Characteristics of water extractable organic carbon fractions in the soil profiles of Picea asperata and Betula albosinensis forests

Objective Soil organic carbon (SOC) in deeper soils may be more protected by mineral particles than SOC in shallower soils; thus, the vertical SOC distribution is closely related to the overall SOC stability. This study aimed to verify the relationship between the solubility temperature dependence of water extractable SOC fractions and their vertical distribution characteristics. Methods Soil samples collected from each soil horizon in natural dragon spruce ( Picea asperata ) and red birch ( Betula albosinensis ) forests were analyzed. Cold water-extracted organic carbon (CWEOC) and hot water-extracted organic carbon (HWEOC) were extracted at 20 °C and 80 °C, respectively. The sum of CWEOC and HWEOC was considered the water-extracted organic carbon (WEOC) content. The carbohydrate-C (Car-C) and phenolic-C (Phe-C) contents extracted by hot water were also determined. Results The CWEOC, HWEOC, Car-C, and Phe-C contents varied significantly ( P