Adenosine 5′-triphosphate measurements in soils containing recently added glucose

A transient ATPase was produced when a grassland soil was incubated with glucose (5000 μg glucose C g−1 soil) and inorganic N. The activity of this enzyme reached a maximum after about 2 days, declining to ambient levels by 10 days. Its formation was strongly repressed by the addition of inorganic phosphate during the incubation with glucose and N. This ATPase was surprisingly resistant to denaturation in the trichloracetic acid-based reagent we use to extract ATP from soil, although it had almost completely disappeared 30 s into extraction. In determining ATP in soil with the TCA-based extractant, a spike of ATP is added to correct for losses of ATP during extraction. These losses can be by hydrolysis (enzymatic or chemical) during extraction, by adsorption on the soil colloids and by quenching during measurement of ATP by the luciferin-luciferase reaction. An ATP spike added at the beginning of the extraction of a soil recently amended with glucose was much more completely broken down than a spike added 30 s into the extraction. Presumably the glucose-induced ATPase was active at the beginning of extraction but almost completely denatured by 30 s. In contrast, the extraction of ATP from the soil microbial biomass did not appear to be influenced by the ATPase, presumably because this ATP was released during extraction and was therefore not all present at the start, unlike spike ATP. Most measurements of soil ATP using TCA-based extractants will not be influenced by this ATPase because it is only active in soils that have recently received substrate. However, even in such soils, valid ATP measurements can be obtained by taking simple precautions — adding the spike after 30 s or cooling the soil before extraction.