Effects of cultivation on the activity and kinetics of arylsulfatase in Saskatchewan soils

Abstract

Arylsulfatases play an important role in the biochemical mineralization of organic ester sulfates in soil. The effects of clearing and cultivation of native North America prairie grassland and forest soils on the activity and kinetics of arylsulfatase were studied. Arylsulfatase activities ranged from 89 to 829 μg p-nitrophenol g −1 soil h −1. Clearing and cultivation of the native soils resulted in significant decreases in enzyme activity in both the grassland and forest soils. Long-term cultivation (69 yr) of the native grassland soil resulted in a 66% reduction in arylsulfatase activity. Likewise, cultivation of the forest soil resulted in 63% decrease in enzyme activity after 5 yr and an 88% decrease in activity after 40 yr. In contrast, clearing the forest soil and leaving it fallow for 5 yr produced only a 30% reduction in arylsulfatase activity. In general, the soil arylsulfatases exhibited typical Michaelis-Menten kinetics. Variations in the kinetic parameters, however, presumably reflected changes in the enzymes brought about by the different land management schemes. Long-term cultivation of the soils resulted in a 74% reduction in the V max of the grassland soil and 90% reduction in the V max of the forest soils. Values of Michaelis constant ( K m) ranged from 1.72 to 9.38 mm and decreased as the intensity (duration) of cultivation increased. Variations in the K m, values obtained for the native soils suggest that the origins of the arylsulfatases in the grassland and forest soils were different. Variations within each cultivation sequence, however, indicate that management had a significant effect on the nature and location of the enzyme. These results demonstrate the important influence of land management on enzymatic processes in soil.