Atmospheric temperatures are steadily rising on a global scale, with the Arctic region experiencing an alarming rate of increase, double that of the global average. This temperature surge not only signifies anticipated changes but also forecasts a consequential rise in winter precipitation. Within the context of climate change, this leads to a significant upturn in net methane (CH₄) emissions. During winter, augmented snow depth enhances thermal insulation of the underlying soil, subsequently increasing soil moisture upon melting. This results in warmer and wetter soil conditions, fostering an anoxic environment that stimulates methanogenic activity. Furthermore, methane emissions are accelerated through plant-mediated CH₄ transport. Studies propose a potential shift in vegetation communities, favoring vascular species with extensive aerenchyma under warming conditions.

While projections suggest an increase in CH₄ flux with greater winter precipitation, the combined effects of heightened snow cover and the presence of vascular plant species on CH₄ production remain largely unexplored. This study, conducted using snow fences installed since 2017 in Council, Alaska, aims to unravel the legacy effect of deepened snow during winter and plant-mediated transport on soil CH₄ emissions during the growing season (Jul–Aug, 2023). Our investigation involves the analysis of soil CH₄ flux, soil chemical properties, and microbial abundance and communities in both control and high snow depth (HS) conditions, comparing bare soil and Eriophorum angustifolium dominant soil.

Results indicate that deeper snow significantly increased the average CH₄ emission rate from 2.65 to 16.6 mg m^-2 day^-1. The presence of E. angustifolium amplified CH₄ emission strength in both control and HS conditions (63.4 and 116 mg m^-2 day^-1, respectively). Increased CH₄ emissions in HS conditions were primarily driven by enhanced carbon source availability and higher ammonium concentrations. Deeper thaw depth in HS conditions increased carbon source availability, particularly in vegetated soils, promoting methanogenic activity. Higher ammonium concentrations in HS conditions contributed to inhibiting methanotrophs from oxidizing CH₄.

Consistent variations in soil characteristics were observed at a microbial scale, confirming increased methanogenic activity and decreased methanotrophic activity in HS conditions, for both bare and vegetated soil. These findings underscore the synergistic legacy effect of increased CH₄ flux resulting from the complex interaction between deepened snow depth and the presence of vascular species, creating conditions conducive to elevated CH₄ production during the growing season.

How to cite: Kim, J. I., Yun, J., Jung, J. Y., Nam, S. J., Lee, J., and Kang, H.: Increased snow depth and vascular plant species promote Arctic soil methane emissions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6894, https://doi.org/10.5194/egusphere-egu24-6894, 2024.

The interaction between plants and soil plays a decisive role in controlling the formation of soil organic matter (SOM) - a critical factor for the functioning of ecosystems and the mitigation of climate change. Carbon compounds that plants release into the soil as root exudates have important impacts on the stability of SOM and can shift with climate change. Yet, a generalizable understanding of the biotic and abiotic controls on the relationships between plant-soil carbon exchanges and large-scale carbon fluxes and SOM formation is still lacking.

Here, I compile data from different forest ecosystems to illustrate: 1) the response of root exudates in distinct ecozones to species mixing, 2) the impact of drought and recovery on plant-soil interactions, and 3) the quantitative correlation between rhizodeposition and ecosystem carbon uptake, as well as its association with SOM formation.

Observations point to a connection between carbon exudation and root growth, with greater root growth leading to reduced exudation rates and vice versa. However, exudation rates across diverse ecozones were highly responsive to even minor alterations in the sampling method, suggesting careful considerations when comparing datasets from different studies. The rhizosphere showed increased levels of stabilized SOM that endured after drought, suggesting the potential for rhizodeposition to enhance the preservation of soil carbon.

Current data indicates that a substantial fraction of carbon in the atmosphere is allocated towards root exudates, likely serving as a crucial element in the ability of ecosystems to respond to climate change. Understanding plant-soil interactions in a global context requires aligning sampling methods within an ecozonal context.

How to cite: Brunn, M.: Controls of atmospheric carbon transfer to soil by root exudates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-276, https://doi.org/10.5194/egusphere-egu24-276, 2024.

High-arctic tundra-soil ecosystems are particularly sensible to global changes due to their proximity to freezing, snow cover, light availability and scarcity of vegetation. Seasonal dynamic are large in these biomes with a very short vegetation growing season. Hydrological fluctuations in these soils are also important, directly impacting the soil biological activity. Yet, little is known on the seasonal dyanmic in the regulation of microbial functions in high-arctic soils and their impact on greenhouses gas exchanges with the atmosphere. Fluxes of greenhouse gases (CO₂, CH₄ and N₂O) and microbial functions linked to C and N cylcing were assessed at each season along a slope toposequence in high-arctic tundra soils near Ny-Ålesund (Svalbard) and compared with prokaryotic and fungal community structures. Microbial functional diversity exhibited strong seasonal patterns, with most microbial functions acquiring C, N and P enhanced in summer, at the peak of the plant growing season. Seasonal dynamics was also evident for greenhouse gas fluxes but were not consistent across seasons. While CO₂ fluxes were clearly increased in summer, CH₄ fluxes were slightly higher in Autumn, especially in the upslope soils, alike methanogenesis gene abundance mcrA which distinctly increased in both biocrust and soil layer of the upslope site in Autumn. N₂O gas fluxes were clearly higher in both shoulder seasons (i.e. Spring and Autumn), when freeze-thaw cycle are frequents. Seasonal microbial functional changes however did not mirror the prokaryotic and fungal community structure, which were more influenced by the microtopography and the soil depth layers (biocrust vs underneath mineral soil). These findings highlight the intricate relationships between microbial functions, diversity, and environmental factors in high-Arctic soils and underscore the importance of considering both seasonal and microtopography factors in understanding soil microbial dynamics in Arctic ecosystems.

How to cite: Frossard, A. and the Climarctic team (Biodiversa ERANET project): Seasonal changes of microbial functions along high-Arctic tundra soil toposequences, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16701, https://doi.org/10.5194/egusphere-egu24-16701, 2024.

The grassland ecosystems of the Tibetan Plateau have witnessed substantial transformations in recent decades, driven by various global factors, including alterations in temperature and precipitation, nitrogen (N) deposition, and regional effects. Despite documented shifts in species richness and distribution towards higher elevations, there is a scarcity of comprehensive plant and soil data along elevation gradients in alpine grasslands. The intricate interplay of soil properties and nutrient supply on vegetation patterns at high altitudes, particularly the response of the "grass-line" to global warming, remains unexplored. To bridge these knowledge gaps, our research investigated the impacts of global changes, specifically warming and N deposition, and soil properties on soil phosphorus (P) transformation and plant P uptake. Leveraging insights from long-term nutrient addition experiments, random sampling, and open-top chamber experiments along elevation gradients in an alpine grassland on the northeastern Tibetan Plateau, the study delved into soil properties such as texture, bulk density, soil organic carbon (SOC), and soil P fractions. Furthermore, it explores plant and microbial P pools, P acquisition strategies, and biomass. Results revealed that N input had a discernible effect on plant P requirements, particularly under conditions of deficient soil available P. Changes in P acquisition strategies wielded a more substantial influence on community structure and composition than alterations in root traits. The addition of P significantly impacted plant growth, signifying a shift from nitrogen to P limitation with increased N input. Soil properties exhibited variations among sites, while pH remained stable in the 0–10 cm soil depth due to the adequate levels of calcium and magnesium in the soil, which could buffer the impact of N deposition on soil acidification in the grassland ecosystem. Strong positive correlations observed between organic P pools, SOC, and total N underscored the pivotal role of soil organic matter in sustaining soil P reserves. More importantly, P limitation did not emerge as the primary factor propelling grasses to higher elevations; instead, other soil properties and nutrients might play a key role. These findings underscore the importance of specific combinations of soil properties in constraining plant growth on the northeastern plateau, thereby influencing biodiversity and biomass production. This research highlights the factors influencing effective soil nutrients and provides valuable insights for predicting the impact of global changes on the stability and productivity of alpine grassland ecosystems.

How to cite: Cao, Z., Gao, Q., Scholten, T., Kühn, P., He, J., Guan, Z.-H., Ganjurjav, H., Hu, G., and Hu, S.: Exploring the interaction between global changes, soil properties and vegetation patterns on soil phosphorus transformation in alpine grasslands of the Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7359, https://doi.org/10.5194/egusphere-egu24-7359, 2024.

Forest soils have significant potential to mitigate climate change through their ability to store large amounts of organic carbon. However, forests are increasingly subject to natural disturbances such as windthrow, wildfire or disease outbreaks, which threaten the permanence of this large carbon stock. In response to increasing disturbances and ongoing climate change, forests are expected to lose their ability to return to pre-disturbance conditions involving a reorganization of tree species composition and stand structure. If tipping points are crossed, even a complete vegetation shift and conversion to non-forest ecosystems is possible. Here we aimed to assess the sensitivity of forest soil carbon to disturbance and its recovery with contrasting successional trajectories by combining two field studies on soil carbon stocks in windthrown forest stands and a global meta-analysis on the effects of different disturbance agents. Our results along an altitudinal gradient in Switzerland show that mountain forests with high carbon stocks in thick organic layers were particularly sensitive to disturbance by windthrow, losing up to 90% of their carbon stored belowground. In contrast, low-elevation forest soils with thin organic layers and smaller carbon stocks were barely affected. These results are consistent with our meta-analysis, which shows that disturbance-induced carbon losses increase with the size of initial carbon stocks. Boreal and high-elevation forests with large soil carbon stocks are highly sensitive to severe and long-lasting carbon losses due to damage from storms, wildfire, insects, and harvesting, while in most temperate and tropical forests soil carbon stocks recover more rapidly and losses are smaller. Results from a disturbance chronosequence in Austria also suggest that vegetation shifts following forest damage can strongly influence the recovery of soil carbon stocks after disturbance. Disturbed sites that remained in a non-forest, grass-dominated state for three decades accumulated about a third more soil carbon than sites that regenerated with trees. In addition to high litter inputs from herbaceous fine roots at grass-dominated sites, we relate this difference to changes in microbial community structure and function. In conclusion, our results underline that the magnitude and duration of soil carbon losses after disturbance depend on the forest type and site specific soil properties. Moreover, vegetation shifts during succession significantly modify the re-accumulation of soil carbon after disturbance.

How to cite: Mayer, M., Hechenblaikner, F., Baltensweiler, A., James, J., Rusch, S., Didion, M., Walthert, L., Zimmermann, S., Rigling, A., and Hagedorn, F.: Soil carbon storage in response to forest disturbance , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19400, https://doi.org/10.5194/egusphere-egu24-19400, 2024.

Soil CO₂ efflux is one of the largest C fluxes between terrestrial ecosystems and the atmosphere and originates from different sources such as rhizosphere respiration and the mineralization of various soil organic matter components. Alterations of soil respiration induced by environmental changes, such as climate and land use change, can thus affect atmospheric CO₂ levels. Land use regulates soil CO₂ fluxes and their source contributions through various factors such as vegetation type, root density, nutrient input, and management. Soil CO₂ fluxes from different land use types are likely to vary in their susceptibility to climate change induced perturbations. However, a systematic comparison of the age and sources of the soil CO₂ efflux between different land use types remains elusive. Isotopic techniques using radiocarbon (¹⁴C) and stable carbon (¹³C) represent a powerful approach to identify the sources of soil CO₂ fluxes. In this study, we investigated how land use affects the age and sources of soil-respired CO₂ across Switzerland and in different seasons by using radiocarbon and stable isotopic approaches.

We measured in situ rates and isotopic signatures (¹⁴C, ¹³C) of soil-respired CO₂ in summer and winter from 18 sites of six dominant land use types in Switzerland: forests, croplands, managed peatlands (original and covered with mineral soil), and grasslands (lowland and alpine). The sites vary in their physico-chemical soil properties and span a climatic as well as elevational gradient from 400 to 3000 m a.s.l. across Switzerland. We further disentangled source contribution (autotrophic vs. heterotrophic respiration) to total soil respiration for each site by separating ¹⁴C, and ¹³C signatures of CO₂ derived from root and soil incubations.

In summer, the age of in situ soil-respired CO₂ increased from lowland grasslands towards alpine grasslands, forests, croplands, and peatlands. We attribute this pattern to an increase of the mean age of soil organic matter along this trajectory. Additionally, we assume a decreasing contribution of rhizosphere respiration from grasslands to forests and arable land. We found managed peatlands to be hotspots of old carbon release, with the respired CO₂ being around 500 to 1500 years old. Grasslands released the most modern CO₂, in the range of contemporary atmospheric ¹⁴CO₂ levels. Within grassland sites, we observed an increased age of soil-respired CO₂ with increasing elevation (lowland towards alpine) which we attribute to slower C turnover in alpine areas due to cooler climatic conditions. CO₂ respired from forest soils originates from bomb-derived decadial old carbon, indicating a reduced turnover as compared to grasslands. Isotopic data of CO₂ derived from soil and root incubations will provide insights into source contribution.

How to cite: Minich, L., Moreno Duborgel, M., Geissbühler, D., Udke, A., McMackin, C., Wacker, L., Gautschi, P., Egli, M., and Hagedorn, F.: The age and sources of respired CO2 from soils of dominant land use types across Switzerland  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9591, https://doi.org/10.5194/egusphere-egu24-9591, 2024.

Atmospheric nitrogen deposition was artificially increased for 27 years (1995-2022) by sprinkling rain water enriched with NH₄NO₃ (+22 kg ha^-1 y^-1 N) to a small headwater catchment in a spruce (Picea abies) forest growing on gley soils at Alptal (central Switzerland). This treatment was compared to a control in a paired catchment design. Nitrate leaching increased already during the first rain events after starting the treatment and continued to increase within the first 5 years. Later, it increased again markedly after part of trees had been girdled then felled in 2010. As shown by ¹⁵N labelling, most of the added N remained in the soil. In plots receiving the same treatment, this lowered the C/N ratio, changed the composition of the fungal community and tended to reduce the total microbial biomass, the abundance of Collembola and soil respiration. Soil acidification was observed in those plots located on small mounds but was effectively buffered in topographical depressions. Denitrification was clearly increased, but other processes like mineralisation were not significantly affected. Over time, trees took up about 1/10 of the added N and used it mainly to build larger needles. Their growth was slightly improved, presumably by a better use of the light in their relatively open canopy. Both the soil microbiote and the trees showed signs of limitation by other nutrients like P and Mg, but the poor aeration remained the major limiting factor of the gley soils on this site.

How to cite: Schleppi, P.: Fate and effects of nitrogen added in a long-term experiment to a sub-alpine forest in Switzerland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10159, https://doi.org/10.5194/egusphere-egu24-10159, 2024.

How climate and soil properties limit mineral-associated organic carbon (MAOC) accrual under afforestation. Findings from a climate gradient study in warm drylands.

David Yalin, William Mlelwa, Eyal Rotenberg, Dan Yakir and José M. Grünzweig

The efficiency of afforestation in climate mitigation has been a matter of debate in recent years. Specifically, there have been doubts about whether afforestation in drylands can be climate-positive. If afforestation can contribute to accumulation of soil organic carbon (SOC) and to the buildup of the mineral-associated organic C (MAOC) pools this may be a significant contribution to long-term C capturing in dry environments. However, there are still gaps in our understanding of how the interactions between vegetation type and climate affect MAOC storage. Furthermore, studies of MAOC dynamics have often disregarded the finite capacity of soils to store MAOC. In this work, we aimed at bridging these gaps by examining SOC and its partitioning between different soil size fractions in sites planted with Aleppo pine over 50 years ago (PF) as compared to neighboring fallow sites which were not actively forested (NF). This was performed at 16 sites along a climate gradient in Israel (ranging from 250-800 mm in annual precipitation) and differing in soil properties. MAOC in the 0-10 cm and 10-20 cm showed a general trend of increase with precipitation (more statistically significant in PF sites). Calcareous sites (>10% CaCO₃ equivalent) showed lower MAOC concentrations, which may arise from smaller fine-grain soil fraction but also from reduced input from vegetation due to poor nutrient availability. MAOC composed between 37-83% of total SOC with a weak decreasing trend with increasing SOC (regardless of afforestation). The decrease in MAOC/SOC points to possible MAOC saturation at~40 g C kg^-1 soil, a value previously suggested for saturation in European soils. To investigate whether saturation could be limiting MAOC accrual, we examined the saturation limit using topsoil samples (collected at the 0-2 cm depth) selected for high total SOC. In the topsoil fine fraction SOC reached 95 g C kg^-1 soil-fine-fraction, slightly above global reports for soils with high activity clays. Based on these topsoil measurements, MAOC even in the high SOC soils (at 0-10 cm depth), reached less than 70% of its capacity, suggesting that saturation was not a limiting factor. However, density fractionation of the topsoil samples raised questions about whether they truly represent soil capacity to associate organic carbon. In the presentation we will discuss the concept of MAOC capacity in light of these findings and its implications for afforestation in dry climates.

How to cite: Yalin, D., Mlelwa, W., Rotenberg, E., Yakir, D., and Grünzweig, J. M.: How climate and soil properties limit mineral-associated organic carbon (MAOC) accrual under afforestation. Findings from a climate gradient study in warm drylands., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14798, https://doi.org/10.5194/egusphere-egu24-14798, 2024.

Climate change induced warming of soils will have a strong impact on the carbon cycle, especially the decomposition of soil organic matter (SOM) is likely to increase with rising temperature. Alpine regions are especially prone to those changes with earlier and higher expected temperature increase compared to the global average. Carbon cycling in these regions has been also increasingly influenced by land-use changes, such as afforestation, the abandonment of alpine pastures and the resulting bush encroachment, as well as an increasing elevation of the tree line. However, it is still largely unknown how these changes affect the degradation of different compound classes of soil organic matter. A one-year laboratory incubation experiment was carried out to investigate the degradation of SOM at a molecular level.

Two soils with different land-use histories including a soil from an afforested subalpine forest site and a nearby pasture soil from the same site located near Jaun (Canton Fribourg, Switzerland) were incubated under controlled conditions. The incubation was carried out under three different temperatures, the current average growing season temperature (12.5 °C) as a control, as well as two increased temperature treatments of +4 °C (16.5 °C) and +8 °C (20.5 °C) that represent the range of temperature increase expected for Alpine regions under a high emission scenario. To trace the decomposition of organic matter input, ¹³C-labelled plant litter was added to a subset of the incubated samples. The incubation ran for a period of one year with six different sampling times (14, 28, 56, 168, 360 days).

In samples without labelled litter, the bulk carbon (C) concentration decreased for pasture and forest soils from initial C concentrations of 45.5 and 43.3 mg/g, respectively, by 3.3 % and 5.6 % on average. This is also reflected in lignin concentrations, with a decrease of 13.8 % for pasture and 20.2 % for forest soils.

With litter addition, the degradation was higher than for samples without labelled litter for bulk C, lignin as well as for free extractable lipid fractions. The strongest degradation was observed already during the initial phase of the incubation experiment. E.g., a decrease of more than 50% of the ¹³C signal of individual lignin phenols could be observed already during the first 14 days, which indicates a fast degradation mainly of the added litter.

In general, the degradation of individual compounds increased with increasing temperature with the highest degradation being observed for the highest temperature treatment.

Higher temperatures have led to increased degradation of SOM during the laboratory incubation experiment, even in seemingly more recalcitrant compounds as lignin. In alpine regions, an expected rise in temperature can therefore lead to increased decomposition of recalcitrant components of SOM. In addition, increased degradation in forest compared to pasture soils indicates a higher vulnerability of forest than pasture soils in alpine regions, which points to complex responses of SOM cycling following land-use changes such as afforestation.

How to cite: Püntener, D., Speckert, T. C., Thomas, C. L., and Wiesenberg, G. L. B.: Temperature-dependent Degradation of Soil Organic Matter in an Incubation Experiment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10828, https://doi.org/10.5194/egusphere-egu24-10828, 2024.

Assessing climate change effects on soils usually involves conducting comparisons of biogeochemical processes under projected future conditions against ambient ones. This is typically achieved through incubation experiments utilizing today’s soils. However, a significant limitation of relying on present-day soils is the oversight of the ongoing evolution of soils in terms of geochemistry and microbiology over several years in response to future climatic conditions.

This study challenges the traditional approach by asking: Can climate change experiments accurately replicate future biogeochemical processes and their outcomes using soils with today's geochemistry and microbiome? To address this question, we collected oxic and anoxic soils from experimental climate studies, exposed to both present-day and concurrently predicted future climate conditions. We reintroduced these soils with varying climate histories to both sets of climatic conditions (ambient/future), employing a crossover design. This unique experimental setup enables us to discern which biogeochemical processes are influenced by the soil’s historical context and which are contingent on the specific incubation conditions imposed.

For the oxic soil, with an eight-year night temperature increase of up to 2°C coupled with altered precipitation patterns (a 10% increase in spring and autumn, a 20% decrease in summer), our findings indicate a notable influence of soil history on soil respiration, surpassing impacts of the incubation climate. This implies that the historical context of the soil wielded a stronger influence than the specific incubation conditions in shaping organic matter pools and turnover within oxic soils. Conversely, iron(III) reduction, as a pivotal indicator of geochemical evolution, was primarily regulated by incubation conditions related to soil moisture rather than being dictated by the soil’s historical background.

In the anoxic soil, with a one-year treatment of temperature increases of 4°C and doubled atmospheric CO₂, a more pronounced reductive iron(III) dissolution occurred in the soil with the future climate history compared to soils with today’s history. This observation suggests that, over the course of soil history, a larger pool of reducible iron became available to microorganisms in soil with a future climate history than in those with today's soil history. Interestingly, the release of arsenic from these ageing iron minerals was higher in soils with a future climate history compared to today’s soils. This indicates that studies investigating arsenic mobility and its impact on crop performances using present-day soils may underestimate the potential environmental consequences of arsenic. Additionally, the history of future soil conditions favoured greater microbial growth than the incubation conditions. However, soil respiration deviated from this pattern, with a predominant increase attributed to the future incubation climate and, to a lesser extent, influenced by soil history.

Complementary data on compositional variations in soil organic matter (LDI-FT-ICR MS) and microbial community (16S rRNA amplicon sequencing) assessing differences based on soil history and short-term experimental conditions will also be presented for both soils.

Our findings indicate that soil history plays a differential role for biogeochemical processes and outcomes of the future with biogeochemical outcomes and temporal trajectories possibly being over- or underinterpreted when studies on climate change utilize present-day soils.

How to cite: Pienkowska, A., Kosel, P., Drabesch, S., Lechtenfeld, O., Simon, C., Fendorf, S., Reitz, T., and Muehe, E. M.: Do we obtain valid data from climate change incubations using soils of today?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11139, https://doi.org/10.5194/egusphere-egu24-11139, 2024.

Achieving climate targets requires mitigation against climate change, but also understanding of the response of land and ocean carbon systems. In this context, global soil carbon stocks and its response to environmental changes is key. In this presentation, the global soil carbon feedbacks to both changes in atmospheric CO₂ and associated climate changes for Earth system models (ESMs) in CMIP6 are quantified. A standard approach is used to calculate the carbon cycle feedbacks, which are defined as soil specific carbon-concentration (β_s) and carbon-climate (γ_s) feedback parameters. Amongst CMIP6 ESMs, it is shown that the sensitivity to CO₂ is found to dominate global soil carbon changes at least up to a doubling of atmospheric CO₂. However, the sensitivity of soil carbon to climate change is found to become an increasingly important source of uncertainty under higher atmospheric CO₂ concentrations.

How to cite: Varney, R., Cox, P., Friedlingstein, P., Chadburn, S., and Burke, E.: Soil carbon-concentration and carbon-climate feedbacks in CMIP6 Earth system models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11870, https://doi.org/10.5194/egusphere-egu24-11870, 2024.

Core-scale soil carbon fluxes are ultimately regulated by pore-scale dynamics of substrate availability and microbial access, which are strongly influenced by soil water. The global water cycle is intensifying, and moisture extremes like drought and flood are increasing in frequency and intensity. It is therefore important to understand how these changing moisture regimes will affect carbon availability and fluxes in soils. We conducted two laboratory incubation experiments to investigate how drought and flood altered soil carbon availability and mineralization. Antecedent moisture conditions were found to be an important control on soil carbon availability, as soil respiration and carbon availability showed distinct hysteresis during drying and rewetting. Additionally, when comparing impacts of drought and flood across different soils, the soil carbon response was not consistent across sites, and was influenced by site-level pedological and environmental factors such as soil texture and historic stress conditions. These studies highlight the importance of pore-scale physicochemical and biochemical properties when studying soil biogeochemical transformations at the core scale.

How to cite: Patel, K., Bailey, V., Bond-Lamberty, B., Fansler, S., Myers-Pigg, A., and Smith, A. P.: Hydrological controls on soil carbon dynamics: from pores to cores, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6587, https://doi.org/10.5194/egusphere-egu24-6587, 2024.

In developing countries, the economy is commonly based on agriculture, and combined with the demand for the expansion of urban centers, large natural territories have been converted into agricultural and urban areas. In Brazil, the productive engine for agricultural activities is mainly situated in the wooded Cerrado biome, which has undergone agricultural expansion that led to almost 50% of the native forest vegetation. Besides being well know the role land cover plays on water fluxes, there is still requirement to further coupling with climate change component. The predicted alteration of climate patterns under future climate change scenarios can potentially alter infiltration/runoff rates, aquifer recharge, and soil-water availability for plants, impacting plant growth and development. In this research, we evaluated changes in water fluxes (surface flux, evaporation, soil-water storage, infiltration, bottom flux, and root uptake) at intermediate (2040-2070) and distant future (2071-2100) due to climate change occurring in the Brazilian Cerrado Biome. The two specific objectives included the calibration and validation of the Hydrus model through an eight-year soil moisture monitoring on experimental plots in Cerrado, pasture, and sugarcane areas (i), as well as the incorporation of outcomes from climate change models (10 CMIP6 models under SSP2-4.5 and SSP5-8.5 scenarios) into the validated Hydrus models (ii). The predicted water fluxes were made by Hydrus, a computational that uses the finite element method to achieve the numerical solution of the Richards Equation to describe saturated/unsaturated flows. The study is composed of experimental plots (100 m² and 9% slope) with weather variables and soil moisture fluctuations from 2011 to 2018. We tested different parameter combinations during calibration and found that for sugarcane and pasture simulations plots, saturated soil water content, parameter N in the soil retention function, and saturated hydraulic conductivity were the most sensitive ones and led to better calibration statistics. The first observation is that we cannot point out that climate change is affecting preferentially superficial fluxes rather than sub-superficial ones since each variable has a singular behavior under climate scenarios. Nonetheless, climate change poses a higher threat to certain water fluxes than others, being at a hierarchical (bottom-top) sequence: soil-water storage, bottom flux, infiltration, surface flux, evaporation, and root uptake. The same sequence is applied to all land cover, differing in magnitudes. Comparing the actual water fluxes due changes in to land cover with those due to climate, we concluded that the intensification of land cover change poses a higher risk of water fluxes than those predicted due to climate change. The intricate relationship between land cover and climate necessitates a nuanced understanding to anticipate and mitigate the consequences on water fluxes.

How to cite: Schwamback, D., Wendland, E., Berndtsson, R., and Persson, M.: Water fluxes under threat by changes in land cover and climate in the Brazilian Cerrado biome, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12234, https://doi.org/10.5194/egusphere-egu24-12234, 2024.

The impact of warming on the carbon cycling of terrestrial ecosystems determines the carbon cycle-climate change feedback and the future climate. Specifically, how warming affects the carbon cycling in deep soils (>20 cm) remains uncertain, because most of existing manipulation experiments only warm surface soils (<20 cm). In 2018, we started a Total-soil-warming Experiment in an Alpine Meadow (TEAM). We have maintained year-round warming (+4 oC) of the whole soil profile (0-100 cm) in an alpine meadow on the Tibetan Plateau. We anticipate running the experiment for >10 years. I will present an overview and some of the results of TEAM during the first 5 years (2018-2023), including treatment effects on plant communities, soil and microbial properties, and ecosystem processes.

First, warming did not significantly affect plant richness and diversity, and above- and belowground biomass and productivity, but changed the relative proportion of plant functional groups in aboveground biomass (decrease in legumes and increase in forbs). Second, soil physico-chemical properties (including organic carbon and total nitrogen concentrations) and microbial community characteristics (such as carbon use efficiency, community diversity and composition) throughout the profile were mostly unresponsive to warming, although they changed dramatically (e.g. declined) with depth. Third, warming significantly stimulated soil respiration (and microbial respiration) and soil N₂O emission, but did not significantly change root respiration and soil CH₄ uptake. Lastly, warming promoted plant growth, soil microbial respiration, and soil fauna feeding by 8%, 57%, and 20%, respectively, but caused dissimilar changes in their phenology during the growing season. Overall, although ecosystem carbon stocks were not significantly affected by the whole-soil-warming, some processes and variables of the alpine grassland ecosystem showed significant responses. We will continue to monitor these processes and variables to gain a long-term mechanistic understanding of the response of ecosystem carbon cycling to whole-soil-warming in the alpine grassland.

How to cite: Zhu, B.: Whole-soil warming effects on carbon cycling of an alpine grassland ecosystem on the Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4917, https://doi.org/10.5194/egusphere-egu24-4917, 2024.

Soil microbes form some of the most diverse biological communities on Earth and are fundamental in regulating the terrestrial carbon cycle. Their response to climate warming could therefore have major consequences for future climate, particularly in tropical forests where high biological diversity coincides with a vast store of soil carbon. We used an in-situ soil warming experiment to test the response of tropical forest soil microbial communities, growth, enzyme activities and respiration to three years of soil warming. We first determined the response to warming of the microbial community composition and asked whether community change was related to a change in the intrinsic sensitivity of microbial growth. Second, we asked whether the response to warming of microbial growth sensitivity could explain the response of heterotrophic soil CO₂ emission under in situ warming. The experiment, SWELTR (Soil Warming Experiment in Lowland TRopical forest) consists of five pairs of circular control and warmed plots (whole-profile warming, using buried resistance cables) distributed evenly within approximately 1 ha of semi-deciduous moist lowland tropical forest on Barro Colorado Island, Panama. Each warmed plot is heated across the full soil profile, resulting in a total of 120 m³ of warmed soil for the experiment. For this study we established two subplots per treatment plot that differed with distance to the heating source, thus providing two treatments of, on average, 3ºC and 8ºC warming of surface soils and performed field campaigns during the wet season (when soil moisture was not limiting to microbial activity). Microbial diversity declined markedly, especially of bacteria. As the microbial community composition shifted under warming, many taxa were no longer detected and others, including taxa associated with thermophilic traits, were enriched. The activity of 7 out of 10 measured soil enzyme activities increased with warming. The community shift resulted in an adaptation of growth to warmer temperatures, which we used to specify a microbial model to predict changes in soil CO₂ emissions. However, the observed in situ soil CO₂ emissions increase exceeded the rates predicted by our model three-fold. Our results show that the soil microbial community and growth response to warming was decoupled from large increases in CO₂ emission, which was potentially boosted by an abiotic effect of warming on soil enzyme activity. Our results suggest that warming of tropical forests will have rapid, detrimental consequences both for soil microbial biodiversity and future climate.

How to cite: Nottingham, A., Bååth, E., Broders, K., Meir, P., Montero-Sanchez, M., Saltonstall, K., Sanjur, A., Scott, J., and Velasquez, E.: Drivers of soil carbon emission in warmed tropical soil, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6341, https://doi.org/10.5194/egusphere-egu24-6341, 2024.

Metal contamination in agricultural soils poses a notable environmental and health concern. When available in soils, metals can be assimilated and accumulated by crops, emphasizing the potential for human exposure to elevated metal levels through the consumption of contaminated agricultural produce. Our recent research shows that future climate change conditions of +4°C, doubled atmospheric CO₂, and reduced soil moisture [1] increases the mobility of the heavy metal Cd in agricultural soils [2]. It remains uncertain whether this climate-augmented Cd bioavailability in agricultural soils transfers into the food chain.

To address this gap in knowledge, we cultivated four varieties of spinach (Spinacia oleracaea) in four soils with diverse geochemistry and heavy metal contents. Spinach, chosen as a model for leafy crops prone to heavy metal accumulation in edible parts, boasts a global production volume of 63 billion kg in 2021 [3]. Under anticipated climatic conditions with +3°C, +300 ppmv CO₂ and 10% less water [1], three out of four spinach varieties yielded more edible biomass compared to today’s climate typical for spring spinach with 20°C daytime temperature and 50% water holding capacity. The non-essential heavy metal Cd and the micronutrient Zn proved most responsive to the imposed future climatic conditions, exhibiting increased accumulation in the edible part. Factors such as soil-root transfer and root to shoot translocation will be discussed to elucidate the climate-induced rise in Cd and Zn contents in spinach leaves beyond soil Cd mobility.

Our findings offer significant insights into forecasting future spinach production and quality, applicable to other leafy vegetables, and underscore the importance of addressing combined climate and heavy metal contamination issues to sustain food quality.

[1] IPCC, 2021. Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change.

[2] Drabesch et al., submitted, Climate induced microbiome alterations increase Cd bioavailability in agricultural soils.

[3] UN Food and Agriculture Organization, 2023. Spinach production in 2021; Crops/Regions/ World/Production Quantity/Year from pick lists.

How to cite: Muehe, M., Pienkowska, A., Glöckle, A., Sánchez, N., Khadela, S., Richter, P.-G., Merbach, I., Herzberg, M., and Reitz, T.: Climate change will increase Cd accumulation in spinach leaves, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5029, https://doi.org/10.5194/egusphere-egu24-5029, 2024.

The rise of atmospheric CO₂ concentrations, with subsequent increase in global warming and the frequency and duration of severe droughts, is altering the terrestrial carbon (C) cycling, with potential feedback to climate change.  Microbial growth, turnover and carbon use efficiency, are major controls of soil carbon fluxes to the atmosphere. Given the prominent role of soil microbial physiology for C cycling, quantifying microbial physiological responses to climate change is essential. Advances in the field now permit the quantification of community-level microbial growth and carbon use efficiency in dry conditions, by introducing stable isotopes in soil water via a water vapor equilibration technique. This has recently allowed, for the first time, to evaluate microbial physiology under drought conditions.

We here used the water vapor equilibration technique to measure deuterium (²H) incorporation into phospholipid and neutral fatty acids (PLFA and NLFA) and polyhydroxybutyrate (PHB). We applied this approach to soil samples collected from a long-term climate change experiment (ClimGrass) where warming, elevated atmospheric CO₂ (eCO₂) and drought are manipulated in a full factorial combination. Samples were taken in the field at four time points: before drought, one month and two months into drought, and few days after rewetting. We used a high-throughput method to extract PLFAs and NLFAs from soil, as well as a newly developed method to extract PHB, and measured ²H enrichment in these compounds via GC-IRMS.

We showed that during drought, bacterial growth rates are reduced, except for Actinobacteria, which maintain similar mass specific growth rates as compared to control conditions. Similarly, fungi growth rates are not affected by drought. Production of NLFAs (belonging to fungi and gram-negative bacteria) increased up to 4 to 6 folds when compared to production of membrane lipids. PHB production rates did not change compared to control conditions, revealing a higher production per unit of active bacteria. Our study demonstrates that climate change can have strong effects on microbial physiology. Investment into storage compounds is a major strategy present across different soil microbial groups in response to drought. Soil fungi and actinobacteria are key taxa in the microbial response to drought, maintaining most of the growth rates of the soil microbial community.

How to cite: Canarini, A., Lauritz, M., Sodnikar, K., Hofmann, T., Fuchslueger, L., Watzka, M., Pötsch, E. M., Schaumberger, A., Bahn, M., and Richter, A.: Soil microbes increase investment into storage compounds during drought conditions., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12840, https://doi.org/10.5194/egusphere-egu24-12840, 2024.

Atmospheric fluxes of greenhouse gases (GHG’s) in the form of CO₂, CH₄ and N₂O from temperate forest soils are an important aspect of the net global warming potential and climate change mitigation function of forests. However, it remains unclear how the magnitude of these atmospheric fluxes of GHG’s will respond to rising atmospheric CO₂ concentrations in mature temperate forests. An increase in carbon capture by temperate forests under elevated atmospheric CO₂ concentration (eCO₂) and its subsequent storage in biomass and soils can have direct impact on the activities of soil microbes. In addition to indirect effects through shifting soil moisture regimes, potentially altering GHG production and consumption processes and hence net emissions from temperate forests. The Birmingham Institute of Forest research established a Free Air Carbon Enrichment Facility (BIFoR-FACE) whereby a mature temperate forest in the UK is exposed to +150 ppm CO₂ above the ambient (aCO2), mimicking future CO₂ conditions. Understanding GHG exchange from soils under elevated atmospheric CO₂ levels is critical for addressing this component of the systems response to eCO₂. Fumigation started in 2017 and continues to date, where the ecological and biogeochemical responses of the forest is being studied. In this abstract, the focus is placed on quantifying ~5-years (2019 – 2024) of GHG flux response to eCO₂ to elucidate shifts in fluxes as influenced by eCO₂ and local microclimatic conditions.

The flux of CO₂ from the soil has been continuously measured within fumigated treatment (eCO₂) and ambient control (aCO₂) arrays since 2017 via LI-COR 8100A long-term measurement systems. With capabilities to additionally measure CH₄ and N₂O being added in 2020 through a coupled Picarro-G2508 analyser. Initial trends from 2017 - 2020 indicated that eCO₂ arrays had a higher efflux of CO₂ relative to paired aCO₂ arrays by +20%. However, from 2020 – 2022 a significant decline of -46.6% in the efflux of CO₂ was detected, in addition to a -76.6% reduction in N₂O effluxes and a -44.3% decline in the CH₄ uptake by the soil component. This period corresponds to a significant decline in soil moisture across the soil profile from the surface (0.05m) to a depth of 0.4m, equivalent to a -36% decline in volumetric water content under eCO₂ relative to aCO₂. Which when coupled with the prevalence of drought periods during the growing seasons of 2021 and 2022 suggest an enhanced drying of soil under eCO_2, which is in turn exacerbated by drought events. During 2023 and the wettest July on record for the UK, the moisture deficit between eCO₂ and aCO₂ shrunk, reducing the variance in the efflux of CO₂ to just ~4.5%. Therefore, it is possible that a functional change in the heterotrophic and autotrophic mediated flux dynamic could be occurring, driven by significant soil drying under eCO₂, an affect which is exacerbated during drought events. Inter and intra-seasonal patterns of GHG fluxes will be examined in further detail, whilst also partitioning between autotrophic and heterotrophic contributions.

How to cite: Armstrong, A., Ullah, S., Hamilton, L., Vanguelova, E., Morecroft, M., Basiliko, N., MacKenzie, R., McNamara, N., and Douwes Dekker, N.: Flux of CO2, CH4 and N2O from temperate woodland soil under elevated CO2, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16689, https://doi.org/10.5194/egusphere-egu24-16689, 2024.