生物炭的电子传递特性对水稻土中甲烷产生的影响

Methane is an important greenhouse gas and contributes to about 15% ~ 20% to the global greenhouse effect. The biochar addition in the soil may accelerate interspecies electron transfer of the corresponding bacteria and promote the production of methane. Thus, it is a major challenge for biochar application to balance between the positive and negative impacts of biochar technique. Thereinto, the key issue is how the electron transfer properties of biochar couple with the interspecies electron transfer among microorganism. To solve this problem, it is essential to identify the roles that different biochar electron transfer channels (direct or oxidation/reduction electron transfer channel) play in accelerating microbial interspecies electron transfer. Therefore, this project will firstly focus on the electron transfer properties of biochar, which will be specifically regulated during biochar modification. Biochar with gradient electron transfer properties will be prepared, and their electron conductivity, electric capacity, and direct electron transfer constant and oxidation/reduction electron transfer constant will be analyzed specifically. Secondly, the methane production in paddy soil after biochar addition will be monitored. The relationship between the enhanced methane production and the electron transfer properties of biochars will also be analyzed. This information will be fundament to interpret methane production mediated by biochars. Finally, the microbial co-culture system for methane production will be established. The contribution of different biochar electron transfer channels to methane production enhancement will be determined by calculating the overall electron transfer in the co-culture system. A model describing methane production in paddy soils through the interspecies electron transfer mediated by biochar will be built up. This study not only deepens our understanding on the virous effect of biochar in the environment, but also provides important theoretical foundation for regulating the greenhouse gas emission from soil.

甲烷对全球温室效应的贡献率可达15%-20%。生物炭在土壤中的施用可能加速相关微生物的种间电子传递，进而促进甲烷的产生。因而，如何权衡生物炭施用的正面和负面效应成为生物炭应用的一个重大挑战。生物炭的电子传递特性如何影响种间电子传递是其中的关键问题，而明晰生物炭两种电子传递途径（直接电子传递和氧化还原电子传递）各自发挥的作用是一个重要突破口。本项目首先聚焦生物炭的电子传递特性，定向调控并梯级制备不同电子传递特性的生物炭，着重分析其电导、电容、直接电子传递常数和氧化还原电子传递常数；其次，通过水稻土的生物炭添加实验，阐释以上电子传递特性与甲烷产生之间的响应关系；最后，构建共生产甲烷体系，通过体系电子流的整体核算确定不同电子传递途径对甲烷产生的贡献比重，建立生物炭介导下水稻土甲烷产生种间电子传递模型。该研究不仅可以加深对生物炭多元环境效益的认识，还可以为调控土壤中的温室气体排放提供重要理论指导。

甲烷在大气中的含量虽然比二氧化碳少得多,但其增温潜势很大，是二氧化碳的25倍，对温室效应的贡献率达15%~20%，其中水稻田所排放的甲烷约占大气甲烷总来源的9-19%。本项目集中关注生物炭的施用对稻田中微生物种间电子传递过程的具体影响机制，尤其是生物炭直接和间接电子传递过程的不用影响。项目首先阐明不同碳化条件对生物炭电子传递特性的影响及机理，尤其是生物炭的电子传递性能会随着碳化温度的升高快速升高；本项目研究发现，在较低碳化温度下，生物炭主要依靠表面官能团的氧化还原反应完成和电子受体或供体之间的电子传递；随着热解温度的升高，表面官能团逐渐减少，生物炭的电子传递方式逐渐变为依靠生物炭碳结构的导电性能；本项目发现生物炭的氧化还原能力主要在新鲜生物炭刚开始介入产甲烷过程时发挥作用；而长期来看，生物炭的电导率发挥出持久的作用。生物炭可以充当电子传递的桥梁，逐渐改变水稻土系统电化学性质，进而富集了电活性细菌及产甲烷菌，促使了水稻土系统的产甲烷模式从乙酸型产甲烷向甲基型产甲烷的转变。本项目的相关研究结果对于准确理解生物炭对稻田甲烷排放的影响及机制具有重要理论意义。