ADENOSINE 5'-TRIPHOSPHATE MEASUREMENTS IN SOILS CONTAINING RECENTLY ADDED GLUCOSE

A transient ATPase was produced when a grassland soil was incubated wi th glucose (5000 mu g glucose C g(-1) soil) and inorganic N. The activ ity 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 an d N. This ATPase was surprisingly resistant to denaturation in the tri chloracetic acid-based reagent we use to extract ATP from soil, althou gh it had almost completely disappeared 30 s into extraction. In deter mining ATP in soil with the TCA-based extractant, a spike of ATP is ad ded to correct for losses of ATP during extraction. These losses can b e by hydrolysis (enzymatic or chemical) during extraction, by adsorpti on 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 mo re 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 e xtraction of ATP from the soil microbial biomass did not appear to be influenced by the ATPase, presumably because this ATP was released dur ing extraction and was therefore not all present at the start, unlike spike ATP. Most measurements of soil ATP using TCA-based extractants w ill not be influenced by this ATPase because it is only active in soil s 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. Cop yright (C) 1996 Elsevier Science Ltd