An experimental approach was attempted for determining the maintenance carbon requirements of the dormant microbial biomass of two agricultural soils (I, II) and one.forest soil (III). The amount of carbon needed for preventing microbial-C loss during incubation expressed as coefficient rn (mg glucose-C-mg 1 biomass-C.h l) was 0.00031, 0.00017 and 0.00017 h -~ at 28Β°C and 0.000043, 0.000034 and 0.000016 h 1 at 15Β°C for soils I, II and III, respectively. Depending on the temperature, the determined m values of the dormant population were two to three orders of magnitude below known values from pure cultures or m values of metabolically activated biomasses under in situ conditions. Corresponding microbial-C loss quotients were comparable to the observed maintenance coefficients but were always above m.
The metabolic quotient q for CO2 (mg CO2-C.mg 1 biomass-C.h l) of the dormant populations in the three soils tested was at q = 0.0018 h -1 (22Β°C) one order of magnitude below metabolically activated cells but did not correspond to the low maintenance values determined, which implies that in addition to possible utilization of native soil organic matter dormant biomasses must largely have an endogenously derived respiratory activity.