Role of the soil matrix and minerals in protecting natural organic materials against biological attack

Natural organic materials in soils consist of a complex mixture of different biochemicals exhibiting numerous morphologies and stages of biological oxidation. A continuum of decomposability exists based on chemical structure; however, this continuum can be altered by interactions with minerals within matrices capable of stabilising potentially labile organic matter against biological oxidation. Protection is not considered to equate to a permanent and complete removal of organic C from decomposition, but rather to a reduced decomposition rate relative to similar unprotected materials. The stabilisation of organic materials in soils by the soil matrix is a function of the chemical nature of the soil mineral fraction and the presence of multivalent cations, the presence of mineral surfaces capable of adsorbing organic materials, and the architecture of the soil matrix. The degree and amount of protection offered by each mechanism depends on the chemical and physical properties of the mineral matrix and the morphology and chemical structure of the organic matter. Each mineral matrix will have a unique and finite capacity to stabilise organic matter. Quantifying the protective capacity of a soil requires a careful consideration of all mechanisms of protection and the implications of experimental procedures. (C) 2000 Elsevier Science Ltd. All rights reserved.