[Fractionation of dissolved organic carbon along soil profiles during the leaching process]

Two distinct soil types in mid-subtropical China were selected for soil sampling at the depth of 0-10, 10-20, 20-40, 40-60, 60-80, 80-100 cm for soil cores preparation. Dissolved organic carbon (DOC) extracted from recently fallen litters of Castanopsis carlesii with ultrapure water was leached through such soil cores to investigate the fractionation and retention pattern when migrating along the soil layers. The results showed the leachates out of deeper soil cores had lower concentrations and were chemically simpler, the hydrophobic pools contributed to the majority of the retention, but the proportion of retained hydrophilic materials gradually increased with the increasing soil depth. The infrared spectrum suggested that the hydrophobic materials containing aromatic rings could be easily absorbed by soils, but alkanes and simple carbohydrates would transport into subsoils with soil solution. Proportional decrease in the highly sorptive DOC restricted C sorption by subsoils, and thus the adsorption occurred mainly in 0-40 cm soil layers, suggesting that the chemical nature of DOC had a greater influence on sorption capacity of the soils than soil physicochemical properties. The retention amounts of DOC by different soil types differed significantly, which were significantly positively correlated with the contents of clay, iron and aluminum oxides.