2.4. Fluorescein diacetate (FDA) hydrolysis

In order to estimate the overall microbial activity in soil samples FDA test was performed (Adam and Duncan, 2001). Briefly, 5 ml of 60 mM sodium phosphate buffer (pH 7.6) and 25 μl of 4.8 mM fluorescein diacetate were added to 0.5 g of fresh soil. Samples were incubated for 20 min at 25 °C and 150 rpm. The reaction was stopped by adding 5 ml of acetone. Samples were centrifuged at 8000 rpm for 10 min at room temperature and the amount of hydrolyzed FDA was determined at 490 nm. A calibration curve was prepared using a fluorescein standard solution (0–100 mg l⁻¹).