水热炭的微生物陈化（Microbial-aged Hydrochar）及其对稻田氨挥发的影响机制

Ammonia volatilization is the most important gaseous loss of nitrogen fertilizer in the paddy field, and has a major negative impact on the atmosphere and water environment. Consequently, it is of great significance to reduce ammonia volatilization in the paddy field. In the recent decade, conventional pyrolytic biochar (pyrochar) had attracted much attention as a soil conditioner for its multiple benefits to soil environment. However, its comparatively high pH has a tendency to promote ammonia volatilization, and its practicability will be undermined. .Herein, hydrochar (HC), a quite different black carbon, will be investigated. HC is a kind of solid product with carbon as the main body. HC is observed weak acidity and existing abundant of oxygen-containing functional groups on the surface. HC is prepared by hydrothermal carbonization at low temperature (usually 180 - 375 oC) and corresponding pressure. Hence, the lower surface pH, wide supply of feedstocks and lower cost will make HC a possible soil additive, to control ammonia volatilization in the paddy field..However, HC was found to have some toxic effect on crops if it was not properly applied, mainly due to the excessive organic acids and phenolic organics introduced to soil system. Hence, pretreatment through some methods of HC is necessary..In this study, HC will be prepared by a microbial-aged process, to produce a microbial-aged hydrochar (MHC). The core of the “microbial-aged process” is the fermentation of HC by liquid anaerobic fermentation technology. It will dissolve and to a certain degree degrade organic acids and organic phenols in Biochar-derived Dissolved Organic Matter (BDOM) as well as other organic components that are not thoroughly carbonized while achieving microbial improvement of the surface characteristics of HCs. Our previous experiment found that MHC has better characteristics than the original HC, especially improving the biocompatibility, and significantly improving the specific surface area and cation exchange capacity, enhanced biochar stability, reduced BDOM content, and significantly increased the adsorption capacity of cation ions..MHC will be for the first time applied to paddy field from the point of controlling ammonia volatilization. Briefly, the study will focus on two key scientific issues: 1) The effect of microbial aging process on the surface characteristics of HC and its adsorption process and mechanisms for ammonium and nitrate; 2) How the ammonia volatilization patterns will be disturbed by adding MHC in paddy fields and what will be the intrinsic mechanisms in affecting ammonia volatilization? As to the second scientific issue, two levels of research will be conducted: a) the disturbance of physical and chemical properties of the soil-water system caused by MHC and b) the influence on the key biological process of the soil-water system caused by MHC..Through this study, from the perspective of ammonia volatilization reduction, we will explore the feasibility of microbial-aged hydrochar applied to rice paddy as a soil additive. Based on the systematic study, we will strive to provide new ideas for biomass utilization, ammonia volatilization reduction, carbon sequestration and atmosphere & water environment improvement.

稻田氨挥发减排具有重大现实意义。同时，常规热解生物炭（Pyrochar）作为土壤添加剂得到广泛关注。Pyrochar虽可以实现固碳减排、土壤改良等环境效益，但其较高的pH有促进氨挥发的趋势。因此，水热炭（Hydrochar）这种通过高压水热反应制备的、表面呈弱酸性且富含可溶性有机质的炭基材料成为可能的替代选择。由于水热炭直接大量应用会对农业生产造成负面影响，因此，本研究创新性的将水热炭在厌氧发酵体系中进行微生物陈化，然后应用于稻田中，并考察其对氨挥发的影响机制。研究围绕两个科学问题展开：1）微生物陈化过程对水热炭表面特性及其铵硝吸附固持能力的影响；2）微生物陈化水热炭（MHC）对稻田氨挥发的调控及内在机制，包括MHC对土水体系理化性质和关键生物过程的影响进行分析。通过本研究，将从氨挥发调控角度阐释MHC作为稻田土壤添加剂的可行性，力争为氨挥发减排背景下的生物质资源化、固碳减排提供新的思路。

项目实施以来，组织开展了连续两年的水稻实验，同时配合微宇宙培养实验，并结合分子生物学技术、高分辨率质谱技术等现代表征分析手段，围绕项目研究目标并结合实验条件，取得系列进展：1）系统分析了水热炭及其微生物陈化产物的特征，并考察了与制备条件的联系。发现微生物陈化过程可显著提升水热炭表面结构特性，增加比表面积并影响表面官能团丰度；且显著弱化了水热炭的酸性特征。2）从分子层面深入解析了微生物陈化过程对水热炭可溶性成分DOM的影响。指出微生物陈化可以大大降低DOM中的酚酸类和多环芳烃类成分等风险成分的含量，从根本上缓解水热炭农用的潜在风险。3）考察了陈化时间对水热炭表面特征和DOM分子特征的影响。通过16个月的陈化试验，发现陈化后的水热炭亲水性/极性指数明显下降；孔隙度、灰分和稳定性显著增加；表面含氧官能团发生变化。4）阐述了水热碳化产生的可溶性组分对稻田土水界面自然生物膜（周丛生物）的影响。发现不同制备条件下的水热碳化可溶性组分对田面水水质和周丛生物的多样性、群落结构、环境特征的相关性和网络特性均产生了不同程度的影响。这为深入理解周丛生物在土壤氮转化中的角色提供了基础。5）分析了水热炭及其陈化改良产物对水稻产量和品质及氮素吸收的影响。连续两年的水稻实验表明，微生物陈化改良水热炭对水稻产量的促进效果相比原始水热炭更突出，其氮肥利用率与对照相比可增加37%-160%。6）考察了水热炭及其陈化改良产物对稻田土壤氨挥发的影响规律及机制。两年的水稻实验表明，不同水热炭及其陈化产物对稻田氨挥发的影响程度存在差异，考虑到增产效应，微生物陈化改良水热炭对于单位产量NH3挥发累积排放量的减排可达54%。稻田氨挥发减排的机制，则主要与田面水铵根浓度，pH，土壤脲酶活性有关。项目支撑发表论文35篇，含IF≥10的论文23篇；授权发明专利5项，转让专利1项到企业。培养4名研究生获得国家奖学金。