Effects of Soil Organic Matter and Exogenous Organic Materials on Methane Production in and Emission from Wetlands
土壤有机质和外源有机物对甲烷产生的影响

The CH 4 concentration in the atmosphere is increasing continuously, with possibly profound consequences for future global climate. Wetlands, including rice paddy fields and mires, contribute between 15 and 45% of global CH 4 emissions. CH 4 emissions from wetlands show a large variation, which can't so far clearly be predicted by environmental and soil variables. This limits the accuracy of estimates of both current and future global CH 4 emission. CH 4 production is a microbiological process, which takes place under anaerobic conditions with supplies of organic substrates. Once anaerobiosis is established, soil organic matter is generally considered as a key limited factor for CH 4 production. The paper reviews the research progresses of the effects of soil organic matter and exogenous organic materials inputting into wetlands on CH 4 production. Under anaerobic conditions, both native organic matter and exogenous organic materials in wetlands are decomposed biologically into simple organic matters and CO 2 via a series of reactions. Methane is produced as a final step of anaerobic degradation of organic matters, mediated by methanogens. Methanogenic bacteria use a limited number of substrates, of which acetate, CO 2, and hydrogen are the most important ones. CH 4 production in and emission from wetlands are not closely related with total organic materials in soils, but significantly with labile organic matter and the organic matter that could be extracted by water under boiling condition. That is to say that CH 4 production and emission in the absence of oxygen are controlled by strongly reducible rather than weakly reducible organic materials. A method that efficiently discriminates the strongly reducible organic carbon from soil organic matter urgently needs to be developed in order to accurately predict the CH 4 production potential in soils. Addition of organic materials to soils usually occurs in most rice-based agroecosystems for improving soil fertility. The stimulation effect of exogenous organic materials on CH 4 emissions relies on their quantity and composition. Strongly reducible organic materials such as cellulose and hemicelluloses can produce more CH 4 than the weakly reducible ones such as polysaccharides and lipoid. Methanol and methylic amino acids can be transformed into CH 4 even more effectively. Plant exudates are also able to stimulate CH 4 production, lying on plant varieties, the quantity and composition of exudates. The mechanisms for stimulation effect of exogenous organic materials on CH 4 production are to provide substrates for CH 4 production, lower soil redox potential, and accelerate decomposition of native organic carbon in soils.