Methanogenesis rice soils

Through numerous research efforts since the 1980s, several factors have been determined to affect CH4 emissions from rice cultivation. Due to the complex balance of methanogenesis and methanotrophy that determines how much CH4 escapes the rice system to the atmosphere along with the large variety of cultural and environmental conditions around the globe, there is large variability in the impact of different factors across time and space. There are a few soil, environmental, and plant factors, however, that seem to have somewhat consistent impacts on CH4 emissions from rice. 

Kliiber H. D. and Conrad R. (1998) Effects of nitrate, nitrite, NO and N2O on methanogenesis and other redox processes in anoxic rice field soil. FEMS Microbiol. Ecol. 25, 301-318. 

Laboratory incubations of wetland soils with nitrogen and phosphorus amendments have shown either no elfect or an inhibitory effect on methanogenesis (Bodelier et al., 2000a,b Bridgham and Richardson, 1992 Wang and Lewis, 1992). A low rate of phosphate supply to rice roots stimulated CH4 emission (Lu et al., 1999), while phosphate concentrations 20mM specifically inhibited acetotrophic methanogenesis (Conrad et al., 2000). 

There have been remarkably few attempts to determine the contribution of Fe(III) reduction to anaerobic carbon metabolism in freshwater ecosystems where it may be the dominant pathway. The most extensive such study examined 16 rice paddy soils collected from China, Italy, and the Philippines (Yao et al., 1999). Fe(III) reduction was 58-79% of carbon metabohsm during the reduction phase (Section 8.08.8.1), with most of the remainder attributed to methanogenesis. Fe(III) reduction contributed —70% of the anaerobic metabolism in a Juncus effusus marsh (Roden and Wetzel, 1996). 

Frenzel P., Bosse U., and Janssen P. H. (1999) Rice roots and methanogenesis in a paddy soil ferric iron as an alternative electron acceptor in the rooted soil. Soil Biol. Biochem. 31, 421-430. 

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