Sorption Selectivity of Dissolved Organic Compounds to Different Soils.

Dissolved organic carbon (DOC) plays an important role in the cycling and retention of C in terrestrial ecosystems. In a previous experiment, we evaluated the maximum DOC sorption capacity of different soil orders upon treating with a natural dissolved organic matter. This study showed that much higher concentrations of the same DOC source are required to saturate all available sorption sites for Mollisols than for Ultisols and Alfisols. Consequently, we hypothesize that Mollisols, which are inherently OC rich, preferentially adsorb specific types of organic functional groups from bulk DOC, and that Ultisols and Alfisols generally do not exhibit preferential adsorption. This hypothesis will be tested by studying the specific sorption and desorption of a variety of organic compounds (e.g., carbohydrates, organic acids, amino acids, phenols, and lignin) on Mollisols, Ultisols and Alfisols using adsorption isotherms. By varying the order of addition of the compounds, we will explore competition for surface sites and the possible re-arrangement of adsorbed OC molecules at the soil surface. Quantification of the proportion of added OC compounds that are adsorbed will be determined using Gas Chromatography/Mass Spectrometry. This study will provide insights on differential sorption capacities of different soil orders for specific organic compounds, as a surrogate for the natural microbial processes of soil organic carbon stabilization in deeper layers.