水稻根表铁膜的增厚对甲烷形成与排放的影响

Rice fields are one of major sources of methane, which is an important trace gas causing green house effect. All existing methods for mitigating methane emission from rice fields do not provide long-term mitigation. Radial oxygen loss (ROL) from rice roots are partly used for iron cycling in flooded soil. Fe(II) is oxidized to produce Fe(III) oxides, some of which precipitates on roots as iron plaque. Rhizosphere soil plus rhizoplane becomes a niche where iron cycling rate is high. Better understanding the activities of both iron-reducing bacteria and methanogens in this compartment will be helpful to find a new way for mitigating methane emission from rice fields. In this study, root porosity, ROL, and iron plaque on roots for the plants grown in hydroponics will be measured and compared among different rice varieties. The varieties with high potential to form more iron plaques will be used for pot tests and field experiments. The relationship between Fe(II) concentration in hydroponics culture and iron plaque on roots will be analysed. The effects of the selected varieties and iron fertilizer application on methane production and emission will be evaluated through biogeochemical data analysis. The microbial communities involved in methane production and iron reduction will be identified by molecular biology technologies. The pot tests and field experiments during four seasons or two years will provide direct evidences for confirming a long-term mitigation of methane emission through planting the varieties with high ROL and iron fertilizer application. Therefore, a long-term mitigation strategy for methane emission from rice paddy fields will be proposed: planting the varieties with high ROL and only one application of iron fertilizer, which can be adopted for all flooded rice soil.

水稻田是重要温室气体- - 甲烷的主要排放源之一。现有的稻田甲烷减排措施不具备良好的持效性。水稻根系具泌氧活性，淹水土壤内的Fe(II)经氧化后可在根表形成铁膜，根面和根际成为铁循环最活跃的生态位。深入了解铁还原菌和产甲烷古菌在这一区域的代谢活动将有助于发现甲烷减排的新途径。本研究利用水培试验，对不同水稻品种的根孔隙度、根系泌氧能力和根表铁膜进行比较，筛选出具有厚铁膜的品种，并评价Fe(II)浓度对根表铁膜的影响。采用生物地球化学技术和和分子生物学技术，进一步探讨厚铁膜水稻品种和铁肥对稻田甲烷形成和排放的综合影响及其动态性，阐明其微生物学机理。连续2年4季的盆栽试验和大田试验将提供可靠的科学数据，以证实厚铁膜水稻品种和铁肥能持久地减少稻田甲烷的排放。为此，可提出稻田甲烷长效减排的对策，即施用铁肥一次，每季种植泌氧能力强的水稻品种就可实现淹水稻田甲烷的可持续性减排，此对策将具有广泛的应用前景。

水稻田是重要温室气体——甲烷的主要排放源之一。现有稻田甲烷减排措施的持效性欠佳。水稻根系的泌氧促使淹水土壤中Fe(II)氧化，并在根表形成铁膜，根面和根际成为铁循环最活跃的生态位。深入了解铁还原菌和产甲烷古菌在这一区域的代谢活动将有助于发现甲烷减排的新途径。本研究利用水培试验，对不同水稻品种的根表铁膜和根孔隙度进行了比较，筛选出了具有厚铁膜的水稻品种。然后，对其中的4个品种进行了盆栽试验，Fe肥能减少“博I优26”的甲烷排放，2次试验中甲烷减排率介于14.38%-17.52%。同时还对这4个品种进行了一次性施Fe和不间断淹水的小区试验，结果表明，Fe肥对连续4季的“博I优26”都有甲烷减排效果，其甲烷减排率介于16.16%-26.05%。盆栽试验和小区试验的结论源自生物地球化学和分子生物学方面的数据支撑，包括稻株不同年龄时的甲烷排放通量、孔隙水甲烷浓度和Fe(II)浓度，根际土、非根际土和根的产甲烷潜力，根际土和非根际土的Fe(II)和Fe(III)含量，根表铁膜和根孔隙度，根际土、非根际土和根的铁还原菌和产甲烷古菌的群落结构和种群数量。施一次铁肥，每季种植厚铁膜水稻品种可以作为稻田甲烷长效减排的一项对策，实现淹水稻田甲烷的可持续性减排，此对策将具有广泛的应用前景。