苏打碱土有机质的结构特征及其转化的微生物驱动机制

Strong alkalinity is the main obstruction factor of saline-sodic soil, however, the soil also features low content of soil organic matter (SOM), which severely limits the production potential of crops. Addition of organic materials can improve soil organic matter, and the chemical natures of SOM predicts its quality. However, it is unclear the dynamics of carbon and nitrogen and the structural changes of organic matter in saline-sodic soil along a sodicity gradient, especially in an extreme saline-sodic soil. More specifically, the fate of organic matter addition and the microbial mechanism underlying the transformation of soil organic matter are largely unknown. In this study, using advanced nuclear magnetic resonance including multiCP/MAS and dipolar dephasing as well as fluorescence excitation emission matrices–parallel factor analysis, we will investigate the structural natures of organic matter in different saline-sodic soil in Songnen Plain and their changes during the laboratory incubation with straw amendment. The organic matter includes whole soil organic matter, organic matter in different wet-sieved aggregates, water extractable organic matter, i.e., dissolve organic matter, and humic extracts (humic substances). We will also focus on the changes of microbial community structure and biodiversity during laboratory incubation with 13C and 15N labeled straw amendment combined with or without inoculation with different soil microorganisms, using 16S high-throughput sequencing technique. Fate of carbon and nitrogen derived from the straw in the saline-sodic soil will be traced. In addition, the coupling relationships of the structure of soil organic matter and that of microbial community will be studied, on the basis of the mechanisms of sodicity affecting chemical natures of soil organic matter and microbial mechanisms driving the straw decomposition in saline-sodic soil. The results obtained from the study will provide the theoretical basis for promotion of organic matter in saline-sodic soil.

苏打盐碱土的主要障碍因子除了强碱性外，有机质含量低下也是导致其生产力低下的主要因素。施用外源有机物料是提升土壤有机质的重要措施，而有机质结构特征是其质量的重要指标。然而外源碳氮在不同碱化梯度土壤中的定量分配特征和有机质结构的变化特征以及导致上述变化的微生物机制尚不明确。本项目拟利用multiCP/MAS和偶极相移等高级13C核磁共振技术及三维荧光光谱-平行因子分析法，从团聚体分级（湿筛法）和化学分组（水和碱液提取）角度立体式研究松嫩平原原位不同碱化梯度土壤及秸秆培育期间碱土有机质结构的变化规律；利用13C-15N标记和高通量测序技术，研究外源秸秆添加和外源微生物接种培育对碱土微生物群落结构和多样性的影响，同时考虑外源碳氮在有机质组分中的分配和转化特征；系统阐述碱度梯度下有机质结构的演变规律、秸秆分解的微生物驱动机理以及有机质-微生物之间的偶联机制。研究结果为苏打碱土有机质提升提供理论依据。

土壤有机质含量的提升和微生物活性的增强对于提高盐渍土生产力具有重要意义。施用外源有机物料是提升土壤有机质的重要措施。然而盐渍条件下微生物群落如何构建，以及微生物在外源物料介导的盐渍土有机质周转中如何响应尚不明确。本项目从盐渍土基本理化性质、土壤微生物群落结构和建群机制、外源有机碳在盐渍土中的转化及其微生物机制，深入研究了盐渍土中有机碳动态变化规律及其机制。结果发现，在盐渍土剖面上土壤性质发生分异，主要为盐碱程度随深度增加而降低，同时土壤有机质组分（土壤有机碳、可溶性有机碳和微生物生物量碳）和养分（全氮、速效氮和速效磷）随深度增加而递减。尽管大多数（79.4~89.2%）OTU在整个土壤剖面上共同分布，但土壤性质的差异也塑造了表层和底层相对独特的物种。亚表层（20~40 cm）担当着调节阀的角色，控制着表层微生物向更深处的扩散。整个剖面上的盐渍土微生物群落结构主要受随机性过程（87.0~92.6%）控制。进一步，向盐渍土中添加外源秸秆碳可增加CO2释放量，引起正向激发效应。其中55.1~66.5%的秸秆碳都矿化为CO2，4.5~5.4%的秸秆碳同化为微生物生物量，最多只有4.48~5.41%的秸秆碳残留在土壤中。培育初期盐渍土中微生物对秸秆添加的响应不如非盐渍土明显，但随培养时间增加则更加活跃，其富集属数量逐渐增加。培育过程中不断溶解的可溶性有机碳可作为微生物利用的底物。微生物优先利用底物中的烷氧碳等相对易分解组分导致DOC芳香性结构更高。盐渍土中的土著耐盐微生物KSA1既可能参与了秸秆的分解，也影响了激发效应。研究结果证明了外源有机物料进入盐渍土后可被土著耐盐微生物利用，为外源物料提升盐渍土肥力提供了理论依据。

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