2.3.3 Soil properties
Soil was also sampled from soil cores along the vertical soil profile (see section 2.3.1). Soil samples from each layer were divided into two subsamples. Fresh subsamples were immediately weighed and oven-dried at 105 °C to determine the soil water content (SWC, g g-1). The remaining soil subsamples were air-dried and passed through a 100-mesh (0.15 mm) sieve to determine soil physicochemical properties. Soil total carbon (TC) and total nitrogen (TN) levels were determined by combustion in an elemental analyzer (Vario MAX; Elementar, Germany), and total phosphorus (TP) was measured using the sulfuric acid-soluble perchlorate acid-molybdenum antimony colorimetric method (Hu et al., 2016). Dissolved organic carbon was extracted with deionized water (1:5 w/v soil to water) and determined using an elemental analyzer (Vario Macro Analyzer; Elementar, Germany). Ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) were extracted in the 2 mol L-1 KCl solution, and the supernatant was measured using a flow analyzer (SEAL Analytical, Germany). Available phosphorus (aP) was extracted with 0.5 mol L-1NaHCO3 at pH 8.5, and then determined by molybdenum antimony anti-colorimetry. Soil pH was determined in a 1:2.5 (w/v) soil-water suspension (SevenEasyS20; Mettler Toledo, USA) (Huang et al., 2023b).