Mechanisms Controlling Methane Emission from Wetland Rice Fields

Abstract

Wetland rice fields are an important source in the global budget of atmospheric {CH4} and, thus, have a significant impact on climate and on atmospheric photochemistry. Methane emission rates from rice fields vary greatly with field site, management, time of day, and season. Field and laboratory studies of {CH4} turnover in paddy soil are reviewed with respect to the mechanisms that control the emission of {CH4} into the atmosphere, i.e., {CH4} production, {CH4} diffusion, {CH4} oxidation, and interaction of {CH4} turnover with nutrients such as nitrogen, iron, and sulfur compounds. Methane production involves a complex anaerobic microbial community that degrades organic matter via various intermediates to {CO2} and {CH4.} The rice aerenchyma allows the diffusion of O2 into the rhizosphere and, thus, provides oxic microsites within the anoxic submerged soil. This allows the oxidation of {CH4} and makes the involvement of other aerobic bacteria in the turnover of {CH4} possible. The rice aerenchyma also provides the predominant route for escape of {CH4} from the soil into the atmosphere and may tap bubbles that constitute {CH4} reservoirs in the submerged soil.