Behavior of urease added to unsterilized, steam-sterilized, and gamma radiation-sterilized black spruce humus

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Abstract
Because of the widespread use of urea fertilizer, it became evident that an assessment of urease addition on natural ureolysis was pertinent. Samples of each layer of the surface organic horizon of a black spruce (Picea mariana Mill.) stand at Baie-Comeau, Quebec, were treated with urease then tested for ureolysis activity. Added urease was active in all samples; the increase of activity was affected by the type of sterilization treatment used and the layer of the surface organic horizon. Additional ureolysis was greatest in unsterilized samples, less in radiation-sterilized samples, least in steam-sterilized samples, and decreased with depth of layers. Autoclaving inhibited activity of urease added previously or subsequently while irradiation had a lesser effect. Every layer had an upper limit of urease adsorption and was characterized by a definite capacity to adsorb urease which increased with depth of layers. The pattern of ureolysis observed when urease was added to solutions obtained from layer samples was similar to that observed when urease was added to the layer samples themselves. All solutions inhibited the action of added urease.

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