Calculation of soil enzyme activity

The S-CAT activity was measured as the degradation of 1 mmol H₂O₂ into an enzyme activity unit per gram of dry soil sample per day. The S-DHA activity was measured as the production of 1 μg TF per gram of soil sample per day at 37°C as an enzyme activity unit. The S-UE activity was measured as the production of 1 μg NH₃-N per gram of soil sample per day as an enzyme activity unit. The S-SC activity was measured as the production of 1 mg reducing sugar per gram of soil sample per day as an enzyme activity unit. The S-ACP was measured as the production of 1 nmol phenol per gram of soil per day at 37°C as an enzyme activity unit. The general formula for enzyme activity calculation is as follows:

where D represents the dilution multiple; ΔA₁ represents the change in the absorbance value of the sample; ΔA₂ represents the change in the absorbance value of the blank control; V_t represents the total volume of the reaction, mL; e represents the molar absorbance value, 6.22 × 10⁻³ mol/L·cm⁻²; V_s represents the enzyme liquid volume, mL; and d represents the light path of the cuvette, 1 cm.