Arylsulfatase activity of microbial biomass in soils as affected by cropping systems
1999
Klose, S. | Moore, J.M. | Tabatabai, M.A.
The impacts of crop rotations and N fertilization on different pools of arylsulfatase activity (total, intracellular, and extracellular) were studied in soils of two long-term field experiments in Iowa to assess the contribution of the microbial biomass to the activity of this enzyme. Surface-soil samples were taken in 1996 and 1997 in corn, soybeans, oats, or meadow (alfalfa) plots that received 0 or 180 kg N ha(-1) before corn, and an annual application of 20 kg P ha(-1) and 56 kg K ha(-1). The arylsulfatase activity in the soils was assayed at optimal pH (acetate buffer, pH 5.8) before and after chloroform fumigation; microbial biomass C (C(mic)) and N (N(mic)) were determined by chloroform-fumigation methods. All pools of arylsulfatase activity in soils were significantly affected by crop rotation and plant cover at sampling time, but not by N fertilization. Generally, the highest total, intracellular, and extracellular arylsulfatase activities were obtained in soils under cereal-meadow rotations, taken under oats or meadow, and the lowest under continuous cropping systems. Total, intracellular, and extracellular arylsulfatase activities were significantly correlated with C(mic) (r > 0.41, P < 0.01) and N(mic) (r > 0.38, P < 0.01) in soils. The averages of specific activity values, i.e., of arylsulfatase activity of the microbial biomass, expressed per milligram C(mic) ranged from 315 to 407 microgram p-nitrophenol h(-1). The total arylsulfatase activity was significantly correlated with the intracellular activity, with r values > 0.79 (P < 0.001). In general, about 45% of the total arylsulfatase activity was extracellular, and 55% was associated with the microbial biomass in soils, indicating the importance of the microflora as an enzyme source in soils.
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