外源氮和锰促进小麦秸秆腐解的协同效应及其作用机理

Crop straw residues returning is an important approach to recycle and use nitrogen, phosphorous, potassium and other nutrients, and the decomposition process is a key step restricting release and use nutrients in crop straw residue. Addition of nitrogen fertilizer accelerates the decomposition of cellulose and hemicullose at the initial stage, meanwhile the manganese can increase decomposition of lignin at the late stage. This means that exogenous nitrogen combines with manganese may accelerate decomposition of holocellulose and lignin at the same time. However, the existing mechanism remains unclear. In this program, the impacts of nitrogen and manganese on the decomposition process of wheat straw, the changes of holocellulose and lignin contents and chemical composition in residue will be investigated by using 13C and 15N double label as well as dipolar phase/magic angle spinning (DP/MAS), 1H-13C heteronuclear correlation (2D HETCOR) and other liquid/solid-state nuclear magnetic resonance analytical technique. The alteration of community structure and biodiversity of bacteria and fungi during the procedure of decomposition of wheat straw will be analyzed using 16S/18S high-throughput sequencing technique. The influence of nitrogen and manganese on the activities of hydrolytic enzymes and oxidizing enzymes for degrading holocellulose and lignin in wheat straw residue will be examined by enzyme analytic methods. The manganese forms in wheat straw resideus will also be analyzed by X-ray photoelectron spectroscopy (XPS) technique.To reveal the synergistic mechanisms of nitrogen and manganese on the decomposition of wheat straw residues, the coupling relationships, interaction pathways and contribution rates among the microbial community, enzymes activities and decomposition process as well as the components and chemical composition of wheat straw residues will be analyzed using the structural equation model. Above results will provide the theoretical facts for promoting decomposition of wheat straw and increasing high use efficiency of nutrients in crop straw.

秸秆还田是循环利用氮磷钾等养分的重要途径，腐解过程是制约秸秆养分释放和利用的关键。增施氮肥可促进植物体内纤维素组分的腐解，锰可加速植物体内木质素组分的腐解，即氮和锰组合具有同时促进植物体内纤维素和木质素腐解的互补作用，但究其协同效应及其作用机理尚不清楚。本项目拟利用13C和15N双标记和系列高级固态核磁共振技术，研究氮和锰影响小麦秸秆腐解过程及纤维素和木质素等含量和化学结构的变化规律；整合运用16S/18S高通量测序和生物信息学分析技术，剖析秸秆腐解微生物群落和多样性的演变特征，剖析微生物量碳/氮含量与结构变化规律；利用酶学分析方法，探究特异降解纤维素、木质素的酶活性变化规律；利用XPS分析技术，探究秸秆体内锰离子形态的变化特征；整合运用结构方程模型，解析小麦秸秆腐解过程与微生物群落及酶活性的耦合关系及作用途径，揭示氮和锰促进小麦秸秆腐解的协同效应及其作用机理，为秸秆快速腐解提供理论支撑。

本项目利用13C和15N双标记和系列高级固态核磁共振技术，研究了氮和锰影响小麦秸秆腐解过程及其化学结构的变化规律；整合运用16S/18S高通量测序和生物信息学分析技术，剖析了秸秆腐解微生物群落和多样性的演变特征，利用酶学分析方法，探究了特异降解纤维素、木质素的酶活性变化规律；整合运用结构方程模型，解析了小麦秸秆腐解过程与微生物群落及酶活性的耦合关系及作用途径，揭示氮和锰促进小麦秸秆腐解的协同效应及其作用机理，为秸秆快速腐解提供理论支撑。.主要结果如下：.1. 外源添加不同形态氮素（硫酸铵、尿素和硝酸钾）均能促进微生物生长，增加微生物生物量，提高了β-葡萄糖苷酶、酸性木聚糖酶、锰过氧化物酶和漆酶等秸秆腐解酶活性，加快对小麦秸秆的降解，其中以尿素和硝酸钾的效果最佳，硫酸铵效果次之。.2. 添加7.5 mg/L Mn2+处理的小麦秸秆残留率最低（82.33%），腐解程度最高，其微生物生物量增加了2.41%-14.16%，β-葡萄糖苷酶活性提高了1.82% -23.13%，酸性木聚糖酶活性提高了23.20% - 186.22%，锰过氧化物酶活性提高了2.52% - 4.33%，漆酶活性提高了5.00% - 78.36%。.3. 氮和锰交互作用条件下小麦秸秆腐解程度最高，残留率最低（75.14%）。氮和锰交互作用条件下微生物生物量增加了45.82%- 86.42%，β-葡萄糖苷酶活性提高了9.33% - 39.21%，酸性木聚糖酶活性提高了55.41% - 240.27%，锰过氧化物酶活性提高了5.56% -12.51%，漆酶活性提高了30.34%-170.74%。氮和锰交互是促进黑曲霉降解小麦秸秆的最佳组合。.4. 结构方程模型结果表明，氮素通过影响微生物生物量（SPC=0.45）提高秸秆降解酶活性，进而促进小麦秸秆降解；低浓度Mn2+（7.5 mg/L）能直接促进小麦秸秆降解（SPC=1.17），也可通过影响微生物生物量（SPC=0.61）促进小麦秸秆降解。因此，低浓度Mn2+（7.5 mg/L）可以促进微生物生长，有利于提高微生物分泌的木质纤维素降解酶活性，尤其是酸性木聚糖酶活性，从而加快小麦秸秆降解；而高浓度Mn2+（30 mg/L）会抑制微生物胞外酶活性，不利于小麦秸秆的降解。