Heterophase Synthesis of Humic Acids in Soils by Immobilized Phenol Oxidases

Abstract

Adsorption complexes of humic substances with soil minerals comprise the bulk of organic matter in humus horizons of cold and temperate soils. They represent the most stable Corg fraction in soils with mean residence time of 102–103 years. A considerable fraction of adsorbed organic matter is represented by high molecular weight (50–100 kDa) humic acid–like polymers. The concept of sorptive preservation cannot explain the origin of such polymers on mineral surfaces, because their migration to adsorption sites should be limited by low solubility. It can be suggested that high molecular weight humic acid–like polymers are formed in situ in mineral soil horizons. A possible mechanism is heterophase polymerization of low molecular weight (and thus soluble) precursor material in presence of catalytically active solid phases. The chapter summarizes available data supporting the concept of surface polymerization of humic acids and provides an evidence for the key role of immobilized phenol oxidases and solid matrix in accelerating this process.