Interactive adsorption of phenolic acids and amino acids on soil minerals Implications for the formation and properties of soil mineral–organic associations

The bioavailability and dynamics of soil organic matter (SOM) depend largely on the association with mineral particles. However, no consensus exists on the formation, composition and structure of the mineral–organic associations (MOAs). The experimental evidence for the multilayer model of MOAs was still lacking. In the batch adsorption experiments, we found phenolic acids (PAs) were preferentially adsorbed on goethite, whereas the phyllosilicates (kaolinite and montmorillonite) were a better adsorbent for amino acids (AAs). Among all tested PAs (Sal, Syr, Fer and Van), Sal was preferentially adsorbed on all minerals. For the AAs, Glu was preferentially adsorbed on goethite and Lys on phyllosilicates. The adsorption of DOM on different minerals followed the order of goethite >> kaolinite > montmorillonite. Higher adsorption of O-DOM (derived from the O-horizon of forest soil) was observed on goethite than L-DOM (derived from forest leaf litter). Moreover, we observed the AAs were more competitive than PAs and partially suppressed the adsorption of PAs on goethite and montmorillonite. The adsorption of PAs or AAs on both minerals was enhanced by surface conditioning with the other group, with larger effects for goethite than montmorillonite. Coating of various minerals with both DOM sources (O-DOM and L-DOM) reduced the adsorption of PAs and acidic AA (Glu), but enhanced the adsorption of basic AA (Lys). These results highlight the importance of the interplay between different OM components in the formation of MOAs. We propose that the cycling of different components of SOM can affect each other via competitive or sequential adsorption on mineral phase.