Temperature changes and the ATP concentration of the soil microbial biomass

Two soils from temperate sites (UK; arable and grassland) were incubated aerobically at 0, 5, 15 or 25 degrees C for up to 23 days. During this period both soils were analysed for soil microbial biomass carbon (biomass C) and adenosine 5' triphosphate contents (ATP). Biomass C did not change significantly in either soil at any temperature throughout, except during days 0 to 1 in the grassland soil. Soil ATP contents increased slowly throughout the 23 days of incubation, from 2.2 to a maximum of 3.1 nmol ATP g-1 soil in the arable soil (a 40% increase) and from 6.2 to a maximum of 11.2 nmol ATP g-1 soil in the grassland soil (an increase of 81%), both at 25 degrees C. Since biomass C did not change either with increasing temperature or increasing time of incubation, it was concluded that an increase in ATP was either due to an increase in adenylate energy charge or de novo synthesis of ATP, or both. During the incubation, biomass ATP concentrations ranged from about 5 to 12 micromol ATP g-1 biomass C but trends between biomass ATP and incubation temperatures were not very obvious until about day 13. On day 23, biomass ATP concentrations were positively and linearly related to temperature: (micromol ATP g-1 biomass C = 6.98 +/- 0.35 + 0.134 +/- 0.023 T0 (r2 = 0.77) with no significant difference in the slope between the grassland and arable soils. At 25 degrees C the biomass ATP concentration was 10.3 micromol g-1 biomass C, remarkably close to many other published values. It was concluded that, although the biomass increased its ATP concentration in response to increasing temperature, the increase was comparatively small. Also, at all temperatures tested, the biomass maintained its ATP concentration within the range commonly reported for micro-organisms growing expontentially in vitro. This is despite the fact that the biomass normally exhibits other features more typical of a "resting" or dormant population--a paradox which still is not resolved.