Elucidating the 3D chemical and physical architecture of soil microstructures by combining spectromicroscopic techniques and developing of novel computational approaches

• Applicant: Dr.-Ing. Carmen Höschen
• Subject Area: Soil Sciences
• Term: from 2018 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 398381278

Soil microstructures are still seen as heterogeneous mixtures of mineral and organic components in random arrangement, while the thorough knowledge about architectural principles governing structure formation at the microscale is lacking. Especially microaggregates (soil microstructures smaller than 250 µm), highly complex associations of mineral and organic constituents of different sizes and chemical composition, are known to play a very important role for long term organic matter (OM) sequestration. While it has previously been impossible to study complex soil microenvironments at the necessary micro- to nanometer spatial resolution, nowadays, by the combination of microscopic and spectroscopic techniques it is possible to spatially resolve the composition, 3D architecture and structural characteristics of intact soil microstructures.We hypothesize that the 3D architecture of soil microstructures on the same soil substrate strongly depends on the bulk OM content (C-depleted, C-intermediate, C-rich) and OM quality (high C/N ratio, low C/N ratio) interconnected with the specific spatial arrangement of soil minerals. To test our hypotheses, we will make use of natural soil material with comparable mineralogical composition but different organic matter content. Using natural soil systems will ensure the study of meaningful structural properties (e.g. surface roughness, pore sizes, cavity structure) together with chemical information (e. g. C and N distribution) fostering the formation of natural soil microstructures.By using the AFM module from LIST integrated into the NanoSIMS at the TUM we can combine the AFM height profiles with the elemental 2D/3D information obtained by NanoSIMS to build the 3D sample surface of complex structures accurately. By using 13C and 15N labelled OM as OM source during the incubation of the natural soil samples, HIM-SIMS will allow the determination of surface characteristics favouring organo-mineral associations at distinct microstructure spots at high spatial resolution, while the AFM-NanoSIMS combination will provide topography corrected data for the accurate determination of the elemental and isotopic OM composition at high mass resolution. We aim to develop correlative surface and volume reconstruction workflows for HIM-SIMS and AFM-NanoSIMS to accurately determine the location and chemical properties of mineral associated OM at the micro-scale. Our study will offer the great opportunity to trace structural principles governing natural soil development at the microscale and will enable a 3D/4D modelling of the formation of organo-mineral associations in soil 3D microstructures.

• DFG Programme: Research Grants
• International Connection: Luxembourg
• Partner Organisation: Fonds National de la Recherche
• Co-Investigator: Professor Dr. Carsten Werner Müller
• Cooperation Partner: Dr. Jean-Nicolas Audinot