2.2 GRSP determination
The glomalin content was estimated by measuring the EE-GRSP and T-GRSP (Rillig et al., 2002). The EE-GRSP was extracted from the soil samples using 20 mM sodium citrate at pH 7.0 and 121 °C for 30 min, while the T-GRSP was extracted using 50 mM sodium citrate at pH 8.0 and 121 °C for 60 min (repeated 4-5 times). The extracts were centrifuged at 10 000 × g to remove soil particles. The protein content of the supernatant was quantified using the Bradford dye-binding assay with bovine serum albumin as the standard (Rillig et al., 2001; Rillig et al., 2002).