Method of measuring invertase activity in soils

Summary Invertase (-D-fructofuranoside fructohydrolase, EC Enzyme Commission] 3.2.1.26) is the enzyme that catalyzes the hydrolysis of sucrose and yields glucose and fructose. The activity of this enzyme was monitored by systematically developing a sensitive and rapid method to detect reducing sugars with the precision of 1.4 to 6.1% C.V. The method involves the colorimetric determination of reducing sugars which react with 3,5-dinitrosalicylic acid when soil is incubated with buffered sucrose solution and toluene at 37°C for 24 h. The detection limit for the method described is 100 g of reducing sugar per ml of soil extract. The color intensity remained constant up to 24 h. Comparative studies showed that the method described was in good agreement to other invertase assay procedures reported in the literature.Studies on the stability and distribution of invertase in soils by using the method described showed that air-drying of field-moist soil samples resulted in decreased activity ranging from 15.3 to 23.7% (avg.=19.8%). Statistical analyses indicated that invertase activity was significantly correlated with total N (r=0.78^***) and organic C (r=0.70^***) in the topsoil of 19 diverse samples. There was no significant correlation between invertase activity and soil pH, cation exchange capacity, percentage of clay and percentage of sand. The activity of this enzyme was concentrated in surface soils and decreased with profile depth. Regression analyses showed that invertase activity was significantly correlated with organic carbon content of three soil profiles examined.