Soil physical and chemical analysis
Soil moisture was determined as the difference from fresh soil to constant weighted 105 ℃ for 24 h. Soil pH was measured with a digital pH meter from a soil water suspension (1:2.5 w : v ). Soil organic C and N were measure with an element analyzer (Vario EL, Elementar Analysensysteme, Hanau, Germany) with the aliquots (approximately 10 g) dried soil samples treated with 10 mL 1N HCL for 24 h at room temperature to remove any soil carbonates. The ammonium (NH4+-N) and nitrate (NO3--N) were measured by a continuous flow analyzer (SAN++; Skalar, Breda, the Netherlands), as described by Yang et al . 2018.