Comparative aspects of cycling of organic C, N, S and P through soil organic matter

Abstract

A conceptual model proposes that C and N are stabilized together and mineralized through biological mineralization, whereas organic P (P o) and sulfate esters are stabilized independently of the main organic moiety and are mineralized through biochemical mineralization. Carbon-bonded S appears to be controlled by mechanisms similar to those for N. Biological mineralization, defined as release of inorganic forms of N and S from organic materials during oxidation of C by soil organisms to provide energy, is driven by the search for energy. Biochemical mineralization, defined as release of inorganic ions of P and S from organic form through enzymatic catalysis external to the cell membrane, is strongly controlled by the supply of and need for the element released rather than the need for energy. Such a dichotomous system controlling both stabilization and mobilization of C and N on one hand, and of P and S on the other, should lead to converging or diverging C:P o and N:P o ratios during soil development, depending upon whether C or P are limiting the system. Field observations relating to the change in C:N:S:P stoichiometry in soil horizons and profiles through chrono-, climo- and toposequences have been used to examine the proposed concept. The proposed conceptual model appears to provide a rational framework within which to interpret the interrelations of C, N, S and P over both geological and biological time scales. Data available in the literature for a wide range of soils appear to be consistent with the hypotheses flowing from the model.