Selective Sorption of Dissolved Organic Carbon Compounds by Temperate Soils

Background: Physico-chemical sorption onto soil minerals is one of the major processes of dissolved organic carbon (OC) stabilization in deeper soils. The interaction of DOC on soil solids is related to the reactivity of soil minerals, the chemistry of sorbate functional groups, and the stability of sorbate to microbial degradation. This study was conducted to examine the sorption of diverse OC compounds (D-glucose, L-alanine, oxalic acid, salicylic acid, and sinapyl alcohol) on temperate climate soil orders (Mollisols, Ultisols and Alfisols). Methodology: Equilibrium batch experiments were conducted using 0-100 mg C L^-1 at a solid-solution ratio of 1:60 for 48 hrs on natural soils and on soils sterilized by γ-irradiation. The maximum sorption capacity, Q_max and binding coefficient, k were calculated by fitting to the Langmuir model. Results: Ultisols appeared to sorb more glucose, alanine, and salicylic acid than did Alfisols or Mollisols and the isotherms followed a non-linear pattern (higher k). Sterile experiments revealed that glucose and alanine were both readily degraded and/or incorporated into microbial biomass because the observed Q_max under sterile conditions decreased by 22-46% for glucose and 17-77% for alanine as compared to non-sterile conditions. Mollisols, in contrast, more readily reacted with oxalic acid (Q_max of 886 mg kg^-1) and sinapyl alcohol (Q_max of 2031 mg kg^-1), and no degradation was observed. The reactivity of Alfisols to DOC was intermediate to that of Ultisols and Mollisols, and degradation followed similar patterns as for Ultisols. Conclusion: This study demonstrated that three common temperate soil orders experienced differential sorption and degradation of simple OC compounds, indicating that sorbate chemistry plays a significant role in the sorptive stabilization of DOC.