我国典型稻田的甲烷产生途径及其对关键因子的响应机制

In the rice-based cropping systems, methane (CH4) are primarily produced from acetate fermentation and CO2/H2 reduction. It is reported that relative contributions of the two methanogenic pathways (fac and fCO2) varied greatly during the rice growth season. Moreover, they are thought to be affected significantly by rice planting pattern, soil water content, organic fertilizer application, inorganic nitrogen fertilization, and temperature, etc. China, the largest rice producing country in the world, has various patterns of rice cultivation, mainly including rice-wheat rotation system, rice-fallow cropping system, and double-rice cropping system. There are large differences in the variations of fac and fCO2 and in the responses to the influencing factors that are mentioned above. To date however, scarce related information has been reported simultaneously in the literature on the 3 kinds of rice cropping systems. In this project, we thereby collected 6 kinds of paddy soils from the 3 typical rice-based cropping systems all over China, which are found to be a great differences in water and heat conditions. The paddy soils are planned to anaerobically incubate with and without a specific inhibitor of acetoclastic methanogenesis (CH3F). We will use the stable carbon isotope technique and the molecular biology technology to study the variations of fac and fCO2 in the 3 typical rice-based cropping systems in China, and then to clarify the microbial mechanisms of fac and fCO2 responses to the influencing factors. Results of this project will help to offset the weaknesses of the research in this field, and meanwhile enhance the knowledge in the mechanisms of CH4 production and in the responses to the key influencing factors. In addition, it can provide reference data and scientific reference for the modelling and simulation research on CH4 production in the paddy fields under climate-change conditions in future.

稻田的CH4产生主要来源于乙酸发酵和CO2/H2还原，这两种CH4产生途径的相对贡献率（f乙酸和fCO2）随水稻生长存在明显的季节变化，并受种植模式、水分含量、有机肥、氮肥和温度等诸多因子的强烈影响。我国是水稻生产大国，耕作模式多样，主要包括稻麦轮作、稻休闲和双季稻等3大类，其f乙酸和fCO2的变化规律及其对上述影响因子的响应很可能存在较大差异，然而目前鲜有文献报道。于这3类典型稻田系统中采集6种水热条件差异悬殊的水稻土，在添加和不添加乙酸产CH4抑制剂（CH3F）条件下进行厌氧培养，通过稳定性碳同位素自然丰度法和分子生物学技术，研究我国典型稻田f乙酸和fCO2的变化规律及其对关键因子响应的微生物学机理。成果有助于弥补本领域研究的不足，提升对稻田CH4产生机理及其对关键因子响应机制的认知，还可为未来气候变化条件下稻田CH4产生的模型模拟研究提供数据参考和科学借鉴。

稻田CH4产生主要有两个途径：乙酸发酵产CH4和CO2/H2还原产CH4，理论上各占2/3和1/3。但实际上，CH4产生途径存在明显的季节变化，且受水肥管理、种植模式、温度等因子的影响。国际上以往有关于不同土壤CH4产生途径的研究多集中于湖泊底泥、湿地土壤等方面，较少涉及到不同类型的稻田土壤，特别是我国典型稻田生态系统CH4产生途径的对比研究严重缺乏。本项目通过室内培养实验，观测了稻麦轮作系统、稻休闲模式和双季稻田的CH4 产生潜力，同时运用稳定性碳同位素自然丰度法和分子生态学技术，评估了稻田乙酸和H2/CO2产 CH4途径的相对贡献率并揭示了其微生物学机制。. 乙酸产CH4的相对贡献率（fac）存在明显季节变化，且因种植模式而异。稻麦轮作系统和双季稻田的fac随水稻生长而增大，并在成熟期取得最大值，变化范围分别为20-56%和 23-59%，而常年淹水稻田的fac先减小后增大，稻季f ac的平均值比稻麦轮作系统和双季稻田的大5-11%；在15-35℃范围内，温度升高总体上减小fac，但稻休闲模式下黑龙江阿城的黑土除外；土水比为0.5-1.5时，土壤含水量升高并未改变稻麦轮作系统和双季稻田的fac，但明显增加稻休闲模式下四川资阳常年淹水土壤的fac；添加不同类型秸秆对土壤CH4产生途径的影响不同，其中稻秆显著降低fac，而玉米秸秆显著增加fac；施氮总体上对fac无明显影响。常年淹水土壤的CH4产生潜力最大，CH4产生潜力与DOC密切相关，温度、水分和秸秆对CH4产生潜力有明显的促进作用，而氮肥则相对抑制CH4产生；fac主要和土壤中的乙酸含量、产甲烷菌丰度及群落组成有关。. 本研究从土壤微生物过程层次上阐明了我国典型稻田CH4产生途径的变化规律及其对种植模式、培养温度、土壤水分、有机肥和氮肥等关键因子的响应机制，结果能为稻田CH4产生途径的模型模拟研究提供数据参考和科学借鉴。