Arylsulfatase activity of microbial biomass in soils

Quantification of the different pools of enzyme activity in soils (intra- and extracellular) is desired to assess the contribution of the microbial community to specific enzyme reactions and ecological changes in soils. Arylsulfatase activity was assayed at optimal pH (acetate buffer, pH 5.8) in 10 surface soils before and after chloroform-fumigation, and microbial biomass C (C-mic) was determined by a chloroform-fumigation-extraction method, and microbial biomass N (N-mic) by a chloroform-fumigation-incubation method. The C-mic values ranged from 31 to 784 mg kg(-1) soil (average = 252 mg kg(-1) soil) and the N-mic values ranged from 6 to 28 mg kg(-1) soil (average = 12 mg kg(-1) soil), resulting in (C/N)(mic) ratios ranging from 5.2 to 30.3 (average = 20.3). The C/N ratios of the soils ranged from 8.6 to 18.1 (average = 12.3). Expressed as percentages of organic C or N, the C-mic values ranged from 0.24 to 1.8% (average = 1.0%) and the N-mic values ranged from 0.36 to 1.2% (average = 0.63%). The activities of total (intra- and extracellular) arylsulfatase after chloroform fumigation without toluene treatment; intracellular arylsulfatase (activity of the microbial biomass), i.e., [(total activity) - (extracellular activity)]; and extracellular arylsulfatase (before chloroform fumigation without toluene treatment) were significantly correlated with C-mic (r = 0.88**, 0.85"*, and 0.94***, respectively) and N-mic (r = 0.81**, 0.83**, and 0.89***, respectively). The total arylsulfatase activity, the activity of the microbial biomass, and the extracellular activity were significantly correlated with organic C (r = 0.88***, 0.90***, and 0.72*, respectively) and total N (r = 0.89***, 0.90***, and 0.77*, respectively). Clay content was also correlated with the activity of total (r = 0.75*) and extracellular arylsulfatase (r = 0.83**). Expressed as percentages of total activity, the arylsulfatase activity of the microbial biomass ranged from 39.6 to 73.1% (average = 57.7%). The remaining activity (26.9-60.4%, average = 42.8%) was extracellular. When toluene was used as a plasmolytic agent in the nonfumigated soils, the arylsulfatase activity resulting from this treatment ranged from 24.6 to 48.1% (average = 40.3%). When expressed per milligram of C-mic (specific activity), the arylsulfatase activity of the microbial biomass ranged from 65 to 955 (average = 455) mu g PN h(-1). The total arylsulfatase activity and the activity of the microbial biomass were underestimated, because tests with arylsulfatase purified from two molluscs (Helix pomatia and Patella vulgata) showed that chloroform fumigation decreased the activity by 50 and 23%, respectively.