Projekte in Kooperation mit dem Deutschen Elektronen-Synchrotron (DESY)
1) Pore space characteristics of soil aggregates determined from synchrotron X-ray images and their impact on carbon sequestration and aggregate stability
Soils are source and sink of carbon and therefore play an important role in the partitioning of greenhouse gasses. The relevance of soil structure and particularly of the formation and stability of (micro)aggregates for long term sequestration of soil organic carbon (SOC) is well known. However, research during the last 50 years produced only a few quantitative studies that consider the interactive effects between soil biota with physical and chemical processes. These interactions in turn are primarily dependent on the spatial arrangement of solids and voids since the geometry and continuity of the pore-network within soil aggregates determine the fluxes of air, water and nutrients and hence control the environment for microorganisms. Advances in synchrotron X-ray tomography and the development of algorithms to quantitatively describe porous media from reconstructed 3D-images greatly contribute to the understanding of the mechanism involved in carbon sequestration and the stabilization of aggregates. We intend to investigate soil aggregates from different land management systems on their flow relevant pore geometrical properties. Furthermore, effects of different numbers of wetting/drying cycles on aggregate pore space will be studied. We hope to gain knowledge, which supports the interpretation of physical, chemical and biological properties on the sub aggregate scale to improve the prediction of changes in soil ecosystems due to land use with focus on global change.
2) Changes of intra-aggregate pore space characteristics by wetting-drying cycles
Soils are complex three phase media where numerous physical, chemical and biological processes control vital ecosystem functions by sustaining life and serving as a filter and buffer. Concerning the transport and transformation of e.g. carbon and/or soil pollutants in natural soils it is inevitable to investigate soil pore networks on the microbial habitat level with most microbes residing in pore regions of a few (tens of) micrometers in size. In view of the dynamics of pore space architectures with changing environmental boundary conditions (i.e. matric potential and related shrink/swell processes) we also need to consider associated pore network functions as dynamic. This, however, has so far been difficult to study in classical soil morphology analysis where usually “destructive” microscopy techniques are applied and where the information gained is inherently 2 dimensional. 3D non-invasive microscopy allowing for successive imaging of the same sample will open new possibilities to describe soil structural changes and to develop a conceptual understanding of soil structure formation and associated functions on the microbial habitat scale. Such data could further our understanding of interactive soil biological, chemical and physical processes in soil aggregates and support the development of pore scale models for numerical simulations of key micro-environment processes.
3) Modelling SOM decomposition in soil aggregates
The project deals with the influence of small scale pore space architectures on the decomposition/mineralisation of organic matter in intra-aggregate pore volumes. It aims at finding and quantifying relationships between the turnover of organic matter and structural attributes/complexity governing fluxes of water and air in associated pore systems of natural soils. New methods will be developed to visualize organic matter distribution in soil aggregates with non-invasive techniques (e.g. TEM-EDS, SR-CT) as well as to measure CO2 evolution on small scale (mm-cm) soil aggregates as a function of matric potential. 3D imaging of soil structure, organic matter distribution and the geometrical configuration of water filled pore regions in intra-aggregate pore spaces will be utilized to simulate carbon decomposition with a previously developed model (MOSAIC). Measurements of CO2 evolution on soil aggregates derived from various long-term field experiments in France and Germany together with the non-invasive imaging of soil structure and organic matter distribution provide valuable data for a further development of process oriented carbon turnover modelling.
4) Gradients and mineralization of C in soil aggregates with contrasting structure
This project builds upon the previous project (Modelling SOM decomposition in soil aggregates) where the influence of small scale pore space architectures on the decomposition/mineralisation of organic matter in intra-aggregate pore volumes was investigated. New staining methods adapted from TEM-EDS analysis were developed to visualize and quantify soil organic matter (SOM) distribution in undisturbed soil aggregates in order to find SOM associations with soil structure. In this project we will apply the staining technique to find and analyse differences in organic matter content and small scale spatial distribution in aggregates from Luvisol cultivated with different preceding crops (Lucerne and Fescue). It is hypothesized that different structures and pore architectures will have an influence on C-gradients from the exterior towards the interior of the aggregates. Physically occluded SOM fractions will be identified. Using a previously developed model of soil organic matter decomposition we will simulate SOM mineralisation in different soil repositories.