Abstract

The entire organic chemistry is based on carbon, an essential element in all substances that form living matter. The carbon cycle in soil comprises a wide variety of processes, involving diverse groups of micro- and macroorganisms. Photoautotrophy and chemoautotrophy are weakly represented, although they are not a negligible source of organic matter. The dominant process, however, is decomposition. Sugars, lipids, proteins, and other categories of compounds are being constantly degraded, through the enzymatic activity of various heterotrophic microorganisms, forming humus (a relatively stable organic complex) and, then, simpler and simpler products. In weakly oxygenated soils, specific phenomena such as methanogenesis and its reverse, methanotrophy, occur.