2.4 Soil pH and microbial biomass
Fresh soil samples were sieved through 1 mm and used to determine soil moisture and soil microbial biomass; after 7 days of air drying, dry soil samples were used to determine soil pH. Soil pH was measured in a 1 : 2.5 soil and water solution using a pH meter (Mettler Toledo, Switzerland, Dick et al., 2000). Soil microbial biomass was determined by substrate-induced respiration (SIR) following Bailey et al. (2002) and Lin et al. (2017). In brief, fresh soil samples equivalent to 1 g dry weight were adjusted to 60 % of the water holding capacity. Then, 1 mL of glucose solution was added to soil to achieve 10 mg glucose g-1 dry weight of soil. Samples were then incubated at 25 °C, and CO2 was determined using an infrared gas analyzer after one hour. SIR was expressed as CO2 per g soil per hour (ppm g-1 dry soil h-1).