Quantification of small-scale physicochemical and microbiological properties of intact macropore surfaces in structured soils

点击翻译按钮获取中文摘要

In structured soils, water and reactive solutes can preferentially move through larger inter-aggregate pores, cracks, and biopores. The surfaces of these structures are often coated by soil organic matter (SOM) and clayey material and can be colonized by microorganisms, which promote turnover processes, e.g., carbon and release from subsoils. The physico-chemical and geometrical properties of structural surfaces influence the preferential flow through soils as well as the water and mass exchange between the different flow domains (macropores and soil matrix). A parametrization of these surface properties is complicated by the vulnerability and complex structure of these surfaces. Parameters from intact structural surfaces were obtained to date only concerning the potential wettability of the soil organic matter and the roughness of the structures. The idea of this project is to extrapolate the two-dimensionally determined properties of structural surfaces for soil horizons by the help of three-dimensional analyses of the spatial arrangement of these macropore structures and thereby to estimate effects of structural surface properties on preferential flow and turnover processes in Bt-Horizons. The objective of this project extension is the quantification of small-scale physico-chemical and microbial properties of intact structural surfaces from Bt-horizons of Luvisols developed on loess and glacial till. Results from the first project (LE 3177/1-1) will be extended by the following work packages:(i) The entire macropore system potentially available during preferential flow will be quantified three-dimensionally using x-ray computer tomography (µCT). The actually available macropores (active during specific flow events) will be determined by the help of dye tracer experiments in order to assess the spatial relevance of surface structures for preferential flow. The combination of µCT measurements of small- and large-sized samples will ensure the consideration of all macropore sizes. Effects of different soil water contents on the soil structure characteristics will be assessed by comparing data from saturated and unsaturated soil water conditions.(ii) The physico-chemical properties of intact structural surfaces (OC content, SOM composition, CEC, microbial activity) will be two-dimensionally quantified using infrared spectroscopy in the diffuse reflectance mode (DRIFT mapping). The use of intact structural surfaces for the calibration of the DRIFT spectra will ensure the prediction of valid absolute values of elemental contents and surface parameters by the help of DRIFT mapping spectra. (iii) The characterization of the spatial distribution of soil microorganisms and their abundance and activities by the help of zymography and DRIFT mapping aims to identify microbial hot spots, to explain local small-scale differences in the SOM composition, and to assess significances of structural surfaces with respect to carbon turnover in subsoils.