节水灌溉稻田温室气体排放对生物炭施用的响应机理与调控

Water-saving irrigation is an effective measure to reduce greenhouse gases emission from paddy fields, but causing a decrease of soil organic carbon. Application of biochar can significantly improve soil fertility and decrease greenhouse gases emission. Abatement effect of greenhouse gases emission from paddy fields and reasonable regulation with combination of the above two measures need intensive study. So changes and comprehensive greenhouse effect of greenhouse gases (carbon dioxide, methane and nitrous oxide) emission from paddy fields under water-saving irrigation with biochar will be analyzed based on field experiments, laboratory analysis and model simulation in this study. In addition, dynamic changes of soil environment, crop growth and meteorological factors will be measured. And the relationships between greenhouse gases emission and the above impact factors will be illuminated to reveal the mechanism of reducing greenhouse gases emission from paddy fields with combination of water-saving irrigation and biochar. DeNitrification-DeComposition model (DNDC) will be improved to simulate greenhouse gases emission, soil organic carbon content and rice yield dynamically with combination of water-saving irrigation and biochar. Detailed scene of water and carbon regulation will be set to simulate the change of greenhouse gases emission, soil organic carbon content and rice yield with long-term use (20 years) of above different simulating scenarios. The simulation results will be used to reveal the effects of different water and carbon regulations on greenhouse gases abatement and soil carbon sequestration. And reasonable application amount of biochar to saving irrigation water, increasing rice yield, fixing soil carbon and reducing greenhouse gases emission for paddy fields under water-saving irrigation will be put forward. The results has important theoretical and practical meaning for enrichment of rice water-saving irigation theory, reduction of greenhouse gases emission and sustainable utilization of soil and water resources of paddy fields.

节水灌溉作为一种有效的稻田温室气体减排措施，同时引起土壤有机碳含量降低，生物炭具有显著提升土壤地力及减排温室气体的作用，两者结合的稻田温室气体减排效应与合理调控有待深入研究。本项目基于田间、室内试验与模型模拟的方法，分析生物炭施用后节水灌溉稻田温室气体（二氧化碳、甲烷和氧化亚氮）排放规律及综合温室效应，结合土壤环境、作物生长与气象等因子的同步变化，研究其与温室气体排放的关系，揭示生物炭对节水灌溉稻田温室气体的减排机理。改进土壤碳氮循环模型-DNDC，实现对两种措施结合稻田温室气体排放、土壤有机碳及产量的动态模拟，设定细化的水碳调控情景，模拟不同情景长期应用（20年）后稻田温室气体排放、土壤有机碳及产量的变化，揭示不同水碳调控的稻田固碳、减排作用，提出稻田节水高产、固碳减排的合理生物碳施用量。研究结果对于丰富水稻节水灌溉理论，实现稻田温室气体减排及水土资源可持续利用具有重要的理论和现实意义。

水稻节水灌溉技术在减少温室气体排放的同时，加速了稻田土壤有机碳的分解，而生物炭具有显著提升土壤地力及减排温室气体的作用，本项目以田间、室内试验及模型模拟的方法，揭示了生物炭施用条件下节水灌溉稻田温室气体排放特征与机理，构建了生物炭与节水灌溉联合调控稻田温室气体排放、土壤有机碳含量及水稻产量的动态模拟模型，提出了节水高产、固碳减排的节水灌溉稻田合理生物炭施用量，研究结果对于丰富水稻节水灌溉理论，实现稻田温室气体减排及水土资源可持续利用具有重要的理论和现实意义。主要结论如下：施加生物炭减小了控制灌溉稻田CH4平均排放通量，20 t ha-1生物炭施用量稻田CH4平均排放通量最小，生物炭施加对稻田N2O排放通量的影响存在年际差异，施用后第1年增加、第2年降低了稻田N2O排放通量。施用生物炭降低了节水灌溉稻田CH4和N2O的综合温室效应，CA，CB与CC处理分别较FC分别显著降低了64.0%，70.7%与69.9%（p<0.05）。生物炭施用提高了节水灌溉稻田土壤肥力、水稻产量及灌溉水分生产率。施用中量生物炭节水灌溉稻田平均Reco和全生育期CO2累积排放量均小于不施炭处理，施用高量生物炭则相反。施用生物炭第2年节水灌溉稻田GPP和全生育期CO2累积吸收量均小于不施炭处理，却促进了第3年全生育期CO2累积吸收量。生物炭施用增加了节水灌溉稻田土壤有机碳、可溶性有机碳及微生物量碳含量，促进了节水灌溉稻田土壤过氧化氢酶、蔗糖酶和脲酶活性，且高量生物炭对三种土壤酶活性的促进作用更大，同时显著增大了节水灌溉稻田土壤细菌、真菌和放线菌丰度。土壤酶活性与微生物丰度显著影响稻田-大气CO2交换。改进稻田灌溉管理模块的DNDC模型能够较好地模拟稻田土壤温度、温室气体排放、水稻产量及土壤有机碳变化。稻田施用生物炭后20年间，稻田CH4、N2O和CO2排放的年累积通量规律并不一致，但均表现为生物炭施用降低节水灌溉稻田温室气体排放。从长期综合温室效应来看，节水灌溉稻田施用40t ha-1生物炭稻田综合温室效应最小。施用生物炭后20年间，施加生物炭增加了节水灌溉稻田的SOC含量，降低了DOC含量，增加了水稻产量（CC>CB>CA），基于未来气候模式下的情景模拟，综合考虑节水高产、固碳减排因素，节水灌溉稻田的最优生物炭施用量是40 t ha-1。