Displays

Mineralization of soil organic carbon (SOC) is driven by temperature and soil moisture. Thus, climate change might affect future SOC stocks with implications for greenhouse gas fluxes from soils and soil fertility of arable land. We used a model ensemble of different SOC models and climate projections to project SOC stocks in German croplands up to 2099 under different climate change scenarios of the Intergovernmental Panel of Climate Change. Current SOC stocks and management data were derived from the German Agricultural Soil Inventory. We estimated the increase in carbon (C) input required to preserve or increase recent SOC stocks. The model ensemble projected declining SOC stocks in German croplands under current management and yield levels. This was true for a scenario with no future climate change (-0.065 Mg ha^-1 a^-1) as well as for the climate change scenarios (-0.070 Mg ha^-1 a^-1 to -0.120 Mg ha^-1 a^-1). Thereby, preserving current SOC stocks would require an increase in current C input to the soil of between 51 % (+1.3 Mg ha^-1) and 93 % (+2.3 Mg ha^-1). We further estimated that a C input increase of between 221 % and 283 % would be required to increase SOC stocks by 34.4 % in 2099 (4 ‰ a^-1). The results of this study indicate that increasing SOC stocks under climate change by a noticeable amount will be challenging since SOC losses need to be overcompensated.

How to cite: Riggers, C., Poeplau, C., Don, A., Frühauf, C., and Dechow, R.: Projected soil organic carbon stocks in German croplands under different climate change scenarios, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8004, https://doi.org/10.5194/egusphere-egu2020-8004, 2020.

Carbon cycle feedbacks represent large uncertainties on climate change projections, and the response
of soil carbon to climate change contributes the greatest uncertainty to this. Future changes in soil
carbon depend on changes in litter and root inputs from plants, and especially on reductions in the
turnover time of soil carbon (τ_s) with warming. The latter represents the change in soil carbon
due to the response of soil turnover time (∆C_s,τ), and can be diagnosed from projections made with
Earth System Models (ESMs). It is found to span a large range even at the Paris Agreement Target
of 2^◦C global warming. We use the spatial variability of τ_s inferred from observations to obtain a
constraint on ∆C_s,τ . This spatial emergent constraint allows us to greatly reduce the uncertainty in
∆C_s,τ at 2^◦C global warming. We do likewise for other levels of global warming to derive a best
estimate for the effective sensitivity of τ_s to global warming, and derive a q10 equivalent value for
heterotrophic respiration.

How to cite: Varney, R., Cox, P., Chadburn, S., Friedlingstein, P., Burke, E., Koven, C., and Hugelius, G.: A spatial emergent constraint on the sensitivity of soil carbon turnover time to global warming, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9866, https://doi.org/10.5194/egusphere-egu2020-9866, 2020.

Soil organic carbon (SOC) losses under a changing climate are driven by the temperature sensitivity of SOC mineralization (usually expressed as Q₁₀, the multiplier of activity with 10 °C temperature increase). The activation energy theory (AET) suggests that, due to higher activation energies, the more complex the carbon, the higher is mineralization Q₁₀. However, studies on Q₁₀ have been inconsistent with regard to AET. Measurements of potential soil enzymes activity Q₁₀ even contradicted AET: Phenoloxidase (representing complex carbon) had consistently lower Q₁₀ than the more labile xylanase and glucosidase. This study used two approaches of examining Q₁₀ in SOC modeling: 1) Bayesian calibration (BC) and 2) using different measured enzyme Q₁₀ as proxies for mineralization Q₁₀ of different SOC pools. The SOC model was DAISY (S. Hansen et al., 2012). BC informed Q₁₀ by field measured data, while the second approach tested if directly using enzyme Q₁₀ (of phenoloxidase, glucosidase and xylanase) for DAISY pools improved simulation results. Both approaches used the temperature sensitive measurements of CO₂ evolution and soil microbial biomass. The measured enzyme Q₁₀ were from field manipulation experiments with bare fallow and vegetated plots in the two regions of Kraichgau and Swabian Jura in Southwest Germany. The enzyme-derived Q₁₀ were used for modelling those fields and furthermore for in‑situ litterbag decomposition experiments at 20 sites in the same region. Two further laboratory experiments with temperature manipulation were included: an incubation of the field residues into soil and an incubation of bare soil from the start and year 50 of a long duration bare fallow (from Ultuna). The BC made use of CO₂ and microbial data to inform about the range of Q₁₀ of different carbon pools for the individual experiments and combined data.

The BC of the residue incubation experiment constrained Q₁₀ for metabolic (~3) and structural litter (~2). Estimated 95% credibility intervals did not overlap. The BC for Ultuna could constrain the slow and fast SOC pool with Q₁₀ ~2.8 and ~3, respectively, but credibility intervals of both pools overlapped. The Q₁₀ of field experiments, which had most abundant data, could not be constrained by BC, probably because their annual temparature variability was too low. However, the model errors of the field experiment could be reduced by the second approach, when the Q₁₀ of phenoloxidase was used for to the structural litter pool as well as for the fast and slow SOC pools. Thus regional enzyme Q₁₀ improved the model fit but only for regional simulations. Therefore, they could be useful proxies when natural temperature range is too small to inform temperature sensitivity by BC. Any trends found in this study contradicted AET, both from measured enzymes and BC of the incubation experiments. This calls for alternative Q₁₀ hypotheses and the need for individual Q₁₀ values for different SOC pool rather than a general one. BC approaches would benefit from a wider temperature range of field experiments and understanding what causes variable enzyme Q₁₀ could help to improve future SOC models.

How to cite: Laub, M., Ali, R. S., Demyan, M. S., Nkwain, Y. F., Poll, C., Högy, P., Poyda, A., Ingwersen, J., Blagodatsky, S., Kandeler, E., and Cadisch, G.: Linking temperature sensitivities of soil enzymes to temperature responses of different organic matter pools in the DAISY model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9716, https://doi.org/10.5194/egusphere-egu2020-9716, 2020.

Increasing temperatures due to the greenhouse effect are known to increase soil respiration, releasing more CO₂ into the atmosphere and resulting in a positive feedback in our climate system. Diurnal oscillations in air temperatures influence soil temperatures and thus may affect soil microbial activities and organic carbon vulnerability. Laboratory incubation studies evaluating the temperature sensitivity of soil respiration frequently use measurements of respiration taken at a constant incubation temperature in soil that has also been pre-incubated at a constant temperature.  However, such constant temperature incubations do not represent the field situation, where soils undergo diurnal oscillations in temperate under the influence of changing air temperature. We investigated the effects of constant and diurnally oscillating temperatures on soil respiration, organic matter and soil microbial community composition. A Grassland soil from the UK was either incubated at a constant temperature of 5, 10 or 15 ºC , or diurnally oscillated between 5 and 15 ºC (increasing or decreasing at 2.5 ºC for 3 hour intervals within each 24 hours). Soil CO₂ flux was measured by temporarily moving incubated soils from each of the abovementioned treatments to 5, 10 or 15 ºC, such that soils incubated at each temperature had CO₂ flux measured at every temperature. Our approach used incubation and measurement temperatures as factors to explore the influence of incubation temperature on the respiration at the measured temperature and to determine temperature sensitivity of CO₂ flux for each incubation treatment. We hypothesised that a higher measurement temperature would result in greater CO₂ flux and that, irrespective of measurement temperature, CO₂ emitted from the 5 to 15 ºC oscillating incubation would be similar to that from the 10 ºC incubation. The results showed that both incubation and measurement temperatures influence soil respiration differently. Soil respiration measured at 15 ºC was greater than that of 5 and 10 ºC, irrespective of the incubation temperature. Incubating soil at a temperature oscillating between 5 and 15 oC resulted in greater CO₂ flux than constant incubations at 10 ºC or 5 ºC, but was statistically similar to 15 ºC. This may be because extracellular depolymerisation is the rate limiting step in soil respiration and the time spent at 15 ºC in the oscillating treatment was sufficient to depolymerise enough polysaccharides to maximise intracellular respiration. The greater CO₂ release in soils incubated at 15 ºC or oscillating between 5 and 15 ºC coincided with depletion of the soil organic carbon and a shift in the phospholipid fatty acid profile of the soil microbial community, consistent with thermal adaptation to higher temperatures. Dissolved organic carbon and C/N ratio significantly decreased in soils incubated at 15 ºC or oscillating between 5 and 15 ºC with attendant increase in the ratios of Gram negative to positive bacteria and cis/trans ratio, and decreased Fungi/Bacteria ratio. Our results suggest that daily maximum temperatures are more important than daily minimum or average temperatures when considering the response of soils to warming. 

How to cite: Adekanmbi, A. A., Zou, Y., Shu, X., Shaw, L., and Sizmur, T.: Legacy of constant and diurnally oscillating temperatures on soil respiration and microbial community structure., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-604, https://doi.org/10.5194/egusphere-egu2020-604, 2020.

Due to the continued ice retreat with global warming, areas of deglaciated forefields will strongly increase in the future, leading to the emergence of new terrestrial ecosystems in many regions of the world. The soil chronosequences resulting from glacier retreat have long been a key tool for studies focusing on the mechanisms of soil formation and soil organic matter storage.

This study aimed at identifying general patterns in soil organic matter (SOM) build-up during the initial stage of soil formation and ecosystem development (0–500 years) in different glacier forefields around the world. For this purpose, we measured total soil organic matter concentration (C and N), its stable isotopic composition (¹³C, ¹⁵N) and its distribution in carbon pools of different biogeochemical stability over time in ten soil chronosequences on glacier forefields (four Andeans, one Canadian Rockies, one Greenland, two Alps, one Caucasus, one Himalaya). The distribution of SOM in carbon pools was estimated with Rock-Eval® thermal analysis. We then tested the effect of time and climatic variables (temperature, precipitation) on the build-up of soil organic matter (total concentration, isotopic signature and distribution in carbon pools).

We found a positive correlation between the rate of SOM accumulation and the average temperature of the warmest quarter (three-month period). We also noted significant traces of atmospheric deposition of anthropogenic origin in some forefield glaciers, particularly in the northern hemisphere. The build-up of soil carbon pools showed consistent trends across the soil chronosequences of the ten glacier forefields. During the first decades of soil formation, the very low SOM quantities were dominated by a very stable carbon with a small but significant labile carbon pool. This may highlight the presence of organic matter derived from ancient carbon on the different forefield glaciers, decomposed by an active living trophic network of soil microorganisms. The overall stability of SOM then slowly decreased with time, reflecting the soil carbon input from plants.

We conclude that while the rate of SOM accumulation is driven by climate (air temperature of the growing season), the build-up of soil carbon pools shows a consistent temporal trajectory on the different glacier forefields around the world.

How to cite: Khedim, N., Cécillon, L., Poulenard, J., Barré, P., Baudin, F., Marta, S., Gielly, L., Ambrosini, R., Rabatel, A., Dentant, C., Cauvy, S., Anthelme, F., Tielidze, L., Messager, E., Choler, P., and Ficetola, F.: Soil organic matter build-up during soil formation in glacier forefields around the world , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9128, https://doi.org/10.5194/egusphere-egu2020-9128, 2020.

Global warming will increase soil microbial activity and thus catalyse the mineralisation of soil organic carbon (SOC). Predicting the dynamics of soil organic carbon in response to warming is crucial but associated with large uncertainties, owing to experimental limitations. Most studies use in-vitro incubation experiments or relatively short-term in-situ soil warming experiments. Long-term observations on the consequences of soil warming on whole-profile SOC are still rare. Here, we used a long-term geothermal gradient in North-West Canada to study effects of warming on quantity and quality of SOC in an aspen forest ecosystem.

The Takhini hot springs are located within the region of discontinuous permafrost in the southern Yukon Territory, Canada. The springs warm the surrounding soil constantly and lead to a horizontal temperature gradient of approximately 10°C within a radius of 100 meters. As these natural springs heat the ground for centuries and the forest ecosystem surrounding the springs is relatively homogenous, the site provides ideal conditions for observing long-term effects of soil warming on ecosystem properties. Soils were sampled at four different warming intensities to a depth of 80 cm and analysed for their SOC content and further soil properties in different depths. 

For the bulk soil, we found a significant negative relationship between soil temperature and SOC stocks. This confirms that climate change will most likely induce SOC loss and thus a positive climate- carbon cycle feedback loop. The response of five different SOC fractions to warming will also be presented.

How to cite: Peplau, T., Gregorich, E., and Poeplau, C.: Soil organic carbon along a geothermal gradient in North-West Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9182, https://doi.org/10.5194/egusphere-egu2020-9182, 2020.

Over half of global soil organic carbon (SOC) is stored in subsurface soils (>20 cm depth), but the vulnerability of this deeper SOC to climate change has only begun to be tested. Most soil warming experiments have either only warmed surface soils or only examined the response of the surface carbon dioxide flux, so the sensitivity of SOC at different soil depths and the potential of various soil depths to generate a positive feedback to climate change is undetermined. As predictive models of terrestrial carbon storage move toward more mechanistic process representations, we need to understand how the carbon cycle differs across soil depths. We present depth-explicit measurements of soil CO₂ production from seven studies, including five in situ deep soil warming experiments and two laboratory incubations. The experiments’ locations ranged from coniferous to hardwood temperate forests in the United States and from volcanic soils in Hawaii to agricultural soils in France. The incubated soils came from a former agricultural field and arctic tundra. We have found that in temperate forests, deep soil carbon is just as vulnerable to warming-induced losses as surface soils and that warming has caused a shift in the source of carbon being respired at all depths. However, where minerals are strongly associated with organic carbon, as in Hawaii, or in degraded soils where much of the organic carbon has been lost, deep soil carbon is not vulnerable to warming-induced losses. Thus, the response of deep soil to climate change seems to be dependent on how available deep soil carbon is to microbes.

How to cite: Hicks Pries, C.: The response of deep soil carbon to climate change: Empirical studies from forests to farmland and the tropics to the arctic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12339, https://doi.org/10.5194/egusphere-egu2020-12339, 2020.

While researchers worldwide have spent much effort on quantitatively evaluating organic carbon at the regional scale, few studies have examined organic carbon pools at different levels, or their driving factors. Comprehensive analysis in this field would facilitate a deeper understanding of carbon pool mechanisms and lay a foundation for future work. In this study, the improved Terrestrial Ecosystem Regional (TECO-R) model was modified and parameters were calibrated for local application. The vegetation, litter, soil, and ecosystem carbon pools in the Xilingol typical steppe region of Inner Mongolia, China were quantitatively modeled for the 2011–2018 period. The organic carbon pools at different levels were compared and analyzed in terms of their spatial distribution, inter-annual variation, and climate-driving factors. Overall, the modified TECO-R model accurately simulated carbon storage, revealing that the various organic carbon pools increased overall and were characterized by different degrees of clustering in their spatial distribution, inter-annual variation, and climate-driving factors. Clear formation mechanisms were observed in the soil, litter, and root carbon pools. As the soil depth increased, the carbon stock of the root carbon pool and the soil carbon pool decreased. Climate factors exerted different degrees of constraints on each carbon pool. Integrated studies, such as this, promote understanding of the compositional differences in grassland carbon pools and the driving mechanism for these carbon pools, which, taken together, can help shape the policy for carbon sink management in grasslands.

How to cite: Lyu, X.: Evaluation of Grassland Carbon Pool Based on a TECO-R Model and a Climate-Driving Function: A Case Study in the Xilingol Typical Steppe Region of Inner Mongolia, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1574, https://doi.org/10.5194/egusphere-egu2020-1574, 2020.

Using long-term observations and experiments, we show that subsoils in the north central United States are a large modern organic carbon sink (~400 kg C ha^-1 y^-1). In this region, which is dominated by arable lands, the strongest signal of global change is a wetter environment. Precipitation amount and intensity have increased while atmospheric vapor pressure deficit has decreased. At the same time, this region has experienced a number of changes in agroecosystem properties and management; agroecosystems have become less diverse and total crop residue inputs to the soil have increased (>100%) due to large increases in crop yield. We used repeated measurements from two independent long-term (>40 years) cropping systems experiments to reject hypotheses that changes in cropping systems diversity and increases in crop residue input can explain the observed increase in subsoil carbon. In contrast, we used regional observations in climate to demonstrate that an increasingly wet environment is coincident with an increase in subsoil moisture content to a level that would inhibit soil carbon mineralization. As a result, we attribute the subsoil carbon sink to a wetter environment that has led to lower subsoil carbon outputs via microbial mineralization.

How to cite: Castellano, M., Archontoulis, S., Mallarino, A., Russell, A., Six, J., Takle, E., and Poffenbarger, H.: Global change has created a large subsoil carbon sink the U.S. Corn Belt, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2208, https://doi.org/10.5194/egusphere-egu2020-2208, 2020.

Global changes can alter the quantity and quality of above-and below-ground inputs, which will affect soil carbon (C) dynamics and nutrient cycles. The effects of detritus from above- and below-ground are not entirely uniform. Although numerous experiments have been conducted, the general patterns of how litter manipulation affect soil biochemical processes and whether such effects varied among changes in above- and below-ground inputs remain unclear.

Here, we conducted a meta-analysis of 2181 observations from 216 published studies to examine the responses of belowground processes to manipulated above- and below-ground litter alterations.Our results showed that, across all studies, litter manipulation generally had significant effects on soil moisture, but had minor effects on soil temperature and pH. Litter addition generally stimulated C and nutrient cycle, and microbial variables, whereas removal of litter, root and both of them generally suppressed or did not change these processes. Specifically, litter addition significantly increased soil respiration (R_s) and soil organic carbon (SOC) content in the mineral soil by 24.5% and 6.2%, respectively. Litter removal, root removal, and no inputs (removal of both litter and root) reduced R_s by 23.6%, 38.1%, and 50.2%, respectively. Litter removal and no inputs on average decreased SOC content in the mineral soil by 19% and 22.8%, respectively, but such negative effect did not occur under root removal. This suggests that aboveground litter may be more valid in soil C stabilization than roots within a relatively short period. In addition, manipulation level also regulated the responses of SOC, R_s and MBC to litter alterations. The direction of litter manipulation effects on multiple variables are basically similar among ecosystem types.

Overall, our findings provide a reference for assessing the impact of primary productivity growth on C and nutrient cycling in terrestrial ecosystems under global changes, and highlight that the effects of aboveground litters and roots should be separately incorporated into soil C models.

How to cite: He, K., Feng, J., and Zhu, B.: Effects of litter manipulation on soil biochemical processes: A global meta-analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4476, https://doi.org/10.5194/egusphere-egu2020-4476, 2020.

Balancing food production with environmentally sustainable land management can have important climate change mitigation co-benefits. Recent reports, including the IPCC latest Special Report, launched at the COP 25 in December 2019, have highlighted the significant role of soil carbon (C) stocks in agricultural soils in achieving CO₂ zero emissons and contributing to CO₂ removal. However, to measure the soil C balance (C-gains and C-losses), a deep understanding of the processes governing the changes in soil C stocks in agricultural systems is required as well as knowledge on the impact of management over long and short time scales under distinct climate conditions. An understanding of the mechanisms underpinning these processes depends on robust evidence-based datasets that can be applied to several different models to model soil C-dynamics over time and make predictions upon future scenarios.  The datasets from long-term experiments (LTEs) can be extremely valuable to facilitate the evaluation of alternative food production systems impact/effect on soil health, as such soil C stocks. Employing modeling tools to analyse these data, would lead to better evaluation of land use and management practices and its environmental impacts around the globe. With the aim of supporting the agricultural science community in meeting this and related objetives, the Global Long-Term Agricultural Experiment Network (GLTEN) was launched in October 2019. The main goal of the network is to assemble and harmonize, following FAIR Data Principle (findable, accessible, interoperable and reusable), metadata from LTEs through the online GLTEN-Metadata Portal (https://glten.org/). This initial scientific investigation of the data shared between the experiments focusses on soil C data analyzed using free available tools to exploit and compare the trade-offs between several agricultural practices and C-offset given the distinct soil type and climate conditions. With the support of the GLTEN-members, we will start these joint analyses applying the Carbon Benefits Tools (https://banr.nrel.colostate.edu/CBP/) and the RothC Model (https://www.rothamsted.ac.uk/rothamsted-carbon-model-rothc). The progress of this collaborative work relies on the commitment and expertise of the GLTEN-members and we expect that the outcome from this investigation will support the knowledge refining and advancing the development of existing modeling tools. Furthermore, we will demonstrate the potential for the GLTEN to provide a platform that supports and facilitates collaborative research among the community.

How to cite: Cardoso Lisboa, C., Storkey, J., Pellegrino Cerri, C. E., Thierfelder, C., Quincke, J. A., Chivenge, P., and Snapp, S.: The Global Long-Term Agricultural Experiment Network, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7283, https://doi.org/10.5194/egusphere-egu2020-7283, 2020.

In Lateglacial and Holocene stratigraphic sequences investigated in the eastern Po Plain (northern Italy), close to Bologna, black horizons are sometimes observed. Earlier paleo-environmental studies concerning this area have not interpreted origin and composition of these black buried horizons. In order to test this hypothesis, we are studying three stratigraphic sequences from Salara (SAL), San Mamolo (SMA) and Marzabotto (MRZ). To emphasize morphological characteristics (e.g., colour and thickness), a pedo-stratigraphic criterion was adopted for each layer observed in all the three stratigraphic sets. Totally, the horizons found are: 15 for SMA (two black), 14 for SAL (two black) and 6 for MRZ (one black); for each layer was sampled 1 kg of soil for the next investigations. Afterwards, the samples were treated in laboratory to carry out i) geochemical analyses of major, minor and trace elements, by XRF-WD Spectrometry, ii) carbon speciation in Organic (TOC) and Inorganic (TIC) fractions, by Soli TOC Cube (elemental analyser working in temperature ramp mode), iii) isotopic (δ¹³C) analysis, by EA-IRMS System. XRF analysis was necessary to understand how the black horizons are enriched or depleted in major, minor and trace elements compared to the other layers of the stratigraphic sections. Black horizons are enriched in Al₂O₃ (>14.95 wt%), Fe₂O₃ (>5.05 wt%), K₂O (>2.27 wt%), TiO₂ (>0.69 wt%), Ce (>45 mg kg^-1), Cr (>148 mg kg^-1), V (>91 mg kg^-1), and depleted in CaO (<4.52 wt%). In the same way, the Soli TOC Cube analyses were useful to make the carbon speciation for all the layers, demonstrating that black horizons are depleted in TIC (<0.87 wt%) with respect to the other layers. Low calcium and TIC in black horizons indicate that these levels are depleted in carbonates. EA-IRMS measurements were useful to understand the nature of black soils and the different climate conditions existing at the time of pedogenesis. δ¹³C has been measured for Total Carbon, TIC and TOC, and the values of black horizons are systematically more negative with respect to the other layers. The resulting values are a proxy of the type of vegetation coverage, reflecting the different proportions of C3 and C4 plants. The extremely negative values of black horizons suggest a prevalence of C3 plants during their formations, supporting the initial hypothesis of a connection with cold climatic periods. During these periods water was more acid thus explaining the paucity of carbonate. Pollen analysis is in progress to constrain this interpretation.

How to cite: Salani, G. M., Bianchini, G., Cremonini, S., De Feudis, M., Vianello, G., and Vittori Antisari, L.: Lateglacial and Holocene paleoenvironments: insights from buried black soils in Emilia (Northern Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7647, https://doi.org/10.5194/egusphere-egu2020-7647, 2020.

Soil organic matter (SOM) is one of five mandatory pools used in reporting of national greenhouse gas inventories under UNFCCC and EU regulations. Reporting on net change in soil organic carbon (SOC) under different land uses over time is challenging. The 2006 IPCC Guidelines for National Greenhouse Gas Inventories suggest that all estimates, including carbon (C) in SOM, should be transparent and consistent throughout the time series. For some countries assessing net change of SOC is often not easy due to lack of data, infrastructure or funding. Consequently, for the mineral part of the soil, frequently used is the simplest approach of assessment (Tier 1) which assumes no change in mineral SOC stocks. However, this assumption should be substantiated.

There is a growing need for the use of higher tiers in reporting of C changes in SOM pool, by providing estimates from field measurements and modelling. While soil C modelling is cost-effective, and in some countries already found applicable for the purpose of reporting, field measurements of soil C stocks are expensive and time-consuming, but necessary for model calibration and validation.

In our research we used Biome-BGCMuSo model, a biogeochemical model that simulates the storage and flux of water, C, and nitrogen (N) in the soil-plant-atmosphere system. Biome-BGCMuSo is a new variant of the well‑known Biome-BGC model with an improved multilayer soil module. We performed spatial modelling of SOC down to 30 cm for four different land-use categories of: deciduous forests, evergreen forests, annual croplands and grasslands, for the period 1990-2014. Eco-physiological parameters for each biome (i.e. land-use) were obtained from the literature. Meteorological data was obtained from open-access meteorological database FORESEE. Management activities (i.e. thinning, planting, mowing, fertilizing, and ploughing) where estimated based on available data and consultations with the local experts. Modelling results of SOC stocks were compared to field measurements. Trends of soil C change in period 1990-2014 under different land-uses were discussed.

How to cite: Ostrogovic Sever, M. Z., Hidy, D., Barcza, Z., and Marjanovic, H.: Tackling climate change reporting needs regarding soil C pool: SOC modelling under different land-use categories in Croatia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8359, https://doi.org/10.5194/egusphere-egu2020-8359, 2020.

Soils are the largest stock of terrestrial carbon, the dynamics of soil organic C (SOC) are controlled by microbial physiology, but how it promotes stable SOC and how it would change with warming, remains unknown. The Huascarán National Park (HNP), the largest mass of tropical glaciers in the world, has lost 20-30% of its glacial cover and the temperatures in this biosphere have risen 0.1°C per decade since 1970. However, no information on the HNP soil carbon stocks is available. As managing SOC is important for global warming mitigation, we study the soil C stocks in Polylepis forests of three valleys in the HNP along a temperature gradient relative to elevation (3300 to 4500 m asl), and their vulnerability to decomposition with increasing temperatures and combined labile C and nutrient (N+P) additions.

We found that higher altitude soils have higher C:N:P ratios which indicates that, as expected, soils at high altitudes are nutrient limited. Also, the activities of the N acquiring enzymes: NAGase and leucine-aminopeptidase, C acquiring enzymes: beta-glucosidase, cellobiosidase, beta-xylosidase and phosphatase were positively correlated with altitude, which indicate that N and P availability decreased with altitude across our gradient. This could make high altitude soils vulnerable to C losses, not just due to increased temperatures, but also due to increased rhizosphere priming effects. Climate warming might increase plant growth and belowground C allocation, which in turn could lead to priming due to nutrient mining.

We found no differences across altitudes in microbial biomass (Cmic) measured with the chloroform fumigation extraction method. We are currently analysing microbial community composition (by PLFA’s and DNA based methods). We will present data on microbial CUE of glucose decomposition, and how it is related to soil C/N ratios, nutrient availability and nutrient requirements, and community composition of the microbes. We also aim to test whether higher CUE is related to higher C stabilisation potential in the form of microbial necromass residues (amino sugars), or higher C loss when microbes efficiently growing on labile substrates will also increase the decomposition of more stable SOC (priming).

How to cite: Martin, A., Meyer, N., Adamczyk, S., Sietiö, O.-M., Kalu, S., Mganga, K., García Bendezu, S., and Karhu, K.: Vulnerability of C stocks in Polylepis forests of the Peruvian Andes under climate change – evidence from laboratory incubations, microbial nutrient constraints and enzyme activities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8509, https://doi.org/10.5194/egusphere-egu2020-8509, 2020.

Climate Change (CC) has evident impacts on the biotic and abiotic components of ecosystems.

Soil is the third largest reservoir of carbon, next to the lithosphere and the oceans, and stores approximately 1500 Gt in the top1 m depth.  Even small changes in soil C stocks could have a vast impact on atmospheric CO₂ concentration. Elevated surface temperature can substantially affect global C budgets and produce positive or negative feedbacks to climate change. Therefore, understanding the response of soil organic carbon (SOC) stocks to warming is of critical importance to evaluate the feedbacks between terrestrial C cycle and climate change.

In comparison to other ecosystems, the areas at high altitudes and latitudes are the most vulnerable. In permafrost areas of the Northern Hemisphere the CC has already determined an increase in greenhouse gas emissions, shrub vegetation and variation in the composition of microbial communities. While numerous studies have been performed in Arctic, much less numerous are available for high altitude areas. These areas are a quarter of the emerged lands  and have suffered strong impacts from the CC. Mountain permafrost makes up 14% of global permafrost, stores large quantities of organic carbon (SOC), and can release large quantities of CO₂ due to climate change. However, permafrost contribution to the IPCC global budget has not yet been correctly quantified, in particular for ecosystems of prairie and shrubland, which alone could incorporate over 80Pg of C between soil and biomass. In the last decades, the plant component has undergone migration of species to higher altitudes, expansion of shrubs, variations in floristic composition and dominance, variations in area distribution. The expansion of the shrubs accelerates the regression of alpine meadows and snow valleys.

The sampling activities have been carried out in July and September, from September 2017 to July 2019 in an area near Stelvio Pass (2,758 m a.s.l.) (Italian Central-Eastern Alps) along an altitude gradient.   Two sampling sites located at 2600 m a.s.l. and 2200 m a.s.l. in altitude, corresponding to about 3° C difference in the average annual air temperature were chosen. At the 2600 m site, warming experiments using open-top chambers (OTCs) to investigate how climate warming affects SOC were performed.

In order to characterize the SOM (Soil Organic Matter), Total carbon (TC), Organic carbon (OC), Total Nitrogen (TN) and Dissolved Organic Carbon (DOC) were determined in soils. TC and TN were determined in biomass. In both soils and biomass were analyzed to quantify the distribution of stable isotopes of C and N, δ¹³C and δ¹⁵N.

How to cite: Zangrando, R., Villoslada Hidalgo, M. C., Turetta, C., Cannone, N., Malfasi, F., and Onofri, S.: Characterization of Soil Organic Matter along an elevation gradient at Stelvio Pass (Italian Alps)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10750, https://doi.org/10.5194/egusphere-egu2020-10750, 2020.

High-elevation ecosystems are considered as systems that have accumulated large amounts of organic carbon in their soils over the past millennia. However, there are still large uncertainties about soil organic matter (SOM) stocks and stability in mountain areas . The fate of SOM in alpine environments is particularly questioned in the context of climate change.

The aim of this study was to investigate SOM stocks and biogeochemical characteristics of SOM along altitudinal gradients to decipher their climatic and biogeochemical drivers. To do so, we used the soil samples set of the French ORCHAMP long-term observatory network. ORCHAMP is built around multiple altitudinal gradients (ca. 1000m of elevation gain representative of the pedoclimatic variability of the French Alps. Each gradient is made of 5 to 8 permanent plots distributed regularly each 200 m of elevation, from the valley (1000 m a.s.l.) to the mountain top (until 3000 m a.s.l.). We studied 18 elevational gradients, including 105 soil profiles and 350 soil horizons. The biogeochemical stability of SOM was estimated with Rock-Eval® thermal analysis.

SOM stocks are extremely variable and do not increase with elevation . The size of the thermally labile SOM  pool strongly increases with elevation. The high lability of SOM revealed by Rock-Eval® thermal analysis suggests a generally high vulnerability of SOM to climate change in alpine environments. The mechanisms explaining the maintenance of this SOM pool in alpine environments are still under study. Hypotheses involving complex balances between climate, nature of fresh organic matter, and enzymatic activities will be discussed.

How to cite: Poulenard, J., Khedim, N., Cecillon, L., Sailard, A., Barré, P., Soucémarianadin, L., Baudin, F., Choler, P., and Thuiller, W.: Soil Organic Matter stability along altitudinal gradients in the French Alps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11036, https://doi.org/10.5194/egusphere-egu2020-11036, 2020.

Global change is likely to increase the drought periods, which may have significant consequences for the turnover of SOM, in particular through their effect on plants. The aim of the study was to assess different compartments of the soil – plant continuum for their response to drought stress by combining field and laboratory experiments. We focused on three common grassland species (Lolium perenne, Festuca arundinacea and Dactylis glomerata) found to constitute grasslands of the temperate climate. We investigated drought impact on (1) plant biochemistry and potential mineralization of this material in soil, (2) decomposition of aboveground plant leaf litter of different quality, (3) plant-mediated soil C fluxes including (4) soil microbial biomass and their enzyme activities in the rhizosphere.

            Plant elemental and biochemical composition showed contrasting changes depending on the species in response to drought stress. The changes in elemental and biochemical composition of leaf litter, ultimately influenced its mineralization in soil. Drought stress highly modified the decomposition dynamics of litter from the three grassland species as a function of litter quality.

                 Moreover, drought stress resulted in significant decrease in both shoot and root biomass in monocultures, while root biomass did not change when they were grown in mixture. Under drought stress, we observed higher belowground allocation of photosynthates and the drought had reduced root-derived respiration. This resulted in significant changes of soil enzyme activities.

                Our results suggest that plant species and community composition strongly influenced drought effects in the rhizosphere. Thus, management interventions should aim at influencing rhizosphere processes through their impact on microbial activities affecting C, N and water cycles. Plant community composition and in particular the introduction of legumes might be a tool to attenuate drought stress not only because of different water use efficiency by plants, but also by their indirect effects on these processes.

How to cite: Rumpel, C., Sanaullah, M., Mora, M. D. L. L., Calabi Floody, M., and Chabbi, A.: Impact of drought on C forms and fluxes in the soil – plant continuum, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12053, https://doi.org/10.5194/egusphere-egu2020-12053, 2020.

Crop residues are an important resource for maintaining soil productivity. The decay of crop residues is linked to many ecosystem functions, affecting atmospheric CO₂, nutrient release, microbial diversity, and soil organic matter quality. The rate of decay, in turn, is regulated by soil type, management, and environmental variables, some of which will be changing in the future. Our objective in this study was to evaluate effects of soil type, climate, residue placement on the decomposition and retention of residue-derived C. ¹³C-labelled barley straw was either placed at the surface or mixed to 10 cm in soils at four sites in Canada and one site in New Zealand representing different soil types and climates. Soils were collected periodically over 10 yr to determine ¹³C remaining. The loss of C from crop residues occurred quickly, most (70-75%) within the first 2 yrs but with only 5-10% remaining after 10 yrs. There were large losses of C from the mixed treatments within the first year, with 20-50% lost after 6 months over winter and 50-70 % lost after one year; after that decomposition slowed. Temperature was the single most important factor regulating the rate of residue decay. Thermal time, expressed as cumulative degree days, explained more of the variability in residue C recovered than time (in calendar years). Slower decay of surface-placed residues may be attributed to lower mean annual precipitation at those sites. Thermal time is a robust, consistent way of predicting crop residue decay rates (or C storage) for comparing C kinetics across sites with different soils and climates.

How to cite: Gregorich, E., Beare, M., Curtin, D., Janzen, H., Ellert, B., and Helgason, B.: Climate and soil type effects on crop residue decomposition, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12086, https://doi.org/10.5194/egusphere-egu2020-12086, 2020.

An evaluation to soil organic carbon (SOC) stock dynamics in alpine regions is crucial for the adaptive management of regional carbon budget under the elevation-dependent warming in mountainous regions. Here, we evaluated the dynamics of SOC stock to 60 cm depth in the Qilian Mountains (1700~5100 m a.s.l.) by combining systematic measurements from 138 sampling sites with a machine learning technique (i.e. random forest, RF). Our results revealed that the combination of systematic measurements with the RF model allowed spatially explicit estimates to be made. The average SOC density (SOC amount per unit area, SOCD) in the middle Qilian Mountains will decrease under future climate change. However, the size and direction of carbon change are elevation- or vegetation-dependent. Specifically, in comparison with the baseline year (1970~2000), the mean annual precipitation will increase by 18.37, 19.80 and 30.80 mm, and the mean annual temperature will increase by 1.9, 2.4 and 2.9°C, respectively, under the RCP2.6 (representative concentration pathway), RCP4.5 and RCP8.5 scenarios in 2050s. Accordingly, the mean SOCD decreased by 0.59, 0.93 and 1.05 kg C m^-2, the SOC stock decreased by 6.23, 9.75 and 11.07 Tg C, respectively under the RCP2.6, RCP4.5 and RCP8.5 scenarios. In addition, the mid-elevation zones (3100-3900 m), especially the subalpine shrub-meadow zone, will be characterized by the strongest carbon loss due to the high standing organic carbon stock under climate warming. By contrast, the high elevation zones (> 3900 m), especially the alpine desert zone, which will experience increase in accumulative temperature, prolongation in growing season, and consequently enhancement in plant productivity due to future climate warming, will be characterized by significant carbon accumulation in the future. Thus, the mid-elevation zones, especially the subalpine shrub-meadow zone should be given priority in terms of reducing CO₂ emissions under future warming in alpine regions.

How to cite: Zhu, M., Liu, W., Feng, Q., Jia, B., and Zhang, C.: Soil organic carbon dynamics as affected by climate warming in a semiarid alpine region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18446, https://doi.org/10.5194/egusphere-egu2020-18446, 2020.

Agriculture is intimately affected by climate change (atmospheric CO₂ concentration, temperature, precipitation and patterns of climate extremes), and there are major societal concerns about climate change effects on agriculture lands and hence food security in the 21st century. Despite those concerns, there is still only poor understanding of the possible impacts of climate change on the productivity and carbon dynamics of rain-fed pastoral systems in France, particularly their direction and magnitude over long time scales. The present study uses 3 scenarios (e.g. RCP 2.6, 4.5 and 8.5) of possible future climatic conditions and assesses their effects on productivity and SOC stocks of mowed and rotationally grazed grasslands. We used the CenW ecosystem model to simulate carbon, water, and nitrogen cycles in response to changes in environmental drivers and management practices. The simulations indicated that grassland productivity was increased through CO₂ fertilization and higher water use efficiencies but that SOC losses between 5% and 23% (if CO₂ fertilization is not accounted for in the simulations) are expected due to higher temperatures and biomass exports. Such losses may further affect climate feedback loop and jeopardize the agroecosystem sustainability. More extreme climate events were expected under more pessimistic climate change scenarios with very different outcomes if the CO₂ fertilization effect is accounted for or not. This study showed that under the current management practices implemented at the study site, soil C losses were expected over the 21st century under climate change conditions, highlighting the need to modify/adapt farming practices.

How to cite: Puche, N., Viovy, N., Kirschbaum, M., and Chabbi, A.: Projections of climate change effects on pasture productivity, GHG exchanges and soil carbon stocks , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11987, https://doi.org/10.5194/egusphere-egu2020-11987, 2020.

The Life Nadapta project (https://lifenadapta.navarra.es/en/inicio) aims to develop a regional-scale integrated strategy for climate change adaptation in the region of Navarre (Spain). This strategy encompasses the most affected economic sectors, including agriculture. Agriculture is highly dependent on climatic conditions, and therefore especially vulnerable to changes in climate. This vulnerability is dependent, among other factors, on soil characteristics and condition. The interaction of this vulnerability with the exposure of agrosystems to climate change impacts (drivers of change) can explain the expected risks associated to these impacts.

Understanding the resilience and possibilities of adaptation of agrosystems requires assessing how they can modulate their vulnerability and/or reduce their exposure. Agricultural management, and in particular, soil organic matter management play a key role in this sense.

In this framework, the project assesses the vulnerability and adaptability of agrosystems in three steps: First, a preliminary diagnosis of soils vulnerability in the territory was conducted, including a division in 12 homogeneous areas and the particular assessment of soil characteristic in each of them. Then, three major strategies of agricultural management aiming to improve the adaptability of agrosystems (namely crop rotations, organic fertilization and conservation agriculture) will be assessed by selecting representative agricultural plots under contrasted management in each of the areas. More than 150 plots will be included in this assessment, that makes a regional network for monitoring. That for, a specific sampling design was developed to effectively reflect the variability and different soil characteristics, and ant the same time, grant homogeneous paired comparisons.  As the three strategies are known to have a potential to increase soil organic C (SOC) stocks, and to modify other soil parameters such as water retention or erodibility, the last phase consists in assessing SOC and other indicators of soil condition, under the light of the projected climate change scenarios and identified impacts in the region.

Preliminary results show differences in vulnerability for the selected areas, and different responses of SOC and other soil indicators to the strategies tested, depending on the natural characteristics of the soils and the historical land-use in the territory.

How to cite: Virto, I., Antón, R., Arricibita, Fco. J., Ruiz-Sagaseta, A., Enrique, A., de Soto, I., Orcaray, L., and Zaragüeta, A.: LIFE Nadapta: A regional-scale strategy using soil condition assessment for evaluating climate change vulnerability and adaptation of agriculture in Navarre, Spain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3298, https://doi.org/10.5194/egusphere-egu2020-3298, 2020.

Soil organic carbon accretion through reforestation has been proposed as one of the most economically feasible and effective alternatives for carbon sequestration. A substantial fraction of these reforestation efforts are expected to occur through intensively managed exotic plantations. Management intensification and forest type conversion into productive plantations can significantly alter SOC inputs and dynamics, reducing the potential positive effect on long-term soil carbon sequestration. To understand how this forest cover change modifies the magnitude and distributions of C as well as the stability of these C pools, we selected five soils of contrasting origin and mineralogy (crystalline to amorphous clays) under both remnants of secondary temperate oak forests and pine plantations in south-central Chile. In each of these sites, two adjacent permanent plots were established, where soils were sampled at 5 points to a depth 2.4m. The sites included volcanic soils formed from recent volcanic ash (Arenosol), young ash deposits (Andosol) and old ash deposits (Ferralsol), and two residuals soils formed from granite (Luvisol) and slate (Lixisol). The recent ash-derived soils displayed clay mineralogy dominated by amorphous minerals, the young-ash by short-range order minerals and meta-halloysite; the old-ash soils have mineralogy dominated by halloysite and goethite; while residuals soils had micaceous clays, kaolinite, gibbsite, and iron oxy-hydroxides clays. Soil types had a strong influence on the C, N, and P pools. The arenosol has the smallest total C pools followed by the Andosol and Ferralsol (e.g., 45 to 56 Mg C/ha), while the largest C pool sizes were found in the residual lixisol (e.g., 387 to 243 MgC /m2). For most sites, plantation forests have lower total C and N pools and higher P pools, except for the ferrosol. Respiration rates vary significantly between sites and forest types. Total soil respiration rates tend to be higher in the native forest soils than in planted soils. Respired FM ¹⁴CO₂ was significantly correlated to bulk soil ¹⁴C FM (p<0.01, R² = 0.7). Surface organic carbon mostly incorporated post-bomb testing ¹⁴C, which tends to become much depleted at deeper horizons. This depth-dependent trend was similar for plantations and native forest soils, but plantation displayed more depleted ∆¹⁴C than native soils at all depths in most soil types. In most soil types, surface layers respired ¹⁴CO₂ was more enriched in the native forests than in plantations, but this relation flipped at depths intervals deeper than 80 cm. The age of the respired carbon was highly dependent on soil type. Soil respiration rates and ¹⁴CO₂ signatures in soils with more active clay mineralogy (2:1 and pseudo crystalline clays) seemed to be less affected by forest conversion than in soils with low stabilization capacity. The arenosol showed modern bulk and respired carbon at all depths as a result of its low carbon retention capacity (sandy textures). Our preliminary results highlight the relevance of the mineralogical control on SOC dynamics and stabilization processes and they also emphasized the need to further asses the effectiveness of planted forests for long-term soil carbon sequestration. Acknowledgments: CONICYT–PCI  MPG190022, FONDECYT-Iniciacion 1160372

How to cite: Aburto, F., Crovo, O., Czimczik, C., Sierra, C., Trumbore, S., and Xu, X.: Assessment of the potential for long-term soil carbon sequestration and stabilization in contrasting soils after native forest conversion to planted forests., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20965, https://doi.org/10.5194/egusphere-egu2020-20965, 2020.