Variations of Stable Carbon Isotopes of CH4 Emission from Three Typical Rice Fields in China

Little is known about the stable carbon isotopes of methane (CH4) emitted (δ13CH4emitte4) from permanently flooded rice fields and double rice-cropping fields. The CH4 emission and corresponding δ13CH4emitte4 under various field managements (mulching, water regime, tillage, and nitrogen (N) fertilization) were simultaneously measured in three typical Chinese rice fields, a permanently flooded rice field in Ziyang City, Sichuan Province, Southwest China, a double-rice cropping field in Yingtan City, Jiangxi Province, Southeast China, and a rice-wheat rotation field in Jurong City, Jiangsu Province, East China, from 2010 to 2012. Results showed different seasonal variations of δ13CH4emitte4 among the three fields during the rice-growing season. The values of δ13CH4emitte4 were negatively correlated with corresponding CH4 emissions in seasonal variation and mean, indicating the importance of CH4 production, oxidation, and transport associated with isotopic fractionation effects to the δ13CH4emitte4. Seasonal variations of δ13CH4emitte4 were slightly impacted by mulching cultivation, tillage, and N application, but highly controlled by drainage. Meanwhile, tillage, N application, and especially mulching cultivation had important effects on seasonal mean CH4 emissions and corresponding δ13CH4emitte4, with low emissions accompanied by high values of δ13CH4emitte4. Seasonal mean values of δ13CH4emitte4 from the three fields were similar, mostly ranging from −60‰ to −50‰, which are well in agreement with previously published data. These demonstrated that seasonal variations of δ13CH4emitte4 mainly depended on the changes in CH4 emission from rice fields and further indicated the important effects of methanogenic pathways, CH4 oxidation, and CH4 transport associated with isotope fractionation effects influenced by field managements on δ13CH4emitte4.