Response of glycosidases in soils to chloroform fumigation

Abstract.

The purpose of this study was to differentiate between biotic and abiontic fractions of four important hydrolases involved in C cycling in soils. Therefore, ten different surface soils, which represent a wide range of physico-chemical properties were fumigated with chloroform for 24 h. The activities of α- and β-glucosidases and α- and β-galactosidases were assayed in these soils and in reference proteins purified from microbial sources before and after chloroform fumigation and in the presence and absence of toluene. Chloroform fumigation decreased the activities of α- and β-glucosidases and α- and β-galactosidases in soils, on average, by 42%, 22%, 43% and 53%, respectively. These results indicated that among the biochemical reactions involved in the degradation of carbohydrates in soils, the hydrolysis of maltose, melibiose and lactose are more inactivated by chloroform fumigation than that involved in the hydrolysis of cellobiose. The activities of all four purified enzyme proteins were decreased after chloroform fumigation, by 7% (β-galactosidase) to 40% (α-glucosidase). Enzyme protein concentrations, calculated for the ten soils were, on average, 3.72, 0.014, 0.027 and 1.56 mg protein kg^–1 soil for α- and β-glucosidases and α- and β-galactosidases, respectively. The results suggest that enzyme activity rates do not necessarily correspond to the amounts of enzyme proteins present in a soil, i.e., some enzymes have greater catalytic efficiencies than others. The activity values of the nonfumigated, toluene-treated soils were generally significantly correlated with contents of clay and microbial biomass C.