Adenosine-triphosphate and microbial biomass in soil

Two methods for measuring adenosine 5'-triphosphate (ATP) in soil were compared, one based on extraction with NaHCO3-CHCl3 and thel other on extraction by a trichloracetic acid-phosphate-paraquat reagent. Recoveries of added ATP were greater with the NaHCO3-CHCl3 reagent but the extraction of “native” soil ATP by NaHCO3-CHCl3 was only about a third of that by TCA-phosphate-paraquat.

Microbial biomass C and ATP were measured in 8 contrasting English soils, using the fumigation method to measure biomass C and the TCA-phosphate-paraquat method to measure ATP. Except in one acid woodland soil, the ratio (ATP content of the soil)/(biomass C content of the soil) was relatively constant, with a mean of 7.3 mg ATP g−1 biomass C for the different soils. This value is very similar to that obtained earlier in a range of 11 grassland and arable soils from Australia. Taking the English and Australian grassland and arable soils together, there is a close (r = 0.975) linear relationship between ATP and microbial biomass C that holds over a wide range of soils and climates. From this relationship, the soil biomass contains 7.25 mg ATP g−1 biomass C, equivalent to an ATP-to-C ratio of 138, or to 6.04 μmoles ATP g−1 dry biomass.

The acid woodland soil (pH 3.9) contained much less biomass C, as measured by the fumigation method, than would have been expected from this relationship. This, and other evidence, suggests that the fumigation method for measuring microbial biomass C breaks down in strongly acid soils.

The ATP content of the biomass did not depend on the P status of the soil, as indicated by NaHCO3-extractable P.