胞外聚合物与土壤活性颗粒互作驱动微团聚体形成机制

Soil micro-aggregates are the foundation of soil formation and development, which are also the hot spots of various physical, chemical and biological reactions, and profoundly affect soil health. Growth of a wide variety of microorganisms in micro-aggregates is accompanied by the production of extracellular polymeric substances (EPS), which have significant effects on microbial transport, biofilm formation, microbial biomineralization, nutrients and pollutants transformation, and also play an important role in soil aggregation and water retention. However, the mechanism of soil micro-aggregates formation controlled by EPS interactions with soil active particles is unclear. In this proposal, some state-of-the-art technologies such as the quartz crystal microbalances, nano-scale secondary ion mass spectrometry, the combination of atomic force microscopy with attenuated total reflection spectroscopy will be used at the molecular level to investigate the adsorption and aggregation kinetics, interaction forces between EPS and soil active particles, conformation and viscoelasticity of adsorbed EPS, and the distribution of chemical and mechanical characteristics of EPS in soil micro-aggregates. The purpose of all combination studies is to clarify the mechanisms of the formation and stability of soil micro-aggregates. The findings obtained in these studies will enrich knowledge of soil chemistry, soil microorganisms and colloidal interface chemistry, and bring up new ideas for in-depth studies of soil mineral-organic matter-microorganism interactions. On the other hand, they will provide the scientific basis for regulating soil microbial activity to improve soil nutrients utilization efficiency in the agriculture.

土壤微团聚体是土壤形成和发育的基础，各种物理、化学和生物反应过程的热区，深刻影响土壤健康。团聚体中微生物在生长代谢过程中释放出胞外聚合物（EPS），这些胞外物质可调控微生物迁移、生物膜形成、微生物成矿、以及养分和污染物转化等过程，同时在土壤保水性和团聚性方面也发挥着重要作用。然而，EPS与土壤活性颗粒互作驱动微团聚体形成机制尚不清楚。本课题拟运用石英晶体微天平、纳米离子二次质谱仪、红外原子力显微镜等现代仪器分析技术，在纳米尺度和分子水平研究EPS与不同类型土壤活性颗粒相互作用的吸附、团聚动力学过程、作用力、吸附态EPS分子构象和粘弹性，以及土壤微团聚体中EPS的化学和力学分布特征等，揭示土壤微团聚体形成与稳定机制。研究结果可丰富土壤化学、土壤微生物学和胶体界面化学理论，为土壤矿物-有机物-微生物相互作用深入研究开辟新思路，在实践上可为调控土壤微生物活性以促进土壤养分高效利用提供科学依据。

胞外聚合物(EPS)是由微生物分泌到其环境中的高分子量天然聚合物，包括多糖、蛋白质、DNA和脂类等。EPS建立了生物膜的功能和结构完整性，被认为是决定生物膜物理化学性质的基本组分。在土壤系统中，EPS在养分和污染物转化，土壤保水性以及团聚性方面发挥着重要作用。开展EPS与土壤活性颗粒互作驱动土壤微团聚体形成机制的研究，将有助于我们加深对土壤结构和功能的理解，更好地保持土壤健康、维护植物生产力和保障生态安全。本项目聚焦EPS与土壤活性颗粒互作机制及其驱动土壤微团聚体形成过程，运用多种现代仪器分析手段，在土壤EPS提取方法、EPS界面过程、生物膜形成、矿物团聚机制等方面取得了系列创新性成果。主要研究结果包括：（1）建立了红壤中EPS的提取方法，解析了阳离子交换树脂（CER）方法对土壤EPS的提取动态过程以及土壤EPS的响应敏感程度；（2）阐明了EPS-水铁矿复合体不同形成途径（吸附与共沉淀）对EPS 组分保留的选择性固持及分子机制；（3）揭示了铁氧化物表面不同土壤组分包被对细菌及其EPS粘附的影响机制，明确了不同环境条件下枯草芽孢杆菌EPS驱动土壤矿物团聚的机制；（4）揭示了土壤矿物介导下细菌生物膜形成机制及其EPS空间分布，阐明了种间互作影响土壤生物膜形成与功能机制。研究成果为发挥土壤EPS功能、调控土壤微生物活性提供了科学依据，也为丰富土壤化学、土壤微生物学及胶体界面化学等学科的理论和内容提供了支撑。