Temperature changes and the ATP concentration of the soil microbial biomass

Two soils from temperate sites (UK; arable and grassland) were incubated ae robically 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 signifi cantly in either soil at any temperature throughout, except during days 0 t o 1 in the grassland soil. Soil ATP contents increased slowly throughout th e 23 days of incubation, from 2.2 to a maximum of 3.1 nmol ATP g(-1) soil i n the arable soil (a 40% increase) and from 6.2 to a maximum of 11.2 nmol A TP g(-1) soil in the grassland soil tan increase of 81%), both at 25 degree s C. Since biomass C did not change either with increasing temperature or i ncreasing 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 o f ATP, or both. During the incubation, biomass ATP concentrations ranged fr om about 5 to 12 mu mol ATP g(-1) biomass C but trends between biomass ATP and incubation temperatures were not very obvious until about day 13. On da y 23, biomass ATP concentrations were positively and linearly related to te mperature: (mu mol ATP g(-1) biomass C = 6.98 +/- 0.35 + 0.134 +/- 0.023 T- 0 (r(2) = 0.77) with no significant difference in the slope between the gra ssland and arable soils. At 25 degrees C the biomass ATP concentration was 10.3 mu mol g(-1) biomass C, remarkably close to many other published value s. It was concluded that, although the biomass increased its ATP concentrat ion in response to increasing temperature, the increase was comparatively s mall. Also, at all temperatures tested, the biomass maintained its ATP conc entration within the range commonly reported for micro-organisms growing ex pontentially in vitro. This is despite the fact that the biomass normally e xhibits other features more typical of a "resting" or dormant population - a paradox which still is not resolved. (C) 2000 Elsevier Science Ltd. All r ights reserved.