7 results on '"Sleutel, Steven"'
Search Results
2. Chemical staining of particulate organic matter for improved contrast in soil X-ray µCT images
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Maenhout, Peter, de Neve, Stefaan, Wragg, Joanna, Rawlins, Barry, De Pue, Jan, van Hoorebeke, Luc, Cnudde, Veerle, Sleutel, Steven, Hydrogeology, and Environmental hydrogeology
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Science ,010501 environmental sciences ,Silt ,01 natural sciences ,Article ,Matrix (chemical analysis) ,chemistry.chemical_compound ,Organic matter ,General ,0105 earth and related environmental sciences ,chemistry.chemical_classification ,Multidisciplinary ,04 agricultural and veterinary sciences ,Carbon cycle ,Particulates ,Staining ,Silver nitrate ,Chemistry ,Soil structure ,chemistry ,Environmental chemistry ,Earth and Environmental Sciences ,Soil water ,040103 agronomy & agriculture ,0401 agriculture, forestry, and fisheries ,Medicine - Abstract
Degradability of organic matter (OM) in soil depends on its spatial location in the soil matrix. A recent breakthrough in 3D-localization of OM combined dual-energy X-ray CT-scanning with OsO4 staining of OM. The necessity for synchrotron-based µCT and the use of highly toxic OsO4 severely limit applications in soil biological experiments. Here, we evaluated the potential of alternative staining agents (silver nitrate, phosphomolybdenic acid (PMA), lead nitrate, lead acetate) to selectively enhance X-ray attenuation and contrast of OM in CT volumes of soils containing specific mineral soil particle fractions, obtained via lab-based X-ray µCT. In comparison with OsO4, administration of Ag+ and Pb2+ resulted in insufficient contrast enhancement of OM versus fine silt (4. However, OM discrimination from other soil phases remained a challenge. Further development of segmentation algorithms accounting for grey value patterns and shape of stained particulate OM may enable its automated identification. If successful in undisturbed soils, PMA staining may form an alternative to OsO4 in non-synchrotron based POM detection.
- Published
- 2021
3. Nitrogen limitations on microbial degradation of plant substrates are controlled by soil structure and moisture content
- Author
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Maenhout, Peter, Van den Bulcke, Jan, Van Hoorebeke, Luc, Cnudde, Veerle, De Neve, Stefaan, Sleutel, Steven, non-UU output of UU-AW members, and non-UU output of UU-AW members
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Agriculture and Food Sciences ,DECOMPOSITION ,Microbiology (medical) ,010504 meteorology & atmospheric sciences ,lcsh:QR1-502 ,Soil contact ,nitrogen availability ,Nitrogen availability ,PORE ,01 natural sciences ,Microbiology ,Decomposer ,lcsh:Microbiology ,CROP RESIDUES ,Microbial community ,Organic matter ,COMPUTED-TOMOGRAPHY ,Water content ,0105 earth and related environmental sciences ,Original Research ,chemistry.chemical_classification ,FUNGAL ,Moisture ,Biology and Life Sciences ,CARBON MINERALIZATION ,04 agricultural and veterinary sciences ,Mineralization (soil science) ,RHIZOCTONIA-SOLANI ,soil contact ,PARTICLE-SIZE ,ORGANIC-MATTER ,Soil structure ,chemistry ,visual_art ,Environmental chemistry ,Earth and Environmental Sciences ,Soil water ,040103 agronomy & agriculture ,visual_art.visual_art_medium ,0401 agriculture, forestry, and fisheries ,C mineralization ,X-ray μCT ,Sawdust ,microbial community ,COMMUNITY STRUCTURE ,X-ray mu CT - Abstract
Mineral nitrogen (N) availability to heterotrophic micro-organisms is known to impact organic matter (OM) decomposition. Different pathways determining the N accessibility depend to a large extent on soil structure. Contact between soil mineral and OM substrate particles can facilitate N transport toward decomposition hot spots. However, the impact of soil structure on N availability to microbes and thus heterotrophic microbial activity and community structure is not yet fully understood. We hypothesized that carbon mineralization (Cmin) from low-N substrate would be stimulated by increased N availability caused by closer contact with soil particles or by a higher moisture level, enhancing potential for N-diffusion. Under opposite conditions retarded heterotrophic activity and a dominance of fungi were expected. A 128-days incubation experiment with CO2 emission monitoring from artificially reconstructed miniature soil cores with contrasting soil structures, viz. high or low degree of contact between soil particles, was conducted to study impacts on heterotrophic activity. The soil cores were subjected to different water filled pore space percentages (25 or 50% WFPS) and amended with either easily degradable OM high in N (grass) or more resistant OM low in N (sawdust). X-ray μCT image processing allowed to quantify the pore space in 350 μm around OM substrates, i.e., the microbial habitat of involved decomposers. A lower local porosity surrounding sawdust particles in soils with stonger contact was confirmed, at least at 25% WFPS. Mineral N addition to sawdust amended soils with small particle contact at 25% WFPS resulted in a stimulated respiration. Cmin in the latter soils was lower than in case of high particle contact. This was not observed for grass substrate particles or at 50% WFPS. The interactive effect of substrate type and soil structure suggests that the latter controls Cmin through mediation of N diffusion and in turn N availability. Phospholipid fatty acid did not reveal promotion of fungal over bacterial biomarkers in treatments with N-limited substrate decomposition. Combining X-ray μCT with tailoring soil structure allows for more reliable investigation of effects on the soil microbial community, because as also found here, the established soil pore network structure can strongly deviate from the intended one.
- Published
- 2018
4. Biochar-induced N2O emission reductions after field incorporation in a loam soil.
- Author
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Ameloot, Nele, Maenhout, Peter, De Neve, Stefaan, and Sleutel, Steven
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BIOCHAR , *NITROGEN oxides emission control , *LOAM soils , *DENITRIFICATION , *SOIL amendments , *HYDROGEN-ion concentration - Abstract
Biochar addition to soils is heralded to reduce N 2 O emissions, but still, the explanatory mechanisms have not been resolved. Moreover, it is uncertain whether N 2 O emission reductions would persist after prolonged biochar incorporation in the field. In this study, we incorporated four biochar types in a loam textured cropland field and intact soil cores were sampled to investigate the physical control of biochar on denitrification after 7 months. During a first incubation experiment, we measured N 2 O emissions from undisturbed and disturbed (i.e. sieved (2 mm) and grounded) soil cores. Both in the disturbed and undisturbed soil cores biochar at water filled pore space (WFPS) of 80% reduced the N 2 O emissions by 50–90%, refuting the hypothesis that biochar exerts an indirect physical control over soil denitrification several months after incorporation. Secondly, we hypothesized that biochar creates denitrification ‘hotspots’ in soil, where complete reduction of N 2 O to N 2 is promoted compared to non-amended soil. In these hotspots biochar particles could act as microlocations with local anaerobic conditions and local higher pH, stimulating in this way complete denitrification. Via the acetylene inhibition method we did not observe a reduction in the N 2 O/(N 2 O + N 2 ) ratio, which could suggest that biochar did not promote the reduction of N 2 O to N 2 . Manipulations likely to promote labile C bioavailability, here either by glucose addition or by soil particulate OM disclosure after disruption of soil aggregates, resulted in the most prominent biochar-induced N 2 O emission reductions. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
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5. Do interactions between application rate and native soil organic matter content determine the degradation of exogenous organic carbon?
- Author
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Mendoza, Orly, De Neve, Stefaan, Deroo, Heleen, Li, Haichao, and Sleutel, Steven
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CARBON emissions , *ORGANIC compounds , *SUBSOILS , *REDUCTION potential , *ISOTOPIC signatures , *CARBON dioxide - Abstract
Although the amendment of various forms of exogenous organic matter (EOM) is a common practice in cropland production, it is to date not clear if its mineralisation in soil depends on application rate. Previous research suggested that spatial concentration of EOM in soil positively impacts its degradability. Here, we seek to test these reports and furthermore to investigate if an interactive effect exists with native soil organic carbon (SOC) concentration. We hypothesised that at a low EOM dose, more EOM remains undecomposed in soil and that this effect becomes stronger at lower SOC level. Moreover, as a secondary goal, we explored if priming of native SOC mineralisation depends on EOM dose. Therefore, we set up seventy-day soil incubation experiments with six varying C4-maize residue (δ13C = −12.7‰) doses (0–6 g kg−1) in soil mesocosms of loamy sand subsoils (δ13C = −25.7‰) with three different native SOC levels (i.e. 0.1, 0.5, and 1.0%). Soil CO 2 emissions and isotopic signature measurements of CO 2 allowed to discern EOM and SOC mineralisation. We found that EOM-derived C mineralisation increased proportionally to EOM dose, refuting the hypothesised relative undecomposed EOM at low concentration. Volumes of larger pore neck size diameter classes (60–100 and >300 μm) almost doubled at high EOM dose, demonstrating formation of macropores. Yet, this apparently did not impact EOM mineralisation, probably because O 2 supply was always sufficient to allow unlimited activity of EOM degraders, even at higher EOM doses, as indicated by generally higher measured redox potential. With EOM dose, fungal marker PLFA abundances increased in the 1% SOC soil and protozoan abundances increased in all three soils, but apparently these shifts did not result in an enhanced relative degradation of the EOM. Increasing EOM doses induced negative priming, e.g. EOM ≥1 g kg−1 reduced SOC mineralisation by >43% and >24% compared to the control in the 0.1 and 0.5% SOC soils, respectively; whereas no priming occurred in soil with 1% SOC. These results were largely explained by the amount of added C relative to microbial biomass carbon, and the theorised switch of slow decomposers (so called K-strategists and involved in recalcitrant compound decomposition) from SOM to preferentially decompose EOM at higher doses. We also postulate that at low SOC %, the obvious increased O 2 consumption with higher EOM dose more readily results in local anaerobic conditions in finer pores, i.e. where SOC is located and mineralised. We conclude that on the short term, agricultural management for SOM thus does not need to consider EOM doses but only the total amount of EOM. • We hypothesised relative OM decomposition to increase at higher concentration in soil. • Dose of maize straw however did not impact its relative degradability in soil. • High doses did enhance soil macroporosity and generally increased soil Eh. • Increasing maize straw dose induced stronger negative priming of SOC at low SOC. [ABSTRACT FROM AUTHOR]
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- 2022
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6. Selective sterilisation of undisturbed soil cores by gamma irradiation: Effects on free-living nematodes, microbial community and nitrogen dynamics
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Buchan, David, Moeskops, Bram, Ameloot, Nele, De Neve, Stefaan, and Sleutel, Steven
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SOIL structure , *GAMMA rays , *STERILIZATION (Disinfection) , *NEMATODES , *PHOSPHOLIPIDS , *FATTY acids , *IRRADIATION , *PLANT nutrients , *BIOMASS - Abstract
Abstract: The techniques available for sterilisation or defaunation of soil in ecological experiments mostly have strongly unwanted effects on soil structure and the dynamics of major nutrients such as nitrogen. The potential for using gamma irradiation to prepare defaunated soil microcosms was investigated by subjecting undisturbed soil cores to a range of irradiation doses (0, 5, 10, 20 and 40 kGy). The absence of living nematodes at the lowest irradiation dose was confirmed by microscopic observation. The effects of irradiation dose on mineral nitrogen (as NO3 − and NH4 +), microbial biomass C (Cmic), and phospholipid fatty acid (PLFA) concentration and composition were determined over a 4 week incubation period. An increase in the concentration of NO3 − occurred during the incubation period after exposure to 0, 5 and 10 kGy but was barely detectable at 20 and 40 kGy. The effect of irradiation dose on NH4 + release was complex and highly variable within treatments, with the 10 kGy dose resulting in the highest concentrations. Microbial biomass carbon was significantly reduced following a 20 kGy irradiation dose and below detection at 40 kGy. Most remarkably, the sum of all measured PLFAs did not differ significantly between most treatments and was not correlated with microbial biomass. In most cases the concentration of signature fatty acids only differed significantly between the control and the highest irradiation dose treatments. To ascertain the sensitivity of microbial taxa to acute gamma irradiation with accuracy, measures of microbial community structure other than PLFA analysis are needed. [Copyright &y& Elsevier]
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- 2012
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7. Observer-dependent variability of the thresholding step in the quantitative analysis of soil images and X-ray microtomography data
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Baveye, Philippe C., Laba, Magdeline, Otten, Wilfred, Bouckaert, Liesbeth, Dello Sterpaio, Patricia, Goswami, Rohit R., Grinev, Dmitri, Houston, Alasdair, Hu, Yaoping, Liu, Jianli, Mooney, Sacha, Pajor, Radoslaw, Sleutel, Steven, Tarquis, Ana, Wang, Wei, Wei, Qiao, and Sezgin, Mehmet
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SOIL testing , *QUANTITATIVE research , *X-rays , *IMAGE analysis , *SOIL scientists , *TOMOGRAPHY , *ALGORITHMS , *SOIL structure , *LATTICE Boltzmann methods - Abstract
Abstract: For the investigation of many geometrical features of soils, computer-assisted image analysis has become a method of choice over the last few decades. This analysis involves numerous steps, regarding which subjective decisions have to be made by the individuals conducting the research. This is particularly the case with the thresholding step, required to transform the original (color or greyscale) images into the type of binary representation (e.g., pores in white, solids in black) needed for fractal analysis or simulation with Lattice–Boltzmann models. Limited information exists at present on whether different observers, analyzing the same soil, would be likely to obtain similar results. In this general context, the first objective of the research reported in this article was to determine, through a so-called “round-robin” test, how much variation exists among the outcomes of various image thresholding strategies (including any image pre-treatment deemed appropriate), routinely adopted by soil scientists. Three test images – of a field soil, a soil thin section, and a virtual section through a 3-dimensional CT data set – were thresholded by 13 experts, worldwide. At the same time, variability of the outcomes of a set of automatic thresholding algorithms, applied to portions of the test images, was also investigated. The experimental results obtained illustrate the fact that experts rely on very different approaches to threshold images of soils, and that there is considerable observer influence associated with this thresholding. This observer dependence is not likely to be alleviated by adoption of one of the many existing automatic thresholding algorithms, many of which produce thresholded images that are equally, or even more, variable than those of the experts. These observations suggest that, at this point, analysis of the same image of a soil, be it a simple photograph or 3-dimensional X-ray CT data, by different individuals can lead to very different results, without any assurance that any of them would be even approximately “correct” or best suited to the objective at hand. Different strategies are proposed to cope with this situation, including the use of physical “standards”, adoption of procedures to assess the accuracy of thresholding, benchmarking with physical measurements, or the development of computational methods that do not require binary images. [Copyright &y& Elsevier]
- Published
- 2010
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