秸秆与水分耦合对稻田净增温潜势的影响及微生物作用机制

The net global warming potential (GWP) from rice paddy includes change of soil organic carbon content, CH4 and N2O emission. Straw return and water management are main factors influencing greenhouse gas budget. At present, straw incorporated into soil under long period flooding causes large amount of CH4 emission. The GWP increased by CH4 emission offsets lager part of or even largely exceeds the GWP decreased by soil carbon sequestration. The GWP from N2O emission is only small percentage of the GWP from CH4 emission. The present study hypothesize that straw mulch combined with aerobic irrigation would accelerate straw aerobic decomposition and inhibit CH4 emission, thus decrease the GWP from paddy when N2O emission was also in consideration. Therefore, the present study plans to utilize ways of straw return (no return, straw incorporation and straw mulch) and water managements (conventional, intermittent and wetting irrigation) coupling experiment, comprehensively analyze the effects of ways of straw return and water managements coupling on net GWP from paddy. The variations of mcrA, pmoA, narG and nosZ-containing communities involved in abundance, composition and gene expression will be also investigated by the methods of the real-time PCR and the terminal restriction fragment length polymorphism (T-RFLP). In combination with the data of soil physicochemical properties, the related microbial mechanism would be well explained. The present study would provide scientific support for the management of straw and water and mitigation of GWP from rice paddy.

稻田净增温潜势包含土壤碳库大小变化、CH4和N2O排放三部分。秸秆还田和水分管理是影响稻田温室气体收支的主要因素。目前长时间淹水下的秸秆翻耕还田导致大量甲烷排放，其所产生的全球增温潜势很大程度上抵消或远远超过了土壤固碳所降低的全球增温潜势。相对于稻田CH4排放来说，N2O排放产生的全球增温潜势只占很小比例。本项目推测通过秸秆覆盖还田结合好氧灌溉方式促进还田秸秆有氧分解，抑制CH4排放，同时考虑N2O排放，从而达到降低稻田净增温潜势的目标。为此，本项目拟利用秸秆还田方式（不还田、翻耕入土、覆盖还田）和水分管理方式（常规灌溉、间歇灌溉、湿润灌溉）耦合试验，全面系统地分析秸秆和水分耦合对稻田净增温潜势的影响，同时监测土壤理化性质，并运用实时定量PCR、T-RFLP等分子生物学技术分析关键功能微生物组成、丰度和基因表达活性，剖析微生物作用机制，从而为稻田秸秆和水分管理以及温室气体减排提供科学支撑。

稻田净增温潜势包含土壤碳库大小变化、CH4和N2O排放三部分。秸秆还田和水分管理是影响稻田温室气体收支的主要因素。目前长时间淹水下的秸秆翻耕还田导致大量甲烷排放，其所产生的全球增温潜势很大程度上抵消或远远超过了土壤固碳所降低的全球增温潜势。相对于稻田CH4排放来说，N2O排放产生的全球增温潜势只占很小比例。本研究推测：通过秸秆覆盖还田结合好氧灌溉方式促进还田秸秆有氧分解，抑制CH4排放，同时考虑N2O排放，从而达到降低稻田净增温潜势的目标。为此，本项目设置了秸秆还田方式和水分管理方式试验，全面系统地分析秸秆和水分管理对稻田净增温潜势的影响，同时运用实时定量PCR、T-RFLP等分子生物学技术分析关键功能微生物丰度和群落组成，剖析了微生物作用机制。主要结论如下：.1) 在耕灌雨养、常规灌溉和长期淹水条件下，CH4累计排放112、376和805 kg ha-1 yr-1，N2O累计排放0.62、0.29和-0.01 kg ha-1 yr-1，土壤固碳速率分别为642、1072和1292 kg ha-1 yr-1，其综合净增温潜势分别为1646、8895和22497 kg CO2-eqv ha-1 yr-1。稻田淹水抑制N2O排放，促进CH4排放和SOC累积。稻田的主要温室气体为CH4，而SOC累积远不能抵消增排CH4的温室效应。2) 稻草入土还田和稻草覆盖还田均会增加CH4、N2O和CO2排放。与稻草混入相比，稻草覆盖处理增加CO2排放，但大幅降低CH4排放，从而大幅降低稻田综合净增温潜势。稻草覆盖降低CH4排放的效应随淹水时间延长而下降。3) 在丘陵农业生态系统中，稻田与旱地多相接相邻。旱地土壤多缺乏有机质，养分贫瘠。将稻草移施旱地可以减少旱地化肥用量，降低旱地N2O排放，同时有利于保持土壤水分，增加作物产量。稻草移施旱地可降低N2O排放23.1-3.5%，提高玉米产量16.5-29.6%。 4) 稻田CH4排放与产甲烷菌功能基因mcrA成正相关，与甲烷氧化菌功能基因pmoA成负相关。mcrA和pmoA群落组成主要受水分影响，而稻草还田对mcrA和pmoA群落组成影响较小，但为CH4产生提供了丰富的碳源。