Microbial Ecology in Tea Soils : II. Soil Protease Activity

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We determined the protease activity to analyze the mechanism of organic nitrogen decomposition (protein degradation) in tea soils. The hydrolyzing activities of N-benzoyl L-arginine amide (BAA), N-benzyloxyearbonyl L-phenylalanyl L-leucine (ZPL), and N-benzyloxycarbonyl glycyl L-phenylalanine (ZGP) were investigated at two depths in five acid tea soils, in upland crop soils and in uncultivated soils (soils with near neutral pH) as controls. Sources of the enzymes and factors that influenced the activities were determined based on the relation between the protease activity and total N, total C, or microbial numbers. 1) In the assay with 0.2_M phosphate buffer (pH 8.1), the BAA-hydro-lyzing activity in all the tea soils, upland crop soils and uncultivated soils was the highest, followed by the ZPL-hydrolyzing activity while the ZGP-hydrolyzing activity was the lowest. 2) Both magnitude of the protease activity and substrate specificity varied with depths and soil types. Proteases in the surface layers (0-20 cm) hydrolyzed all the used substrates faster than those in the lower layers (20-40 cm). The proteases in the lower layers hydrolyzed specifically BAA more than those in the surface layers. The BAA-and ZPL-hydrolyzing activities were higher in volcanic ash soils than in non-volcanic ash soils. 3) Tea, upland crop cultivation, and absence of cultivation affected the magnitude of protease activity. The soil cultivated with upland crops (hereafter referred to as "upland crop soils") and uncultivated soils hydrolyzed specifically BAA more than the tea-cultivated soils (hereafter referred to as "tea soils"). 4) There were close relationships between the soil microbial group and BAA- or ZPL-hydrolyzing activity. It is therefore assumed that the enzymes hydrolyzing BAA and ZPL in the acid tea soils originated from the soil microorganisms.
社団法人日本土壌肥料学会の論文

Microbial Ecology in Tea Soils : II. Soil Protease Activity

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