可变电荷土壤与细菌相互作用影响土壤/细菌界面电化学性质的机制

Bacteria can be regarded as charged biological colloids. The interactions between bacteria and soil particles affect chemical, biochemical and bio-geochemical reactions in soils. The interactions between bacteria and constant charge soils and pure minerals have been investigated extensively. However, few of studies have involved in the interactions of bacteria with variable charge soils from tropical and subtropical regions. In this project, modern analytical technologies and electrochemial methods combined with chemical analytical methods will be used to investigate the interactions of representative bacteria and their extracellular polymeric substances (EPS) with typical variable charge soils systematically and elucidate the binding mechanisms for bacteria and EPS to surfaces of the soils. Subsequently, the effects of bacteria adhesion and EPS adsorption on surface charge and electrokinetic properties of the soils will be studied and the relative contribution of electric double layer-interaction and transference of charge from bacteria and EPS to the soils will be evaluated. The mechanisms for the effects of bacteria and EPS on surface electrochemical properties of the soils will be uncovered. The effects of bacteria and EPS on the chemical behaviors of Al in the soils and the adsorption of Ca2+、Mg2+ and K+ by the soils will also be investigated and the mechanisms for the effects will be elucidated through the research activities. The research achievements will enrich the electrochemical principles of variable charge soils and provide conditions for the establishment of electrochemistry of soil/bacteria interfaces. The results obtained in the project will also provide the important references for fertility improvement, amelioration and management of variable charge soils.

细菌是土壤中广泛存在的一类带电生物胶体，它们与土壤的相互作用对土壤中一系列化学、生物化学和生物地球化学过程产生重要影响。虽然细菌与恒电荷土壤和纯矿物之间的相互作用已开展大量工作，但它们与热带和亚热带地区的可变电荷土壤之间的作用急需深入研究。本项目拟将现代分析技术和土壤电化学方法与常规化学实验方法相结合，系统研究代表性细菌及其胞外聚合物与典型可变电荷土壤之间的相互作用，阐明细菌和胞外聚合物在土壤表面的键合机制；研究细菌粘附和胞外聚合物吸附对土壤表面电荷和动电性质的影响，区分双电层作用和电荷转移对土壤表面电荷变化的相对贡献，阐明细菌和胞外聚合物影响土壤表面电化学性质的机制；研究细菌和胞外聚合物对土壤铝化学行为和土壤吸附Ca2+、Mg2+和K+的影响，阐明其影响机制。研究结果可进一步完善可变电荷土壤的电化学理论，为土/生界面电化学的建立创造条件，并为可变电荷土壤改良、培肥和管理提供理论依据。

细菌是土壤中广泛存在的一类带电生物胶体，它们与土壤之间的非生物相互作用对土壤中一系列化学和生物地球化学过程产生重要影响。虽然细菌与恒电荷土壤和纯矿物之间的相互作用已开展大量工作，但它们与可变电荷土壤之间的作用急需深入研究。本项目将现代分析技术与电化学方法相结合，系统研究了枯草芽孢杆菌和荧光假单胞菌及其胞外聚合物(EPS)与典型可变电荷土壤之间的相互作用并与恒电荷土壤进行了比较，研究了细菌及其EPS对土壤表面电荷及土壤吸附各种金属阳离子的影响，研究了细菌及其EPS对土壤酸化和铝活化的抑制作用，阐明了相关的作用机制。吸附等温线和吸附动力学的实验结果表明，可变电荷土壤对细菌和EPS的吸附量大于恒电荷土壤，土壤铁铝氧化物含量和阳离子交换量是影响吸附量的主要因素。细菌及其EPS的吸附主要受土壤胶体与它们之间静电作用的影响，细菌和EPS表面的羧基和磷酸基可在土壤铁铝氧化物表面形成化学键，也对吸附有重要贡献。细菌在土壤矿物表面的吸附抑制了其迁移性，铁铝氧化物的影响大于层状硅酸盐矿物。由于细菌和EPS主要带负电荷，因此它们在可变电荷土壤表面的吸附使土壤表面正电荷减少，表面负电荷增多。而细菌和EPS吸附对恒电荷土壤表面电荷性质的影响较小。细菌和EPS在土壤表面的吸附增加了土壤表面负电荷，因此促进了可变电荷土壤对Ca2+和Mg2+等盐基性养分离子的吸附。枯草芽孢杆菌在土壤表面的吸附量及对表面负电荷的增加量均大于荧光假单胞菌，前者对土壤吸附阳离子的促进作用大于后者。细菌和EPS也促进了可变电荷土壤对Cu(II)、Cd(II)和Pb(II)等重金属的吸附，其机制涉及静电作用和表面三元络合物的形成。细菌和EPS在可变电荷土壤表面的吸附增强了土壤的抗酸化能力，抑制了土壤铝的活化，其机制主要涉及细菌和EPS官能团的质子化。本项目的研究结果可进一步完善可变电荷土壤的电化学理论，为土壤/微生物界面电化学的建立创造了条件。