Adsorption Characteristics Of Dissolved Organic Carbon In Soils Of Different Qualities In Mid-subtropical

We select soils of different qualities in mid-subtropical China,after extracting DOC from the collected recent litters of Castanopsis carlesii with ultrapure water,we leached the DOC through different soil horizons in the laboratory,so we can research the interception of DOC in different soil horizons and its relationship with soil properties.To clarify different soil types preferential adsorption to DOC,we used the ultraviolet,fluorescence,the infrared spectrum and studied the changes in structural compositions of DOC before and after leaching.At the same time,in order to explore the DOC migration fractionation phenomenon in the soil profiles,we also leached the DOC through the successive layers in the laboratory,so we can further understand the soil organic carbon cycle and carbon sequestration potential of the subtropical evergreen broad-leaved forest and how DOC leaching contributes to some underlying scientific problems such as the deep soil organic carbon's accumulation.The results showed:(1)DOC will be trapped in soils during the process of migration due to the adsorption,the hydrophobic and macromolecular materials such as aromatic compounds will be preferential adsorbed,DOC interception in subsoils was greater than that in topsoils.The hydrophilic and hydrophobic DOC competed for binding sites on soil surfaces,the percengtage of hydrophilic DOC in the total interception increased with depth;(2)infrared spectrum suggested that hydrophobic materials such as aromatic substances and ethers were much more ready to be adsorbed than alkane materials,while indigenous hydrophilic substances such as phenols,alcohols can be displaced by hydrophobic substances of DOC;(3)there was significant positive correlation between DOC interception and the content of clay and free iron oxide,and there was significant negative correlation between DOC interception and the content of sand and soil organic carbon,in which the content of soil organic carbon is the key factor under forest of mid-subtropical China;(4)due to the soil organic carbon,iron and aluminum oxide,and the content of clay,the soil adsorption capacity of red soils is significantly higher than that of red-yellow soils;(5)during the process of the DOC migration in the soil profile,due to the topsoils can preferentially adsorb to hydrophobic macromolecules in the original DOC,the DOC arrived subsoils can not be easily adsorb to the soils,despite its has a high content of clay and iron and aluminum oxide,so lower soil horizons can not demonstrate fully their adsorption capacity,therefore we believe chemical properties of DOC have greater effects on adsorption than soil properties;(6)in both single and successive leaching process,the content of soil DOC and its chemical structure in all soil horizons had no significant difference before and after leaching,except in 0-40 cm of red soils which have a strong sasorption ability,indicating that most of DOC which was absorbed by soils is irreversible.Infrared spectrum also proved that after leaching the content of aromatic compounds in DOC increased,but the content of alkane and carboxyl,alcohol and other small molecular substances has decreased in some extent.