SSS5.3 | Mechanisms of soil organic matter transformation, stabilization and storage
EDI
Mechanisms of soil organic matter transformation, stabilization and storage
Co-organized by BG3/CL3, co-sponsored by IUSS
Convener: Claudio Zaccone | Co-conveners: Guido Wiesenberg, Boris Jansen, Karen Vancampenhout, Layla Márquez San EmeterioECSECS, Beatrice GiannettaECSECS, César Plaza
Orals
| Tue, 25 Apr, 08:30–12:30 (CEST)
 
Room -2.20
Posters on site
| Attendance Wed, 26 Apr, 08:30–10:15 (CEST)
 
Hall X3
Orals |
Tue, 08:30
Wed, 08:30
Soil organic matter (SOM) is well known to exert a great influence on physical, chemical, and biological soil properties, thus playing a very important role in agronomic production and environmental quality. Globally SOM represents the largest terrestrial organic C stock, which can have significant impacts on atmospheric CO2 concentrations and thus on climate. The changes in soil organic C content are the result of the balance of inputs and losses, which strongly depends on the processes of organic C stabilization and protection from decomposition in the soil. This session will provide a forum for discussion of recent studies on the transformation, stabilization and sequestration mechanisms of organic C in soils, covering any physical, chemical, and biological aspects related to the selective preservation and formation of recalcitrant organic compounds, occlusion by macro and microaggregation, and chemical interaction with soil mineral particles and metal ions.

Orals: Tue, 25 Apr | Room -2.20

Chairpersons: Claudio Zaccone, Karen Vancampenhout, Guido Wiesenberg
08:30–08:35
08:35–08:45
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EGU23-10362
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ECS
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On-site presentation
Paige Hansen, Alison King, Jocelyn Lavallee, Meagan Schipanski, and M. Francesca Cotrufo

Identifying global controls on soil carbon (C) storage, as well as where soil C is most vulnerable to loss, are essential to realizing the potential of soils to mitigate climate change via C sequestration. However, we currently lack a comprehensive understanding of the global drivers of soil C storage, especially with regards to particulate (POC) and mineral-associated organic carbon (MAOC). To better understand global controls on these two C fractions, we synthesized climate, and net primary production (NPP), and soils data from 73 published studies and databases. This large dataset is representative of multiple land cover types, including broadleaved and coniferous forests, grasslands, shrublands, wetlands, tundra, and wetlands. We then applied structural equation modeling (SEM) to assess hierarchical, interactive controls on global POC and MAOC pools (i.e., g POC or MAOC per kg soil) in topsoils. Our SEM tested relationships between NPP and climate (i.e., mean annual temperature (MAT) and effective moisture, assessed as mean annual precipitation minus potential evapotranspiration), as well as the extent to which climate and NPP, along with soil texture and pH, govern POC and MAOC storage. We found that NPP is positively related to MAT and effective moisture. Additionally, POC storage is negatively related to both MAT and pH, while MAOC storage is positively related to NPP and effective moisture, but negatively related to soil % sand. Given that temperature and pH impose constraints on microbial decomposition, these results indicate that POC storage is primarily controlled by C output limitations. In contrast, strong relationships with variables related to plant productivity constraints and to mineral surfaces available for sorption indicate that MAOC storage is primarily controlled by climate-driven C input limitations and C stabilization mechanisms. Together, we demonstrate that divergent controls govern C storage in POC and MAOC, and that these controls are consistent across multiple ecosystem types.

How to cite: Hansen, P., King, A., Lavallee, J., Schipanski, M., and Cotrufo, M. F.: Divergent controls on particulate and mineral-associated organic carbon formation and persistence, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10362, https://doi.org/10.5194/egusphere-egu23-10362, 2023.

08:45–08:55
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EGU23-11969
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ECS
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Highlight
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On-site presentation
Steffen Schweizer

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 functions, and highlight opportunities for research approaches based on the patchy and piled-up arrangement of OM at the microscale and nanoscale.

How to cite: Schweizer, S.: Taking a closer look: How spectromicroscopic imaging of organo-mineral associations leads to a novel perspective on interrelated soil functions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11969, https://doi.org/10.5194/egusphere-egu23-11969, 2023.

08:55–09:05
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EGU23-3957
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On-site presentation
Qingmei Lin, Shuotong Chen, Xiao Feng, and Genxing Pan

Soil organic matter (SOM) is a key player in soil functioning and services in forest lands, which had been subject to accelerated land degradation particularly in karst terrain in Southwest China. So far, there had been poor knowledge of pool and molecular composition of SOM associated with soil aggregates across lithologic origins of karst soil. In this study, undisturbed topsoil (0-10 cm) samples were collected in forest lands on sandstone (SS), dolomite (DS) and limestone (LS) sedimentary rocks in a karst terrain from Guizhou, Southwest China. Changes in SOM pool distribution and molecular composition of water-stable aggregates were explored using size and density fractionation and GC/MS detection of extracted biomarkers. The OC content ranged from 41.05 g kg-1 on SS to 50.94 g kg-1 while the mean weight diameter of sand-free soil water-stable aggregates ranged from 420.9 μm on SS to 544.4 μm on DS, across the lithologic sequence. With biomarker molecular assay, the higher SOC storage was relevant to the higher abundance of plant-derived organics (lignin, cutin, suberin, wax and phytosterols) in macro- and micro- aggregates. Whereas, the higher OC in silt & clay fraction of topsoil on DS and LS could be explained by the higher abundance of microbial lipids plus cutin and suberin. Also, the higher ratio of (Ad/Al)v to (Ad/Al)s of silt-clay fraction pointed to a stronger degradation of lignin thereby. Thus, the forest soil of dolomite and limestone origin preserved a relatively high level of SOC storage in topsoil, mainly with accumulation of POC physically protected in macro- and micro- aggregates. Moreover, the high SOC of topsoil on dolomite could also be attributed to enrichment of SOC in the clay silt fraction, mainly with mineral association of microbially degraded OCs.

How to cite: Lin, Q., Chen, S., Feng, X., and Pan, G.: Pool distribution and molecular composition of organic matter among water-stable aggregate size fractions of karst topsoil across a lithologic sequence from Guizhou, Southwest China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3957, https://doi.org/10.5194/egusphere-egu23-3957, 2023.

09:05–09:15
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EGU23-12839
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ECS
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On-site presentation
Giorgio Galluzzi, César Plaza, Simone Priori, Beatrice Giannetta, and Claudio Zaccone

This study aims to investigate the mechanisms of soil organic carbon (SOC) sequestration with depth as a function of time and climate. Two chronosequences located along a climate gradient were investigated. The first chronosequence (ADI) consisted of fluvial terraces, whereas the second (LED) of fluvio-glacial terraces. Four sites (Q2, Q3, Q4 and Q5) located in 3 terraces (T1, T2, and T3), with age ranging from about 125,000 to 2,000 yr, were investigated for ADI, while 3 sites (Q1, Q2, and Q3) in 3 terraces (T1, T2, and T3, respectively), with age range from about 16,000 to 10,000 yr, were selected for LED. All sites were grasslands. Soil samples were collected (1 profile and 2 cores per site) by horizon, and each horizon sub-sampled by depth (each 5 cm). The sub-samples were characterized for pH, EC, total organic C, total N, texture, mineralogy, total and extractable elements, and for soil respiration. Particulate organic matter (POM) and mineral-associated organic matter (MAOM) were isolated and characterized by elemental and thermal analyses.

In ADI, the oldest site (ADIQ2) stocks 2 times more C in the topsoil (15 cm) than the youngest site (ADIQ5) (60 and 27 MgC/ha, respectively). Furthermore, in ADIQ3, 38% of the total SOC accumulated between 30 and 80 cm (48 MgC/ha). In LED, the youngest site (LEDQ3) shows the highest SOC stock to both 15 and 30 cm (86 and 138 MgC/ha, respectively). In LEDQ1, 46% of the total SOC accumulated between 30 and 90 cm (94 MgC/ha). Among sites having same age but different climate, LEDQ3 (the wettest and coldest site) stocks ~2 times more carbon than ADIQ3 (the driest and warmest site) to the first 30 cm of depth.

In LED, the ratio between the organic C in MAOM/POM in the topsoil ranges between 0.6 and 1.8, while in ADI between 1.1 and 3.9. Thermal indices (e.g., WL400-550/200-300, TG-T50) show that the stability of bulk SOM and pools generally increased with depth in ADI sites, whereas remained constant in LED. ADI soils had similar cumulative respiration (RHCUM), whereas LEDQ3 exhibited the highest RHCUM along the first 30 cm. Indeed, LEDQ3 had a 3× higher RHCUM than ADIQ3 in topsoil.

Our data show that significant amounts of organic C were accumulated in deeper soils (>30cm). Moreover, soil organic matter (SOM) stability, and especially that of MAOM, in ADI increased with depth. The relative contribution of POM to C storage was more important in LED than in ADI, especially in the topsoil. Overall, our data suggest that climate has a greater influence on the size of SOC stocks than age, which in turn exerts a major influence on the stability of SOM.

How to cite: Galluzzi, G., Plaza, C., Priori, S., Giannetta, B., and Zaccone, C.: Dynamics and stability of soil organic matter: climate vs. time, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12839, https://doi.org/10.5194/egusphere-egu23-12839, 2023.

09:15–09:25
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EGU23-7318
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ECS
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On-site presentation
Stephen Boahen Asabere, Axel Don, Tino Peplau, and Daniela Sauer

Urbanization is a major land use change factor affecting soils. There is little understanding of how expansions of tropical West African cities have affected soil organic matter (SOM) composition and dynamics. In such cities, urban agriculture is common, playing an essential role in food security and urban sustainability. However, tropical soils tend to have low nutrient contents and cation exchange capacity. Thus, management strategies that enhance soil fertility and carbon (C) sequestration are needed. Developing such strategies requires a thorough understanding of how SOM dynamics alter in response to urban growth. Here, our objective was to assess how urbanization has affected the relatively stable mineral-associated-SOM (MAOM) and the labile particulate-SOM (POM) fractions in rainfed urban arable maize fields of Kumasi, a typical expanding city in Ghana (West Africa).

Using a grid-based satellite approach, and keeping other factors constant (including climate, topography, parent material and soil type), we took topsoil samples (0–10 cm) along an urban-intensity (UI) gradient, distinguishing: (i) low UI, located >400 m away from any primary road and having been under urbanization for <30 years, (ii) mid-low UI, located ≤400 m from a primary road and having been under urbanization for <30 years, (iii) mid-high UI, located >400 m from primary road and having been under urbanization for ≥30 years, (iv) high UI, located within ≤400 m from a primary road and having been under urbanization for ≥30 years. SOM fractions were isolated from the soils using a size separation approach, whereby the sand-sized fraction (0.063 - 2 mm) was regarded as POM and the clay- and silt-sized fraction (<0.063 mm) as MAOM. Prepared samples were ultimately analyzed for SOC using a Leco temperature ramp C analyzer, where a temperature threshold of 600 ºC was used to separate organic from inorganic C.

We found that mean SOC contents of the POM fraction increased markedly from 7.7 g kg-1 in the low UI topsoils to 13 g kg-1 in their high UI counterparts, suggesting an increase in POM with increasing urbanization. This trend was not observed for the MAOM that showed SOC contents of 4.5, 4.1, 4.9, and 4.1 g kg-1 for the low, mid-low, mid-high, and high UI topsoils, respectively. Moreover, the share of SOC contents of POM in the bulk SOC increased from 51% in the low UI topsoils to 64% in the high UI topsoils, whereas that of MOAM decreased by 6% from 31% to 25%, respectively. These findings suggest that while there is evidence of strong anthropogenic contributions of SOM to urban arable soils, urbanization does not seem to promote SOC storage in the relatively stable MAOM fraction. Consequently, rainfed urban arable soils in Kumasi will need management interventions for keeping appropriate long-term SOM levels to maintain soil functions.       

How to cite: Asabere, S. B., Don, A., Peplau, T., and Sauer, D.: Soil organic matter stability decreases with increasing urbanization in highly weathered rainfed tropical arable soils, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7318, https://doi.org/10.5194/egusphere-egu23-7318, 2023.

09:25–09:35
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EGU23-8543
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ECS
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On-site presentation
Friederike Neiske, Joscha N. Becker, Maria Seedtke, Daniel Schwarze, and Annette Eschenbach

The capability of coastal wetland soils to store large amounts of organic carbon (OC) has been increasingly recognised. Stabilisation mechanisms (e.g. aggregation or mineral association) and stability of organic matter (OM) (recalcitrant vs. labile) are important features for the long-term storage of soil organic carbon (SOC). In estuarine marshes, SOC storage is dominated by a complex and dynamic interaction of abiotic conditions such as tidal inundation or changes in salinity. However, little is known on OC stabilisation and stability in these transitional ecosystems and how they are affected by system-specific characteristics. Therefore, our aim was to assess the effect of flooding and salinity on (i) OC stabilisation by aggregation and mineral association and (ii) the stability of the OC pool in estuarine marsh soils.

We analysed topsoil (0 – 10 cm) and subsoil (10 – 30 cm) samples from 9 marsh zones along the salinity gradient (salt, brackish and freshwater) and flooding gradient (pioneer zone, low and high marsh) of the Elbe Estuary for their SOC contents, OC stabilisation mechanisms (density fractionation), OC stability (incubation with one- and two-compartment model fits) and dissolved organic carbon (DOC) concentrations.

Total SOC contents were highest in the freshwater marsh and decreased towards topsoils with higher salinity. Flooding frequency had no uniform effect on SOC contents: While there was a positive tendency with decreasing flooding frequency, subsoils of the freshwater marsh showed the opposite trend. Total SOC contents were positively correlated with mineral-associated OC (CMAOM) and pedogenically unprotected particulate OM (CfPOM). The highest proportion of CMAOM was found in topsoils of freshwater marshes and it decreased towards higher salinities in topsoils of high marshes and pioneer zones. The OM protection by aggregation (CoPOM) increased in topsoils of high marshes. The proportion of CfPOM was less directly affected by salinity and flooding than by the CN ratio of the aboveground biomass (CNlitter). Furthermore, CfPOM correlated positively with the potential mineralisable C (Cpot) and labile C (Clabile) and negatively with the recalcitrant C pool (Crecalcitrant) that were derived from the one- and two-compartment models. Labile C, Cpot and Crecalcitrant were also strongly influenced by CNlitter. Moreover, Crecalcitrant was linked to the proportion of CMAOM. Concentrations of DOC increased with total SOC and Cpot but decreased with CoPOM.

We conclude that SOC stabilisation in the Elbe Estuary is mainly related to mineral association of OM. With increasing terrestrial influence, physical protection in aggregates becomes more important. Besides these pedogenic stabilisation mechanisms, recalcitrance is strongly determined by vegetation characteristics.

How to cite: Neiske, F., Becker, J. N., Seedtke, M., Schwarze, D., and Eschenbach, A.: Organic carbon stabilisation mechanisms in estuarine marsh soils: Effect of salinity and flooding frequency, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8543, https://doi.org/10.5194/egusphere-egu23-8543, 2023.

09:35–09:45
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EGU23-2423
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On-site presentation
Mauro De Feudis, Gloria Falsone, William Trenti, Gilmo Vianello, and Livia Vittori Antisari

Forest soils are recognized to be important organic carbon storage, but the role of surface and subsurface soil horizons on such function and its drivers are still field of debate. In this context, we examined the dynamics of soil organic carbon (SOC) for a chestnut forestry system in a temperate area of northern part of Apennine mountain range in Italy. Specifically, we questioned: what are the main i) SOC forms both in mineral surface and subsurface soil horizons? ii) factors affecting SOC stabilization?. Soil samples were collected by horizon and SOC was separated into organic C of the particulate organic matter (POM_C), sand–size aggregates (sand_C) and the mineral–associated organic C (MAOM_C). The easily oxidizable C (EOC), water–soluble organic C (WSOC), the microbial biomass–C and its respiration, and the total and easily extractable glomalin–related soil protein (T–GRSP and E–GRSP, respectively) were also estimated. Then, the E–GRSP–to–T–GRSP and E-GRSP–to–SOC ratios, the metabolic (qCO2) and microbial (qMIC) quotients were calculated. The POM_C, sand_C and MAOM_C showed the highest concentrations in A horizon (26.5, 14.6 and 13.9 g kg–1, respectively) highlighting the importance of the litter floor on the organic matter pools quantity in the topsoil. Further, the A horizon was enriched of the most labile organic C forms (i.e., EOC and WSOC) indicating the key role of A horizon for the development and growth of chestnut forest ecosystems. In fact, the labile organic C forms provide several ecosystem services, such as plant growth and yield. Unlike A horizon, the subsurface horizons preserved SOC mostly in the most stable form (63.8 %, on average). Because of the role of fungal biomass and its exudates to increase SOC capture and stabilization, the great potential of the subsurface horizons to store MAOM_C can be attributed both to the higher release of exogenous GRSP (higher E–GRSP–to–T–GRSP ratio) by mycorrhizal fungi and fungal mycelium expansion (higher E-GRSP–to–SOC ratio) within such horizons (0.504  and 0.061, respectively) compared to the A horizon (0.244 and 0.034, respectively). Therefore, the subsurface soil horizons seemed to have more favourable conditions for microorganisms compared to surface one as shown by the lower qCO2 and the higher qMIC values found in the former than in the latter. Overall, the present investigation highlighted the importance of subsurface soil horizons of chestnut forests on C stabilization processes compared to the A horizon likely due to the better edaphic conditions for the microbial communities. Thus, our results pointed out the key role that the subsurface soil horizons of chestnut forests could have for mitigating the current climate change.

How to cite: De Feudis, M., Falsone, G., Trenti, W., Vianello, G., and Vittori Antisari, L.: The subsoil horizons are the preferential location for organic carbon stabilization in chestnut forests, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2423, https://doi.org/10.5194/egusphere-egu23-2423, 2023.

09:45–09:55
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EGU23-17329
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ECS
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On-site presentation
Long-term resilience of mineral associated organic matter in soils of a Mediterranean forest burned in 1994 at different severities
(withdrawn)
Eduardo Augusto Garcia Braga, Antonio Peñalver-Alcalá, Noelia Garcia-Franco, Martin Wiesmeier, Ingrid Kögel-Knabner, Joaquim Farguell, and Xavier Úbeda
09:55–10:05
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EGU23-15729
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ECS
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On-site presentation
Lucas Raimundo Bento, Steffen A. Schweizer, Patrícia P. A. Oliveira, José R. M. Pezzopane, Alberto C. de C. Bernardi, Ingrid Kögel-Knabner, and Ladislau Martin-Neto

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.

A DP area located in São Carlos, São 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:  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 13C 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-3, respectively.

Our results showed that the conversion of FO into DP decreased soil C stocks.  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 13C 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.

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.

How to cite: Bento, L. R., Schweizer, S. A., Oliveira, P. P. A., Pezzopane, J. R. M., Bernardi, A. C. D. C., Kögel-Knabner, I., and Martin-Neto, L.: Managed pastures enhance soil carbon stocks from degraded pasture in Ferralsol of Brazilian Cerrado, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15729, https://doi.org/10.5194/egusphere-egu23-15729, 2023.

10:05–10:15
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EGU23-3272
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On-site presentation
Guoxiang Niu, Jianh Huang, Xiankai Lu, and Johannes Rousk

ABSTRACT: Global nitrogen (N) deposition has impacted the structure and functioning of soil microbial communities, translating into important changes to the cycling of soil organic matter (SOM). Recent frameworks have proposed that portioning the particulate and mineral-associated organic matter (POM and MAOM) fractions can help us better understand SOM cycling. However, how N deposition affect the fractionation of SOM into MAOM and POM forms, and how soil microbes process these across soil profile all remain unclear. Here we examined the microbial phospholipid fatty acids and determined N and soil organic carbon (SOC) content in POM and MAOM at depths of 0–10, 30–40 and 70–100 cm after 10-year N addition at rates of 0, 2, 10 and 50 g m-2 yr-1 in a temperate steppe. We found that N addition remarkably shifted microbial communities by increasing the relative abundances of bacteria and gram-positive (GP) bacteria, and decreasing gram-negative bacterial across the three soil layers. These effects of N addition tended to increase with the N addition rate but diminished with soil depth probably as pH decreased with the N addition rate but increased with soil depth. Both N addition and soil depth may cause similar microbial community shifts, through which fungi and GP bacteria become dominant, but may through different mechanisms. More than 60% of total SOC and N are stored as MAOM in this grassland. The share of SOC and total N in the MAOM was slightly decreased by N addition in 0-10 cm but significantly increased in deeper soils. The ratios of POM-C/MAOM-C and POM-N/MAOM-N significantly decreased with soil depth regardless of N addition treatments. Moreover, N addition increased the two ratios in 0-10 cm soil, but decreased them in deeper soil layers. N addition increased the stocks of SOC (MAOM: +11 %; POM: +23 %) and total N (MAOM: +10 %; POM: +27 %) in 0–10 cm soil, but increased only in MAOM in 30–40 cm (SOC: +24 %; total N: +24 %) and 70–100 cm (SOC: +15 %; total N: +13 %) soils. Soil physicochemical features exerted stronger controls than microbial properties in the distribution of SOC and total N in the two fractions regardless of soil depth because of eight soil features explaining more of the total variation than eight microbial properties. Our findings imply that increase in N deposition may make more SOC stabilized as MAOM fraction in grassland soils.

Keywords: Nitrogen deposition, Soil microbiome, Mineral-associated organic matter, Subsoil

How to cite: Niu, G., Huang, J., Lu, X., and Rousk, J.: Decadal nitrogen addition enhanced soil C and N storage in mineral-associated organic matter by altering soil abiotic and microbial properties in a temperate grassland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3272, https://doi.org/10.5194/egusphere-egu23-3272, 2023.

Coffee break
Chairpersons: Boris Jansen, Beatrice Giannetta, Layla Márquez San Emeterio
10:45–10:55
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EGU23-12085
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ECS
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On-site presentation
Susanne Ulrich, De Shorn Bramble, Ingo Schöning, Robert Mikutta, Klaus Kaiser, and Marion Schrumpf

Formation of mineral-associated organic matter (MAOM) supports accumulation and stabilization of carbon in soil, and thus, is a key factor in the global carbon cycle. Little is known about the interplay of mineral type, land use, and management intensity on the extent of MAOM formation. We addressed this research question by exposing mineral containers with pristine minerals (goethite, as a representative of oxide-type mineral phases, and illite, representing layered aluminosilicate minerals) for five years to ambient soil conditions at 5 cm depth in 150 grassland and 150 forest plots in three regions across Germany. After recovery, the content of organic carbon (OC) of the minerals was determined by dry combustion. Results show that irrespective of land use and management intensity, more OC accumulated on goethite than illite (on average 0.23 and 0.06 mg m-2 mineral surface, respectively), demonstrating that mineral type was the most crucial factor for MAOM formation. Carbon accumulation was consistently greater in coniferous forests than in deciduous forests and grasslands. Structural equation models revealed that in grasslands, fertilization had contradictory effects on carbon accumulation, with the positive effect being mediated by enhanced plant productivity and the negative effect by reduced plant species richness. Overall, our results suggest that OC stabilization in soil is primarily driven by mineral type, in particular iron and other metal oxides. The mineral-driven MAOM formation is further modified by land use and management intensity.

How to cite: Ulrich, S., Bramble, D. S., Schöning, I., Mikutta, R., Kaiser, K., and Schrumpf, M.: Mineral type, land use, and management intensity drive the formation of mineral-associated organic matter in temperate soils, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12085, https://doi.org/10.5194/egusphere-egu23-12085, 2023.

10:55–11:05
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EGU23-16928
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On-site presentation
Laura Ercoli, Gaia Piazza, Thorunn Helgason, and Elisa Pellegrino

Under conservation agriculture (CA), soil aggregates physically protect soil organic C, creating microhabitats with heterogeneities in nutrient availability. These may become rich in microbial taxa with structured interconnections, and thus maintain the equilibrium between C sources and sinks. A long-term experiment on tillage and N fertilization located in the Mediterranean was used to investigate the microbiota within small macroaggregates (sM), and occluded microaggregates (mM). At surface layer N fertilization was the main driver of diversity of prokaryotes and fungi in soil aggregates, whereas at subsurface layer tillage intensity was the primary driver. Moreover, although along the soil profile a conserved core microbial community was found across managements in soil aggregates, some taxa were unique to certain managements. At surface layer, N fertilization significantly modified the prokaryotic community structure in sM and mM under conventional tillage, whereas in the subsurface layer, tillage modified the community structure of prokaryotes in both soil aggregates, and of fungi in mM. The fungal community structure in sM was strongly modified by the interaction between tillage and N fertilization at both soil layers and in mM only at surface layer. Overall sM had a higher diversity of prokaryotes and a lower diversity of fungi than mM. Small macroaggregates and mM had distinctive microbial community structures. Prokaryotic taxa, such as Actinobacteria, Chloroflexi and Thermomicrobia, and fungi, such as Agaricomycetes, Dydimellaceae, and Mortierellaceae, characterized sM, whereas others prokaryotes (Betaproteobacteria, Sphingobacteriia, Blastocatellia) and fungi (Sordariales, Lasiosphaeriaceae and Glomeraceae) characterized mM. Within- and cross-domain network were more complex in mM than sM at surface layer, and the opposite occurred at subsurface. Some prokaryotic and fungal taxa (Chloroflexi and Sordariomycetes), found abundant in hubs within soil aggregate networks, were consistently positively related to C cycling and soil structuring. We can therefore conclude that soil aggregation should be included in a more complete ‘multifunctional’ perspective of soil ecology, and that a full understanding of soil processes requires analyses emphasizing feedbacks between soil structure and soil microbiota, rather than a unidirectional approach simply addressing single members in bulk soil. As CA systems and soil structure were strongly connected to soil microbiome and function, the application of CA practices should be supported for the restoration of disturbed soils, the prevention of soil erosion and the enhancement of SOC storage. Overall, the higher diversity and differentiated soil microbial structures observed in minimum and fertilized tillage systems may offer biological buffering capacity and maintain agriculturally relevant soil functions. This study allows to improve the knowledge on taxa resistant and sensitive to modifications induced by tillage and N fertilization, according to soil aggregation size. We also demonstrate that linking taxonomy to function is a priority for explaining the ecological interactions that promote SOC accumulation in soil aggregates.

How to cite: Ercoli, L., Piazza, G., Helgason, T., and Pellegrino, E.: Microbiome structure and interconnection in soil aggregates across conservation and conventional agricultural practices allow to identify taxa related to soil functioning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16928, https://doi.org/10.5194/egusphere-egu23-16928, 2023.

11:05–11:15
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EGU23-2051
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ECS
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On-site presentation
Xinxin Jin, Roland Bol, Tingting An, Lihong Zheng, Shuangyi Li, Jiubo Pei, and Jingkuan Wang

Plastic film mulching (PFM) is critical for agricultural planting and production in semi-arid and arid areas. Particulate organic matter (POM) is assumed to be a sensitive indicator of evaluating the effects of different agricultural practices on soil fertility and soil organic carbon (SOC) pool. Soil aggregates are the main storage sites for POM. However, there is limited information regarding how PFM and fertilization influences the dynamic changes of newly added stalk-derived POM in Brown earth. Consequently, a depth-study of the fate of carbon (C) and nitrogen (N) derived from maize stalk residues as the POC and PON fractions in soil aggregates will help in predicting the active organic matter component sequestration in the soil. The dynamics and contribution of the newly added maize stalk C and N as POC and PON in different soil aggregates (using dry sieving method divided to > 2, 1-2, 0.25-1and < 0.25 mm) was analyzed by an in-situ 13C15N-tracing technique under 27-year long term PFM and different fertilization treatments. Over the 360 d cultivation, the POC and PON contents were significantly (P < 0.05) higher in the nitrogen (N) and organic manure (M) treatments than other fertilizer addition treatments. Compared with no PFM, PFM accelerated the decomposition of maize stalk C in the N fertilizer treatment, exhibiting an increase of 64% in stalk-derived POC in the initial cultivation time. In addition, stalk-derived POC tended to accumulate in 1-2 mm aggregates in the summer and fall as a result of long-term PFM coupled with fertilization. However, the stalk-derived PON was decreased with the cultivation time in different four aggregates. Stalk-derived POM was tended to accumulate in the macroaggregate size fraction (> 0.25 mm) over 360 days of cultivation in the field conditions. Accordingly, PFM application and fertilization practices had important effects on accumulation of newly added stalk-derived POM in soil aggregates.

How to cite: Jin, X., Bol, R., An, T., Zheng, L., Li, S., Pei, J., and Wang, J.: Long-term fertilization and PFM changed the accumulation of stalk-derived POM in soil aggregates under field conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2051, https://doi.org/10.5194/egusphere-egu23-2051, 2023.

11:15–11:25
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EGU23-8025
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ECS
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On-site presentation
Tchodjowiè Israel Kpemoua, Pierre Barré, Sabine Houot, François Baudin, Cédric Plessis, and Claire Chenu

The implementation of agroecological practices can lead to an additional soil organic carbon (SOC) storage. The carbon sink effect will be more effective, even in the short and medium term, if the additional storage is realized in the form of persistent organic carbon (OC) and not in labile OC. The objective of this study was to evaluate the biogeochemical stability of additionally C stored by agroecological practices. Biogeochemical stability was assessed using particles size and density fractionation and Rock-Eval (RE) thermal analyses with PARTYsoc machine learning model. Samples were collected from the QualiAgro experiment, where organic wastes products (OWPs) including biowaste compost (BIOW), residual municipal solid waste compost (MSW) and farmyard manure (FYM) were applied, and from the La Cage experiment, where conservation (CA) and organic (ORG) agriculture had been established for 20 years. The plots that received the OWPs showed that 60-66% of the additional C was stored in mineral-associated organic matter (MAOM-C) and 29 - 39% in particulate organic matter (POM-C), whereas in CA and ORG, 77 - 84% of the additional C was stored in MAOM-C versus 15 - 23% in POM-C. While leading to additional C stocks of similar sizes, MSW and FYM exhibited higher proportions of the additionally stored C as POM-C (39 and 29% respectively) compared to CA (15%). This suggests a recalcitrance of POM under OWPs management compared to CA. The PARTYSOC model using RE thermal analysis parameters allows to predict the active (30 - 40 years) and stable (>100 years) carbon pools as defined in the AMG model. The results revealed that most, if not all, of the additional C belonged to the active C pool. These findings suggest that although additional SOC is mainly associated with MAOM-C, it is probably not stored in a form with a mean residence time exceeding ~30 years. The agroecological practices implemented in both long-term field experiments have resulted in substantial short-term additional C storage, but this storage will only be maintained at a high level if these storing practices are continued.

How to cite: Kpemoua, T. I., Barré, P., Houot, S., Baudin, F., Plessis, C., and Chenu, C.: Is the additional organic carbon stored thanks to alternative cropping systems and organic waste products application predominantly stable at a decadal timescale?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8025, https://doi.org/10.5194/egusphere-egu23-8025, 2023.

11:25–11:35
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EGU23-3538
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ECS
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On-site presentation
Neha Begill, Axel Don, and Christopher Poeplau

Subsoils have gained increasing attention due its slower soil organic carbon (SOC) turnover than in topsoil. Thus, subsoil with low content of mineral associated organic matter but a large number of exchange sites on mineral surfaces represents the potential to accumulate and sequester carbon (C). Generally, it has been assumed that the carbon turnover mechanism in topsoil and subsoil is influenced by similar environmental factors, with the difference of a lower C content in subsoil. In contrast, diverse abiotic variables prevalent in subsoils, like low temperature, high moisture, nutrient availability, etc., have been shown to imply different processes influencing C turnover in subsoils. Therefore, differences in processes and factors affecting SOC turnover in topsoil and subsoil are incompletely identified and understood.

Our objective is to investigate whether C decomposition and stabilisation mechanisms in topsoil and subsoil differ given the same added substrate content, as well as how it responds to increasing substrate C content. To assess these questions, a long-term (total duration 20-year) field incubation experiment was conducted at three different locations with varied soil textures in which soil was mixed and labelled with isotopically (13C) enriched beech litter substrate with different C contents of 8, 16, 32, and 64 g substrate kg-1 in topsoil (10 cm) and 2, 4, 8, and 16 g substrate kg-1 in subsoil (60 cm), filled in mesocosms, and buried. Soil samples were collected after one, two, and four years. Soil was fractionated into particulate organic matter (>20µm) and mineral-associated organic matter (<20µm) to find out how carbon is stabilised in these fractions, and stable C isotopes were measured. Our results indicate that the decomposition of the identical litter substrate strongly depends on the soil depth. The results of four years of buried field-microcosms will be presented, which will shed more light on differences in mechanisms responsible for SOC dynamics and the fate of litter substrate into different SOC pools of topsoil and subsoil.

 

How to cite: Begill, N., Don, A., and Poeplau, C.: Investigating soil organic matter dynamics in topsoil and subsoil by burying isotopically labelled litter substrate for four years, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3538, https://doi.org/10.5194/egusphere-egu23-3538, 2023.

11:35–11:45
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EGU23-10208
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ECS
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On-site presentation
Laudelino Vieira da Mota Neto, Marcelo Valadares Galdos, Vladimir Eliodoro Costa, and Ciro Antonio Rosolem

Intercropping maize along with forages fertilized with N can potentially increase soil carbon sequestration, contributing to climate change mitigation. However, there is a lack of knowledge if the input of new C sources in this production system impacts the cycling of the original soil C and SOM fractions, especially in tropical soils. To investigate this, soil samples were taken up to 80 cm depth from a 7-year experiment where ruzigrass (Urochloa ruziziensis), palisadegrass (Urochloa brizantha) and Guinea grass (Megathyrsus maximus) were intercropped with maize fertilized with (270 kg N ha-1) or without N. In these samples, SOM was fractionated by size into particulate (POM) and mineral-associated (MAOM) organic matter and submitted to 13C natural abundance measurements. Intercropping with Guinea grass reduced the δ13C values in comparison to ruzigrass and palisadegrass, especially under N fertilization. Forage grasses reduced the δ13C values up to 40cm, indicating the contribution of the grasses for the cycling of the original carbon of the soil. Nitrogen supply increased the contribution of C from the grasses to the POM fraction if compared to the no N application. Further, 13C  in POM at 0-10 and 10-20 cm differed from deeper layers, probably due the above- and belowground C inputs on the uppermost soil layers. Under N supply, Guinea grass lowered the δ13C value, which did not occur in the palisade and ruzigrass treatments. In contrast to POM, the δ13C values of MAOM decreased in all depths, with the highest change at the uppermost soil layer. Our findings showed that intercropping influenced the cycling of total C and SOM fractions , with differences in the soil profile. However, only Guinea grass changed δ13C values under N supply.

How to cite: Vieira da Mota Neto, L., Valadares Galdos, M., Eliodoro Costa, V., and Antonio Rosolem, C.: Assessing soil carbon cycling as a function of intercropped maize-forage systems and nitrogen rates using 13C natural abundance, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10208, https://doi.org/10.5194/egusphere-egu23-10208, 2023.

11:45–11:55
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EGU23-5557
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On-site presentation
Claudia Guidi, Marco Lehmann, Katrin Meusburger, Matthias Saurer, Valentina Vitali, Martina Peter, Ivano Brunner, and Frank Hagedorn

Soil organic matter (SOM) originates from various sources such as foliar litter, roots and microbial (e.g. fungal) components. The relative sources contribution represents one of the key unknowns in SOM dynamics. Our study aimed to explore whether stable isotope ratios of non-exchangeable hydrogen (Hn) bound to organic matter can be used to differentiate SOM sources, since natural 2Hn abundance can strongly differ between root and foliar tissues. We also investigated if long-term irrigation with 2H-depleted water in a pine forest can be used to track Hn incorporation into organic matter inputs and eventually in the soil pools.

In a 17-year-long irrigation experiment in a dry pine forest, we assessed variations in natural abundance of 2Hn, 13C, and 15N in SOM sources (foliar litter, fine roots, fungal mycelia), decomposing litter, soil (organic layers and uppermost 5 cm-mineral soil) and particle-size fractions. We then applied a Bayesian mixing model (including δ2Hn,δ13C, and δ15N) to estimate the relative sources contribution to SOM.

Natural 2Hn abundance was significantly higher in roots vs. foliar litter (up to +39‰), and in fungal mycelia vs. roots (up to +41‰). Results from Bayesian mixing model suggest that foliar litter contributed to approximately 68 ± 10% of SOM in organic layers and in coarse particulate organic matter (POM). Foliar litter and roots contributed similarly to upper 2 cm of mineral soil (46 ± 11%), while 2-5 cm of mineral soil were largely derived from roots (61 ± 13%). Fungal mycelia contributed to 18 ± 8% of mineral-associated organic matter (MOM), while only to 1-2% of coarse and fine POM. Bayesian mixing models provided only a general indication of the sources contribution to SOM, also considering that isotopic signatures shifted during decomposition. Measurements of isotope signatures in microbial necromass might allow a more accurate assessment of the different SOM sources contribution.

The δ2Hn depletion of soil water under irrigation was paralleled by a comparable decrease in δ2Hn of roots (~12‰). In comparison, the natural 2Hn abundance in fresh needles and foliar litter decreased less strongly (~ 7‰ and 4‰, respectively), likely due to photosynthetic adjustments that may have counterbalanced the irrigation water 2H-depletion. Similar to soil water 2H-depletion, δ2Hn values in coarse POM were 11‰ lower in irrigated vs. dry plots, suggesting that nearly all organic Hn turned over or exchanged with soil water in less than two decades. In contrast, δ2Hn values in fine POM and MOM decreased only by 3‰ under irrigation, which indicate that these fractions comprise slower cycling Hn pools.

Our study showed that the natural 2Hn abundance represents a promising tool to differentiate among SOM sources. While 13C and 15N did not clearly separate between roots and foliar litter, Hn isotopic signatures allowed a good discrimination between SOM sources. In addition, long-term irrigation can provide a potential in situ 2H-labelling of SOM, which may help to examine organic Hn turnover rates across SOM pools.

How to cite: Guidi, C., Lehmann, M., Meusburger, K., Saurer, M., Vitali, V., Peter, M., Brunner, I., and Hagedorn, F.: Tracing sources and turnover of soil organic matter in a long-term irrigated dry forest - a non-exchangeable hydrogen isotope approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5557, https://doi.org/10.5194/egusphere-egu23-5557, 2023.

11:55–12:05
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EGU23-1525
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ECS
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Highlight
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On-site presentation
Alba Otero-Fariña, Helena Brown, Ke-Qing Xiao, Juan Antelo, Sarah Fiol, Pippa Chapman, Joseph Holden, Steven Banwart, and Caroline Peacock

To mitigate climate change, it is of vital importance to increase the stocks of global soil organic carbon (SOC), which also improves soil resilience, soil fertility and thus food security. 

The preservation of SOC heavily depends on its vulnerability to microbial degradation. Two processes and their interplay strongly influence carbon protection: the formation of primary organo-mineral (O-M) complexes via the sorption of dissolved organic carbon (DOC) to fine-grained soil minerals, and the aggregation of these to form micro and macroaggregates. To date, research suggests that the chemistry of the SOC and the mineralogy of the soil matrix play a key role in the formation of O-M complexes and their stability against microbial degradation, but whether and to what extent these factors help control micro and macroaggregation are unknown. 

We focus our investigation on how the chemistry of the SOC source affects the stability and aggregation of iron (oxyhydr)oxide O-M complexes. Thus, we determine the sorption behaviour of different SOC sources chosen to represent different functional group chemistries, using sorption isotherm experiments and electrophoretic techniques. We also conduct long-term aggregation experiments to track aggregate particle size using a novel Particle Size and Shape Analyzer technique.  

Our findings suggest that the stability and aggregation modes of O-M complexes are a function of SOC chemistry, and that aggregation patterns are strongly influenced by the presence of microbial exudates and communities. 

How to cite: Otero-Fariña, A., Brown, H., Xiao, K.-Q., Antelo, J., Fiol, S., Chapman, P., Holden, J., Banwart, S., and Peacock, C.: Carbon preservation in soils: The role of carbon chemistry in soil aggregate formation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1525, https://doi.org/10.5194/egusphere-egu23-1525, 2023.

12:05–12:15
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EGU23-17105
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ECS
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On-site presentation
Jeewan Gamage, James Longstaffe, Adam Gillespie, Andy Lo, Sameer Al-Abdul-Wahid, and Paul Voroney

Understanding the molecular make-up of recalcitrant organic matter (rSOM) is important to postulate the capability of soil organic matter (SOM) to sequester carbon and mitigate climate change. Humic acid (HA) extracted from the river bed sediment (RS) from the West Holland river was analyzed, aiming to characterize and quantify the fused ring aromatic structures (FRA) portion. FARs can be formed through condensation and polymerization reactions and act as an important skeletal structure of the rSOM which has a mean residence time >1000 years. We conducted a series of nuclear magnetic resonance (NMR) experiments, 13C Direct Polarization Magic Angle Spinning (DP-MAS) NMR spectroscopy, and Dipolar dephased (dd) DPMAS NMR, chemical shift anisotropy (CSA) cross-polarization (CP) total sideband suppression (TOSS) NMR experiment and a dd-CSA filtered CPTOSS to accurately quantify the proportion of FRAs in the sediment HA sample. We compared the proportions of the functional groups of the RS with the surface (0-20 cm, TS) and deep (>90 cm, CS) soil HAs of the nearby Holland Marsh, Muck Crops Research Station to understand the linkages and the transformations of SOM happened while transportation (wind erosion and horizontal seepage) to the muck river sediment. We found that 90% of the aromatic C in the RS is non-protonated, and 32% of the aliphatic region was non-protonated. The DPMAS spectral comparison between RS, TS and CS clearly showed that RS contains characteristic peaks of both TS and CS. Moreover, the proportion of non-protonated aliphatics in RS (32%) is high compared to TS (18%) and CS (29%). Our results indicate that in muck river sediment soil HA, non-protonated aliphatics (CRAM-like structures) contribute to the rSOM more than FRAs, while in TS and CS, FRAs' contribution is higher than the non-protonated aliphatics. Collectively our results show the link between terrestrial organic matter transportation to the river sediment and the transformation that occur in the rSOM fraction in the river sediment SOM. This new knowledge allows us to understand the structural changes that happen in the sequestered carbon in different soil environments.

How to cite: Gamage, J., Longstaffe, J., Gillespie, A., Lo, A., Al-Abdul-Wahid, S., and Voroney, P.: Evidence for the diagenetic formation of fused aromatic ring structures in an organic soil, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17105, https://doi.org/10.5194/egusphere-egu23-17105, 2023.

12:15–12:25
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EGU23-13926
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ECS
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On-site presentation
Aswin Thirunavukkarasu, Mats Öquist, Jurgen Schleucher, Tobias Sparrman, Mattias Hedenstrom, Mats Nilsson, and Stefan Bertilsson

The amount of carbon stored in boreal forests soil as Soil organic matter (SOM) is significant. Carbohydrate polymers such as cellulose and hemicellulose constitute 40-50% of the SOM mass in the surface mor layer, even in SOM that has been decomposed for decades to centuries. This is in contrast to conceptual decomposition models assuming aromatic and aliphatic polymers to constitute the fraction of recalcitrant SOM. One prevailing view for support is that lignin manifest itself as a factor in the stabilization of carbohydrate polymers as SOM. However, detailed elucidation of how the complex array of molecular moieties making up SOM decompose over time is lacking. Here we investigated the effect of lignin content and composition during the progressive degradation of polymeric carbohydrates, lignin, and lipids in the lab during a year-long soil decomposition study using Aspen (Populus tremula) wood as a model substrate. To specifically address lignin decomposition we used a range of Aspen clones that varied naturally in their lignin content (high lignin 30% - low lignin 25%) with boreal coniferous forest soil obtained from the surface moor layer (O-horizon). The decomposition of the different molecular moieties of the model substrate was evaluated by Two-dimensional (2D) liquid state 1H–13C nuclear magnetic resonance (NMR) spectroscopy. In addition, the CO2 production during decomposition was monitored continuously and assays for exo-enzymatic activity was carried out at selected time points.

The NMR spectroscopy revealed that for different periods of decomposition, saprotrophic microorganisms preferred different monomers of polymeric lignin, carbohydrates, and lipids. The relative degradation of resinol, spirodienone, and cinnamyl alcohol were higher among lignin interlinkages and the relative degradation of p-hydroxybenzoate and syringyl were higher among lignin subunits. For carbohydrates, the relative degradation of mannose and glucose were higher than that of e.g. xylose. The relative degradation of unsaturated fatty acids was higher among lipids. The lignin: carbohydrates ratio decreased linearly over the period of decomposition. This showed that the initial degradation of lignin compounds was greater compared to the decomposition of carbohydrate compounds. The significant difference in the relative degradation of mannose among model substrate with different lignin content showed that lignin had no effect on cellulose degradation but may have had an effect on the preferential degradation of hemicelluloses. The high-resolution decomposition patterns we observe are crucial for obtaining a detailed mechanistic understanding of plant polymer decomposition by soil microorganisms during the initial stages of SOM genesis.

 

Keywords: Soil organic matter (SOM), Lignin, Carbohydrates, 2D NMR, Decomposition

How to cite: Thirunavukkarasu, A., Öquist, M., Schleucher, J., Sparrman, T., Hedenstrom, M., Nilsson, M., and Bertilsson, S.: The role of lignin in the saprotrophic degradation of plant biomass in boreal forest soil., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13926, https://doi.org/10.5194/egusphere-egu23-13926, 2023.

12:25–12:30

Posters on site: Wed, 26 Apr, 08:30–10:15 | Hall X3

Chairpersons: Karen Vancampenhout, Layla Márquez San Emeterio, Beatrice Giannetta
X3.80
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EGU23-2255
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ECS
Nicasio T. Jiménez-Morillo, Nuno Guiomar, Ana Z. Miller, José M. De la Rosa, and José A. González-Pérez

Forest fires are a recurrent ecological phenomenon in the Mediterranean basin. They induce molecular changes in soil organic matter (SOM) leading to immediate and long-term environmental consequences [1]. The SOM is of paramount importance as indicator of soil health [2]. Fire-induced changes in SOM include the alteration of biogenic chemical structures and the accumulation of newly formed ones, enhancing dynamics in the complex balance between the different C-types [2,3]. Therefore, understanding SOM molecular composition, before and after fire, is fundamental to monitor changes in soil health, as well as its natural or man-mediated recovery [3,4]. Our aim was to assess the molecular composition of organic matter in fire-affected leptosols, at two depths (0–2 and 2–5 cm) under different vegetation types located in the southwestern of Portugal (Aljezur, Algarve). The SOM characterization was conducted by analytical pyrolysis (Py-GC/MS), a technique based on the thermochemical breakdown of organic compounds in the absence of oxygen at elevated temperatures [5]. The Py-GC/MS has been found suitable for the structural characterization of complex organic matrices [4], providing detailed structural information of individual compounds considered fingerprinting of SOM. However, due to the relative high number of molecular compounds released by analytical pyrolysis, the use of graphical-statistical methods, such as van Krevelen diagrams, are usually applied to help monitoring SOM molecular changes produced by fire [3,4]. This work represents the first attempt to evaluate the fire effects in SOM using a detailed molecular characterisation of SOM under different vegetation canopies, recently affected by wildfire, in southern Portugal.

 

References:

[1] Naveh, Z., 1990. Fire in the Mediterranean – a landscape ecological perspective. In: Goldammer, J.G., Jenkins, M.J. (Eds.), Fire in Ecosystems Dynamics: Mediterranean and Northern Perspective. SPB Academic Publishing, The Hague.

[2] González-Pérez, J.A., González-Vila, F.J., Almendros, G., Knicker, H., 2004. The effect of fire on soil organic matter—a review. Environ. Int. 30, 855–870.

[3] Jiménez-Morillo, N.T., De la Rosa, J.M., Waggoner, D., et al., 2016. Fire effects in the molecular structure of soil organic matter fractions under Quercus suber cover. Catena 145, 266–273.

[4] Jiménez-Morillo, N.T.; Almendros, G.; De la Rosa, J.M.; et al., 2020. Effect of a wildfire and of post-fire restoration actions in the organic matter structure in soil fractions. Sci. Total Environ. 728, 138715.

[5] Irwin, W.J., 1982. Analytical pyrolysis—a comprehensive guide. In: Cazes, J. (Ed.), Chromatographic Science Series, 22: Chapter 6. Marcel Dekker, New York.

 

Acknowledgments: This work was funded by national funds through FCT–Fundação para a Ciência e a Tecnologia (EROFIRE project, ref. PCIF-RPG-0079-2018) and by the EU-FEDER co-funded project MARKFIRE (ref. P20_01073) from Junta de Andalucía. This research was also funded by the European Union through the European Regional Development Funds in the framework of the Interreg V A Spain-Portugal program (POCTEP) through the CILIFO (Ref.: 0753_CILIFO_5_E) and FIREPOCTEP (Ref.: 0756_FIREPOCTEP_6_E) projects. A.Z.M. and N.T.J.M. thank the FCT for contracts CEECIND/01147/2017 and 2021/00711/CEECIND, respectively. N.T.J.M. and A.Z.M. were also supported by MCIN “Ramón y Cajal” contracts (RYC2021-031253-I and RYC2019-026885-I, respectively).

How to cite: Jiménez-Morillo, N. T., Guiomar, N., Miller, A. Z., De la Rosa, J. M., and González-Pérez, J. A.: Molecular characterisation of fire-affected soil organic matter by a 5th generation wildfire in SW-Portugal, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2255, https://doi.org/10.5194/egusphere-egu23-2255, 2023.

X3.81
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EGU23-3581
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ECS
Xu Liu, Roland Bol, Tingting An, Yaocen Liu, Hongbo Wang, Chang Peng, Shuangyi Li, and Jingkuan Wang

Plastic film mulching is a common agricultural management to increase crop yield in the dry and cold regions. The improved soil hydrothermal environment under mulching conditions could change soil microbial activities and soil aggregation, thereby affecting soil organic carbon (C) sequestration. However, it remains not clear that how mulching regulates microbial necromass C accumulation and distribution within soil aggregates, especially under different fertilizer applications. We analyzed the contents of fungal and bacterial necromass C (taking amino sugar as biomarkers) and their contributions to organic C within soil aggregates under mulching combined with different fertilization treatments (no fertilization, CK; inorganic fertilizer application, IF; and manure fertilizer application, MF) in a 900-day in-situ field experiment. On day 360, the contents of fungal and bacterial necromass C within macroaggregates were 25% and 12% higher in the mulching combined with IF treatment, and were 20% and 32% higher in the mulching combined with MF treatment relative to the corresponding no-mulching treatments, respectively. On day 900, the mulching combined with CK and IF treatments decreased microbial necromass C content within soil aggregates, while the mulching combined with MF treatment promoted microbial and fungal necromass C accumulation within macroaggregates (>0.25 mm), compared with the corresponding no-mulching treatments. Mulching increased the fungal/bacterial necromass C ratio within macroaggregates on day 900, but decreased this ratio within microaggregates during the whole incubation period compared with the corresponding no-mulching treatments. Moreover, microbial necromass C occupied 28%–43% and 40%–56% of organic C within macroaggregates and microaggregates on day 900, respectively. Overall, mulching combined with the application of manure fertilizer greatly promoted microbial necromass C accumulation, and thus increased organic C sequestration within macroaggregates.

How to cite: Liu, X., Bol, R., An, T., Liu, Y., Wang, H., Peng, C., Li, S., and Wang, J.: Plastic film mulching combined with manure fertilizer application promotes microbial necromass carbon accumulation within soil macroaggregates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3581, https://doi.org/10.5194/egusphere-egu23-3581, 2023.

X3.82
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EGU23-2772
Boris Jansen

Lipids from the wax layers of plant leaves and plant roots as preserved in soils and sediments have been used for decades as proxies for environmental reconstructions. In particular the n-alkanes of higher chain-lengths (ca. C25-C37) are used to this end. The past decade has seen an increased research attention for the use of plant lipids as molecular proxies. This includes an emerging interest in applications aimed at unravelling the dynamics of soil organic matter (SOM) rather than answering purely palaeo-ecological questions[1] as well as in reconstructing multiple environmental factors at once. Here I highlight these developments via two examples of recent work by our group. In the first example we applied analysis of n-alkanes and n-alcohols preserved in plaggic Anthrosols to reconstruct the origin of the plant material that was used as the stable fillings that were applied to fertilize the soils in this unique agricultural system. In the second example we examined plant derived n-alkanes preserved in soils along an altitudinal transect in the Ecuadorian Andes as part of a coupled reconstruction of palaeo-vegetation and palaeo-climate. I discuss both the exciting new insights gained as well as the challenges that still remain.

References

[1] J.M. van Mourik, T.V., Wagner, J.G. de Boer, B. Jansen, (2016). The added value of biomarker analysis to the genesis of plaggic Anthrosols; the identification of stable fillings used for the production of plaggic manure. SOIL, 2, 299-310

[2] B. Jansen, H. Hooghiemstra, S.P.C. de Goede, J.M. van Mourik, (2019). Chapter 5 - Biomarker analysis of soil archives, Eds. J.M. van Mourik, J.J.M. Van der Meer, Developments in Quaternary Sciences, 18: 163-222

[3] M.L. Teunissen van Manen, B. Jansen, F. Cuesta, S. León-Yánez, S., W.D. Gosling, (2020). From leaf to soil: n-alkane signal preservation, despite degradation along an environmental gradient in the tropical Andes. Biogeosciences, 17, 5465-5487

How to cite: Jansen, B.: Plant lipids as proxies to trace the origin and dynamics of soil organic carbon, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2772, https://doi.org/10.5194/egusphere-egu23-2772, 2023.

X3.83
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EGU23-3868
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ECS
Tatjana Carina Speckert and Guido Lars Bruno Wiesenberg

In alpine areas of the European Alps, many of the pastures are no longer economically profitable and are converted into forests (Bolli et al., 2007). Afforestation on former pastures affects soil organic matter (SOM) dynamics through alteration of quality and quantity of root and aboveground biomass litter input. Compared with pasture OM, forest OM is less decomposable and characterized by increased C:N ratio as well as increased lignin concentration (Hiltbrunner et al., 2013). Therefore, it could be expected that long-term afforestation on a centennial scale may have a severe impact on SOM dynamics, an aspect that remains so far unknown as most of the earlier studies focused on successions between 30 and 50 years (Vesterdal et al., 2002).

In the current study, we aimed to identify the major sources of SOM in a subalpine afforestation sequence (40-130 years) with Norway spruce (Picea abies L.) on a former pasture in Jaun, Switzerland. Therefore, we combined plant- and microorganism-derived molecular proxies from several compound classes such as free-extractable fatty acids and phospholipid fatty acids.

We observed a decline in soil organic carbon (SOC) stock (9.6 ± 1.1 kg m-2) after 55 years and a recovering of the SOC stock 130 years (12.7 ± 0.9 kg m-2) after afforestation. Overall, there is no alteration of the SOC stock in the mineral soil following afforestation of former pasture (13.3 ± 0.9kg m-2) after 130 years. But if we consider the additional SOC stock accumulated in the organic horizons (between 0.8 and 2 kg m-2), the total SOC stock slightly increased, although OM in organic horizons is less stabilized than mineral-bound OM. An increase of the C:N ratio in the Oi-horizon with increasing forest age (40yr: 36.9 ± 2.6; 55yr: 40.9 ± 4.1; 130yr: 42.4 ± 6.6) reflects the alteration in litter quality towards poorly decomposable compounds in older forests. In addition, preliminary results show an increase in the abundance of Gram+ (+3%) and Gram- bacteria (+6%), especially in the young (40yr) forest. Thus, the bacterial community seems to proliferate in the early succession before the fungal-dominated community takes over. Thus, the change in SOM source and quality following afforestation may not result in considerable stock changes, but results in better stability of SOM in the mineral soil.

References

Bolli, J. C., Rigling, A., Bugmann, H. (2007). The influence of changes in climate and land-use on regeneration dynamics of Norway spruce at the treeline in the Swiss Alps. Silva Fennica, 41, 55.

Hiltbrunner, D., Zimmermann, S., Hagedorn, F. (2013). Afforestation with Norway spruce on a subalpine pasture alters carbon dynamics but only moderately affects soil carbon storage. Biogeochemistry, 115, 251-266.

Vesterdal, L., Ritter, E., Gundersen, P. (2002). Change in soil organic carbon following afforestation of former arable land. Forest Ecology and Management, 169, 137-147.

How to cite: Speckert, T. C. and Wiesenberg, G. L. B.: Alterations of soil organic matter following 130 years of afforestation assessed by molecular markers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3868, https://doi.org/10.5194/egusphere-egu23-3868, 2023.

X3.84
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EGU23-6229
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ECS
Łukasz Musielok, Mateusz Stolarczyk, Anna Rudnik, and Krzysztof Buczek

The sequestration of carbon in the form of organic compounds in the soil is considered one of the main strategies for mitigating climate change. Mountain ecosystems have a great potential to store soil organic carbon (SOC) due to relatively lower temperatures and higher precipitation, which slow down the rate of organic matter decomposition. However, mountains are also regions particularly vulnerable to changes caused by direct and indirect human activity, in particular climate change and land cover change. All these changes have an impact on soil properties and thus on SOC stocks and their stability. One of the changes that has been particularly evident in mountainous regions in recent decades is the rapid succession of forests over grasslands, due to the land abandonment and the effects of global warming. In addition, the soil cover of mountainous regions is characterized by a large natural diversity of soil-forming processes, which is reflected in differences in the SOC sequestration potential. Thus, the aim of this research was to determine the effect of different soil-forming processes compared to different land cover on SOC stock and SOC stability. 
The SOC stock was measured in soils subjected to various soil-forming processes (podzolization, brunification, peat accumulation) and with different land cover (ancient forests, succession forests, meadows) in three similar study areas in the Carpathians (S Poland). The highest SOC stocks in the first 30 cm of soil were found in ancient forests (between 4.2 kg m-1 and 8.8 kg m-1) and the lowest in meadows dominated by tall-grass communities (1.3–2.0 kg m-1). The SOC stock was significantly higher in Podzols than in Cambisols and Histosols; however, most of the soils subjected to podzolization were found in forests. In addition, in mineral soils with contrasting pedogenic pathways (Podzols and Cambisols) soil organic matter fractionation was carried out. The preliminary results indicate that Podzols are characterized by much higher SOC content outside water-stable aggregates and in light fractions (particulate organic matter), which suggests relatively a weaker stability of organic matter in this type of soils than in Cambisols.
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 952327 (HES-GEO) and has been supported by a grant from the Priority Research Area Antropocene (Young Labs) under the Strategic Programme Excellence Initiative at Jagiellonian University.

How to cite: Musielok, Ł., Stolarczyk, M., Rudnik, A., and Buczek, K.: The role of soil-forming processes and changes in land cover in the storage and stabilization of soil organic carbon - preliminary results from the Carpathians (Southern Poland), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6229, https://doi.org/10.5194/egusphere-egu23-6229, 2023.

X3.85
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EGU23-6849
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ECS
|
Amicie Delahaie, Lauric Cécillon, Claire Chenu, Dominique Arrouays, Line Boulonne, Claudy Jolivet, Céline Ratié, Nicolas Saby, Marija Stojanova, Antonio Bispo, Manuel Martin, Pierre Arbelet, Jussi Heinonsalo, Christopher Poeplau, Kristiina Karhu, Pierre Roudier, Samuel Abiven, Lorenza Pacini, and Pierre Barré

Assessing soil organic carbon biogeochemical stability is critical for estimating future changes in soil carbon stocks. Several methods for the assessment of soil organic carbon (SOC) biogeochemical stability have been proposed but very few can be implemented on large sample sets. Indeed, to date, only simple physical fractionation protocols (e.g. Lavallee et al., 2020) and Rock-Eval® thermal analysis techniques (Delahaie et al., 2022, SOIL discussion) have been implemented on data sets larger than a few hundred samples. Simple fractionation techniques allow separating a particulate organic carbon fraction (POC; considered labile) and an organic fraction associated with minerals (MaOC; considered more stable). Regarding thermal analyses, Rock-Eval® results associated to the PARTYsoc machine-learning model (Cécillon et al., 2021) provide a measure of the active (mean residence time of ca. 30 years) and centennially stable SOC fractions.

In this study, we present the results of physical fractionations performed on ca. 1000 samples and thermal analyses performed on ca. 2000 samples from French mainland topsoils (RMQS program). We compare the amount and the drivers of each fraction. Our results show that most of the MaOC fraction is not stable at a centennial timescale. However, we show using a Random Forest model that the MaOC content and the centennially stable SOC content are similarly influenced by a common set of drivers: clay, pH and climatic conditions (mean annual temperature and mean annual precipitation). Finally, we discuss the complementarity of these two types of relatively high-throughput fractionation protocols.

 

References

  • Cécillon, L., Baudin, F., Chenu, C., Christensen, B. T., Franko, U., Houot, S., Kanari, E., Kätterer, T., Merbach, I., van Oort, F., Poeplau, C., Quezada, J. C., Savignac, F., Soucémarianadin, L. N., & Barré, P. (2021). Partitioning soil organic carbon into its centennially stable and active fractions with machine-learning models based on Rock-Eval® thermal analysis (PARTY SOC v2. 0 and PARTY SOC v2. 0 EU). Geoscientific Model Development14(6), 3879-3898.
  • Delahaie, A. A., Barré, P., Baudin, F., Arrouays, D., Bispo, A., Boulonne, L., Chenu, C., Jolivet, C., Martin, M. P., Ratié, C., Saby, N. P. A., Savignac, F., & Cécillon, L. (2022). Elemental stoichiometry and Rock-Eval® thermal stability of organic matter in French topsoils. EGUsphere, 1-31.
  • Lavallee, J. M., Soong, J. L., & Cotrufo, M. F. (2020). Conceptualizing soil organic matter into particulate and mineral‐associated forms to address global change in the 21st century. Global Change Biology26(1), 261-273.

How to cite: Delahaie, A., Cécillon, L., Chenu, C., Arrouays, D., Boulonne, L., Jolivet, C., Ratié, C., Saby, N., Stojanova, M., Bispo, A., Martin, M., Arbelet, P., Heinonsalo, J., Poeplau, C., Karhu, K., Roudier, P., Abiven, S., Pacini, L., and Barré, P.: Complementarity and drivers of thermal and physical soil organic carbon fractions at the scale of mainland France, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6849, https://doi.org/10.5194/egusphere-egu23-6849, 2023.

X3.86
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EGU23-7982
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ECS
Beatrice Giannetta, Antonio G. Caporale, Danilo Oliveira De Souza, Paola Adamo, and Claudio Zaccone

Future long-term space missions beyond Low Earth Orbit (e.g., to Mars) depend on the development of bioregenerative life support systems able to produce food crops based on in situ resource utilization. Mars regolith potentially contains most of the essential nutrients for plant growth, except for organic matter (OM). Several strategies and treatments can be applied to improve nutrient deficiency of simulants and enhance their performance as plant growth substrates. Although Mars regolith simulants have been characterized by mineralogical, physico-chemical and hydraulic properties, no data are available to date in the scientific literature about the stabilization of exogeneous OM by minerals, including iron (Fe) oxides, over time.

This study aims at understanding the mineral transformation and OM turnover in the early stages of terraforming. The Mojave Mars Simulant MMS-1, alone (R100) and with a commercial compost 70:30 v:v (R70C30), was compared to a fluvial sand, alone and with compost (S100 and S70C30). Potato was grown on these substrates for 99 days in greenhouse. Samples were fractionated, obtaining particulate OM (POM) and mineral associated OM (MAOM), andcharacterized for total nitrogen and organic carbon (OC), total element concentration (ICP-OES) and by Fe K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS).

In the whole medium, OC increased in S70C30 (10×) and R70C30 (25×). As expected, most of the OC accumulated in the POM fraction of both growing media (10× in S70C30 and 20× in R70C30), while OC in the MAOM was 3-times higher in R70C30 than in S70C30. Chlorite, smectite and goethite were the main Fe species in S100, according to XANES, while Fe(III)-OM was found in both fractions of S70C30. Moreover, according to EXAFS, hematite occurred in POM, whereas goethite in MAOM. XANES revealed the occurrence of smectite, maghemite and ferrihydrite in R100, and of nontronite and hematite in the MAOM and POM, respectively.

Revealing Fe species involved in the formation of organo-mineral interactions will help to identify the main critical aspects and future challenges related to sustainable space farming improving the in-situ use of Martian resources.

How to cite: Giannetta, B., Caporale, A. G., Oliveira De Souza, D., Adamo, P., and Zaccone, C.: Formation of organo-Fe (oxyhydr)oxide interactions during the first stages of Martian regolith simulant terraforming, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7982, https://doi.org/10.5194/egusphere-egu23-7982, 2023.

X3.87
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EGU23-8035
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ECS
Ying Wang, Anna Gunina, and Yakov Kuzyakov

Following the developed concept of carbon (C) flows during soil organic matter (SOM) formation, from which the probable C pathways between the aggregates and SOM fractions can be suggested based on the natural changes of the 13C/12C ratios, we have prepared the review based on 42 publications. The data were collected from the existing databases using the following keywords: “soil organic matter fractions and 13C”, “density fractionation and 13C”, and “soil aggregates and 13C”; publications contained the data from forest, shrubland, grassland, and cropland ecosystems that were located in the Temperate, Mediterranean, subtropical and tropical climatic zones were chosen; only the top 20 cm were considered. Besides the δ13C data, the main soil properties, including pH, total C and nitrogen contents, texture, and the dominant type of soil minerals, were collected. All data for the isotopic composition of aggregates (>2000, 250-2000, 52-250, and <53 µm) and density fractions (<1.4, 1.4-1.6, 1.8-2.0, and >2.2 g cm-3) were normalized to the δ13C values of bulk soils. The preliminary analyses have shown that the isotopic composition of density fractions separated from the soils allocated in temperate and Mediterranean climates followed the previously established order, namely was getting heavier with the increase of particle densities. In contrast, density fractions separated from the soils of subtropical and tropical zones did not show prominent trends, or isotopic composition showed the enrichment in 12C with increased particle density. The isotopic composition of fractions separated from forest soils was also found with more minor variations compared to cropland and grassland. The data related to the probability of C flow between the density fractions and aggregates during SOM formation were also calculated and will be presented, as well as the concept explaining the effect of land use and climatic variables on the changes of the isotopic composition of density fractions and aggregates.

How to cite: Wang, Y., Gunina, A., and Kuzyakov, Y.: 13C natural abundance for analysis of steps of organic carbon transformation in soil: application for various ecosystems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8035, https://doi.org/10.5194/egusphere-egu23-8035, 2023.

X3.88
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EGU23-13825
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Highlight
Karen Vancampenhout, Judith Schellekens, Sascha Nijdam, Keunbae Kim, Maria I.J. Briones, Bart Muys, Ellen Desie, and Boris Jansen

European and Flemish climate-change policies aim to enhance carbon (C) storage in soils of conservation areas, including natural areas such as forests, grasslands and wetlands. Soil capability and condition however may impact C persistence and material cycles in soils, and therefore the sustainability of this policy effort, by making soil C stocks more vulnerable to climatic anomalies, shocks and disturbances. Edaphic limitations in terms of nutrients, acidity, temperature or moisture availability have been shown to affect soil C persistence, but processes behind this effect remain elusive and poorly quantified.

In this contribution, we therefore present several case studies in western European forests and wetlands, where we assess how the molecular composition of several soil organic matter fractions varies along gradients of soil cover, edaphic conditions and perturbation intensity. Furthermore, by comparing different fractions and markers, we evaluate the suitability of different methods to evaluate changes in soil carbon dynamics, as a tool to predict the potential impact of anthropogenic stresses and management interventions on soil carbon persistence.

How to cite: Vancampenhout, K., Schellekens, J., Nijdam, S., Kim, K., Briones, M. I. J., Muys, B., Desie, E., and Jansen, B.: How does edaphic context affect soil organic matter persistence?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13825, https://doi.org/10.5194/egusphere-egu23-13825, 2023.

X3.89
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EGU23-15659
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ECS
Shuhui Wang, Nan Sun, Shuo Liang, Shuxiang Zhang, Jeroen Meersmans, Gilles Colinet, Minggang Xu, and Lianhai Wu

Enhancing soil organic carbon (SOC) stocks through fertilization and crop rotation will contribute to sustaining crop productivity and mitigating global warming. Although it is known that cropping systems may affect SOC stocks by influencing the balance between C input and C decomposition, only few studies focused on the impact of different rice cropping systems on SOC stock changes in paddy soils. In this study, we analyzed the differences in SOC stocks and their driving factors in the topsoil (0–20 cm) with various fertilization measures in two rice-based cropping systems (i.e. rice-wheat rotation and double rice rotation systems) over the last four decades from seven long-term experiments in the Yangtze River catchment. The treatments include no fertilizer application (CK), application of chemical nitrogen, phosphorus and potassium fertilizers (NPK) and a combination of NPK and manure (NPKM). Results showed that during the last four decades, the topsoil SOC stock significantly increased by 8.6 t ha-1 on average under NPKM treatment in rice-wheat system and by 2.5–6.4 t ha-1 on average under NPK and NPKM treatments in double rice system as compared with CK. A higher SOC sequestration rate and a longer SOC sequestration duration were found in NPKM treatment than that in NPK treatment in both cropping systems. The highest relative SOC stock percentage (SOC stock in fertilized treatments to CK) was observed under the NPKM treatment in both cropping systems, though no significant difference was found between these two cropping systems. However, the fertilization-induced relative increase of the SOC stock was 109.5% and 45.8% under the NPK and NPKM treatments, respectively in the rice-wheat system than that in the double rice system. This indicates that the rice-wheat system is more conducive for SOC sequestration. RF and SEM analyses revealed that the magnitude and influencing factors driving SOC sequestration varied between two systems. In the double rice system, continuous flooding weakens the influence of precipitation on SOC sequestration and highlights the importance of soil properties and C input. In contrast, soil properties, C input and climate factors all have important impacts on SOC sequestration in rice-wheat system. This study reveals that the rice-wheat system is more favorable for SOC sequestration despite its lower C input compared to the double rice system in China’s paddies.

How to cite: Wang, S., Sun, N., Liang, S., Zhang, S., Meersmans, J., Colinet, G., Xu, M., and Wu, L.: SOC sequestration affected by fertilization in rice-based cropping systems over the last four decades, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15659, https://doi.org/10.5194/egusphere-egu23-15659, 2023.

X3.90
|
EGU23-12386
Diana Hofmann, Gisela Preuss, Pietro Fontana, and Christian Mätzler

As a result of global warming, now evident also in temperate latitudes, longer periods of snow-free winters, instead with plenty of precipitation are becoming increasingly common. If the temperatures then fall below freezing point, one can, with a little luck, discover hair ice - hair-like, flexible structures reaching up to 10 cm in length without any ramifications.

This natural phenomenon, already described in 1918 by Alfred Wegener, was a mystery for a long time. Only in the 21st century a fungus (Exidiopsis effusa) was discovered as the causative agent [1].

Hair ice develops exclusively on rotten hardwoods on/in which this fungus is present, at high humidity, preferably windless, and temperatures slightly below freezing. Once infected, corresponding branches can be repeatedly elicited hair-rise growth under optimal conditions (field & climate chamber). Hair ice, unlike frost needles, arises from the base. At the onset of hair-ice melt a very thin fibre becomes apparent, which carries brownish water drops. Melting water samples show complex mass spectra similar to dissolved organic carbon e.g. from terrestrial/ marine waters, soil extracts or aerosols.

Hair ice samples of various tree species were desalted, concentrated by solid phase extraction and subsequently analyzed by flow injection analysis in a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer, equipped with an ESI source and a 7 T supra-conducting magnet (LTQ-FT Ultra, ThermoFisher Scientific) - the key technique for the analysis of complex samples, simultaneously providing molecular level details of thousands of compounds. As main result, complex, but almost identical spectra were found. For their chemical characterization van Krevelen diagrams, typical to classify samples regarding polarity and aromaticity were plotted. By comparison with references biopolymer substance classes were derived. As result, lignin and tannin could be detected as the main hair-ice substance classes, supposed to act as freezing catalyst as well as recrystallization inhibitor.

For the question, if and what happens in summer, we sampled in several years guttation droplets, too – of this fungus and for comparison from a fungus of another family. Both samples were carbon riche, but only the samples from Exidiopsis effusa show such a complex DOC-spectrum, but in contrast to hair ice peak depleted with mainly tannin assignment.

Popular scientific publications have led to an increasing interest in hair ice and related phenomena in recent years. We have received spectacular photos of various ice structures, followed by first samples of needle ice and ice ribbons. After initial measurements for their C content, HPLC-MS investigations still with a triple quadrupole mass spectrometer have been performed. For final analyses a cooperation with a FTICRMS working group is now sought.

[1] D. Hofmann, G. Preuss and C. Mätzler (2015) Biogeosciences 12: 4261–4273

How to cite: Hofmann, D., Preuss, G., Fontana, P., and Mätzler, C.: Hair-ice, fungal guttation droplets, ice ribbons and needle ice from a chemical perspective, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12386, https://doi.org/10.5194/egusphere-egu23-12386, 2023.

X3.91
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EGU23-13410
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ECS
Layla M. San-Emeterio, José Antonio González-Pérez, Rafael López-Núñez, Lorena M. Zavala, Yakov Kuzyakov, and Anna Gunina

 Carbon isotopic composition of soils subjected to C3–C4 vegetation change can be used to estimate C turnover in bulk soil, but more specifically in soil organic matter (SOM) pools with fast and intermediate turnover rates. Analysis of phospholipid fatty acids (PLFA) has been widely used to evaluate rapid changes in soil microbial populations. In this study we investigated the effect a C3–C4 vegetation change experiment, along with a sustainable practice versus tillage soil microbial community composition as well as their isotopic C composition by compound-specific PLFA 13C analysis.

Soils (Calcaric Cambisol) from an agricultural trial located in Southern Spain were sampled, which are characterized by high carbonate content (~27%) low fertility and low organic matter contents. The experimental trial consisted in replacing former C3 vegetation by maize crop (C4 plant) since February 2017, comprising two different treatments: A) after harvesting, maize surpluses were chopped and applied to surface soil, hereafter known as aboveground biomass “A” treatment; B) the total part of maize plant was left out after harvesting, including the roots, known as belowground biomass “B” treatment. Moreover, untreated soil was taken as control plots, “C”, where soil was tillaged and kept the same isotopic signature as the former land use. Composite soil samples (0-5 cm) were taken.

PLFA profiles revealed a great abundance of bacterial activity, comprising gram-positive and gram-negative, along with branched (i-14:0, i-&a- 15:0, i:16:0, i-&a- 17:0) and mono- and polyunsaturated groups (16:1n7, 18:2n6, 18:1w9c and 18:1w7c). Significant increase of fungal abundance in “B” treatment may indicate decrease of litter decomposability, which facilitates fungal development. The “A” treatment also indicated a greater microbial activity, though intermediate in most of the groups compared to control. Lastly, in control plots, it is observed a significant decrease of G- bacteria, which correlates well with lower C content. indicates the low amount of easily available root exudates (Gütlein et al., 2017), which are the preferred C source for this microbial group. On the other hand, significant 13C enrichment of PLFAs varied across microbial groups. “B” plots showed greater 13C contribution for fungi, whereas the application of aboveground biomass contributes greatly to the gram-positive and gram-negative bacteria. PLFA 13C mean residence times were much longer for bacteria compared to the rest of microbial groups.

Our results indicate that the addition of biomass in SOM-depleted agricultural soils resulted an increase of microbial biomass, denoting a predominant bacterial activity. Over 5 years of C3-C4 vegetation change, fungi and actinobacteria showed the fastest turnover rates compared to bacteria, which appeared to play a major role in the rapid acquisition of C into the soil microbial community. Fungi and actinobacteria appeared to have a delayed utilization of C or to prefer other C sources upon application of grounded biomass. Further discussion will be made on the implications of sustainable practices for enhancing C sequestration under Mediterranean climate.

How to cite: M. San-Emeterio, L., González-Pérez, J. A., López-Núñez, R., M. Zavala, L., Kuzyakov, Y., and Gunina, A.: Turnover of soil organic matter and microbial biomass under C3-C4 vegetation change: implications for carbon sequestration in Mediterranean agricultural soils., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13410, https://doi.org/10.5194/egusphere-egu23-13410, 2023.

X3.92
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EGU23-7186
|
ECS
Anna Gunina and Yakov Kuzyakov

The transformation of “energy to (soil organic) matter’’ has long been the focus of scientific attention, but a definitive conceptual framework does not yet exist. Following the classical definition of energy given by Odum and Odum (1977) and the principles and laws of energy, we have developed an experiment-based review of the complex process of microbial conversion of energy and carbon (C) from litter to soil organic matter (SOM). Based on the transformation rate of plant residues, the amount of plant-derived energy persisting in soil (after one year) ranges from 7 to 20 % of total energy input depending on the plant community (for example, spruce and broadleaf forests and grasslands were taken). This represents 0.8-10 % of the energy already stored in SOM but only adds 0.4-5 % C to the existing SOM pool. We have introduced two new parameters - energy quality representing primarily substance, and energy availability representing the ability of microorganisms to utilize that substance (or pool of substances) under actual soil conditions. According to these parameters, we have assigned the main classes of organic substances to one of the three groups that show the availability of energy stored in microorganisms. When the energy availability is >1, microorganisms gain more energy than invest by the decomposition of organic substances; when energy availability is <1, then energy investment is required for the co-mining of nutrients, and some compounds are unsuitable for energy mining due to low efficiency, and in this case, they will be partially decomposed by co-metabolism (no energy gain). We have estimated the energy investment of soil microorganisms for exoenzyme production and concluded that the disadvantage of enzymatic degradation could explain the ‘stability’ of the SOM because the energy input (investment) required for degradation exceeds the energy gain. Following the linear decrease in energy density (by 106 kJ mol-1 C) of a broad range of organic substances per nominal oxidation state of C (NOSC) unit upon oxidation and experimental data on litter decomposition, we have developed the concept showing changes in the NOSC and the energy content of plant residues during decomposition and formation of SOM. Mineralization, recycling, and accumulation processes control energy and NOSC changes in organic pools. Mineralization processes lead to energy losses and an increase in NOSC, while SOM accumulation increases energy content and decreases NOSC. Recycling can shift both the energy content and NOSC values depending on the environmental conditions of the soil and the quality/quantity of litter input. As a result, the SOM pool is different from the initial litter in the energy content and NOSC. The SOM has a more diverse molecular composition but a narrower range of NOSC values than plant residues, consists of microbial necromass and substances recycled by microorganisms, and contains, on average, substances with a higher energy content than the initial plant residues. Based on the developed concept, we have concluded that plant-derived C and energy that persist in the form of SOM ensure energy fluxes in the soil system.

How to cite: Gunina, A. and Kuzyakov, Y.: Soil organic matter as a mediator of energy fluxes - a new perspective, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7186, https://doi.org/10.5194/egusphere-egu23-7186, 2023.