灌丛根际土壤-细菌间界面作用对无机氮转化过程的影响

Previous studies reporting the soil nitrogen cycling mainly focused on forest, grassland and agricultural soils. However, less attention has been paid to the shrub ecosystems. The interfacial interactions between nitrogen-transforming microorganisms and soil components remain poorly understood. In this study, the materials such as shrub rhizosphere soil, nitrifying and denitrifying bacteria are selected. Adsorption simulation experiments will be conducted to quantify the soil-bacteria interfacial behaviors. Scanning electron microscope, zeta potential analyzer, DLVO model, potentiometric titration, fourier transform infrared spectroscopy, micro-calorimetric, and nitrogen form-analysis techniques will be utilized to investigate the effects of various soil components (mineral, humic substances, clay, silt and sand), environmental factors (pH, temperature and ionic strength), and surface properties on soil-bacteria interfacial interactions. The adsorption parameters, surface appearances, interaction forces, functional groups, metabolic activities, and nitrification/denitrification rates of bacteria in different soil components are obtained. The above information is used to comprehensively explain the interfacial mechanisms of bacterial adsorption on soil surfaces, and their impacts on nitrogen transformation processes. This project will be valuable for understanding the distribution and physiological activities of nitrifying/denitrifying bacteria in rhizosphere soil components. This work also has important implications for enhancing soil fertility and improving shrub soil ecological environment.

土壤氮循环以往研究主要集中在森林、草地和农田土壤，较少关注灌丛生态系统，且对氮转化微生物与土壤组分的界面作用相知甚少。本研究选取灌丛根际土壤、硝化细菌和反硝化细菌为实验材料，采用室内控制吸附实验对土壤-细菌界面行为进行定量，综合运用扫描电子显微镜、zeta电位仪、DLVO模型、电位滴定、傅里叶变换红外光谱、微量热和氮素形态分析技术，考察多种土壤组分（矿物、腐殖质、粘粒、粉粒和砂粒）、环境因素（pH、温度和离子强度）和表面性质对土壤-细菌界面作用的影响，获得细菌在不同土壤组分中的吸附参数、表面形貌、作用力、官能团、代谢活性、硝化/反硝化速率等信息，用以全面揭示细菌在土壤表面的界面作用机制及其介导的氮转化过程。本项目实施有助于了解硝化/反硝化细菌在根际土壤组分中的分布规律和生理活性，对于提高土壤肥力和改善灌丛土壤生态环境具有重要意义。

在土壤氮转化过程影响因素研究方面，前人工作主要集中在土壤理化性质、微生物类群、气候条件、土地利用方式等，并将土壤颗粒视为一个整体，忽略了氮转化细菌在不同土壤组分中的界面作用。本课题选取欧洲亚硝化单胞菌模式菌株，采集窄叶鲜卑花灌丛根际土壤，分析二者间的界面行为对细菌氨氧化作用的影响。结果表明，亚硝化单胞菌在土壤粘粒（< 0.002 mm）界面上的吸附量与吸附亲和力最强，其次是粉粒（0.002-0.05 mm）、细砂粒（0.05-0.25 mm）和粗砂粒（0.25-2 mm）；细菌的氨氧化能力与吸附能力成反比，随静电斥力升高而增大。粗砂粒拥有较低的比表面积和更大的粒径，为细菌生长繁殖和提供足够的空间，促进细菌的降解活性。细菌与铵态氮大量吸附在固相界面，增加了固定态细菌与底物的接触机会，界面作用促进了铵态氮向亚硝态氮的转化。本研究明确了氮转化细菌在灌丛土壤组分中的界面分布规律与降解活性，提出通过改善土壤质地、促进土壤大团聚体（>0.25 mm）形成等手段可有助于土壤亚硝态氮的积累，从而提高土壤肥力并促进山地灌丛有效氮的吸收。

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