Urease Activity in a Black Spruce Humus Sterilized by Gamma Radiation
1968
Roberge, M. R. | Knowles, R.
The activity of urease was studied in a black spruce (Picea mariana (Mill.) BSP.) surface organic horizon from Baie-Comeau, Quebec. Samples were sterilized by ⁶⁰Co radiation, incubated with urea for 8 hours at 20C and analyzed for ammonia. Urease activity decreased with an increase in humus decomposition. Field fertilization with 450 kg urea-N/ha 2 years prior to humus sampling increased the urease activity by 40%. Laboratory preincubation of field-fertilized and unfertilized humus with 3,500 ppm of urea-N resulted in increased urease activity of 90%. Enzyme assays performed with 21,000 and 63,000 ppm of urea-N gave similar relative activities to those performed with 3,500 ppm. Some mineralization of N occurred during and following irradiation in the absence of any added substrate. A direct relationship was found between enzyme activity and total and ureolytic numbers of microorganisms.
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