 0 to 140 cm depth, microbial biomass C decreased by 96%, biomass N by 97%, the adenylates ATP, ADP, and AMP as well as the basal respiration rate by 89%. No ergosterol was measured at 120—140 cm depth. All soil biological properties decreased in distinct steps after 30 cm and 50 cm depth. At 30—90 cm depth, the amounts of soil organic C and microbial biomass C per hectare of the present colluvium exceeded nearly three‐fold those in undisturbed aeolian loess sediments. The cation exchange significantly affected the relationships between microbial biomass C, biomass N, and the adenylates. As a consequence, none of the ratios between the soil microbial biomass properties revealed constant gradients throughout the profile. The adenylate energy charge (AEC) varied between the different soil layers insignificantly around a mean of 0.71. It was the most stable ratio down the profile showing absolutely no depth gradient, the lowest depth‐to‐depth variation, and also the lowest within depth variability. The other ratios between soil organic C, basal respiration, ergosterol, microbial biomass C and biomass N also did not reveal any marked changes in the microbial community structure. |
