SSS5.5 | Soil heterogeneity and its role in biogeochemical processes across scales
Soil heterogeneity and its role in biogeochemical processes across scales
Co-organized by BG3
Convener: Steffen A. SchweizerECSECS | Co-conveners: Emily LacroixECSECS, Maya EngelECSECS, Nele MeyerECSECS, Maik LucasECSECS, Sara KönigECSECS, Edith HammerECSECS
Orals
| Tue, 16 Apr, 16:15–17:55 (CEST)
 
Room -2.21
Posters on site
| Attendance Tue, 16 Apr, 10:45–12:30 (CEST) | Display Tue, 16 Apr, 08:30–12:30
 
Hall X3
Posters virtual
| Attendance Tue, 16 Apr, 14:00–15:45 (CEST) | Display Tue, 16 Apr, 08:30–18:00
 
vHall X3
Orals |
Tue, 16:15
Tue, 10:45
Tue, 14:00
Soil systems harbor a highly diverse spatial organization of its functions shaping biogeochemical cycles. From microbial microenvironments via physical soil structure and various chemical differentiation by pedogenetic or anthropogenic processes up to the landscape scale. In this session, we invite diverse studies that open our views on the spatial heterogeneity in soils from biological, physical, and chemical perspectives related to organic matter dynamics and other biogeochemical cycles.

We look forward to discuss insights across different scales and structures. Zooming in provides the opportunity to observe microbial habitats and processes, probe highly active spheres around roots or detritus, and follow the interactions of organic matter with mineral phases. Aggregated structures and a network of soil pores provides a dynamic scaffolding, which can protect soil components and influence local water retention and elemental distribution. Pedogenetic soil processes drive the differentiation at pedon scale and can result from a combination of small-scale processes determining soil ecosystem fluxes up to the landscape scale.

This session is of interest to soil scientists with complementary biogeochemical and physical backgrounds working at different scales. We especially encourage contributions that address the importance of spatial heterogeneity and architecture for ecosystem-relevant soil functions, such as the occlusion of organic residues, microbial colonization, provision of water and nutrients, the fate of soil contaminants, and many more. Different experimental imaging approaches, analytical techniques and data-driven modelling works are invited. We aim to discuss recent achievements, current obstacles, and future research directions to strengthen our conceptual understanding of the linkage of spatial heterogeneity with soil functions, biogeochemical cycling, and organic matter dynamics across scales.

Session assets

Orals: Tue, 16 Apr | Room -2.21

Chairpersons: Maya Engel, Steffen A. Schweizer
Solicited Oral Presentation 1: Eva Lippold
16:15–16:25
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EGU24-15762
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ECS
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solicited
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On-site presentation
Eva Lippold, Magdalena Landl, Eric Braatz, Steffen Schlüter, Rüdiger Kilian, Carmen Höschen, Gertraud Harrington, Carsten W. Mueller, Andrea Schnepf, Robert Mikutta, Martina I. Gocke, Eva Lehndorff, and Doris Vetterlein

Plant roots create chemical gradients within the soil rhizosphere but little information exists on the effect of root types and ages on the distribution of chemical gradients. Research aim was to develop an imaging workflow and to analyze and model the effects of radial root geometry, root hairs, and ages on nutrient gradients around roots.

The presented correlative imaging workflow is suitable for targeted sampling of roots in their 3D context and assessing the imprint of roots on chemical properties of the root-soil contact zone at µm to mm scale. Maize (Zea mays) was grown in 15N-labelled soil columns and pulse-labelled with 13CO2 to visualize the spatial distribution of carbon inputs and nitrogen uptake together with the redistribution of other elements. Soil columns were scanned by X-ray computed tomography (X-ray CT) at low resolution (45 µm) to enable image-guided subsampling of specific root segments. Resin embedded subsamples were then analysed by X-ray CT at high resolution (10 µm) for their 3D structure and chemical gradients around roots using micro X-ray fluorescence spectroscopy (µXRF), nanoscale secondary ion mass spectrometry (NanoSIMS), and laser-ablation isotope ratio mass spectrometry (LA-IRMS). NanoSIMS and LA-IRMS detected the release of 13C into soil up to a distance of 100 µm from the root surface, whereas 15N accumulated preferentially in the root cells.

Concentration gradients with different spatial extents could be identified by µXRF. The observed concentration gradients were compared to simulated gradients generated by a process-based, radially symmetric 1D rhizosphere model. An accumulation of calcium and sulfur was observed, particularly around old root segments. Our model simulations indicated that this phenomenon originates from the radial structure of the root, leading to enhanced nutrient transport towards the root surface. Gradients of calcium and sulfur could be accurately predicted by the model around a single growing root, when they were mainly caused by sorption.

However, at the pore-scale, phenomena like local precipitation, which could be visualized using our methodology, were inadequately accounted for by the classic model approach. Nonetheless, the observed extension of the gradients was well described by the model. The presented approach combining targeted sampling of the soil-root system and correlative microscopy opens new avenues for unravelling rhizosphere processes in situ.  

 

 

How to cite: Lippold, E., Landl, M., Braatz, E., Schlüter, S., Kilian, R., Höschen, C., Harrington, G., Mueller, C. W., Schnepf, A., Mikutta, R., Gocke, M. I., Lehndorff, E., and Vetterlein, D.: Continuum and particle scale analysis of nutrient gradients in the rhizosphere , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15762, https://doi.org/10.5194/egusphere-egu24-15762, 2024.

16:25–16:35
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EGU24-7710
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On-site presentation
Floriane Jamoteau, Mustafa Kansiz, and Marco Keiluweit

Interactions among microbes, minerals, and organic matter are key controls on carbon, nutrient, and contaminant dynamics in soil and sediments. However, probing these interactions at relevant scales and through time remains an analytical challenge due to both their complex nature and the lack of tools permitting non-destructive time-step analysis. The recent development of optical photothermal infrared (O-PTIR) microscopy has opened the way for non-invasive analysis of these interactions at submicron resolution through time. Here we demonstrate the ability of O-PTIR microscopy to analyze mineral-organic microstructures down to 400 nm, without contact, allowing the time-resolved, non-destructive characterization of both mineral and organic components. Results showed that, while all these mineral-organic microstructures can be analyzed without measurable beam damage using the appropriate laser power, poorly crystalline minerals, and high-molecular-weight compounds are more sensitive to damage than crystalline minerals and low-molecular-weight compounds, respectively. Despite these differences in beam damage sensitivity, we found analytical conditions under which all materials were analyzed without damage and could therefore be analyzed repeatedly over time. With synthetic mineral-organic microstructures, we localized mineral-bound and unbound organic compounds, down to the sub-micron scale. Our results highlight the potential of and provides analytical recommendation for the application of O-PTIR microscopy to resolve microbe-mineral-organic matter interactions in soil and sediments.

How to cite: Jamoteau, F., Kansiz, M., and Keiluweit, M.: Probing microbe-mineral-organic matter interactions in soils with photothermal infrared spectromicroscopy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7710, https://doi.org/10.5194/egusphere-egu24-7710, 2024.

Solicited Oral Presentation 2: Claire Chenu
16:35–16:45
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EGU24-14399
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solicited
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On-site presentation
Claire Chenu, Charlotte Védère, Israel Kpemoua, Naoise Nunan, Valérie Pot, Patricia Garnier, Clémentine Chirol, and Laure Vieublé-Gonod

Soil moisture is a main driver of soil organic matter dynamics of soil organic matter and is an important environmental variable in all models predicting changes in soil carbon stocks from site to global scales. Despite this, the mechanisms determining the response of heterotrophic soil respiration to soil moisture remain poorly quantified, being represented in most current carbon cycle models as simple empirical functions. Soils are extremely complex and heterogeneous environments and many properties observed at the profile or at the plot the scale are, in fact, determined by microscale conditions and processes.

The spatial heterogeneity of soil constituents and assemblages defines a myriad of contrasted micro-habitats, hosting diverse microorganisms, with contrasted moisture related characteristics and presumably contrasted levels of microbial activity. In addition, the respective spatial distributions of organic resources and microbial decomposers and the transfer rates between them, that depend on soil moisture, explain that similar organic compounds may have contrasted residence times in soil, being stabilized or not.

We consider how do soil moisture and soil spatial heterogeneity may explain the stabilisation of organic matter. Different pore size classes exhibit different rates of microbial decomposition, when considering different soils, across published studies and in a single laboratory experiment. Soil moisture affects the dynamics of biogeochemical hotspots, such as the detritusphere.

Regarding destabilization of soil organic matter, priming effect was revealed to be soil moisture dependent, that can be explained by varying access of newly produced enzymes to native soil organic matter. The Birch effect, a well-described flush of mineralization observed after rewetting dry soils, may also be partly explained at the microscale by changes in the local architecture of soils.

Overall, considering the interplay between soil spatial heterogeneity, soil moisture and the activity of microbial decomposers offers insights in understanding the stabilisation and de-stabilisation of soil organic matter. Incorporating this process level understanding into soil organic matter dynamics models is a challenge, as it requires the identification of relevant soil structure descriptors of these processes, at different time scales.

How to cite: Chenu, C., Védère, C., Kpemoua, I., Nunan, N., Pot, V., Garnier, P., Chirol, C., and Vieublé-Gonod, L.: The interplay of soil spatial heterogeneity and water in stabilizing and destabilizing soil organic matter, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14399, https://doi.org/10.5194/egusphere-egu24-14399, 2024.

16:45–16:55
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EGU24-13293
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On-site presentation
Vincent Noël, Samuel Webb, and Kristin Boye

Redox reactions essentially underlie several biogeochemical processes and are typically spatiotemporally heterogeneous in soils and sediments. However, redox heterogeneity has yet to be incorporated into mainstream conceptualizations and modeling of soil biogeochemistry. Anoxic microsites, a defining feature of soil redox heterogeneity, are non-majority oxygen depleted zones in otherwise oxic environments. Neglecting to account for anoxic microsites can generate major uncertainties in quantitative assessments of greenhouse gas emissions, C sequestration, as well as nutrient and contaminant cycling at the ecosystem to global scales. However, only a few studies have observed/characterized anoxic microsites in undisturbed soils, primarily, because soil is opaque and microsites require µm-cm scale resolution over cm-m scales. Consequently, our current understanding of microsite characteristics does not support model parameterization.

To resolve this knowledge gap, we simultaneously (i) study impact from anoxic microsites on biogeochemical cycles at the soil scale and (ii) detect, quantify, and characterize anoxic microsites directly from natural cores.

We have examined the influence of anoxic microsites on biogeochemical cycles of nutrients (C, S, and Fe) and contaminants (Zn, Ni, As, U), combining results from experimental columns and natural cm-scale anoxic microsites of floodplain sediments at the upper Colorado River Basin scale. In parallel, we have demonstrated through a proof-of-concept study that X-ray fluorescence (XRF) 2D mapping can reliably detect, quantify, and provide basic redox characterization of anoxic microsites using solid phase “forensic” evidence. Rapid screening of large cores at high spatial and energy resolution, i.e. 1-100 µm resolution over cm-m areas, followed by systematic algorithm-driven data processing, allows for relatively quick identification, quantification, and characterization of actual anoxic microsites. To date, these investigations have revealed direct evidence of anoxic microsites in predominantly oxic soils such as from an oak savanna and toeslope soil of a mountainous watershed, where anaerobicity would typically not be expected. We also revealed preferential spatial distribution of redox microsites inside aggregates from oak savanna soils. We anticipate that this approach will advance our understanding of soil biogeochemistry and help resolve “anomalous” occurrences of reduced products in nominally oxic soils.

How to cite: Noël, V., Webb, S., and Boye, K.: Laboratory for Observing Anoxic Microsites in Soils (LOAMS), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13293, https://doi.org/10.5194/egusphere-egu24-13293, 2024.

16:55–17:05
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EGU24-13732
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On-site presentation
Joseph Roscioli, Joanne Shorter, Elizabeth Lunny, Scott Herndon, Nuria Gomez-Casanovas, and Peter Byck

Subsurface cycling of nitrogen and carbon is central to our understanding of biosphere-atmosphere exchange and can strongly impact the ability of soil to be a greenhouse gas source or sink.  The underlying processes exhibit strong environmental dependence that can lead to substantial spatiotemporal heterogeneity across scales.  Here we present a study that explores how that variability manifests in subsurface greenhouse gases and their isotopes under a cattle grazing pasture in the southeastern U.S.  We used an automated array of 24 diffusive soil gas probes connected to a tunable infrared laser direct absorption spectrometer (TILDAS) to produce real-time maps of nitrous oxide isotopes, carbon dioxide, and oxygen with high spatial (meters) and temporal (hours) resolution.  We discuss ways to visualize and process the heterogeneity data, including using Lorenz plots and two-dimensional correlation, to reveal the magnitude and persistence of spatial heterogeneity of these gases.  CO2 is found to be much more spatially homogeneous than N2O, indicating a stronger dependence of N processing upon the local environment.  Analysis of N2O isotopic signatures shows that the last step in subsurface N-cycling, N2O reduction, is spatially heterogeneous and related to the magnitude of “hot spots” of N2O production.   

How to cite: Roscioli, J., Shorter, J., Lunny, E., Herndon, S., Gomez-Casanovas, N., and Byck, P.: Exploring subsurface heterogeneity of nitrogen and carbon cycling under a southeastern U.S. cattle grazing pasture , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13732, https://doi.org/10.5194/egusphere-egu24-13732, 2024.

17:05–17:15
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EGU24-139
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ECS
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On-site presentation
Jingjing Liu, Yu Tian, and Shenggao Lu

Soil pore structure, dictated by factors such as porosity, size distribution, and geometry, is crucial for various soil processes and is significantly influenced by soil organic carbon (SOC). As the primary architect of pore geometry within soil aggregates, SOC plays a vital role in determining soil functionality and ecosystem services, yet traditional in-situ analysis methods have fallen short in accurately depicting its intricate distribution. The study employed a two-fold approach to analyze soil structure: a hydrogen peroxide fogging system was used to selectively remove organic carbon from soil aggregates, followed by synchrotron radiation micro-computed tomography (SR-μCT) for in-depth three-dimensional imaging. The results revealed that hydrogen peroxide treatment variably reduced organic carbon in soil aggregates, with Cambisol showing a higher removal efficiency (68-79%) compared to Ultisol (42-47%). The data highlighted the transformation of smaller pores and an increase in larger pore spaces following organic carbon removal, with Cambisol aggregates experiencing the most substantial alterations in pore structures. The impact of organic carbon on the shaping of pore structure within soil aggregates was profound and varied distinctly between the two studied soils—Ultisol and Cambisol. In Ultisol, the organic carbon, initially minimal, played a subtle role in pore structure formation, leading to limited changes post-removal, which suggested a structural resilience possibly due to its inherent mineralogy and physicochemical characteristics. In contrast, Cambisol, with higher initial organic carbon content, showed dramatic alterations in pore structure upon organic carbon removal. This indicated a more critical role of organic carbon in maintaining pore space configurations, with significant increases in larger pore spaces and a decrease in smaller, disconnected pores. These changes highlighted the organic carbon’s crucial function in not only sustaining pore integrity but also in facilitating the complex soil functions such as water retention and root penetration.

How to cite: Liu, J., Tian, Y., and Lu, S.: Investigating the influence of soil organic carbon on pore structure within aggregates a comparative study of Ultisols and Cambisols in China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-139, https://doi.org/10.5194/egusphere-egu24-139, 2024.

Solicited Oral Presentation 3: Hannes Schmidt
17:15–17:25
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EGU24-16443
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Virtual presentation
Hannes Schmidt, Naoise Nunan, Xavier Raynaud, Steffen Schlueter, Vincent Felde, Berit Zeller-Plumhoff, Gaëlle Marmasse, Alberto Canarini, Lucia Fuchslueger, and Andreas Richter

Soil is a complex system with a high degree of physical, chemical, and biological heterogeneity. Soil structure is organized into entangled pore networks that provide an immense surface area and are partially filled with gases and aqueous solutions. This heterogeneous landscape houses a multitude of active and inactive organisms of which soil bacteria and fungi are considered the driving forces of nutrient cycling and biogeochemical processes. Standard analyses such as soil respiration are meaningful measures to estimate processes on a meso- and macroscale while the biological agents whose actions we measure are mainly to be found on the microscale. Yet, our understanding of microbial living conditions in soil and their consequences for activity, growth, and turnover is severely limited. In this presentation I will focus on a microbial perspective and present data from various experiments where soil microbial identity and/or activity were investigated while acknowledging spatial aspects of their microenvironments. I will provide an updated view on spatial distribution of microbial communities within soils, including evidence that suggests that the density of bacteria in soils has likely been underestimated by orders of magnitudes for decades. Microbial density arguably is a major determinant of cell-to-cell interactions, and thus many processes involved in microbial nutrient cycling that we measure on a larger scale. I will further argue to embrace soil heterogeneity rather than minimizing it, for example by using intact soil cores instead of sieved soils for stable isotope labelling experiments. I will present data on in situ bacterial and fungal growth which suggests that preserving soil physical architecture while investigating microbial parameters could bring experimental measurements significantly closer to field conditions, while also opening new avenues to improve our understanding of spatial aspects of soil microbiology.

How to cite: Schmidt, H., Nunan, N., Raynaud, X., Schlueter, S., Felde, V., Zeller-Plumhoff, B., Marmasse, G., Canarini, A., Fuchslueger, L., and Richter, A.: Embracing the structural framework of soil in microbiological and ecological research, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16443, https://doi.org/10.5194/egusphere-egu24-16443, 2024.

17:25–17:35
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EGU24-4761
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ECS
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On-site presentation
Michael Bitterlich, Eric bönecke, and Jörg Rühlmann

Soil particle size distribution determines the soil water and nutrient availability, but the spatial variance of the soil texture is often unknown in agricultural fields. This knowledge gap limits demand-oriented and ecological nutrient and water management of crops. It also hampers our understanding of the crop resource use in the field as mediated by soil microbes such as the arbuscular mycorrhizal symbioses. To better understand to which soil conditions maize-mycorrhiza associations respond, we used proximal sensing of soil texture to map within-field variation soil particle size in high spatial resolution and related soil texture to the mycorrhization of organic maize.

To obtain the soil texture maps, we used the mobile sensor platform Geophilus electricus [1]. This proximal soil sensing system deploys a multi-sensor approach to discriminate soil properties by simultaneously measuring the electrical resistivity (up to 1.5m depth) via rolling electrodes and the natural gamma activity, whilst a DGPS guarantees the required precision in geo-referencing during mapping [2]. After calibration of the sensor data with soil samples of the selected fields, the final output is a high-resolution map of the mean soil particle diameter (MPD), which was then used as the independent variable in correlations with the mycorrhization of maize.

The soil texture mapping took place for three investigated fields in 2020 at an organic farm in Lower Saxony, Germany, which is dominated by sandy soils and on which a crop rotation with maize was deployed. The plant and soil sampling took place in 2017, 2020 and 2021 at the respective sites with maize. For each field, the sampling of soils and plants occurred equidistantly in 12 parallel transects along the moving lane direction. We analyzed plant and soil C/N, P, K, Mg, soil pH and organic matter and root colonization by native mycorrhizal fungi during the maize culture.

According to our expectations, we found that the MPD and the clay fraction are accurate describers of the soil P, N, Mg and Corg concentrations for the three years and fields in the crop rotation, while soil K was not responding to the soil texture. Interestingly, we also found a conserved correlation between root colonization by arbuscular mycorrhizal fungi and the MPD of the soil surrounding the roots of the sampled plants. Lower MPD (i.e. higher clay contents) gave rise to stronger maize-mycorrhiza root associations. This response pattern was conserved in years markedly different in mean annual temperature and precipitation. However, the lowest rates of root colonization by mycorrhizas were observed in the dry year of 2020.

We discuss that precision farming technologies may have the potential to guide the management of crops for improved and microbe-assisted resource use. 

 

 

[1] Lück, E., & Rühlmann, J. (2013). Resistivity mapping with GEOPHILUS ELECTRICUS—information about lateral and vertical soil heterogeneity. Geoderma, 199, 2–11. [2] Meyer, S. et al. (2019). Creating soil texture maps for precision liming using electrical resistivity and gamma ray mapping. In Stafford, J. V. (Ed.) Precision Agriculture’19 Proceedings of the 12th European Conference on Precision Agriculture Wageningen (pp. 92). Wageningen, The Netherlands: Wageningen Academic Publishers.

How to cite: Bitterlich, M., bönecke, E., and Rühlmann, J.: Mycorrhiza likes clay - High resolution soil texture maps reveal a conserved correlation of maize mycorrhization to soil particle size across years and fields, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4761, https://doi.org/10.5194/egusphere-egu24-4761, 2024.

17:35–17:45
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EGU24-11128
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On-site presentation
Ksenia Guseva, Carlos Arellano, Magdalena Rath, Paul Prinz, Moritz Mohrlok, and Christina Kaiser

The soil pore space constitutes a highly heterogeneous habitat that harbors a rich microbial diversity. Microbial processes within soils are intricately linked to the physical and chemical characteristics of micro-environments of pores where they reside. The dynamics of decomposition of organic matter therefore is shaped by the dispersion dynamics or spatial constraints imposed on microorganisms and their enzymes. Therefore, incorporating the complex soil architecture into computational models at the microscale is a crucial step to improve our predictions of the dynamics of soil organic matter (SOM) turnover.

In this work, we employ theoretical models to elucidate the impact of soil structural complexity and heterogeneity on organic matter decomposition dynamics, and characterize mechanisms that enhance or constrain it. In the first part, we show the impact of compartmentalization of the substrate on enzyme activity, considering a scenario where microbes have no direct physical access to the substrate and only smaller freely diffusing enzymes can reach it. Our findings reveal that, in this context, enzyme lifetime imposes limitations on the turnover rate of the reaction, subsequently affecting the uptake and growth rates of microorganisms. In the second part, we examine the effect of soil architecture on microbial decomposition dynamics. Our results highlight two contrasting aspects necessary for rapid decomposition: on one hand there is a need for refuges/shelters where microbial activity is boosted trough accumulation of enzymes, and on the other there is a need for high connectivity (accessibility) of the pore space for the microbial population to spread. Through our examination, we unveil the intricate interplay between these apparently conflicting conditions and their profound effects on population growth and substrate decomposition rates.

How to cite: Guseva, K., Arellano, C., Rath, M., Prinz, P., Mohrlok, M., and Kaiser, C.: The influence of structural complexity of microbial habitats on soil organic matter decomposition: a theoretical analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11128, https://doi.org/10.5194/egusphere-egu24-11128, 2024.

17:45–17:55
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EGU24-15015
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ECS
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Highlight
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On-site presentation
Samuel Bickel and Dani Or

The highly fragmented soil physical environment and the dynamic aqueous phase jointly constrain bacterial life by limiting cell dispersion and modulating diffusion and access to patchy nutrients. A modeling framework that integrates soil hydration conditions with soil organic carbon inputs provides systematic estimates of size distributions and interaction distances among soil bacterial populations. The patterns of bacterial community microgeography provide an important building block for interpreting soil ecological functioning. Experiments and mechanistic modelling show that soil bacterial cluster sizes (measured by counting cell numbers within a community) follow an exponentially truncated power law with parameters (e.g., largest community size) that vary with mean soil water content and carbon inputs across biomes. Theory predicts that similar to human settlement size distributions, tree sizes and other systems in which growth rates are defined by the environment independent of the object size, the resulting bacterial community size distributions is likely to obey the so-called Gibrat’s law. Our results support a potential for generalization using positively skewed distributions of soil bacterial community sizes (e.g., log normal and Gamma). We show that soil bacteria reside in many small communities (with over 90% of soil bacterial communities having less than 100 cells), supported by theoretical predictions of log-normal distribution for non-interacting soil bacterial community sizes with scaling parameters that vary with biome characteristics. We will use estimates of the fraction of the largest bacterial communities where anoxic conditions may develop under prevailing conditions to constrain the number of anoxic hotspots per soil volume.

How to cite: Bickel, S. and Or, D.: On the Microgeography of Soil Bacterial Communities, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15015, https://doi.org/10.5194/egusphere-egu24-15015, 2024.

Posters on site: Tue, 16 Apr, 10:45–12:30 | Hall X3

Display time: Tue, 16 Apr 08:30–Tue, 16 Apr 12:30
Chairpersons: Sara König, Maik Lucas
X3.140
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EGU24-627
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ECS
Laura Gismero Rodríguez, Inés Aguilar-Romero, José Alfonso Gómez, Ángel Valverde, and Heike Knicker

In Mediterranean regions, olive plantations are commonly located on steep 
slopes, leading to significant erosion. To mitigate soil loss, sustainable management 
practices often involve allowing natural vegetation cover to grow in the inter-tree 
spaces. 

To provide insights into the impact of different management forms on soil quality, we 
collected topsoil samples (0-15 cm) from an olive orchard with an 11% slope located in 
Southern Spain (Benacazón, Seville). Samples were taken along the slope of plots
managed with conventional tillage (CT) and with natural cover (NC). Additionally, soils
from the tree line, treated with herbicide (TL-Herb.), were included. To account for 
seasonality effects, sampling campaigns were conducted in autumn 2022 (following the 
dry season) and spring 2023 (after the rainy season). 

Soil organic matter content will be correlated with the management practices, slope 
location and microorganism abundance, determined through phospholipid fatty acid 
analysis (PLFA). Microbial respiration analysis will be also performed, using MicroResp
to assess microbial activity. The main hypothesis is that plots with vegetation cover will 
have higher SOM and total microbial biomass contents. We also expect an impact of 
slope location not only on the size of the microbial pool but also on the microbial 
biodiversity.

How to cite: Gismero Rodríguez, L., Aguilar-Romero, I., Gómez, J. A., Valverde, Á., and Knicker, H.: The effect of slope on soil organic matter and on microbial communities under different soil management practices., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-627, https://doi.org/10.5194/egusphere-egu24-627, 2024.

X3.141
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EGU24-4322
Carla Restrepo and Yakshi Ortiz

Landsliding creates new substrates upon which ecosystems develop. From a recovery perspective, these substrates may limit plant growth due their harsh conditions. Yet, from a soil formation perspective, these substrates may enhance weathering rates due to a combination of abiotic and biotic factors. Central to both is the role that mycorrhiza may play in ecosystem development, including biogeochemical cycles. Given that at mountainscape scales landslide populations are diverse due to variation in underlying climatic and edaphic conditions, we hypothesize that plant-mycorrhizal associations and their functions will mirror this diversity. To test this hypothesis, we focus on the Sierra de Las Minas in Guatemala (SLM), a mountain range that offers contrasting climatic characteristics associated with aspect (south aspect is dry to mesic and north aspect wet) and steep elevation gradients (400 – 2600 m a.s.l.). Leveraging plant and soil inventories conducted in forest and landslide habitats in the SLM we ask 1) How do plant-mycorrhizal associations vary with aspect, elevation, and habitat? 2) What is the contribution of soil chemistry to the observed variation in plant-mycorrhizal associations? And 3) How do plant-mycorrhizal associations and environmental conditions explain variation in weathering rates? To answer these questions, we integrated our plant inventories with a global database on plant-mycorrhizal associations. The former contains species composition and soil elemental analyses that we used to estimate a variety of weathering indices. The latter was used to assign plants from our field inventories to one or more mycorrhizal type.

Plant-mycorrhizal associations were diverse and greatly contributed to the separation of plant communities in multivariate space. Aspect followed by habitat explained a large fraction of the observed variability. Subsets of soil variables correlated with different dimensions derived from principal component analyses suggesting that plant-mycorrhizal associations contribute diverse functions. In general, weathering indexes differed with aspect and habitat. For example, Vogt Residual Index and Chemical Index of Alteration, were higher in landslide than forest and this difference was more pronounced in the wet than dry to mesic aspects. Further analyses will allow us to examine the contribution of plant-mycorrhizal associations to ecosystem development and soil formation in tropical mountainscapes influenced by landslide activity.

How to cite: Restrepo, C. and Ortiz, Y.: Plant-mycorrhizal associations vary with climate and soil in tropical mountainscapes influenced by landslides: Implications for ecosystem development and soil formation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4322, https://doi.org/10.5194/egusphere-egu24-4322, 2024.

X3.142
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EGU24-4570
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ECS
Maya Engel, Vincent Noel, Samuel Pierce, Tristan Babey, Libor Kovarik, Ravi Kukkadapu, Qian Zhao, Rosalie Chu, Kristin Boye, and John Bargar

High concentrations of Fe-rich colloids have been detected in the anoxic zones of our Slate River floodplain field site (CO, USA) since 2018. We speculated that the composition and abundance of the colloids is controlled by the seasonal dynamics and spatial heterogeneities of the subsurface. Therefore, our goals were to 1) decipher the structure and chemical composition of Fe-rich colloids, 2) identify mechanisms of colloid transformation and 3) understand their biogeochemical function.

TEM analysis revealed nano-spheres and nano-assemblages that consist mainly of Fe, O, Si, and C, with lower contributions from Al, S and Ca. Based on this elemental distribution, we hypothesized that the colloids are composed of Fe minerals that are associated with organic matter and Si. This was further confirmed through Mössbauer spectroscopy and Fe-EXAFS that indicated the colloids consist ferrihydrite associated with organic matter and Si. NanoSIMS imaging detected co-localities of Fe, S, Si, and O, as well as C and N, which demonstrate once more that these are ferrihydrite-based colloids that are embedded in an organic matter-Si matrix.

 These findings are intriguing as they demonstrate high abundance of ferrihydrite-based colloids in anoxic depths of our field site. The stability of the colloids is likely attributed to the coating of organic matter and Si that serves as a protective layer against the reducing conditions. Nevertheless, our data also showed that colloids collected during snowmelt (Spring 2021) contained a higher proportion of Fe(II) than colloids collected during baseflow conditions (Summer 2021). XPS analysis measured higher atomic percentages of C and Si compared to Fe and O in baseflow versus snowmelt colloids, indicating a decrease in the organic-Si protective layer under baseflow conditions, allowing for Fe(II) oxidation and an increase in Fe(III)/ferrihydrite content. The fact that there is an occurrence of S species only in the more reduced snowmelt colloids illustrates the dynamic and delicate composition of these environmental colloids during seasonal changes in hydrology and porewater chemistry.

We are also in the process of interpreting our seasonal data that will shed light on the controls over the seasonal dynamics of the colloids. We have already linked Fe(II) colloid abundance to lower vertical porewater velocities and higher organic matter levels, and are working on additional analyses including data acquired from FT-ICR-MS analysis of the organic composition of the colloids.

How to cite: Engel, M., Noel, V., Pierce, S., Babey, T., Kovarik, L., Kukkadapu, R., Zhao, Q., Chu, R., Boye, K., and Bargar, J.: Seasonal floodplain dynamics control Fe-rich colloid characteristics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4570, https://doi.org/10.5194/egusphere-egu24-4570, 2024.

X3.143
|
EGU24-5851
Nina Siebers, Eva Voggenreiter, Prachi Joshi, Janet Rethemeyer, and Liming Wang

Understanding the formation and stability of soil aggregates is crucial for sustaining soil functions. This study investigates the impact of organic matter (OM), pedogenic Fe (oxyhydr)oxides, and aggregate size on aggregate stability in an arable soil. Samples were collected from the Ap and Bt horizons of a Luvisol after 14 years of bare fallow, and results were compared with a control field under permanent cropping. In the Ap horizon, bare fallow led to a 26% reduction in the median diameter of the 53-250 µm size fraction, indicating decreased stability of larger microaggregates. Simultaneously, the mass of the 20-53 µm size fraction increased by 65%, suggesting reduced stability, particularly of larger soil microaggregates, due to the absence of fresh OM input. The 14carbon (14C) fraction of modern C (F14C) under bare fallow ranged from 0.50 to 0.90, lower than the cropped site (F14C between 0.75 and 1.01). This difference was most pronounced in the smallest size fraction, indicating the presence of older C. Higher stability and reduced C turnover in <20 µm aggregates were attributed to their elevated content of poorly crystalline Fe (oxy)hydroxides, acting as cementing agents. Colloid transport from the Ap to the Bt horizon was observed under bare fallow treatment, highlighting the release of mobile colloids. This transport may initiate elemental fluxes with potential unknown environmental consequences. In conclusion, the absence of OM input decreased microaggregate stability, releasing mobile colloids and initiating colloid transport.

How to cite: Siebers, N., Voggenreiter, E., Joshi, P., Rethemeyer, J., and Wang, L.: Synergistic relationships between the age of soil organic matter, Fe speciation, and aggregate stability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5851, https://doi.org/10.5194/egusphere-egu24-5851, 2024.

X3.144
|
EGU24-6272
Maik Lucas, Lina Rohlmann, and Kathrin Deiglmayr

Perennial bioenergy crops like Silphium perfoliatum (cup plant) are a promising alternative to currently used energy crops such as maize because of their positive feedbacks on various soil properties including carbon sequestration, edaphon activity and erosion control. This study investigates the long-term impact (over 10 years) of the cup plant on soil organic carbon and soil structural parameters in comparisons to a to a nearby ploughed reference site.

We employed tension infiltrometers to measure water infiltration rates at two soil depths (5 and 45 cm). Following this, 100 cm³ aluminum soil cores were extracted for X-ray computed tomography at a resolution of 35 µm. The image analysis, enhanced by machine learning, classified structures including roots, particulate organic matter (POM), biopores, and two types of soil matrix: dense and loose, the latter indicating higher carbon content or more pores slightly below image resolution. The dataset was complimented by the determination of total carbon content and the root length distribution with RhizoVisionExplorer.

The results indicate significant differences in pore structure, primarily in the topsoil, where the cup plant site showed a greater volume of biopores than the reference site. In contrast, the subsoil differences were less marked. Organic carbon content analysis demonstrated a notable increase in the upper soil layer (10-15 cm) at the cup plant site, contributing to a higher soil organic carbon stock than the reference site. However, this effect diminished with depth, becoming negligible at 50-55 cm. In the topsoil, extensive bioturbation/biomixing was observed, as indicated by the darker, more loosely structured soil matrix, which often had the shape of biopores. This bioturbation, which mixed particulate organic matter (POM) into the soil, significantly enhanced soil organic carbon, as evidenced by linear regression analysis.

These findings underscore the substantial impact of the perennial cup plant in enhancing soil structure and carbon content, particularly in the topsoil.

How to cite: Lucas, M., Rohlmann, L., and Deiglmayr, K.: Long-Term Effects of Silphium perfoliatum on Soil Pore Dynamics and Organic Carbon Accumulation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6272, https://doi.org/10.5194/egusphere-egu24-6272, 2024.

X3.145
|
EGU24-8956
|
ECS
Olivia Rasigraf, Anne Riedel, Alexander Bartholomäus, Timothy Clough, Thomas Friedl, and Dirk Wagner

Landslides are an important erosion mechanism in mountainous terrain. They strip large quantities of organic material from ecosystems and expose bedrock to weathering. At the west side of New Zealand’s Southern Alps, super-humid climate and slope instabilities create ideal conditions for frequent landslides, allowing studies of soil formation processes in short-term chronosequences. Here, we investigated soils from three landslides that occurred in 2019 (“young”), 1997 (“intermediate”), and 1965±5y (“old”), respectively. Additionally, reference forest soils located outside of landslide areas were sampled at each location. Closed PVC chambers were installed at different positions on landslide surfaces and reference soils, and gas samples were collected for flux analysis. Soil samples were collected at the same positions from the surface and 20 cm depth and investigated for physico-chemical parameters and microbial community composition.

Net CO2 emissions reached 830 mg h-1m-2 at the “old” site in summer and remained below 356 mg h-1m-2 in winter. Net N2O emissions showed a patchy spatial pattern, reaching rates of 0.2 mg h-1m-2 at the “old” site in summer. At most locations, N2O flux was below the detection limit during winter.

Soils were dominated by bacterial phyla Acidobacteria, Bacteroidota, Chloroflexi, Gemmatimonadota, Planctomycetota, Proteobacteria and Verrucomicrobiota. Dominant archaeal phyla comprised Thermoplasmatota and Crenarchaeota. Beta diversity analysis revealed distinct community composition patterns with the “young” site forming a separate cluster from the older landslides and reference soils. Surface- and depth-associated microbial communities showed high similarity at the “young” site, but they became increasingly distinct at the “intermediate”, “old” and reference soil sites. Community composition at the “old” site showed the least difference to reference sites, indicating that ecosystem development rapidly reached a state similar to older mature forests.

In general, the three landslide sites showed a gradient in the development of soil chemical parameters, microbial community composition and soil respiration rates, with the “old” site being closest to reference sites. Soil respiration rates showed strong seasonal dependence and soil temperature sensitivity.

Our results indicate that respiration rates and microbial community composition of landslide soils reach those of older mature forest soils within a few decades after mass wasting events, if no reactivation occurs and soil development can proceed without disturbance.

How to cite: Rasigraf, O., Riedel, A., Bartholomäus, A., Clough, T., Friedl, T., and Wagner, D.: Seasonal greenhouse gas flux and microbial community dynamics along a landslide soil chronosequence at the west side of New Zealand's Southern Alps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8956, https://doi.org/10.5194/egusphere-egu24-8956, 2024.

X3.146
|
EGU24-9465
Karin Eusterhues, Jürgen Thieme, Thomas Ritschel, Pavel Ivanov, and Kai Uwe Totsche

At numerous open pits worldwide, carcinogenic and geno‐toxic tar oil is still exposed to the environment. To understand ongoing tar degradation under different environmental conditions we studied soil structure, water retention, tar composition, and microbial biomass of a technosol under a small tar-oil spill at a former brown coal processing site. We observed that microbial biomass increased with pore volume on our study site: Generally, contaminated layers of the technosol were more porous than uncontaminated control soils and accommodated more microbes. However, the relationship was not linear. We therefore wondered whether the redox regimes within the aggregates of the different layers provide comparable conditions for microbial degradation.

We used the chemical state of S as a proxy for the prevailing redox-conditions and µXANES on thin sections (5 µm spatial resolution) to analyze the S speciation in relation to soil structure. First results show that the tar is not homogeneously composed and that the proportion of reduced S compounds increases with soil depth: Particularly S-rich domains within the tar are often roundish, up to 200 µm in size and composed of varying proportions of inorganic sulfide-S, organic monosulfide-S or thiol-S, sulfoxide-S, and sulfonate-S. The topmost layer (0-5 cm) of the technosol is very porous. Here, the tar matrix is dominated by sulfonate-S. At more than 5 cm depth, the soil also has a high porosity due to large pores > 50 µm but at the same time includes mm-sized, compact aggregates with only few small pores (1-10 µm and 10-50 µm). The tar matrix within these aggregates contains sulfidic S in addition to the sulfonate-rich component. However, adjacent to pore surfaces we observe 5-15 µm thick (oxidized) rims with only sulfonate-S.

Our data show that the tar is not only chemically complex, but also heterogeneous in composition at the µm scale. Below a soil depth of 5 cm, we can assume that microbial tar degradation is slowed down because of the anoxic conditions within the aggregates, although pores > 50 µm are abundant and bacterial cell counts are high.

How to cite: Eusterhues, K., Thieme, J., Ritschel, T., Ivanov, P., and Totsche, K. U.: Mapping redox conditions in a tar-oil contaminated technosol by S K-edge XANES at the micrometer scale, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9465, https://doi.org/10.5194/egusphere-egu24-9465, 2024.

X3.147
|
EGU24-11265
|
ECS
Danielle Alderson, Martin Evans, Mark Garnett, and Fred Worrall

Floodplains are dynamic ecosystems that cycle carbon, which is both delivered from upstream catchment sources and produced in-situ by pedogenesis. These landforms are being progressively acknowledged as important environments of carbon processing, with the capacity for both substantial carbon sequestration in addition to acting as hotspots of carbon mineralisation. The balance between storage and release is dependent on a number of controls including landscape position, environmental conditions and soil characteristics. This study focuses on three headwater floodplains in a single catchment (approximately 10km in length), downstream of a highly eroded blanket bog peatland in the Peak District, UK. Aged organic carbon of peatland origin has been found in floodplains in this area based on prior research, and therefore we aimed to understand whether the allochthonous carbon was being mineralised in this context. We examined sediment cores and analysed the radiocarbon (14C) content of CO2 respired from the floodplain soils using a partitioning approach to scrutinise the depth and age relations of respiration in the individual floodplains and patterns of age distributions downstream. As such, we examined whether soil heterogeneity as a function of distance downstream and within individual floodplain profiles had an impact on age of respired CO2.

Aged organic carbon was released from the upper and mid floodplain sites (14C ages of 682 and 232 years BP, respectively), whereas only modern dates were recorded at the lower site. The sedimentology was in accordance with the radiocarbon dates, suggesting primarily allochthonous deposition at the upper sites, but a dominance of in-situ soil development at the lower site. There was no age-depth relationship within individual floodplains, suggesting that the floodplain sediments were well-mixed and that aged organic matter was being processed both at the surface and at depth in the uppermost sites. An isotope mass balance mixing model indicated the control of two sources of CO2; recently fixed C3 organic matter and CO2 produced by methanogenesis. The results indicate that floodplains in a relatively narrow halo around eroding headwater peatlands could be important sites of aged carbon turnover originally derived from upstream sources, with those further downstream playing a different role. Reworked carbon does not transfer passively through the system and experiences periods of deposition where it can be subject to microbial action. In areas where organic carbon has previously been ‘locked up’ (e.g., permafrost regions) but is now under the threat of release due to climate change, this is an important consideration.

How to cite: Alderson, D., Evans, M., Garnett, M., and Worrall, F.: Aged carbon mineralisation from headwater peatland floodplains in the Peak District, UK, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11265, https://doi.org/10.5194/egusphere-egu24-11265, 2024.

X3.148
|
EGU24-11474
|
ECS
Nathan Chin, Egon Van Der Loo, Kristen DeAngelis, and Marco Keiluweit

Manganese (Mn) has been demonstrated to be a significant driver of litter decomposition in forest soils, regulating nutrient cycling, CO2 production, and ultimately soil carbon storage across forest systems globally. Recent evidence suggests that Mn-driven litter decomposition is dependent on ubiquitous oxic-anoxic interfaces in soils, which act as potential hotspots for the formation of reactive Mn(III) oxidants. Here we will show how oxic-anoxic interfaces in forest soils, arising from spatiotemporal variations in moisture, affect Mn(III)-driven litter decomposition. To do this, we tested the effect of in-field Mn additions on litter decomposition along a deciduous forest upland-to-wetland transect exhibiting dynamics in oxic-anoxic transitions. Within Mn-amended litterbags incubated across the transect, we monitored spatiotemporal variations in Mn(III) formation and litter decomposition. Over the course of the experiment, increased Mn amendments in litter correlated with both enhanced CO2 production as greater mass loss compared to untreated litter, particularly during periods of greater Mn(II) oxidation. Wet-chemical extractions revealed increasing Mn(II) oxidation over the growing season in elevated Mn treatments, resulting in enhanced Mn(III) formation. Additionally, the greater abundance of Mn(III) phases in Mn treated litter compared to untreated litter was significantly correlated to a greater degree of oxidation in the litter and greater water extractability of litter carbon, demonstrating enhanced litter decomposition in Mn amended litter. Across the forest transect, Mn oxidation and Mn(III) formation were greatest at sites with greater presence of oxic-anoxic transitions, which coincided with the sites exhibiting higher litter decomposition. Therefore, our results show that Mn(III)-mediated litter decomposition occur in hotspots present at oxic-anoxic interfaces across spatiotemporal gradients in forest soils. These findings provide first insights into the spatiotemporal links between Mn and carbon coupled redox cycling in forest ecosystems.

How to cite: Chin, N., Van Der Loo, E., DeAngelis, K., and Keiluweit, M.: Spatiotemporal variations of manganese-mediated litter decompositions across oxic-anoxic transitions in deciduous forest soils, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11474, https://doi.org/10.5194/egusphere-egu24-11474, 2024.

X3.149
|
EGU24-14407
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ECS
Carlos Arellano-Caicedo, Ara Fadhel, Pelle Ohlsson, and Edith C. Hammer

The way microbes interact in nature can vary widely depending on the spatial characteristics they are located in. This aspect of the microbial environment can determine whether processes such as organic matter turnover, community dynamics, or microbial speciation, among others, occur and their impact on soil functions. Investigating how the geometry of microhabitats influences microbes has been traditionally challenging due to methodological limitations. A major challenge in soil microbial ecology is to reveal the mechanisms that allow a wide diversity of microorganisms to co-exist. This study is directed towards answering the question of how spatial complexity affects bacterial competition, and how this can lead to organic matter turnover.

Using microfluidic chips that mimic the inner soil pore physical geometry, and fluorescence microscopy, we followed the effect of an increasing complexity in the growth and substrate degradation of two soil bacterial strains. The parameters used to define complexity were two: the turning angle and order of pore channels, and the fractal order of pore mazes. When we tested the effect of an increasing in turning angle sharpness on microbial growth, we found that in sharper angles, both species coexisted, but only until certain sharpness where both populations decreased. We also found that substrate degradation was highest in the same sharp angles that permitted the coexistence of both strains. Our next series of experiments, testing the effect of maze fractal complexity showed that both strains could coexist and degrade the most substrate in complex mazes that had dead ends as opposed to mazes that were highly connected. Our results demonstrate the relevance of microhabitat complexity in bacterial competition and substrate degradation, showing that complex habitats allow bacterial strains to coexist and perform functions with higher efficiency than in less complex ones.

How to cite: Arellano-Caicedo, C., Fadhel, A., Ohlsson, P., and Hammer, E. C.: The effect of habitat complexity on bacterial competition, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14407, https://doi.org/10.5194/egusphere-egu24-14407, 2024.

X3.150
|
EGU24-15127
Carsten Simon and Oliver Lechtenfeld

A large fraction of organic matter in soils is associated with mineral phases. This association is mediated by manifold processes (reactive transport, drying-rewetting cycles, biofilm formation, digestion of mineral particles, etc.) and ultimately leads to a stabilization of organic matter in soil [1]. Adsorption describes the mechanism for this association at the molecular level. Ultrahigh resolution mass spectrometry like FT-ICR-MS has gained interest in the study of adsorption processes because of its high sensitivity, resolving power and mass accuracy which allow to study the complex organic mixtures present in soils, and therefore provides molecular insight [2]. For that, supernatant composition can be compared before and after adsorption, but this indirect approach is often not sensitive enough to detect the sorption of small amounts of organic matter, i.e., during initial adsorption to pristine mineral surfaces. An alternative approach is to use laser desorption ionization (LDI) to directly analyze the adsorbed molecules on the mineral surfaces. The method theoretically allows laser spot size of ~ 20-50 µm and even allows imaging of thin sections; methodological advances could therefore improve our understanding of soil organic matter and its spatial heterogeneity [3].

We applied LDI-FT-ICR-MS to study the ionization of individual molecules with and without the presence of DOM (SRFA and pine/ beech litter extracts), and measured adsorption isotherms of individual molecular formulas in dissolved organic matter on quartz, illite and goethite after 24h of contact. Analog to organic matrices used in matrix-assisted LDI, detectability of model compounds improved by factor 2.5 – 40 when spiked into a DOM matrix. In case of sinapic acid, presence of DOM shifted the ionization towards the monomer ion [M-H]- as compared to a mixture of mono-, di- [2M-H]- and trimer [3M-H]- species when analyzed in pure form. These results suggest that soil organic matter and its soluble analogs act as suitable matrices in LDI experiments that ensure proper ionization of the mixture as a whole. In a next step, ion abundance data from sorption experiments was used to model the adsorption process of individual molecular formulas by a Langmuir isotherm approach. We derived estimates of sorption capacity and sorption affinity for each molecular formula, and identified the molecular properties explaining differences in both estimates, as well as their differences between mineral phases. Our data highlight the benefits of LDI-FT-ICR-MS for the study of sorption phenomena in soils, and opens perspectives for resolution of spatial heterogeneity in soils.

References

[1] Kleber, M., Bourg, I. C., ... & Nunan, N. (2021): Dynamic interactions at the mineral–organic matter interface. Nature Reviews Earth & Environment 2: 402-421.

[2] Bahureksa, W., Tfaily, M. M., ... & Borch, T. (2021): Soil organic matter characterization by Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS): A critical review of sample preparation, analysis, and data interpretation. Environmental Science & Technology 55: 9637-9656.

[3] Lohse, M., Haag, R., ... & Lechtenfeld, O. J. (2021). Direct imaging of plant metabolites in the rhizosphere using laser desorption ionization ultra-high resolution mass spectrometry. Frontiers in Plant Science 12: 753812.

How to cite: Simon, C. and Lechtenfeld, O.: Adsorption of dissolved organic matter to mineral phases studied by laser desorption ionization mass spectrometry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15127, https://doi.org/10.5194/egusphere-egu24-15127, 2024.

X3.151
|
EGU24-16904
|
ECS
Yahan Hu, Johann Zollner, Martin Werner, Steffen Schweizer, and Carmen Höschen

In the soil, mineral particles, organic matter, and soil organisms are arranged in a complex architecture which can influence organic matter dynamics. Nanoscale secondary ion mass spectrometry (NanoSIMS) provides insights into the microscale arrangement of soil minerals and organic compounds at a resolution of approximately 50 nm. However, current NanoSIMS image processing lacks methods to analyze large datasets automatically and requires manual intervention. We developed a two-step unsupervised clustering method for batch analyses of NanoSIMS images. Our two-step method consists of K-Means clustering as the first step generating around 100 clusters, followed by hierarchical agglomerative clustering (HAC) re-grouping the K clusters into less than 10 cluster groups. The elbow method, HAC linkage method and gap statistics are used to automatically select the optimal clustering numbers. Subsequently, soil minerals and organic matter can be spatially segmented and identified as different species. Further, this method could apply to the spatial arrangement of mineral-dominated and organic matter-dominated parts or different mineral types. Moreover, this method enables the analyses of larger datasets with >100 NanoSIMS images providing insights of organo-mineral interactive hotspots or even micro function domains involved in soil organic matter dynamics.

How to cite: Hu, Y., Zollner, J., Werner, M., Schweizer, S., and Höschen, C.: Two-step unsupervised clustering method on soil nanoscale secondary ion mass spectrometry (NanoSIMS) images to determine the spatial arrangement of minerals and organic matter, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16904, https://doi.org/10.5194/egusphere-egu24-16904, 2024.

X3.152
|
EGU24-17573
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ECS
Tom Guhra, Jona Schönherr, and Kai Uwe Totsche

Plant derived photosynthates are a component of the biotic organic matter involved in carbon cycling and storage due their mobility and formation of organo-mineral associations and (micro-)aggregates. Such photosynthates are typically found as components of mucilage or generate during the germination of seeds in the soil environments. While the effect of, e.g., mucilage, on soil physical properties has been intensively investigated, their role for carbon transport, adsorption, and aggregation process is rather unclear. Most of the knowledge available originates from studies that used single compounds, e.g., oxalic acid, glucose, polygalacturonic acid or mixtures of those in aqueous solutions. In our study, we utilized hydrogel-freed plant exuded photosynthates (PDE) extracted from four different seed types (Linum usitatissimum, Plantago ovata, Ocimum basilicum and Salvia hispanica) to investigate their interactions with minerals typically for temperate soil. In batch experiments, PDE adsorbed to both illite and goethite minerals with a preference of polysaccharide-rich PDE to goethite. During the adsorption, organo-mineral associations were formed leaving behind a less mineral-affine fraction of PDE prone to transport or degradation. Hence, PDE transport was also studied in column experiments using quartz functionalized with reactive minerals where we measured the breakthrough of PDE exploiting their distinct fluorescence. Furthermore, we followed the gravity-constrained aggregation dynamics of PDE-mineral associations using tensiometric measurements. We showed that low PDE concentrations facilitate aggregation via polymer bridges leading to a rapid sedimentation of aggregates while PDE available in excess prevents aggregation via steric repulsion and thus decelerates sedimentation. These results showed that PDE extracted from seeds might serve as better surrogates of natural plant exudates to study their role for the formation and transport of organo-mineral associations and aggregates in soils.

How to cite: Guhra, T., Schönherr, J., and Totsche, K. U.: Plant-derived organic exudates in soil: Mobility and aggregation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17573, https://doi.org/10.5194/egusphere-egu24-17573, 2024.

X3.153
|
EGU24-18568
|
John Lester Pide, Johann Holdt, Vitor Patricio Cantarella, Adrian Mellage, Olaf Cirpka, Carsten Leven-Pfister, Jan-Peter Duda, Daniel Buchner, and Christian Griebler

Nitrate (NO3-) is one of the most serious contaminants in groundwater, frequently deteriorating water quality and groundwater use as drinking water. Nitrate can, at specific environmental conditions, be removed within the subsurface environment via natural biogeochemical processes, such as denitrification and dissimilatory nitrate reduction to ammonium (DNRA). Traditionally, research has concentrated on the NO3- attenuation potential and microbial activity in groundwater, largely overlooking an aquifers’ sediment matrix as a reaction contributor. We hypothesize that the sedimentary deposits host the major potential for NO3- reduction, carrying the majority of microorganisms as well as different sources of electron donors. Moreover, diverse hydrogeological settings harbor different sources and varying amounts of electron donors such as reduced iron minerals and organic matter. Therefore, subsurface physicochemical heterogeneity, determined by sedimentology, controls the potential of an aquifer to reduce nitrate. We hypothesize that locations where physicochemical conditions favor NO3- reduction, we may expect microbes involved in these processes to be more abundant and highly active, leading to a fast NO3- removal from groundwater.

Here, we present results from temperature-controlled (12°C) batch incubations and flow-through experiments conducted over several months using fresh sediments from an alluvial, tufaceous unconfined aquifer, with embedded peat layers, in an agricultural landscape in southwest Germany. Batch experiments received an addition of NO3- of 50 mg L–1. Sediment columns were supplied with nitrate-spiked groundwater collected from the site at a maximum inlet concentration of 150 mg L and run in continuous injection mode. Batch experiments showed a gradual decrease in the initially high hydrogen sulfide (H2S) concentration, becoming undetectable after Day 7, compared to an untreated control, which revealed a slow conversion of HS-. These preliminary findings indicate a strong autotrophic denitrification with NO3- reduction coupled to aqueous HS- oxidation. In contrast to nitrate, NH4+ concentrations remained stable in all experiments. In the column experiments, the sediment exhibited a substantial NO3- reduction capacity in the early phase but rapidly declined with time. We hypothesize that a dual contribution to denitrification via easily bioavailable electron donors in the groundwater followed by slower denitrification coupled to organic matter in the sediment matrix is responsible for the observed dynamics. Our ongoing experiments, including groundwater and sediments from other, hydrogeologically different aquifers, will dissect the individual redox processes and key microorganisms involved in turnover of prominent nitrate and carbon species in the context of different hydrogeological settings. 

How to cite: Pide, J. L., Holdt, J., Cantarella, V. P., Mellage, A., Cirpka, O., Leven-Pfister, C., Duda, J.-P., Buchner, D., and Griebler, C.: Intrinsic potential and activity of nitrate turnover examined for different hydrogeological aquifer settings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18568, https://doi.org/10.5194/egusphere-egu24-18568, 2024.

X3.154
|
EGU24-18644
|
ECS
|
Maximilian Rötzer, Alexander Prechtel, Eva Lehndorff, and Nadja Ray

Mathematical models serve as valuable tools for unraveling the spatial heterogeneity and evolution of soil particles and carbon, particularly on the pore scale, that might be challenging to measure directly. The model we provide facilitates the exploration of interactions in the rhizosphere by the manipulation of different drivers and their parametrization. 

The focus of our study is on the residence time and spatial distribution of carbon originating from particulate organic matter and rhizodeposits. This process of turnover and distribution is influenced by a number of drivers. We provide insights into the role of some of these drivers across different stages of root growth, including carbon occlusion due to aggregation, chemical composition of rhizodeposits, and root morphology. We employ a spatially and temporally explicit mathematical model in which different components such as soil particles, carbon and a dynamic root interact. It is realized within a cellular automaton framework combined with an organic matter turnover model. Through numerical simulations, we track the temporal evolution of mineral soil particles bound by gluing agents. Spatially resolved datasets of soil texture and organic matter distribution are used to implement different soil types comparable with field experiments. Realistic parametrizations are derived from a laboratory experiment conducted in a rhizobox, measuring the carbon-to-nitrogen ratio at distinct temporal states of root growth and varying spatial distances from the biopore.

We compare and quantify the individual impact that soil, root and rhizodeposit characteristics have on the residence time and dispersal of carbon. Using an image-based modeling approach, we gain insight into spatiotemporal patterns and analyze the properties of regions with low turnover, so-called cold spots. 

How to cite: Rötzer, M., Prechtel, A., Lehndorff, E., and Ray, N.: Investigating the distribution and residence time of carbon in the rhizosphere by image-based modelling at the pore-scale, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18644, https://doi.org/10.5194/egusphere-egu24-18644, 2024.

Posters virtual: Tue, 16 Apr, 14:00–15:45 | vHall X3

Display time: Tue, 16 Apr 08:30–Tue, 16 Apr 18:00
Chairperson: Emily Lacroix
vX3.19
|
EGU24-11964
|
ECS
Rhizobiota links landsliding and the carbon cycles through rock weathering
(withdrawn after no-show)
Yakshi Ortiz-Maldonado, Filipa Godoy-Vitorino, and Carla Restrepo