大气CO2浓度与气温升高下生物质炭输入对稻田土壤CH4和N2O排放的影响及其机理

Paddy soil ecosystem, as a typical agricultural ecosystem in China, is a main emission source of global greenhouse gases (CH4 and N2O). Recent studies suggest that elevated atmospheric CO2 and temperature can significantly stimulate GHGs emissions from paddy ecosystems, while biochar for soil amendment appears to be a promising method of carbon sequestration and GHGs reduction for tackling global climate change. So, as the new material for combatting global climate change, will biochar for soil amendment play an important role in CH4 and N2O reduction from paddy soil under elevated CO2 and temperature? This project is the first study which combines climate change and biochar’s role in carbon sequestration and GHGs reduction, two international hot focuses. In this study micro-climate simulation system platforms are used to investigate the influences of rice-straw derived biochar amendment on CH4 and N2O emissions and carbon and nitrogen transformation characteristics in paddy soil under elevated CO2 and temperature. Q-PCR and metagenomics techniques are applied to uncover the main microorganisms which involved in carbon and nitrogen cycling in response to the rice-straw biochar amendment under elevated CO2 and temperature. Results of the study are expected to elucidate the reduction effect and microbial mechanisms of biochar amendment on CH4 and N2O emissions from paddy soil under elevated CO2 and temperature, providing theoretical evidences for developing new techniques in reducing GHGs emissions from paddy soil in China for combatting future global climate change.

稻田是我国典型的农业生态系统，也是温室气体CH4和N2O的重要排放源。研究发现大气CO2浓度和气温升高将显著促进稻田生态系统温室气体排放，而生物质炭则有望成为稻田生态系统固碳减排的新途径。那么，作为应对气候变化的新材料，生物质炭在大气CO2浓度和气温升高下是否依然能够发挥其对稻田CH4和N2O的高效减排作用？项目首次将气候变化与生物质炭固碳减排作用两大国际热点相结合，拟通过微气候模拟系统平台，以水稻秸秆生物质炭为试材，分析大气CO2浓度和气温升高下生物质炭输入对稻田CH4和N2O排放特征以及碳氮物质转化规律的影响；借助q-PCR和宏基因组分析技术，揭示大气CO2浓度和气温升高下参与土壤碳氮循环过程的主要功能微生物对生物质炭化还田的响应机制；从而阐明大气CO2浓度和气温升高下生物质炭输入对稻田CH4和N2O的减排效应及其机理，为气候变化条件下稻田生态系统温室气体减排新技术研发提供理论依据。

针对秸秆生物质炭在未来大气CO2浓度和气温升高下是否还具有温室气体减排作用这一核心问题，以水稻秸秆为研究对象，研究了在未来大气CO2浓度和气温升高下生物质炭输入稻田土壤CH4和 N2O的排放特性及其机理。研究表明，在气温与大气CO2浓度升高的条件下，生物质炭输入依然能够改良土壤基本理化特性，包括在水稻生长期内提高土壤pH值、EC值、TOC和TN含量以及C/N值，其中对土壤pH值的调节能力，受到气温与大气CO2浓度升高的制约；并且老化的生物质炭仍然具有明显的芳香化结构，依然具备高度的稳定性和良好的固碳潜力；生物质炭输入在气温与大气CO2浓度同时升高的条件下依然能够有效发挥对稻田土壤CH4排放的减控作用并且对稻田土壤N2O排放的促进效应相比正常气温与大气CO2浓度下减弱；生物质炭输入通过增加土壤含水率、pH值，同时减少土壤DOC含量，显著降低土壤中产甲烷古菌与甲烷氧化细菌的功能基因丰度比值（16s RNA/pmoA），提高Ⅰ型甲烷氧化细菌相对丰度，增加甲烷氧化细菌群落多样性，从而增强土壤氧化CH4能力，减少土壤CH4排放量；然而，生物质炭调节土壤pH值的能力受到气温与CO2浓度同时升高的制约，生物质炭输入对土壤氨氧化的强化作用减弱，导致其对N2O排放的促进效应减弱。