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Microbial processes influencing methane emission from rice fields
Author(s) -
Krüger Martin,
Frenzel Peter,
Conrad Ralf
Publication year - 2001
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1046/j.1365-2486.2001.00395.x
Subject(s) - methane , methanogenesis , paddy field , environmental chemistry , chemistry , anaerobic oxidation of methane , growing season , agronomy , biology , organic chemistry
Summary Irrigated rice fields are an important source of atmospheric methane. In order to improve our understanding of the controlling processes, we measured in situ CH 4 emission and CH 4 oxidation in an Italian rice field in 1998 and 1999, and studied CH 4 production in soil and root samples. The CH 4 emission rates were correlated with diurnal temperature variations and showed pronounced seasonal and interannual variations. The contribution of CH 4 oxidation to total CH 4 flux, determined by specific inhibition with difluoromethane, decreased from 40% at the beginning to zero at the end of the season. The stable carbon isotopic composition of the emitted CH 4 also decreased. The CH 4 ‐oxidizing bacteria probably became limited by nitrogen as indicated by the seasonal decrease of NH 4 + . Thus, CH 4 oxidation had little effect on CH 4 emission. Methane production on rice roots was relatively constant over the season. Methane production in soil slowly increased after flooding and was highest in the middle of the season. Pore water concentrations of CH 4 showed a similar seasonal pattern. In 1999, CH 4 production increased later in the season and reached lower rates than in 1998. An additional drainage in 1999 resulted in higher ferric iron concentrations, higher soil redox potentials and lower acetate concentrations. As a result, acetate‐utilizing methanogens were probably out‐competed by iron‐reducers so that a larger percentage of [2– 14 C]acetate was converted to 14 CO 2 instead of 14 CH 4 . The residual CH 4 production was relatively low and was mainly due to H 2 /CO 2 ‐dependent methanogenesis. Experiments with radioactive bicarbonate and with methyl fluoride as specific inhibitor showed that the theoretical ratio of 7:3 of methanogenesis from acetate vs. H 2 /CO 2 was only reached later in the season when total CH 4 production was at the maximum. In conclusion, our results give a mechanistic explanation for the intraseasonal and interannual differences in CH 4 emission.