TY - JOUR A1 - Puppe, Daniel A1 - Leue, Martin A1 - Sommer, Michael A1 - Schaller, Jörg A1 - Kaczorek, Danuta T1 - Auto-fluorescence in phytoliths BT - a mechanistic understanding derived from microscopic and spectroscopic analyses JF - Frontiers in Environmental Science N2 - The detection of auto-fluorescence in phytogenic, hydrated amorphous silica depositions (phytoliths) has been found to be a promising approach to verify if phytoliths were burnt or not, especially in archaeological contexts. However, it is unknown so far at what temperature and how auto-fluorescence is induced in phytoliths. We used fluorescence microscopy, scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX), and Fourier transform infrared spectroscopy to analyze auto-fluorescence in modern phytoliths extracted from plant samples or in intact leaves of winter wheat. Leaves and extracted phytoliths were heated at different temperatures up to 600 degrees C. The aims of our experiments were i) to find out what temperature is needed to induce auto-fluorescence in phytoliths, ii) to detect temperature-dependent changes in the molecular structure of phytoliths related to auto-fluorescence, and iii) to derive a mechanistic understanding of auto-fluorescence in phytoliths. We found organic compounds associated with phytoliths to cause auto-fluorescence in phytoliths treated at temperatures below approx. 400 degrees C. In phytoliths treated at higher temperatures, i.e., 450 and 600 degrees C, phytolith auto-fluorescence was mainly caused by molecular changes of phytolith silica. Based on our results we propose that auto-fluorescence in phytoliths is caused by clusterization-triggered emissions, which are caused by overlapping electron clouds forming non-conventional chromophores. In phytoliths heated at temperatures above about 400 degrees C dihydroxylation and the formation of siloxanes result in oxygen clusters that serve as non-conventional chromophores in fluorescence events. Furthermore, SEM-EDX analyses revealed that extractable phytoliths were dominated by lumen phytoliths (62%) compared to cell wall phytoliths (38%). Our findings might be not only relevant in archaeological phytolith-based examinations, but also for studies on the temperature-dependent release of silicon from phytoliths and the potential of long-term carbon sequestration in phytoliths. KW - fluorescence microscopy KW - FTIR spectroscopy KW - SEM-EDX KW - burnt phytoliths; KW - carbon sequestration Y1 - 2022 U6 - https://doi.org/10.3389/fenvs.2022.915947 SN - 2296-665X VL - 10 PB - Frontiers Media CY - Lausanne ER - TY - JOUR A1 - Leue, Martin A1 - Hoffmann, Carsten A1 - Hierold, Wilfried A1 - Sommer, Michael T1 - In-situ multi-sensor characterization of soil cores along an erosion deposition gradient JF - Catena : an interdisciplinary journal of soil science, hydrology, geomorphology focusing on geoecology and landscape evolution N2 - Soil landscape research is faced with wide-ranging questions of soil erosion, precision farming, and agricultural risk management. Digital Soil Morphometrics is a powerful tool to provide respective answers or recommendations but requires soil data from the pedon-to-field scale with high horizontal and vertical resolutions, including the subsoil. We present an efficient sampling and measurement method for easily obtainable soil driving cores with low-destructive preparation. Elemental contents and soil organic and mineral matter composition were measured rapidly and in large numbers using a multi-sensor approach, i.e., visible and near infrared (Vis-NIR), diffuse reflectance infrared Fourier transform (DRIFT), and X-ray fluorescence (XRF) spectroscopy. The suitability of the approach with respect to three-dimensional soil landscape models was tested using soils along a slope representing different stages of erosion and deposition in a hummocky landscape under arable land use (Calcaric Regosols, Calcic Luvisols, Luvic Stagnosols, Gleyic-Colluvic Regosols). The combination of soil core sampling, pedological description, and three spectroscopic techniques enabled rapid determination and interpretation of horizontal and vertical spatial distributions of soil organic carbon (SOC), soil organic and mineral matter composition, as well as CaCO3, Fe, and Mn contents. Depth profiles for SOC, CaCO3, and Fe contents were suitable indicators for site-specific degrees of erosion and matter transport processes at the pedon-to-field scale. Fe and Mn profiles helped identifying zones of reductive and oxic domains in subsoils (gleyzation). Further methodical developments should implement plant-availability of nutrients, characterization of Fe oxides, and calibration of the spectroscopic techniques to field-moist samples. KW - Digital soil morphometrics KW - VIS-NIR spectroscopy KW - DRIFT spectroscopy KW - XRF spectroscopy KW - Soil organic carbon KW - Soil erosion Y1 - 2019 U6 - https://doi.org/10.1016/j.catena.2019.104140 SN - 0341-8162 SN - 1872-6887 VL - 182 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Leue, Martin A1 - Gerke, Horst H. A1 - Godow, Sophie C. T1 - Droplet infiltration and organic matter composition of intact crack and biopore surfaces from clay-illuvial horizons JF - Journal of plant nutrition and soil science = Zeitschrift für Pflanzenernährung und Bodenkunde N2 - The organic matter (OM) in biopore walls and aggregate coatings may be important for sorption of reactive solutes and water as well as for solute mass exchange between the soil matrix and the preferential flow (PF) domains in structured soil. Structural surfaces are coated by illuvial clay-organic material and by OM of different origin, e.g., earthworm casts and root residues. The objectives were to verify the effect of OM on wettability and infiltration of intact structural surfaces in clay-illuvial horizons (Bt) of Luvisols and to investigate the relevance of the mm-scale distribution of OM composition on the water and solute transfer. Intact aggregate surfaces and biopore walls were prepared from Bt horizons of Luvisols developed from Loess and glacial till. The mm-scale spatial distribution of OM composition was scanned using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The ratio between alkyl and carboxyl functional groups in OM was used as potential wettability index (PWI) of the OM. The infiltration dynamics of water and ethanol droplets were determined measuring contact angles (CA) and water drop penetration times (WDPT). At intact surfaces of earthworm burrows and coated cracks of the Loess-Bt, the potential wettability of the OM was significantly reduced compared to the uncoated matrix. These data corresponded to increased WDPT, indicating a mm-scaled sub-critical water repellency. The relation was highly linear for earthworm burrows and crack coatings from the Loess-Bt with WDPT >2.5 s. Other surfaces of the Loess-Bt and most surfaces of the till-derived Bt were not found to be repellent. At these surfaces, no relations between the potential wettability of the OM and the actual wettability of the surface were found. The results suggest that water absorption at intact surface structures, i.e., mass exchange between PF paths and soil matrix, can be locally affected by a mm-scale OM distribution if OM is of increased content and is enriched in alkyl functional groups. For such surfaces, the relation between potential and actual wettability provides the possibility to evaluate the mm-scale spatial distribution of wettability and sorption and mass exchange from DRIFT spectroscopic scanning. KW - preferential flow KW - soil organic matter KW - infrared spectroscopy KW - clay organic coating KW - mass exchange Y1 - 2015 U6 - https://doi.org/10.1002/jpln.201400209 SN - 1436-8730 SN - 1522-2624 VL - 178 IS - 2 SP - 250 EP - 260 PB - Wiley-VCH CY - Weinheim ER -