LEVELS OF ACTIVITIES OF SOME CARBOHYDRASES, PROTEASE, LIPASE, AND PHOSPHATASE IN ORGANIC SOILS OF DIFFERING COPPER CONTENT

Abstract

Representative pairs of muck and peat (sapric and hemic Histosol) samples were collected from a mildly cupriferous virgin bog under a normal mixed forest flora near Sackville, New Brunswick, Canada. Samples within each pair were similar in their physical and chemical properties except for their copper contents, in which they have varied widely for a long time. In agreement with the evidence of the mitigating effect of copper on decomposition, already in the literature, a muck (sapric) sample containing 2922 parts per million of total copper lost carbon through aerobic soil respiration at half the rate of a muck sample containing 1159 ppm Cu. Similarly the soil respiration rate of the peat (hemic) sample containing 797 ppm Cu was half that of the peat sample with 408 ppm Cu. Within each pair of samples, which were air-dried following a 6-week incubation, C1-cellulase, Cx-cellulase, cellobiase, xylanase, chitinase, lichenase, inulase, pectinase, amylase, invertase, lactase, maltase, lipase, protease, and acid phosphatase enzyme activities were all found to be lower in samples containing higher Cu. Enzyme activities were decreased on an average by 79 ± 10.5 percent and 66.2 ± 7.1 percent, apparently due to the natural increments of the Cu contents of the muck and peat samples, respectively. Assays of invertase, amylase, phosphatase, and protease activities in moist soil samples incubated at 21°C for 368 days indicated that, as expected, the mitigating effect of Cu on degradative activities of the enzymes functioned in microbially active soils also. These results thus suggest that the suppressive effect of Cu on levels of accumulated enzyme activities noted earlier in soils that contained increased concentrations of Cu for only a decade or two, in fact prevails for a long time and may, therefore, be useful in mitigating the decomposition and therefore the subsidence of some Histosols. It is suggested that, due to the greater abundance of substrates in organic soils, accumulated degradative soil enzymes normally play a more important role there than in mineral soils and, therefore, contribute to the decomposition and subsidence of some Histosols.