2.5 Chemical analysis
Total soil organic carbon (SOC) and nitrogen (TN) were determined using an elemental analyzer after carbonate was removed by 1 N HCl solution (Elementar Vario Microcude, Hesse, Germany). Total phosphorus contents (TP) in soils were measured by the ammonium molybdate-ascorbic acid method. Soil samples were dried in an aluminum box to a constant weight, and soil moisture contents (SWC) and bulk density (BW) were calculated by weighting mass loss before and after soil oven at 105℃ for 8 h.
Dissolved organic carbon (DOC) was extracted by mixing 5.00 g soil with 30.0 mL deionized water in Erlenmeyer flasks. After shaking for 30 min, the mixtures were centrifuged and filtered through a 0.45µ m filter. Filtrates were analyzed for total organic carbon using a TOC-VCPH analyzer (Gangdong, Tianjin, China).