Roughness of biopores and cracks in Bt-horizons assessed by confocal laser scanning microscopy

摘要

In structured soils, water and reactive solutes can preferentially move through larger inter-aggregate pores, cracks, and biopores. The surface roughness of such macropores is crucial for describing microbial habitats and the exchange of water and solutes between macropores and the soil matrix together with other properties. The objective of this study was to compare the roughness of intact structural surfaces from the Bt-horizons of five Luvisols developed on loess and glacial till and to test the applicability of confocal laser scanning microscopy. Samples of 5 to 10cm edge length with intact structural surfaces including cracks with and without clay-organic coatings, earthworm burrow walls, and root channels were prepared manually. The surface roughness of these structures was determined with a confocal laser scanning microscope of the type Keyence VK-X100K. The root-mean-squared roughness (R-q) the curvature (R-cu) and the ratio between surface area and base area (R-A) were calculated from selected surface regions of interest of 0.342mm(2) with an elevation resolution of 0.02 mu m. The roughness was smaller for coated as compared to uncoated cracks and earthworm burrows of the Bt-horizons. This reduction of roughness by the illuviation of clayey material was similar for the structural surfaces of the coarser textured till-Bt and the finer-textured loess-Bt. This similarity suggested a dominant effect of pedogenesis and a minor effect of the parent material on the roughness levels of structural surfaces in the Bt-horizons. An expected smoothing effect of burrow wall surfaces by earthworm activity was not reflected in the roughness values compared to those of uncoated cracks at the chosen spatial scale. However, for root channel walls from one loess-Bt, the roughness was reduced as compared to that of other structures. These results suggest that the surface roughness of the structural surface types should separately be considered when describing preferential flow and macropore-matrix exchange or analysing root growth, microbial habitats, and colloidal transport in structured soils. The confocal laser scanning microscopy technique was found useful for characterizing the roughness of intact structural surfaces.