Steffen Schweizer - Profile on Academia.edu (original) (raw)
Papers by Steffen Schweizer
Nature Communications, Sep 2, 2022
The soil carbon (C) saturation concept suggests an upper limit to the storage of soil organic car... more The soil carbon (C) saturation concept suggests an upper limit to the storage of soil organic carbon (SOC). It is set by the mechanisms that protect soil organic matter from mineralization. Biochar has the capacity to protect new C, including rhizodeposits and microbial necromass. However, the decadal-scale mechanisms by which biochar influences the molecular diversity, spatial heterogeneity, and temporal changes in SOC persistence, remain unresolved. Here we show that the soil C storage ceiling of a Ferralsol under subtropical pasture was raised by a second application of Eucalyptus saligna biochar 8.2 years after the first application-the first application raised the soil C storage ceiling by 9.3 Mg new C ha -1 and the second application raised this by another 2.3 Mg new C ha -1 . Linking direct visual evidence from one-, two-, and threedimensional analyses with SOC quantification, we found high spatial heterogeneity of C functional groups that resulted in the retention of rhizodeposits and microbial necromass in microaggregates (53-250 µm) and the mineral fraction (<53 µm). Microbial C-use efficiency was concomitantly increased by lowering specific enzyme activities, contributing to the decreased mineralization of native SOC by 18%. We suggest that the SOC ceiling can be lifted using biochar in (sub)tropical grasslands globally.
Goldschmidt2022 abstracts, 2022
SSRN Electronic Journal
Pyrogenic organic matter (PyOM) is a product of incomplete combustion during wildfires and an imp... more Pyrogenic organic matter (PyOM) is a product of incomplete combustion during wildfires and an important pool of soil organic carbon (SOC). The dynamics of PyOM and SOC in boreal and permafrost-affected soils are largely unknown, while storing large amounts of global carbon and being vulnerable to climate change. Here, we traced the vertical mobility, allocation in soil fractions and decomposition losses of highly 13 C-labeled PyOM and its precursor ryegrass organic matter (grass OM) after two years of in-situ incubation in soil cores installed in the upper 10 cm of continuous (northern sites) and discontinuous to sporadic (southern sites) permafrost-affected forest soils in Northern Canada. At the northern sites, up to three times more PyOM was lost by decomposition (39% of initial) compared to the southern sites (11% of initial). Losses of grass OM were substantial (69-84% of initial) and larger in southern soils. The vertical incorporation was limited and >90% of recovered PyOM and grass OM were found at the applied depth (0-3 cm). The PyOM strongly interacted with mineral surfaces, as indicated by around 40% recovered in the mineral-associated heavy density fractions (<63 μm). Microscale analyses by SEM and NanoSIMS showed that PyOM was mainly allocated towards the fine fraction in a particulate and aggregated form, highlighting the importance of abiotic processes for the incorporation of PyOM in permafrost-affected soils. The grass OM was mainly recovered in the mineral fractions at southern soils with enhanced allocation towards mineral surfaces as well as increased distribution at the microscale after initial decomposition, while it remained as particulate OM in northern soils. Our results highlight that permafrostaffected boreal forest soils are sensitive to fresh PyOM and OM inputs with substantial losses. Especially PyOM persistence depended on site and soil specific properties and not solely on its physico-chemical persistence. The responses are decoupled for PyOM and non-pyrolyzed OM and require a better understanding to evaluate carbon feedbacks of high-latitude soils with global warming and associated shifts in vegetation and wildfire regimes.
Valuable phosphorus retained by ironstone gravels can be measured as bicarbonate extractable P
Geoderma, 2022
Schweizer et al_Soil structure Vertisol_data.xls
Results of field and laboratory analyses made available in relation with a study in the journal L... more Results of field and laboratory analyses made available in relation with a study in the journal Land Degradation & Development.
How soil sodification and pH restrict microbially mediated organic carbon turnover and aggregate formation: An artificial soil microcosm study
&lt;p&gt;Exchangeable sodium can have pronounced influences on physicochemical so... more &lt;p&gt;Exchangeable sodium can have pronounced influences on physicochemical soil properties whereas the combined impact on microbial turnover of organic carbon (OC) remains elusive. In this work, we aimed to differentiate the effects of exchangeable sodium and soil pH on microbially mediated aggregate formation and turnover of cattle slurry. We incubated the soils under controlled laboratory conditions using artificial soil model minerals containing quartz grains, montmorillonite and goethite. The montmorillonite was pre-treated with NaCl solutions of sodium adsorption ratios (SAR) 0, 1 and 5 which resulted in exchangeable sodium percentages (ESP) of 1, 7 and 19 on average. The soil pH was adjusted within two treatments to 7.5 and 8.5 for each ESP at the start of the incubation. We incubated these six treatments with and without cattle slurry ground to &lt; 200&amp;#160;&amp;#181;m after addition of a combined microbial inoculum, extracted from a Cambisol (pH&lt;sub&gt;H2O&lt;/sub&gt; 7.5, Germany) and a Calcaric Solonchak (pH&lt;sub&gt;H2O&lt;/sub&gt; 9.3, Spain) added to all samples. The microcosms were incubated with three replicates over a period of 30 days at constant pF of 2.2. The CO&lt;sub&gt;2&lt;/sub&gt; emission measurements of the microcosms with exchangeable sodium indicated a delayed respiration. The respiration under ESP&amp;#160;19 increased rapidly within the first days of incubation, whereas it was more delayed under ESP&amp;#160;7 until 15 days of incubation. The delayed CO&lt;sub&gt;2&lt;/sub&gt; respiration might be related to inhibited structural formation in treatments with higher exchangeable sodium. To test this, we are investigating the data on water-stable aggregation by wet sieving. The delayed CO&lt;sub&gt;2&lt;/sub&gt; respiration was reflected in lower microbial biomass, extracted after the incubation. The microbial biomass under ESP&amp;#160;19 and pH 8.5 was highest whereas the amount of leached C after two rainfall events (at day 7 and 15) was lowest, which could be related to a higher microbially mediated OC sequestration. The composition of exchangeable cations was monitored before and after the whole incubation which might help explaining the processes of microbially mediated aggregate formation and microbial carbon turnover under different levels of exchangeable sodium.&lt;/p&gt;
How rice roots form their surrounding: Distinctive sub-zones of oxides, silicates and organic matter
The ethical matrix as an instrument for teaching and evaluation
Climate change and sustainable development, 2012
This contribution presents how the Ethical Matrix was used in teaching and evaluating a course on... more This contribution presents how the Ethical Matrix was used in teaching and evaluating a course on ‘Ethics of Food and Nutrition Security’ (EFNS) at Hohenheim University in the winter semester 2010/2011 and in the winter semester 2011/12. We will first provide some information on the development of the course and present the results of the general evaluation of the course by the department. We will then introduce the newly developed instrument in which the Ethical Matrix was embedded. The instrument aims at testing individual skills necessary for identifying ethical issues. Finally, we will draw some conclusions that refer to the further development of the instrument.
Social Science Research Network, 2022
Pyrogenic organic matter (PyOM) is a product of incomplete combustion during wildfires and an imp... more Pyrogenic organic matter (PyOM) is a product of incomplete combustion during wildfires and an important pool of soil organic carbon (SOC). The dynamics of PyOM and SOC in boreal and permafrost-affected soils are largely unknown, while storing large amounts of global carbon and being vulnerable to climate change. Here, we traced the vertical mobility, allocation in soil fractions and decomposition losses of highly 13 C-labeled PyOM and its precursor ryegrass organic matter (grass OM) after two years of in-situ incubation in soil cores installed in the upper 10 cm of continuous (northern sites) and discontinuous to sporadic (southern sites) permafrost-affected forest soils in Northern Canada. At the northern sites, up to three times more PyOM was lost by decomposition (39% of initial) compared to the southern sites (11% of initial). Losses of grass OM were substantial (69-84% of initial) and larger in southern soils. The vertical incorporation was limited and >90% of recovered PyOM and grass OM were found at the applied depth (0-3 cm). The PyOM strongly interacted with mineral surfaces, as indicated by around 40% recovered in the mineral-associated heavy density fractions (<63 μm). Microscale analyses by SEM and NanoSIMS showed that PyOM was mainly allocated towards the fine fraction in a particulate and aggregated form, highlighting the importance of abiotic processes for the incorporation of PyOM in permafrost-affected soils. The grass OM was mainly recovered in the mineral fractions at southern soils with enhanced allocation towards mineral surfaces as well as increased distribution at the microscale after initial decomposition, while it remained as particulate OM in northern soils. Our results highlight that permafrostaffected boreal forest soils are sensitive to fresh PyOM and OM inputs with substantial losses. Especially PyOM persistence depended on site and soil specific properties and not solely on its physico-chemical persistence. The responses are decoupled for PyOM and non-pyrolyzed OM and require a better understanding to evaluate carbon feedbacks of high-latitude soils with global warming and associated shifts in vegetation and wildfire regimes.
Calcium (Ca) can increase soil organic carbon (SOC) persistence by mediating physico-chemical int... more Calcium (Ca) can increase soil organic carbon (SOC) persistence by mediating physico-chemical interactions between organic compounds and minerals. Yet, Ca is also crucial for microbial adhesion, potentially affecting colonization of plant and mineral surfaces. The relative importance of Ca as a mediator of microbe-mineral-organic matter interactions and resulting SOC transformation has hereto been overlooked. We incubated 44Ca labeled soils with 13C15N labeled leaf litter to study the effects of Ca on microbial transformation of plant litter and formation of mineral associated organic matter. Ca additions promoted hyphae-forming bacteria, which often specialize in colonizing surfaces, increased incorporation of plant litter into microbial biomass by 20% and carbon use efficiency by 40%, and reduced cumulative CO2 emission by 5%, while promoting associations between minerals and microbial byproducts of plant litter. These findings expand the role of Ca in SOC persistence from solely ...
Taking a closer look: How spectromicroscopic imaging of organo-mineral associations leads to a novel perspective on interrelated soil functions
A wide range of image-based techniques revealed mounting evidence of a heterogeneous arrangement ... more A wide range of image-based techniques revealed mounting evidence of a heterogeneous arrangement of mineral-associated organic matter (OM) in soils at the microscale and nanoscale. Spectromicroscopic approaches using such as NanoSIMS, STXM-NEXAFS, AFM, STEM-EELS, and others have provided insights about a patchy and piled-up arrangement of OM. This arrangement is determined by different local OM properties and mineral composition as well as OM-OM interactions. The emerging conceptual framework of the microscale arrangement of OM affects our understanding of soil functions: By compartmentalizing and decoupling local carbon sequestration in the mineral soil matrix, by localizing the mechanical stabilization of soil structure, by altering surface properties and re-distributing ion exchange sites, and by shaping distinct biotic microenvironments. After an overview on the spectromicroscopic evidence, this contribution will illustrate the emerging conceptual framework of localized soil fun...
New opportunities to unravel the microarchitecture of soil organo-mineral associations by NanoSIMS using the upgraded Oxygen source
<p>Organic matter (OM) and soil mineral constituents interact closely at the submic... more <p>Organic matter (OM) and soil mineral constituents interact closely at the submicron scale forming structural units and providing biogeochemical interfaces. Soil structure itself plays a key role for carbon storage, microbial activity and soil fertility and pollutant mitigation. A better understanding to which extent biogeochemical processes and interactions in the soil are driven by the spatial arrangement of OM and mineral constituents requires advanced efforts to apply novel microspectroscopy approaches.</p> <p>NanoSIMS, allowing unique elemental and isotopic analyses at nanometer spatial resolution, provide valuable insights into the architecture of soil organo-mineral constituents and crucial processes taking place at the microscale.</p> <p>The instrument is equipped with two ion sources: the Cesium source (Cs<sup>+</sup>) convenient to detect ions related to organic matter distribution and the Oxygen source (O<sup>-</sup>) favourable to provide information on mineral phases or metals in samples. With a spatial resolution similar to the Cesium source and high stability, the upgraded radio frequency (RF) plasma Oxygen source &#160;recently installed at the TUM is now best suited for novel analytical approaches to probe elemental and isotopic composition of soil organo-mineral constituents in soils at the microscale.</p> <p>We will show examples of how the two primary ion sources, single or correlatively applied, enable novel experimental designs in soil biogeochemistry. Novel combinations of the OM distribution (<sup>12</sup>C, <sup>13</sup>C and <sup>14</sup>N, <sup>15</sup>N) detected by the Cs<sup>+</sup> source with the distribution of e.g. Si, Al, Fe, Ca, Mg, K, and Na of minerals as revealed by the O<sup>-</sup> source are now possible.</p> <p>Post-processing tools for unsupervised clustering and supervised segmentation facilitate the comparison and quantitative analysis of the spatial architecture within intact soil structures. These ongoing developed tools can contribute to the extent of our understanding of biogeochemical processes taking place at organo-mineral and mineral-mineral interfaces in soil systems at the microscale.</p>
The sequestration of organic matter (OM) is linked with soil microaggregates and mineral surfaces... more The sequestration of organic matter (OM) is linked with soil microaggregates and mineral surfaces. This work aimed to resolve the distribution and arrangement of OM in soils and how they are influenced by fine mineral particle surfaces and microaggregation. Distinct spatial interactions were found to govern the sequestration of OM at the microscale. A successive development of OM patches and a piled-up arrangement were revealed. The effect of soil microaggregates on OM depends on soil texture and aggregate diameters, which are controlled by different failure mechanisms.Die Bindung organischer Substanz (OBS) ist verknüpft mit Bodenmikroaggregaten und mineralischen Oberflächen. Diese Arbeit zielt auf ein besseres Verständnis der Verteilung und der Anordnung von OBS in Böden ab und wie diese von feinen mineralischen Partikeloberflächen und Mikroaggregierung beeinflusst werden. Es wurde festgestellt, dass räumlich ausgeprägte Interaktionen die Bindung von OBS auf der Mikroskala maßgebli...
Susceptibility of new soil organic carbon to mineralization during dry-wet cycling in soils from contrasting ends of a precipitation gradient
Soil Biology and Biochemistry
Organic matter in black sand soils related to alkyl carbon and organo-mineral structures at the microscale
<p><span>Agricultural sandy soils with high organic matter (OM) contents are generall... more <p><span>Agricultural sandy soils with high organic matter (OM) contents are generally unexpected under the current paradigm of organic matter formation and stabilization. These so-called black sand soils occur in North-Western Europe and have been related to historical heathland vegetation. The properties and mechanisms of the high OM sequestration in these soils are not clear as they exceed common observations of OM stored in coarse-textured soils. In this study, we analyzed a subset of samples with ‘black sand’ properties from the European soil database “Land Use/Cover Area frame statistical Survey” (LUCAS). Through particle size fractionation, we isolated the fine fraction <20 µm which contained, on average, 55 % of the total soil organic carbon (OC), in only 8 % of the corresponding soil mass. The fine fraction <20 µm contained 301 mg OC g<sup>-1</sup> with a C:N ratio of 17.4 on average and was positively correlated with the bulk soil OC. The characterization of OM composition in the fine fractions by solid-state <sup>13</sup>C nuclear magnetic resonance (NMR) spectroscopy revealed that the share of alkyl C increased with OC concentrations whereas O/N-alkyl C decreased. To analyze the distribution of OM at the microscale, we analyzed five samples from the <20 µm fraction containing a gradient of 245-378 mg OC g<sup>‑1</sup> with nanoscale secondary ion mass spectrometry (NanoSIMS) at a spatial resolution of 120 nm. These microscale measurements revealed fine mineral particle structures associated with heterogeneously distributed OM. Using image analysis, we found that the proportion of OM-dominated area (indicated by <sup>12</sup>C<sub>2</sub><sup>-</sup> and <sup>26</sup>CN<sup>-</sup>) increased from 52 to 80 % on average with increasing OC concentration of the fine fractions. A majority of OM-dominated area was correlated with higher <sup>42</sup>AlO<sup>-</sup> counts, which might suggest a preferential co-localization. In turn, the particle area which was dominated by minerals (indicated by <sup>16</sup>O<sup>‑</sup>, <sup>28</sup>Si<sup>‑</sup>, <sup>42</sup>AlO<sup>‑</sup> and <sup>72</sup>FeO<sup>‑</sup>) contained less Al and more Si. This shows that the more alkylated and OM-rich fine fractions are related with distinct patterns of organo-mineral structures at the microscale.</span></p>
Conference on International Research on Food Security, Natural Resource Management and Rural Development Food Ethics: A new and necessary Academic Approach to Improve Food and Nutrition Security
Nature Communications, 2021
The largest terrestrial organic carbon pool, carbon in soils, is regulated by an intricate connec... more The largest terrestrial organic carbon pool, carbon in soils, is regulated by an intricate connection between plant carbon inputs, microbial activity, and the soil matrix. This is manifested by how microorganisms, the key players in transforming plant-derived carbon into soil organic carbon, are controlled by the physical arrangement of organic and inorganic soil particles. Here we conduct an incubation of isotopically labelled litter to study effects of soil structure on the fate of litter-derived organic matter. While microbial activity and fungal growth is enhanced in the coarser-textured soil, we show that occlusion of organic matter into aggregates and formation of organo-mineral associations occur concurrently on fresh litter surfaces regardless of soil structure. These two mechanisms—the two most prominent processes contributing to the persistence of organic matter—occur directly at plant–soil interfaces, where surfaces of litter constitute a nucleus in the build-up of soil c...
Nature Communications, Sep 2, 2022
The soil carbon (C) saturation concept suggests an upper limit to the storage of soil organic car... more The soil carbon (C) saturation concept suggests an upper limit to the storage of soil organic carbon (SOC). It is set by the mechanisms that protect soil organic matter from mineralization. Biochar has the capacity to protect new C, including rhizodeposits and microbial necromass. However, the decadal-scale mechanisms by which biochar influences the molecular diversity, spatial heterogeneity, and temporal changes in SOC persistence, remain unresolved. Here we show that the soil C storage ceiling of a Ferralsol under subtropical pasture was raised by a second application of Eucalyptus saligna biochar 8.2 years after the first application-the first application raised the soil C storage ceiling by 9.3 Mg new C ha -1 and the second application raised this by another 2.3 Mg new C ha -1 . Linking direct visual evidence from one-, two-, and threedimensional analyses with SOC quantification, we found high spatial heterogeneity of C functional groups that resulted in the retention of rhizodeposits and microbial necromass in microaggregates (53-250 µm) and the mineral fraction (<53 µm). Microbial C-use efficiency was concomitantly increased by lowering specific enzyme activities, contributing to the decreased mineralization of native SOC by 18%. We suggest that the SOC ceiling can be lifted using biochar in (sub)tropical grasslands globally.
Goldschmidt2022 abstracts, 2022
SSRN Electronic Journal
Pyrogenic organic matter (PyOM) is a product of incomplete combustion during wildfires and an imp... more Pyrogenic organic matter (PyOM) is a product of incomplete combustion during wildfires and an important pool of soil organic carbon (SOC). The dynamics of PyOM and SOC in boreal and permafrost-affected soils are largely unknown, while storing large amounts of global carbon and being vulnerable to climate change. Here, we traced the vertical mobility, allocation in soil fractions and decomposition losses of highly 13 C-labeled PyOM and its precursor ryegrass organic matter (grass OM) after two years of in-situ incubation in soil cores installed in the upper 10 cm of continuous (northern sites) and discontinuous to sporadic (southern sites) permafrost-affected forest soils in Northern Canada. At the northern sites, up to three times more PyOM was lost by decomposition (39% of initial) compared to the southern sites (11% of initial). Losses of grass OM were substantial (69-84% of initial) and larger in southern soils. The vertical incorporation was limited and >90% of recovered PyOM and grass OM were found at the applied depth (0-3 cm). The PyOM strongly interacted with mineral surfaces, as indicated by around 40% recovered in the mineral-associated heavy density fractions (<63 μm). Microscale analyses by SEM and NanoSIMS showed that PyOM was mainly allocated towards the fine fraction in a particulate and aggregated form, highlighting the importance of abiotic processes for the incorporation of PyOM in permafrost-affected soils. The grass OM was mainly recovered in the mineral fractions at southern soils with enhanced allocation towards mineral surfaces as well as increased distribution at the microscale after initial decomposition, while it remained as particulate OM in northern soils. Our results highlight that permafrostaffected boreal forest soils are sensitive to fresh PyOM and OM inputs with substantial losses. Especially PyOM persistence depended on site and soil specific properties and not solely on its physico-chemical persistence. The responses are decoupled for PyOM and non-pyrolyzed OM and require a better understanding to evaluate carbon feedbacks of high-latitude soils with global warming and associated shifts in vegetation and wildfire regimes.
Valuable phosphorus retained by ironstone gravels can be measured as bicarbonate extractable P
Geoderma, 2022
Schweizer et al_Soil structure Vertisol_data.xls
Results of field and laboratory analyses made available in relation with a study in the journal L... more Results of field and laboratory analyses made available in relation with a study in the journal Land Degradation & Development.
How soil sodification and pH restrict microbially mediated organic carbon turnover and aggregate formation: An artificial soil microcosm study
&lt;p&gt;Exchangeable sodium can have pronounced influences on physicochemical so... more &lt;p&gt;Exchangeable sodium can have pronounced influences on physicochemical soil properties whereas the combined impact on microbial turnover of organic carbon (OC) remains elusive. In this work, we aimed to differentiate the effects of exchangeable sodium and soil pH on microbially mediated aggregate formation and turnover of cattle slurry. We incubated the soils under controlled laboratory conditions using artificial soil model minerals containing quartz grains, montmorillonite and goethite. The montmorillonite was pre-treated with NaCl solutions of sodium adsorption ratios (SAR) 0, 1 and 5 which resulted in exchangeable sodium percentages (ESP) of 1, 7 and 19 on average. The soil pH was adjusted within two treatments to 7.5 and 8.5 for each ESP at the start of the incubation. We incubated these six treatments with and without cattle slurry ground to &lt; 200&amp;#160;&amp;#181;m after addition of a combined microbial inoculum, extracted from a Cambisol (pH&lt;sub&gt;H2O&lt;/sub&gt; 7.5, Germany) and a Calcaric Solonchak (pH&lt;sub&gt;H2O&lt;/sub&gt; 9.3, Spain) added to all samples. The microcosms were incubated with three replicates over a period of 30 days at constant pF of 2.2. The CO&lt;sub&gt;2&lt;/sub&gt; emission measurements of the microcosms with exchangeable sodium indicated a delayed respiration. The respiration under ESP&amp;#160;19 increased rapidly within the first days of incubation, whereas it was more delayed under ESP&amp;#160;7 until 15 days of incubation. The delayed CO&lt;sub&gt;2&lt;/sub&gt; respiration might be related to inhibited structural formation in treatments with higher exchangeable sodium. To test this, we are investigating the data on water-stable aggregation by wet sieving. The delayed CO&lt;sub&gt;2&lt;/sub&gt; respiration was reflected in lower microbial biomass, extracted after the incubation. The microbial biomass under ESP&amp;#160;19 and pH 8.5 was highest whereas the amount of leached C after two rainfall events (at day 7 and 15) was lowest, which could be related to a higher microbially mediated OC sequestration. The composition of exchangeable cations was monitored before and after the whole incubation which might help explaining the processes of microbially mediated aggregate formation and microbial carbon turnover under different levels of exchangeable sodium.&lt;/p&gt;
How rice roots form their surrounding: Distinctive sub-zones of oxides, silicates and organic matter
The ethical matrix as an instrument for teaching and evaluation
Climate change and sustainable development, 2012
This contribution presents how the Ethical Matrix was used in teaching and evaluating a course on... more This contribution presents how the Ethical Matrix was used in teaching and evaluating a course on ‘Ethics of Food and Nutrition Security’ (EFNS) at Hohenheim University in the winter semester 2010/2011 and in the winter semester 2011/12. We will first provide some information on the development of the course and present the results of the general evaluation of the course by the department. We will then introduce the newly developed instrument in which the Ethical Matrix was embedded. The instrument aims at testing individual skills necessary for identifying ethical issues. Finally, we will draw some conclusions that refer to the further development of the instrument.
Social Science Research Network, 2022
Pyrogenic organic matter (PyOM) is a product of incomplete combustion during wildfires and an imp... more Pyrogenic organic matter (PyOM) is a product of incomplete combustion during wildfires and an important pool of soil organic carbon (SOC). The dynamics of PyOM and SOC in boreal and permafrost-affected soils are largely unknown, while storing large amounts of global carbon and being vulnerable to climate change. Here, we traced the vertical mobility, allocation in soil fractions and decomposition losses of highly 13 C-labeled PyOM and its precursor ryegrass organic matter (grass OM) after two years of in-situ incubation in soil cores installed in the upper 10 cm of continuous (northern sites) and discontinuous to sporadic (southern sites) permafrost-affected forest soils in Northern Canada. At the northern sites, up to three times more PyOM was lost by decomposition (39% of initial) compared to the southern sites (11% of initial). Losses of grass OM were substantial (69-84% of initial) and larger in southern soils. The vertical incorporation was limited and >90% of recovered PyOM and grass OM were found at the applied depth (0-3 cm). The PyOM strongly interacted with mineral surfaces, as indicated by around 40% recovered in the mineral-associated heavy density fractions (<63 μm). Microscale analyses by SEM and NanoSIMS showed that PyOM was mainly allocated towards the fine fraction in a particulate and aggregated form, highlighting the importance of abiotic processes for the incorporation of PyOM in permafrost-affected soils. The grass OM was mainly recovered in the mineral fractions at southern soils with enhanced allocation towards mineral surfaces as well as increased distribution at the microscale after initial decomposition, while it remained as particulate OM in northern soils. Our results highlight that permafrostaffected boreal forest soils are sensitive to fresh PyOM and OM inputs with substantial losses. Especially PyOM persistence depended on site and soil specific properties and not solely on its physico-chemical persistence. The responses are decoupled for PyOM and non-pyrolyzed OM and require a better understanding to evaluate carbon feedbacks of high-latitude soils with global warming and associated shifts in vegetation and wildfire regimes.
Calcium (Ca) can increase soil organic carbon (SOC) persistence by mediating physico-chemical int... more Calcium (Ca) can increase soil organic carbon (SOC) persistence by mediating physico-chemical interactions between organic compounds and minerals. Yet, Ca is also crucial for microbial adhesion, potentially affecting colonization of plant and mineral surfaces. The relative importance of Ca as a mediator of microbe-mineral-organic matter interactions and resulting SOC transformation has hereto been overlooked. We incubated 44Ca labeled soils with 13C15N labeled leaf litter to study the effects of Ca on microbial transformation of plant litter and formation of mineral associated organic matter. Ca additions promoted hyphae-forming bacteria, which often specialize in colonizing surfaces, increased incorporation of plant litter into microbial biomass by 20% and carbon use efficiency by 40%, and reduced cumulative CO2 emission by 5%, while promoting associations between minerals and microbial byproducts of plant litter. These findings expand the role of Ca in SOC persistence from solely ...
Taking a closer look: How spectromicroscopic imaging of organo-mineral associations leads to a novel perspective on interrelated soil functions
A wide range of image-based techniques revealed mounting evidence of a heterogeneous arrangement ... more A wide range of image-based techniques revealed mounting evidence of a heterogeneous arrangement of mineral-associated organic matter (OM) in soils at the microscale and nanoscale. Spectromicroscopic approaches using such as NanoSIMS, STXM-NEXAFS, AFM, STEM-EELS, and others have provided insights about a patchy and piled-up arrangement of OM. This arrangement is determined by different local OM properties and mineral composition as well as OM-OM interactions. The emerging conceptual framework of the microscale arrangement of OM affects our understanding of soil functions: By compartmentalizing and decoupling local carbon sequestration in the mineral soil matrix, by localizing the mechanical stabilization of soil structure, by altering surface properties and re-distributing ion exchange sites, and by shaping distinct biotic microenvironments. After an overview on the spectromicroscopic evidence, this contribution will illustrate the emerging conceptual framework of localized soil fun...
New opportunities to unravel the microarchitecture of soil organo-mineral associations by NanoSIMS using the upgraded Oxygen source
<p>Organic matter (OM) and soil mineral constituents interact closely at the submic... more <p>Organic matter (OM) and soil mineral constituents interact closely at the submicron scale forming structural units and providing biogeochemical interfaces. Soil structure itself plays a key role for carbon storage, microbial activity and soil fertility and pollutant mitigation. A better understanding to which extent biogeochemical processes and interactions in the soil are driven by the spatial arrangement of OM and mineral constituents requires advanced efforts to apply novel microspectroscopy approaches.</p> <p>NanoSIMS, allowing unique elemental and isotopic analyses at nanometer spatial resolution, provide valuable insights into the architecture of soil organo-mineral constituents and crucial processes taking place at the microscale.</p> <p>The instrument is equipped with two ion sources: the Cesium source (Cs<sup>+</sup>) convenient to detect ions related to organic matter distribution and the Oxygen source (O<sup>-</sup>) favourable to provide information on mineral phases or metals in samples. With a spatial resolution similar to the Cesium source and high stability, the upgraded radio frequency (RF) plasma Oxygen source &#160;recently installed at the TUM is now best suited for novel analytical approaches to probe elemental and isotopic composition of soil organo-mineral constituents in soils at the microscale.</p> <p>We will show examples of how the two primary ion sources, single or correlatively applied, enable novel experimental designs in soil biogeochemistry. Novel combinations of the OM distribution (<sup>12</sup>C, <sup>13</sup>C and <sup>14</sup>N, <sup>15</sup>N) detected by the Cs<sup>+</sup> source with the distribution of e.g. Si, Al, Fe, Ca, Mg, K, and Na of minerals as revealed by the O<sup>-</sup> source are now possible.</p> <p>Post-processing tools for unsupervised clustering and supervised segmentation facilitate the comparison and quantitative analysis of the spatial architecture within intact soil structures. These ongoing developed tools can contribute to the extent of our understanding of biogeochemical processes taking place at organo-mineral and mineral-mineral interfaces in soil systems at the microscale.</p>
The sequestration of organic matter (OM) is linked with soil microaggregates and mineral surfaces... more The sequestration of organic matter (OM) is linked with soil microaggregates and mineral surfaces. This work aimed to resolve the distribution and arrangement of OM in soils and how they are influenced by fine mineral particle surfaces and microaggregation. Distinct spatial interactions were found to govern the sequestration of OM at the microscale. A successive development of OM patches and a piled-up arrangement were revealed. The effect of soil microaggregates on OM depends on soil texture and aggregate diameters, which are controlled by different failure mechanisms.Die Bindung organischer Substanz (OBS) ist verknüpft mit Bodenmikroaggregaten und mineralischen Oberflächen. Diese Arbeit zielt auf ein besseres Verständnis der Verteilung und der Anordnung von OBS in Böden ab und wie diese von feinen mineralischen Partikeloberflächen und Mikroaggregierung beeinflusst werden. Es wurde festgestellt, dass räumlich ausgeprägte Interaktionen die Bindung von OBS auf der Mikroskala maßgebli...
Susceptibility of new soil organic carbon to mineralization during dry-wet cycling in soils from contrasting ends of a precipitation gradient
Soil Biology and Biochemistry
Organic matter in black sand soils related to alkyl carbon and organo-mineral structures at the microscale
<p><span>Agricultural sandy soils with high organic matter (OM) contents are generall... more <p><span>Agricultural sandy soils with high organic matter (OM) contents are generally unexpected under the current paradigm of organic matter formation and stabilization. These so-called black sand soils occur in North-Western Europe and have been related to historical heathland vegetation. The properties and mechanisms of the high OM sequestration in these soils are not clear as they exceed common observations of OM stored in coarse-textured soils. In this study, we analyzed a subset of samples with ‘black sand’ properties from the European soil database “Land Use/Cover Area frame statistical Survey” (LUCAS). Through particle size fractionation, we isolated the fine fraction <20 µm which contained, on average, 55 % of the total soil organic carbon (OC), in only 8 % of the corresponding soil mass. The fine fraction <20 µm contained 301 mg OC g<sup>-1</sup> with a C:N ratio of 17.4 on average and was positively correlated with the bulk soil OC. The characterization of OM composition in the fine fractions by solid-state <sup>13</sup>C nuclear magnetic resonance (NMR) spectroscopy revealed that the share of alkyl C increased with OC concentrations whereas O/N-alkyl C decreased. To analyze the distribution of OM at the microscale, we analyzed five samples from the <20 µm fraction containing a gradient of 245-378 mg OC g<sup>‑1</sup> with nanoscale secondary ion mass spectrometry (NanoSIMS) at a spatial resolution of 120 nm. These microscale measurements revealed fine mineral particle structures associated with heterogeneously distributed OM. Using image analysis, we found that the proportion of OM-dominated area (indicated by <sup>12</sup>C<sub>2</sub><sup>-</sup> and <sup>26</sup>CN<sup>-</sup>) increased from 52 to 80 % on average with increasing OC concentration of the fine fractions. A majority of OM-dominated area was correlated with higher <sup>42</sup>AlO<sup>-</sup> counts, which might suggest a preferential co-localization. In turn, the particle area which was dominated by minerals (indicated by <sup>16</sup>O<sup>‑</sup>, <sup>28</sup>Si<sup>‑</sup>, <sup>42</sup>AlO<sup>‑</sup> and <sup>72</sup>FeO<sup>‑</sup>) contained less Al and more Si. This shows that the more alkylated and OM-rich fine fractions are related with distinct patterns of organo-mineral structures at the microscale.</span></p>
Conference on International Research on Food Security, Natural Resource Management and Rural Development Food Ethics: A new and necessary Academic Approach to Improve Food and Nutrition Security
Nature Communications, 2021
The largest terrestrial organic carbon pool, carbon in soils, is regulated by an intricate connec... more The largest terrestrial organic carbon pool, carbon in soils, is regulated by an intricate connection between plant carbon inputs, microbial activity, and the soil matrix. This is manifested by how microorganisms, the key players in transforming plant-derived carbon into soil organic carbon, are controlled by the physical arrangement of organic and inorganic soil particles. Here we conduct an incubation of isotopically labelled litter to study effects of soil structure on the fate of litter-derived organic matter. While microbial activity and fungal growth is enhanced in the coarser-textured soil, we show that occlusion of organic matter into aggregates and formation of organo-mineral associations occur concurrently on fresh litter surfaces regardless of soil structure. These two mechanisms—the two most prominent processes contributing to the persistence of organic matter—occur directly at plant–soil interfaces, where surfaces of litter constitute a nucleus in the build-up of soil c...