Rapid mineralization of mineral-bound carboxyl-carbon of salicylic acid and phenylalanine

Ligand-bound carboxylic acids are considered a stabilized fraction of mineral-adsorbed carbon in soil. Carboxyl- 14 C labeled phenylalanine or salicylic acid were adsorbed onto goethite, kaolinite, or illite, and subsequently incubated in both loamy and sandy arable topsoil for three weeks. Contrary to our expectations, more mineral-adsorbed carboxyl-C was mineralized than remaining C in salicylic acid and phenylalanine irrespective of mineral type or soil due to competitive desorption followed by preferential mineralization. Factors that control the desorbability of organic molecules are more important for their stabilization in the soil than sorption strength. • Carboxyl- 14 C labeled acids were adsorbed onto minerals, then incubated in arable topsoil • More mineral-adsorbed carboxyl-C was mineralized than the compounds' remaining C • Competitive desorption likely overrides ligand-bound carboxyl C stability