金属(氢)氧化物参与木质素微生物转化形成类胡敏酸的结构特征分析

Structural Characteristics of Humic-like Acid from Microbial Transformation of Lignin Participated by Metal (hydro) Oxides

以木质素为碳源,并添加针铁矿、三羟铝石及δ-MnO 2,采用液体摇瓶培养法培养混合菌株,基于扫描电子显微镜(SEM)和固态13 C核磁共振波谱(CPMAS 13 C-NMR)对110 d培养期间矿物-菌体残留物提取的类胡敏酸(HLA)进行结构分析。结果表明,针铁矿、三羟铝石和δ-MnO 2参与木质素转化形成HLA的微观结构各不相同,形态分别为大小不一的片状、不规则且带有皱状边缘的球状以及表面凹凸不平、多褶皱的木耳状,由δ-MnO 2参与形成的HLA颗粒间有聚集趋势;与木质素相比,3种(氢)氧化物参与形成的HLA品质均有所改善,脂族化和亲水化程度加强;与国际腐殖质协会(IHSS)推荐的胡敏酸(HA)相比,针铁矿更易促进HLA的疏水化程度,增强木质素的保护机制,使脂族化程度相对稳定,而δ-MnO 2在提高HLA品质及亲水化程度方面更有优势;金属(氢)氧化物参与形成HLA的峰位及归属与秸秆还田土壤HA相似,但保留了木质素残余成分,部分芳香碳结构被O、N所取代,羧酸含量远低于IHSS推荐的HA。其中,由δ-MnO 2参与形成的HLA分子中出现了醌基,表明δ-MnO 2在促进木质素腐殖化作用方面优于针铁矿和三羟铝石,能够为腐殖质形成提供前体物质。

Lignin can provide fundamental materials for the formation of humus (HS). The process of HS formation can benefit from the microorganisms and their microbial residues. To reveal the contribution of metal (hydro) oxides in promoting the conversion of lignin to HS, a method of liquid flask culture was adopted with lignin as C source. During the process, the fluid medium added with goethite, bayerite and δ-MnO 2 respectively was inoculated with the mixed inoculant composed of nine strains. During the culture of 110 d, the mineral-microbial residue was dynamically collected, from which the humic-like acid (HLA) was extracted and analyzed by scanning electron microscope (SEM) and 13 C cross-polarization magic-angle-spinning nuclear magnetic resonance spectrum (CPMAS 13 C-NMR ). The results showed different micro-structures of HLA molecules were formed from the transformation of lignin because of the additions of goethite, bayerite and δ-MnO 2. From the perspective of microscopic appearance, the shapes were, respectively: flaky structures in different sizes, irregular spheres with wrinkled edges, and black fungus with uneven surface and irregular wrinkles, among which the HLA particles formed by δ-MnO 2 had a tendency to aggregate together. Compared with lignin, the qualities of HLA formed by the participations of three metal (hydro) oxides were improved, and their aliphaticity and hydrophobicity degrees were also enhanced. Compared with humic acid (HA) recommended by the International Humic Substances Society (IHSS), goethite was more likely to promote the hydrophobicity degree of HLA, enhance the protection mechanism to lignin, and stabilize the degree of aliphaticity, while δ-MnO 2 had more advantages in improving the quality and hydrophilicity of HLA. Peak positions and their attributions of HLA formed by three metal (hydro) oxides had huge similarity to HA from a soil with straw returning. However, there were some residual components from lignin remained in the HLA molecules. Part of the aromatic C structure in HLA molecules might be replaced by O, N, and the content of carboxylic acid was lower than that of HA recommended by IHSS. Under the participation of δ-MnO 2 , quinone groups were observed in the HLA molecules, which was a necessary precursor for HS formation. It indicated that δ-MnO 2 was superior to goethite and bayerite in promoting lignin humification and could provide precursors for HS formation.