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  • 1
    Language: English
    In: Soil Biology and Biochemistry, September 2018, Vol.124, pp.210-217
    Description: It is widely accepted that soil microorganisms are not evenly distributed but are often concentrated in spatially segregated hotspots that are characterized by higher substrate availability compared to the surrounding bulk soil. However, microorganisms outside of hotspots may be in a dormant or inactive state, since they have depleted all available substrates within their vicinity. So far, the knowledge about the spatial distribution and dynamics of microbial activity in subsoil is very scarce, since most available data has been acquired from either homogenized soil samples or as bulk signals from undisturbed soil cores. In this study, we introduced a new incubation approach combining soil zymography and substrate addition on undisturbed soil core surfaces. We mapped three extracellular enzymes (β-glucosidase, chitinase and acid phosphatase) on a subsoil sample from 60 cm depth and analyzed their activity-patterns using different geostatistical and spatial analyses. After initial enzyme mapping, the soil was homogenously sprayed with 14C glucose as model substrate and incubated for 14 days. Soil zymography was suitable for detecting hotspots in undisturbed soil, making up a proportion of 2.4% on average of the total area. Consequently, microbial-driven biogeochemical processes can be expected to be limited to small areas in this subsoil, while the major part of the soil volume is not contributing. Glucose additions considerably increased enzyme activities up to 900% in initial non-hotspots, while the effect was far lower in initial hotspots. These results show that microorganisms in the subsoil outside of hotspots can be activated and release enzymes when substrate is supplied. Thus, dormant or inactive microorganisms outside of hotspots are able to contribute to SOC mineralization when substrate limitation is overcome, thus most likely inducing positive priming effects. Our results clearly demonstrate the benefits of combining enzyme mapping with substrate additions on undisturbed soil to gain new insights about microbial hotspots and C-cycling in subsoils using spatial analyses. In contrast to traditional incubation experiments, this method gives high spatial information about microbial activity, allowing a more differentiated interpretation of incubation results. •Introducing a new incubation approach for subsoils.•Application of soil zymography combined with glucose addition on undisturbed soil.•Soil zymography was suitable for detecting hotspots in undisturbed soil.•It was revealed that microbial activity outside of hotspots is substrate limited.•The approach allows a more differentiated interpretation of incubation results.
    Keywords: Microbial Hotspots ; Soil Zymography ; Substrate Limitation ; Subsoil ; Phosphor-Imaging
    ISSN: 0038-0717
    E-ISSN: 18793428
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  • 2
    Language: English
    In: Soil Systems, 6/2018, Vol.2(2), p.35
    ISSN: Soil Systems
    E-ISSN: 2571-8789
    Source: CrossRef
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  • 3
    Language: English
    In: Geoderma, May 2015, Vol.245-246, pp.56-64
    Description: Biochar is suggested for soil amelioration and carbon sequestration, based on its assumed role as the key factor for the long-term fertility of Terra preta soils. Several studies have shown that certain biochar properties can undergo changes through ageing processes, especially regarding charge characteristics. However, only a few studies determined the changes of different biochars under the same incubation conditions and in different soils. The objective of this study was to characterize the changes of pine chip (PC)- and corn digestate (CD)-derived biochars pyrolyzed at 400 or 600°C during 100days of laboratory incubation in a historical kiln soil and an adjacent control soil. Separation between soil and biochar was ensured by using mesh bags. Especially, changes in charge characteristics depended on initial biochar properties affected by feedstock and pyrolysis temperature and on soil properties affected by historic charcoal production. While the cation exchange capacity (CEC) markedly increased for both CD biochars during incubation, PC biochars showed no or only slight increases in CEC. Corresponding to the changes in CEC, ageing of biochars also increased the amount of acid functional groups with increases being in average about 2-fold higher in CD biochars than in PC biochars. Further and in contrast to other studies, the surface areas of biochars increased during ageing.Changes in CEC and surface acidity of CD biochar were more pronounced after incubation in the control soil, while surface area increase was higher in the kiln soil. Since the two acidic forest soils used in this study did not greatly differ in physical or chemical properties, the main process for inducing these differences in the buried biochar most likely is related to the differences in dissolved organic carbon (DOC). Although the kiln soil contained about 50% more soil organic carbon due to the presence of charcoal particles, extractable DOC was lower and less aromatic than in the adjacent control soil, likely due to strong sorption of dissolved organic matter (DOM) onto charcoal particles. We suggest that higher sorption of DOM onto the surface of biochar in the control soil provided additional acid functional groups and thus increased the surface charge to a greater extent than in the DOC poorer kiln soil. Hence, biochars incubated in the kiln soil showed less changes in CEC and surface acidity. Higher availability of DOM in the control soil could also stimulate microbial activity to a larger extent, resulting in higher oxidation rates of biochars incubated in the control soil. •Biochar ageing depended on feedstock, pyrolysis temperature, and soil.•Surface areas of biochars increased during ageing.•Changes in surface charge were more pronounced for biochars aged in the control soil.•Dissolved organic matter plays a major role for increasing biochars surface charge.
    Keywords: Biochar ; Simulated Ageing ; Surface Charge ; Dissolved Organic Matter
    ISSN: 0016-7061
    E-ISSN: 18726259
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  • 4
    Language: English
    In: Geoderma, 15 April 2017, Vol.292, pp.111-117
    Description: Studies on factors controlling C-stability in subsoils are very scarce. Recent results suggest a lack of labile C substrates and N limitations in subsoils as a reason for suppressed C-turnover. The catalytic activity of soil enzymes plays an important role for the decomposition of organic matter in soils and can be a powerful tool to shed further light on substrate and N-limitation as a hypothesized controlling mechanism for C-stability in subsoils. Therefore, we studied the impacts of 14C-labelled citric acid and of NH4NO3 on changes in soil organic carbon (SOC)-mineralization and enzyme activities of dehydrogenase and 9 extracellular enzymes involved in C-, N-, P- and S-cycle. For this approach, we sampled a sandy Cambisol at three different depths (2–12, 35–65 and 135–165cm) and conducted a laboratory incubation experiment for 63days at 10°C. N-addition reduced SOC-mineralization in the topsoil layer by 43%, while no N-effect was observed in both subsoil layers. In the topsoil samples, dehydrogenase-activity also decreased after the incubation with N additions. Further, the activity of extracellular enzymes involved in P- and N-cycling was differently affected in top- and subsoils, indicating that microorganisms in different soil depths have different demands for N or P after adding inorganic N. Additions of citric acid increased SOC mineralization by about 1.9- and 2.2-fold in the upper (35–65cm) and lower subsoil (135–165cm) samples, but only by about 32% in the topsoil samples (2-12cm). The observed priming effect in the topsoil samples was not accompanied by an increased enzyme activity which indicates “apparent priming”. In contrast, priming effects in both subsoil layers were rated as “real priming” indicated by increased enzyme activities and continuously higher SOC-mineralization rates throughout the incubation compared to the controls. •N-addition reduced SOC-mineralization in the topsoil.•No N-effect on C-turnover in subsoils.•Enzymes were differently affected in top- and subsoils by citric acid and N.•Priming effect in the topsoil was rated as “apparent priming”.•Priming effect in both subsoil layers was rated as “real priming”.
    Keywords: Enzyme Activities ; Nitrogen Limitation ; Priming Effect ; Subsoil
    ISSN: 0016-7061
    E-ISSN: 18726259
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  • 5
    Language: English
    In: Geoderma, 15 September 2017, Vol.302, pp.89-99
    Description: The generally high apparent 14C age of soil organic carbon (SOC) in subsoils suggests a high stability against microbial degradation. However, the SOC decomposition in subsoils may also be limited by easily available substrates and nutrients, such as N and P. In topsoils, priming effects in response to substrate additions are largely determined by substrate quality which also differently affects the microbial community, while the knowledge for deep soil layers is very scarce. In order to gain further insight into processes controlling SOC decomposition in subsoils, we conducted a laboratory incubation experiment for 105days to investigate the impact of different substrates and mineral N and P on SOC mineralization in a Dystric Cambisol sampled at 2–12, 35–65 and 135–165cm. We studied the impacts of 14C-labeled citric, vanillic and palmitic acid and of N or P alone and in combination with two of the substrates on changes in SOC mineralization. The choice of substrates was based on their nominal oxidation state of carbon, which reflects the energy yield and the biogeochemical reactivity of a compound. Further, the impact of the treatments on the activity of six extracellular enzymes involved in C-, N-, P- and S-acquisition, of peroxidase and phenoloxidase and of the intracellular dehydrogenase was investigated to clarify if substrate qualities and nutrients differently affect the decomposition potential and nutrient demand of the microbial community. Our results show that microbial metabolism is limited by N in both subsoil layers, although the upper subsoil (35–65cm) may have become P limited during the later stage of incubation. Even after 105days, C-cycling enzymes and dehydrogenase activity were highly elevated in the lower subsoil (135–165cm) in response to N additions which indicates a sustained higher decomposition potential and activity of the microbial community once the N-limitation is overcome. In the upper subsoil (35–65cm), we found high amounts of labile C, indicating a high proportion of fast cycling SOC. Furthermore, all added substrates induced negative priming effects, while positive priming effects were only induced with N addition which was related to N limiting metabolism. The suppressed SOC mineralization likely occurred because the present microbial community was adapted to more labile carbon compounds, resulting in preferential substrate utilization. In the lower subsoil (135–165cm), real positive priming was induced by vanillic acid and palmitic acid, while citric acid had no effect on SOC mineralization. This clearly reflects that substrate quality matters for inducing positive priming in this subsoil. Altogether, this study evidently shows that in consequence of altered substrate and N input deep SOC storage is destabilized in forest soils. •Microbial metabolism was limited by N in both subsoil layers.•Enzyme activities were highly elevated by N in subsoils.•N highly increased SOC mineralization, especially in 135–165cm depth.•All added C-substrates induced negative priming in 35–65cm depth.•Real positive priming was induced by C additions in 135–165cm depth.
    Keywords: Enzyme Activitiy ; Nutrients ; Priming Effect ; Subsoil ; Substrate Quality
    ISSN: 0016-7061
    E-ISSN: 18726259
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  • 6
    Language: English
    In: Geoderma, 1 October 2018, Vol.327, pp.119-129
    Description: Spatio-temporal analyses of soil properties are important for more profound insights into soil processes. Up to now, non-invasive approaches analyzing physical and biological soil properties and dynamics at the microscale are not available due to methodological, instrumental, and analytical challenges. In this study, we evaluate the use of active and passive infrared thermography (IRT), a non-invasive and non-contact technique, for the detection of surface temperature-based parameters on soil surfaces. The potential and possibilities of IRT were analyzed with a focus on the detection and calibration of soil moisture using active IRT and the determination of microbial activity using passive IRT. A pool of 51 soil samples was used to cover a wide range of chemical, physical, and biological soil properties. The samples were rewetted to 16 different moisture contents, filled into vessels, and placed in an air-proof glove box with an adjusted relative humidity of about 92% to reduce soil drying. Immediately after rewetting, the soil surface temperature was determined using active and passive IRT procedures at a high temporal resolution (1 min for passive IRT, hourly for active IRT) and a spatial resolution of 0.283 mm. Soil material was also sterilized by γ-irradiation in order to obtain sterile samples for validating the passive IRT procedure. Active IRT measurements were qualified for the detection of soil surface moisture due to changing specific heat capacity at varying water contents. The mean volumetric water contents explained up to 88% of active IRT values, which were a good approximation for relative differences in the spatial and temporal distribution of moisture contents. Passive IRT measurements are useful for the detection of microbial activity on soil sample surfaces since temperature increases by up to 0.5 K were detected on the surfaces of all non-sterile samples immediately after rewetting. In sterile samples, rewetting did not result in heat production. With regard to the commonly observed “Birch”-CO2-pulse, these results strongly suggested that the heat evolution on the surface of the non-sterile soils was associated with the rapidly increasing microbial activity from consuming dead and easily available soil biomass. In conclusion, IRT is a promising mapping tool of soil surface processes especially for undisturbed soil samples, since IRT techniques allow studying moisture and microbial activity of intact soil structures. Unlabelled Image •IRT enables spatially and temporally high resolution analysis of soil samples.•Active IRT identifies soil surface moisture contents and structural patterns.•Passive IRT detects increased heat production from microbial activity.•Combining active and passive IRT gives more profound information on soil processes.
    Keywords: Infrared Thermography ; Soil Moisture Calibration ; Microbial Activity Dynamics ; Spatio-Temporal Approach ; Microscale
    ISSN: 0016-7061
    E-ISSN: 18726259
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  • 7
    In: Ecohydrology, September 2018, Vol.11(6), pp.n/a-n/a
    Description: By applying the newly developed flow cell (FC) concept, this study investigated the impact of small‐scale spatial variations (millimetre to centimetre) in organic matter (OM) composition (diffusive reflectance infrared Fourier transform spectroscopy), biological activity (zymography), and wettability (contact angle [CA]) on transport processes (tracer experiments, radiography). Experiments were conducted in five undisturbed soil slices (millimetre apart), consisting of a sandy matrix with an embedded loamy band. In the loamy band increased enzyme activities and OM (10 mm apart) were found compared with the sand matrix, with no interrelations although spatial autocorrelation ranges were up to 7 cm. CAs were increased (0–110°) above the loamy band and were negatively correlated with acid phosphatase. Missing correlations were probably attributed to texture variations between soil slices. A general correlation between CA and C content (bulk) were confirmed. Variability in texture and hydraulic properties led to the formation of heterogeneous flow patterns and probably to heterogeneously distributed interfacial properties. The new FC concept allows process evaluation on the millimetre scale to analyse spatial relations, that is, between small‐scale textural changes on transport processes and biological responses. The concept has been proved as a versatile tool to analyse spatial distribution of biological and interfacial soil properties in conjunction with the analysis of complex micro‐hydraulic processes for undisturbed soil samples. The concept may be improved by additional nondestructive imaging methods, which is especially challenging for the detection of small‐scale textural changes.
    Keywords: Drift Spectroscopy ; Extracellular Enzyme Activity ; Flow Cell ; Soil Water Repellency ; Transport Processes ; Undisturbed Soil ; X‐Ray Radiography
    ISSN: 1936-0584
    E-ISSN: 1936-0592
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  • 8
    Language: English
    In: Proceedings of the Ninth International Conference on future energy systems, 12 June 2018, pp.378-379
    Description: The integration of variable renewable energy sources (RES) with increased share in power supply systems leads to new challenges in power system models. In this context, flexibility options have a high potential to balance fluctuating renewable energy feed-in in a cost efficient and low emission way [8, 9]. However, the combination of model parameters like simulation time, space, sectors with increasing level of detail call for advances in model reduction techniques [6]. Hence, a trade-off between the increasing complexity introduced by introducing flexibility options and the required computational effort has to be found. In Section 1, the extension of storage units in the energy system as one of these flexibility options is investigated with the eGo model [4]. Furthermore, the model can take into account several other possibilities of flexibility options such as demand side management or power-to-X, which can be modelled as functional storage. The latter will gain in importance when the heat and transport sector are decarbonized by the use of sector coupling [1]. Section 2 presents an approach of the technoeconomic assessment of flexibility options from an operator's point of view, based on a large-scale energy system model.
    Keywords: Systemmodellierung ; Modellreduktion ; Modellparameter ; Erneuerbare Energiequelle ; Transportsektor ; Erneuerbare Energie ; Stromversorgungssystem ; Stromnetz ; Wärme ; Großsystem ; Simulationszeit ; Bedarfsmanagement;
    ISBN: 9781450357678
    ISBN: 1450357679
    Source: ACM Digital Library (Association for Computing Machinery)
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