Steffen Schweizer - Academia.edu (original) (raw)
Papers by Steffen Schweizer
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 ...
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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...
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<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>
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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...
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Soil Biology and Biochemistry
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<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>
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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...
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The soil carbon saturation concept suggests an upper limit to store soil organic carbon (SOC), se... more The soil carbon saturation concept suggests an upper limit to store soil organic carbon (SOC), set by the mechanisms that protect soil organic matter from decomposition. 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 of SOC persistence remain unresolved. Here we show that the soil C saturation ceiling of a Ferralsol under subtropical pasture could be elevated by 2 Mg (new) C ha-1 by the application of Eucalyptus saligna biochar 8.2 years after the first application. Using one, two-, and three-dimensional analyses, significant increases were observed in the spatial distribution of root-derived 13C in microaggregates (53-250 µm, 11 %) and new C protected in mineral fractions (<53 µm, 5 %). Microbial C-use efficiency was concomitantly improved by lowering specific enzyme activities, contributing to the decr...
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Geoderma, 2019
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Fungal Biology and Biotechnology, 2017
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Science of The Total Environment, 2018
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Soils, 2017
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Biogeochemistry, 2021
Correlations between organic carbon (OC) and fine mineral particles corroborate the important rol... more Correlations between organic carbon (OC) and fine mineral particles corroborate the important role of the abundance of soil minerals with reactive surfaces to bind and increase the persistence of organic matter (OM). The storage of OM broadly consists of particulate and mineral-associated forms. Correlative studies on the impact of fine mineral soil particles on OM storage mostly combined data from differing sites potentially confounded by other environmental factors. Here, we analyzed OM storage in a soil clay content gradient of 5–37% with similar farm management and mineral composition. Throughout the clay gradient, soils contained 14 mg OC g−1 on average in the bulk soil without showing any systematic increase. Density fractionation revealed that a greater proportion of OC was stored as occluded particulate OM in the high clay soils (18–37% clay). In low clay soils (5–18% clay), the fine mineral-associated fractions had up to two times higher OC contents than high clay soils. Sp...
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<p>The conversion of native vegetation into agricultural lands is often associated ... more <p>The conversion of native vegetation into agricultural lands is often associated with a decrease in soil C. The soils from the Brazilian savannah (named Cerrado), with 200 million hectares, are rich in Fe and Al (hydr)oxides, which could result in more organo-mineral associations and lead to particularly high C storage. The changes in the C stocks from the conversion of native forest into degraded pasture (DP), and the adoption of proper management to recover DP and increase C stocks in such Ferralsols are not well understood. To provide insights into the drivers of C storage, this study compared the C stocks across depth in the top 1m and the distribution of C in the soil fractions 24 years after the adoption of different management systems in degraded pastures in the Brazilian Cerrado.</p> <p>A DP area located in S&#227;o Carlos, S&#227;o Paulo, Brazil was converted into different management systems: (i) RMS: rainfed pasture with moderate animal stocking rate, (ii) RHS: rainfed pasture with higher animal stocking rate, and (iii) IHS:&#160; irrigated pasture with higher stocking rate. As a control, the adjacent native vegetation (FO) was also evaluated. The adoption of management started in 1996 with RMS and in 2002 for RHS and IHS. Except for the DP, all areas were limed and N-fertilized. RMS with 200 kg N ha, RHS 400 kg N ha, and IHS with 600 kg N ha. Soil sampling was carried out in 2020 and the C stocks were evaluated up to 1 m deep. To state vegetation change from C3 (native forest) to C4 (introduced pasture) the isotopic natural abundance of <sup>13</sup>C was analyzed. To evaluate the contribution of mineral-associated and particulate organic matter forms to C storage, we performed a physical fractionation by size and density with SPT 1.8 g cm<sup>-3</sup>, respectively.</p> <p>Our results showed that the conversion of FO into DP decreased soil C stocks.&#160; Otherwise, the adoption of management in DP with RMS and RHS increased C stocks achieving levels similar to FO. RMS showed the highest C stocks with the lower dosage of N-fertilizer and animal stocking rate. IHS area did not increase their C stocks compared to DP, which may be related to limited root growth after irrigation decreasing the C input. Around 50% of the C stocks in RHS and RMS systems are pasture-derived (C4 plants) according to the <sup>13</sup>C abundance. This shows that half of C stocks from rainfed pastures is of preserved organic matter from previous FO. While in the IHS and DP systems, the organic matter composition is mainly pasture-derived. Our preliminary data showed that the RMS topsoil contained more free particulate organic matter than the FO, suggesting that the C stocks were enhanced mainly by pasture-derived biomass input. The contribution of mineral-associated organic matter still will be evaluated.</p> <p>Our study shows that the recovery of degraded pasture soils by management leads to increased OC stocks derived from fertilized pasture but also higher maintenance of OC from FO.</p>
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Geochimica et Cosmochimica Acta
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Soil Biology and Biochemistry
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Geoderma
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&lt;p&gt;The structure of soil aggregates plays an important role for the turnove... more &lt;p&gt;The structure of soil aggregates plays an important role for the turnover of particulate organic matter (POM) and vice versa. Analytical approaches usually do not disentangle the continuous re-organization of soil aggregates, caught between disintegration and assemblage. This led to a lack of understanding of the mechanistic relationship between aggregation and OM sequestration in soils.&lt;/p&gt;&lt;p&gt;In this study, we take advantage of a process-based mechanistic model that describes the interaction between the dynamic (re-)arrangement of soil aggregates, based on realistic shapes obtained by dynamic image analysis of wet-sieved aggregates, the turnover of POM, and simultaneous alteration of soil surface properties in a spatially and temporally explicit way.&lt;/p&gt;&lt;p&gt;We used this modeling approach to investigate the impact of the following factors for aggregation: soil texture, OM input and OM decomposition rate. Our model enabled us to quantify the temporal development of the aggregate size distribution, the amount of OC in POM fractions of different ages and the surface coverage.&lt;/p&gt;&lt;p&gt;The simulations provided important implications for the sequestration of OM in soils. Firstly, aggregation was largely determined by the POM input and mostly decoupled from the soil texture. Secondly, the OM storage in terms of POM increased with clay content, with both findings confirming experimental results. Thirdly, we were able to contribute to the understanding of a structural priming effect in which the increased input of POM stimulated the mineralization of old POM.&lt;/p&gt;
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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 ...
Bookmarks Related papers MentionsView impact
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...
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<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>
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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...
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Soil Biology and Biochemistry
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<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>
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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...
Bookmarks Related papers MentionsView impact
The soil carbon saturation concept suggests an upper limit to store soil organic carbon (SOC), se... more The soil carbon saturation concept suggests an upper limit to store soil organic carbon (SOC), set by the mechanisms that protect soil organic matter from decomposition. 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 of SOC persistence remain unresolved. Here we show that the soil C saturation ceiling of a Ferralsol under subtropical pasture could be elevated by 2 Mg (new) C ha-1 by the application of Eucalyptus saligna biochar 8.2 years after the first application. Using one, two-, and three-dimensional analyses, significant increases were observed in the spatial distribution of root-derived 13C in microaggregates (53-250 µm, 11 %) and new C protected in mineral fractions (<53 µm, 5 %). Microbial C-use efficiency was concomitantly improved by lowering specific enzyme activities, contributing to the decr...
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Geoderma, 2019
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Fungal Biology and Biotechnology, 2017
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Science of The Total Environment, 2018
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Soils, 2017
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Biogeochemistry, 2021
Correlations between organic carbon (OC) and fine mineral particles corroborate the important rol... more Correlations between organic carbon (OC) and fine mineral particles corroborate the important role of the abundance of soil minerals with reactive surfaces to bind and increase the persistence of organic matter (OM). The storage of OM broadly consists of particulate and mineral-associated forms. Correlative studies on the impact of fine mineral soil particles on OM storage mostly combined data from differing sites potentially confounded by other environmental factors. Here, we analyzed OM storage in a soil clay content gradient of 5–37% with similar farm management and mineral composition. Throughout the clay gradient, soils contained 14 mg OC g−1 on average in the bulk soil without showing any systematic increase. Density fractionation revealed that a greater proportion of OC was stored as occluded particulate OM in the high clay soils (18–37% clay). In low clay soils (5–18% clay), the fine mineral-associated fractions had up to two times higher OC contents than high clay soils. Sp...
Bookmarks Related papers MentionsView impact
<p>The conversion of native vegetation into agricultural lands is often associated ... more <p>The conversion of native vegetation into agricultural lands is often associated with a decrease in soil C. The soils from the Brazilian savannah (named Cerrado), with 200 million hectares, are rich in Fe and Al (hydr)oxides, which could result in more organo-mineral associations and lead to particularly high C storage. The changes in the C stocks from the conversion of native forest into degraded pasture (DP), and the adoption of proper management to recover DP and increase C stocks in such Ferralsols are not well understood. To provide insights into the drivers of C storage, this study compared the C stocks across depth in the top 1m and the distribution of C in the soil fractions 24 years after the adoption of different management systems in degraded pastures in the Brazilian Cerrado.</p> <p>A DP area located in S&#227;o Carlos, S&#227;o Paulo, Brazil was converted into different management systems: (i) RMS: rainfed pasture with moderate animal stocking rate, (ii) RHS: rainfed pasture with higher animal stocking rate, and (iii) IHS:&#160; irrigated pasture with higher stocking rate. As a control, the adjacent native vegetation (FO) was also evaluated. The adoption of management started in 1996 with RMS and in 2002 for RHS and IHS. Except for the DP, all areas were limed and N-fertilized. RMS with 200 kg N ha, RHS 400 kg N ha, and IHS with 600 kg N ha. Soil sampling was carried out in 2020 and the C stocks were evaluated up to 1 m deep. To state vegetation change from C3 (native forest) to C4 (introduced pasture) the isotopic natural abundance of <sup>13</sup>C was analyzed. To evaluate the contribution of mineral-associated and particulate organic matter forms to C storage, we performed a physical fractionation by size and density with SPT 1.8 g cm<sup>-3</sup>, respectively.</p> <p>Our results showed that the conversion of FO into DP decreased soil C stocks.&#160; Otherwise, the adoption of management in DP with RMS and RHS increased C stocks achieving levels similar to FO. RMS showed the highest C stocks with the lower dosage of N-fertilizer and animal stocking rate. IHS area did not increase their C stocks compared to DP, which may be related to limited root growth after irrigation decreasing the C input. Around 50% of the C stocks in RHS and RMS systems are pasture-derived (C4 plants) according to the <sup>13</sup>C abundance. This shows that half of C stocks from rainfed pastures is of preserved organic matter from previous FO. While in the IHS and DP systems, the organic matter composition is mainly pasture-derived. Our preliminary data showed that the RMS topsoil contained more free particulate organic matter than the FO, suggesting that the C stocks were enhanced mainly by pasture-derived biomass input. The contribution of mineral-associated organic matter still will be evaluated.</p> <p>Our study shows that the recovery of degraded pasture soils by management leads to increased OC stocks derived from fertilized pasture but also higher maintenance of OC from FO.</p>
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Geochimica et Cosmochimica Acta
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Soil Biology and Biochemistry
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Geoderma
Bookmarks Related papers MentionsView impact
&lt;p&gt;The structure of soil aggregates plays an important role for the turnove... more &lt;p&gt;The structure of soil aggregates plays an important role for the turnover of particulate organic matter (POM) and vice versa. Analytical approaches usually do not disentangle the continuous re-organization of soil aggregates, caught between disintegration and assemblage. This led to a lack of understanding of the mechanistic relationship between aggregation and OM sequestration in soils.&lt;/p&gt;&lt;p&gt;In this study, we take advantage of a process-based mechanistic model that describes the interaction between the dynamic (re-)arrangement of soil aggregates, based on realistic shapes obtained by dynamic image analysis of wet-sieved aggregates, the turnover of POM, and simultaneous alteration of soil surface properties in a spatially and temporally explicit way.&lt;/p&gt;&lt;p&gt;We used this modeling approach to investigate the impact of the following factors for aggregation: soil texture, OM input and OM decomposition rate. Our model enabled us to quantify the temporal development of the aggregate size distribution, the amount of OC in POM fractions of different ages and the surface coverage.&lt;/p&gt;&lt;p&gt;The simulations provided important implications for the sequestration of OM in soils. Firstly, aggregation was largely determined by the POM input and mostly decoupled from the soil texture. Secondly, the OM storage in terms of POM increased with clay content, with both findings confirming experimental results. Thirdly, we were able to contribute to the understanding of a structural priming effect in which the increased input of POM stimulated the mineralization of old POM.&lt;/p&gt;
Bookmarks Related papers MentionsView impact