Sorption reduces the biodegradation rates of multivalent organic acids in volcanic soils rich in short-range order minerals

Sorption can limit biodegradation of low-molecular-weight organic acids (LMWOAs), while this validity needs to be accessed in volcanic soils rich in short range order (SRO) Al/Fe minerals and organic matter. We tested whether both sorption and microbial mineralization of LMWOAs are controlled by the amounts of SRO minerals and organo-Al/Fe complex in volcanic soils. We analyzed the soil solution concentrations, sorption isotherms, and mineralization kinetics of 14C-radiolabeled acetate, oxalate, malate, citrate, and glucose. The sorption of LMWOAs increased with increasing amount of SRO minerals and organo-Al/Fe complex, irrespective of indigenously adsorbed organic matter levels. Mineralization of multivalent LMWOAs (oxalate, malate, and citrate) displays a contrary pattern to sorption and decreased with increasing amount of SRO minerals and organo-Al/Fe complex. Sorption consistently reduces microbial mineralization rates through removal of LMWOAs from soil solution, but it can also suppress microbial activity of multivalent LMWOA mineralization. Both sorption and microbial mineralization of multivalent LMWOAs are more strongly controlled by the amounts of SRO minerals and organo-Al/Fe complex than acetate. Sorption-induced retardation of multivalent LMWOA mineralization contributes to preservation of organic matter in volcanic soils.