Some factors influencing the estimation of dehydrogenase activities of some soils under pasture

Abstract

The influence of some experimental variables on the estimation of dehydrogenase activities of four topsoils was determined by measuring the triphenylformazan (formazan) they produced by reduction of triphenyltetrazolium chloride (TTC) under various assay conditions. Formazan formation was significantly greater in systems incubated anaerobically than in systems incubated without complete anaerobiosis. Rates of formation of formazan declined in most assay systems after incubation for a few hours. More formazan was formed in systems containing 0.5m HEPES, TES, or Tris buffers at initial pH 7.6 than in systems containing calcium carbonate or water without adjustment of pH. A satisfactory assay procedure for these strongly acid to nearly neutral topsoils is described. Preliminary experiments may be desirable to determine initial pH values of buffer and TTC concentrations for optimal formazan formation by other soils. Some factors possibly limiting levels of dehydrogenase activity were also studied. Amounts of reducing sugars produced by incubating soil in buffered systems were compared with amounts of formazan formed in similar buffered systems. The addition of glucose, NAD or NADP to assay systems increased the amounts of formazan formed by some samples of soil and the addition of glucose-6-phosphate increased the formazan formed by all samples. However, the addition of glucose and NAD together did not prevent a decline in rates of formazan formation on prolonged incubation.