Dichotomy of gluing and cementing agents in soil microaggregation

只有将相关成分的表面化学与微团聚体的形成和性质联系起来，才有可能确定土壤微团聚体的机制。我们的目标是确定不同的聚集体形成剂(有机物、粘土矿物、金属氧化物)在微团聚体形成和稳定性中的作用。为此，我们将通过一系列批次和微观实验以及土壤地形序列来研究微团聚体(20-250？m)及其建筑单元(&lt；20？m)的形成及其物理化学性质的时空变化。我们的基本分析方法依赖于微聚集体的X射线光电子能谱(XPS)来确定无机和有机表面的元素组成。微团聚体的表面化学(XPS)、形貌(扫描电子显微镜)、颗粒和孔径分布(激光衍射、汞测孔仪、气体吸附)以及润湿性(接触角分析)将与微团聚体的稳定性有关。环境条件变化对微团聚体稳定性的影响将通过微生物还原FeIII氧化物、有机物矿化和pH变化来选择性地去除聚集体形成剂来评估。这些研究将为微团聚体的建模提供机制背景，并对土壤有机质稳定产生相关影响。

The identification of mechanisms in soil microaggregation is only possible by linking the surface chemistry of involved components to the formation and properties of microaggregates. We aim at identifying the role of different aggregate-forming agents (organic matter, clay minerals, metal oxides) involved in microaggregate formation and stability. For this, we will investigate the formation and temporal and spatial change of physicochemical properties of microaggregates (20-250 ¿m) and their building units (<20 ¿m) in a series of batch and microcosm experiments as well as in a soil toposequence. Our basic analytical approach relies on X-ray photoelectron spectroscopy (XPS) of microaggregates to determine the elemental composition of inorganic and organic surfaces. The microaggregate surface chemistry (XPS), morphology (scanning electron microscopy), particle and pore size distribution (laser diffraction, Hg porosimetry, gas adsorption), as well as wettability (contact angle analysis) will be related to the stability of microaggregates. Consequences of changing environmental conditions to microaggregate stability will be assessed upon selective removal of aggregate-forming agents via microbial reduction of FeIII oxides, organic matter mineralization, and pH shifts. These studies will provide a mechanistic background for modeling microaggregation with relevant implications for soil organic matter stabilization.