Carbon isotope fractionation reveals distinct process of CH(4) emission from different compartments of paddy ecosystem

Carbon isotopic fractionations in the processes of CH(4) emission from paddy field remain poorly understood. The δ(13)C-values of CH(4) in association with production, oxidation and transport of CH(4) in different pools of a paddy field were determined, and the stable carbon isotope fractionations were calibrated to assess relative contribution of acetate to CH(4) production (f(ac)) and fraction of CH(4) oxidized (f(ox)) by different pathways. The apparent isotope fractionation for CO(2) conversion to CH(4) (α(app)) was 1.041–1.056 in the soil and 1.046–1.080 on the roots, indicating that f(ac) was 10–60% and 0–50%, respectively. Isotope fractionation associated with CH(4) oxidation (α(ox)) was 1.021 ± 0.007 in the soil and 1.013 ± 0.005 on the roots, and the transport fractionation (ε(transport)) by rice plants was estimated to be −16.7‰ ~ −11.1‰. Rhizospheric f(ox) was about 30–100%, and it was more important at the beginning but decreased fast towards the end of season. Large value of f(ox) was also observed at the soil-water interface and soil and roots surfaces, respectively. The results demonstrate that carbon isotopic fractionations which might be different in different conditions were sensitive to the estimations of f(ac) and f(ox) in paddy field.