Carbon isotopic fractionations in the processes of CH4 emission from paddy field remain poorly understood. The δ13C-values of CH4 in association with production, oxidation and transport of CH4 in different pools of a paddy field were determined, and the stable carbon isotope fractionations were calibrated to assess relative contribution of acetate to CH4 production (fac) and fraction of CH4 oxidized (fox) by different pathways. The apparent isotope fractionation for CO2 conversion to CH4 (αapp) was 1.041–1.056 in the soil and 1.046–1.080 on the roots, indicating that fac was 10–60% and 0–50%, respectively. Isotope fractionation associated with CH4 oxidation (αox) was 1.021 ± 0.007 in the soil and 1.013 ± 0.005 on the roots, and the transport fractionation (εtransport) by rice plants was estimated to be −16.7‰ ~ −11.1‰. Rhizospheric fox was about 30–100%, and it was more important at the beginning but decreased fast towards the end of season. Large value of fox 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 fac and fox in paddy field.
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机译：稻田CH4排放过程中的碳同位素分馏仍然知之甚少。确定了稻田不同池中CH4的δ 13 C值与CH4的产生，氧化和运输的关系，并校准了稳定的碳同位素分馏，以评估乙酸盐对甲烷的相对贡献。 CH4的产生量（fac）和CH4的氧化分数（fox）通过不同的途径。 CO2转化为CH4（αapp）的表观同位素分馏在土壤中为1.041–1.056，在根部为1.046–1.080，表明fac分别为10–60％和0–50％。与CH4氧化相关的同位素分馏（αox）在土壤中为1.021±0.007，在根部为1.013±0.005，水稻植物的转运分馏（εtransport）估计为-16.7‰〜-11.1‰。根际狐狸约为30–100％，在开始时更为重要，但在季节结束时迅速下降。还分别在土壤-水界面以及土壤和根部表面观察到了较大的狐狸值。结果表明，不同条件下碳同位素分馏对稻田中f ac 和f ox 的估算很敏感。
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