Abstract
Soil is a heterogeneous mixture of various organic and inorganic parent materials. Major soil functions are driven by their quality, quantity and spatial arrangement, resulting in soil structure. Physical protection of organic matter (OM) in this soil structure is considered as a vital mechanism for stabilizing organic carbon turnover, an important soil function in times of climate change. Herein, we present a technique for the correlative analysis of 2D imaging visible light near-infrared spectroscopy and 3D X-ray computed microtomography (mCT) to investigate the interplay of biogeochemical properties and soil structure in undisturbed soil samples. Samples from the same substrate but different soil management and depth (no-tilled topsoil, tilled topsoil and subsoil) were compared in order to evaluate this method in a diversely structured soil. Imaging spectroscopy is generally used to qualitatively and quantitatively identify OM with high spatial resolution, whereas 3D X-ray mCT provides high resolution information on pore characteristics. The unique combination of these techniques revealed that, in undisturbed samples, OM can be found mainly at greater distances from macropores and close to biopores. However, alterations were observed because of disturbances by tillage. The correlative application of imaging infrared spectroscopic and X-ray mCT analysis provided new insights into the biochemical processes affected by soil structural changes.
Highlights
Soils are heterogeneous and complex mixtures of organic matter (OM), mineral particles and pore space
We present an approach for the identification and correlation of soil chemical composition and pore structure in intact soil cores
We developed a novel combination of 2D Imaging Vis-NIR (imVNIR) and 3D μCT through registration and correlative analysis
Summary
Soils are heterogeneous and complex mixtures of organic matter (OM), mineral particles and pore space. Their inherent functionality emerges from the spatial arrangement of these constituents on various spatial scales (Ritz et al, 2004; Portell et al, 2018; Wanzek et al, 2018). To understand the relationship between soil structure, carbon dynamics and biogeochemical processes, it is crucial to characterize undisturbed soil samples. This relationship is often investigated by techniques based on soil disturbance, e.g., by extracting aggregate fractions (Young et al, 2008) from the bulk soil, which provides insights into microscale processes, but the complete image of the soil architecture is lost (Baveye et al, 2018)
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