SOIL MICROBIAL PROCESSES AND THE CYCLING OF ATMOSPHERIC TRACE GASES

Soil microbial processes involved in the flux between soil and atmosphere of the atmospheric trace gases methane (CH4), hydrogen (H-2), carbon monoxide (CO) carbonyl sulphide (OCS): nitrous oxide (N2O), and nitric oxide (NO) are reviewed. The flux of a trace gas between soil and atmosphere is usually the result of simultaneous production and consumption reactions, so that a compensation concentration exists, at which the net flux is zero. With some of the trace gases, different suites of processes operate at different gas concentrations, so that the processes that consume a trace gas that is produced within the soil are often different from those that consume the trace gas entering the soil from the atmosphere. Certain groups of soil microorganisms can metabolize more than one of these trace gases. The processes involved in the cycling of a trace gas in anoxic wetland soils are often different from those operating in upland soils.