Hydrolase activities during and after the chloroform fumigation of soil as affected by protease activity

CHCl3 fumigation was used to induce changes in hydrolase activities of a Vertisol under different management (woodland, grassland and arable soils). Measurements were made during the standard 24 h CHCl3 fumigation period used for biomass measurement and after incubation following fumigation. Fumigation of soil was very effective in killing microorganisms as shown by the marked decrease in the ATP content after 4 h of CHCl3 exposure. However, it did not change or slightly decreased β-glucosidase, acid phosphomonoesterase, alkaline phosphomonoesterase and protease as measured by hydrolysis of N-benzoylargininamide, markedly decreased urease activity and increased arylsulphatase activity. CHCl3 fumigation of soils for 24 h in the presence of several protease inhibitors decreased N-benzoylargininamide hydrolising activities by more than 50% and increased urease and phosphomonoesterase activities, demonstrating that enzymes released during cell lyses can undergo to proteolysis during the CHCl3 fumigation. During the incubation following fumigation, respiration increased following the typical trend. ATP content also increased in all soils because of the growth of the small microbial population surviving the fumigation. During the incubation following fumigation, β-glucosidase and phosphomonoesterase activities recovered to values not significantly different from those of unfumigated and incubated soil. Arylsulphatase activity decreased in all fumigated soils reaching values not significantly different from those of the unfumigated soils after 24 h. Benzoylargininamide hydrolyzing activities showed only minor changes during the incubation of unfumigated and fumigated soils. Urease activity decreased to low levels in the woodland soil and was not measurable in the grassland and arable soils. N metabolites, derived from the microbial NH4+ immobilization during the incubation following fumigation, may have inhibited the urease synthesis in microbial cells.