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Draining peatlands for agriculture induces peat decomposition, subsidence, and carbon (C) and nitrogen (N) losses, thereby contributing to soil degradation and climate change. To sustain the agricultural productivity of these organic soils, coverage with mineral soil material has increasingly been used. To evaluate the effect of this practice on the N flows within the plant–soil system, we conducted a 15N tracer experiment on a drained peatland that was managed as an intensive meadow. This peatland was divided into two parts, either without (reference “Ref”) or with ~ 40 cm mineral soil cover (coverage “Cov”). We applied 15NH415NO3 on field plots to follow the fate of 15N in plant–soil system over 11 months. In addition, N mineralization was determined by laboratory incubation. The field experiment showed that Cov lost less 15N (p 15N uptake was similar at both sites. The lower net N loss from the Cov site was accompanied by higher soil 15N retention. The laboratory incubation revealed a ~ 3 times lower N mineralization at Cov than at Ref, whereas the N release per unit soil N was around two times higher at Cov than at Ref, suggesting a faster SOM turnover rate at Cov. Overall, the mineral soil cover increased the retention of fertilizer-N in the soil, thus reducing the system N losses. Our result indicates that agricultural production on drained peatland is less harmful to the environment with mineral soil coverage than using drained peatland directly.

Carbon sequestration has become a buzz word and generates large expectations on ecosystems to take up carbon (C) from the atmosphere. These so-called negative emissions could compensate greenhouse gas emissions and help to stabilise the global climate. However, the term C sequestration is often misleadingly used fostering biased conclusions and exaggerated expectations. C sequestration is defined as net uptake of C from the atmosphere. Soils have a particularly large potential to take up C yet many soils currently continuously loose C. Measures to build up soil C may only reduce soil C losses (C loss mitigation) but will not result in a net C sequestration. While checking 100 recent papers we found only 5% correctly using the term C sequestration. Even worse, 13% of the papers used C sequestration equivalent to soil C stocks. Here we call for a rigorous and concise use of the term C sequestration and discuss implications of misleading applications.

Amending biomass with wood ash (2-10%) is a novel strategy in biochar production to increase the amount of biomass carbon retained in the solid phase (biomass to biochar) during pyrolysis by up to 35%. Thereby, the carbon sink potential of industrial biochar production could be substantially increased, when such ash-amendments would be used on large scale. Also, this research enables insight on the impact of ash-derived minerals on the resulting carbonaceous compounds during pyrolysis. In addition to pyrolysis conditions and initial biomass carbon speciation, the content of alkali and alkaline earth metals (AAEM) in the biomass ash phase may be another important factor determining the speciation of the resulting pyrogenic carbon. Here, we will present data on the thermal stability analyzed with differential scanning calorimetry and the carbon speciation of ash-amended biochars investigated with 13C and 1H Nuclear Magnetic Resonance spectroscopy. Differential scanning calorimetry revealed a lower thermal stability of these ash-amended biochars compared to biochars without an ash amendment, which may indicate the formation of carbon species of lower persistence during pyrolysis induced by the added minerals. While the persistent carbon pool of biochar is made of numbers of fused aromatic carbon rings, the semi-persistent carbon pool is including aliphatic, small aromatic and heteroaromatic carbon frameworks. Therefore, analyzing the differences in carbon speciation of ash-amended biochars compared to non-amended biochar gives a closer insight on the impact of AAEM and other ash components on pyrogenic carbon speciation and how resulting biochars may persist in soil.

Peatlands are a vast and vulnerable carbon stock. Although they cover only 3% of the land area, globally the organic matter stored in peat accounts for 20% of soil carbon. In peat-rich countries, peat soils contribute much to the carbon dioxide (CO2) emissions from croplands and grasslands in the national greenhouse gas (GHG) budgets. This may seriously diminish any possible net carbon sink of the land use sector. Owing to their high emission reduction potential per area, cultivated peat soils are often considered as a very effective target for GHG mitigation measures in the agriculture and land use sector. This goal can be achieved by rewetting. Rewetting often comes with synergies such as water protection, as peat soils are also high sources of dissolved organic matter and nutrient efflux. In wet soil transformation is driven by anaerobic processes and the resulting methane emissions can be considered a tradeoff of CO2 savings by wet management. How groundwater table raise influences GHG emissions depends e.g. on peat properties, environmental conditions and site management. The goal of the EU project EJP Soil INSURE, to which our research project belongs, is to evaluate the significance of different factors regulating the GHG balance of wet cultivated peat soils at different European sites and to seek for indicators of successful GHG mitigation. We contribute to this goal by analyzing the organic matter of peat profiles. We study the molecular composition of the different peats using analytical pyrolysis GC-MS, in conjunction with organic matter stoichiometry. Our aim is to better understand the role of peat properties for the biogeochemical cycles in rewetted peatlands and their GHG balance. By using different classes of compounds, we were able to distinguish between transformed organic matter and peat that is relatively rich in undecomposed plant material. We identified marker compounds that were highly specific for fresh plants, transformed plant material or microbial abundance. For example, the abundance of undecomposed plants can be linked to levosugars, decomposed plant material is pictured by low weight polysaccharides such as 5-methyl-2-furalaldehyde and microbial matter is displayed by specific nitrogen compounds, as pyridines, pyrroles and indene’s, such as 1H-indene, 3-methyl. In addition, we studied the correlation between peat stoichiometry, compound abundance and the degree of transformation. We find that for example a high C/N ratio is negatively correlated with a high amount of low weight polysaccharides and compounds indicative for microbial abundance. We conclude that our method gives a detailed insight of peat composition. Further, it enhances our knowledge of peat quality and could therefore help to gain insights into the dependency of GHG emissions on peat quality.

Peatland rewetting is a nature based solution and considered a low hanging fruit that may substantially contribute to reaching the net zero goal. Its overall climate impact is very much determined by the interplay of CO2 and CH4 emissions that both strongly and non-linearly depend on water table depth. Rewetting peatlands acts instantaneously, and its overall climate effect depends on the considered time horizon.In this study, which extends an approach developed for carbon sequestration in mineral soils (Leifeld & Keel 2022), the radiative forcing [W m-2] of peatland rewetting is calculated along a gradient of water table depths of between -60 and +2 cm, based on recently published parameterizations for the temperate zone (Tiemeyer et al. 2020; Evans et al. 2021), for a time horizon of up to 1000 years. Two metrics, the cumulated radiative forcing and the switchover time, are considered.Switchover times, i.e. the length of time after which the positive radiative forcing due to increases in CH4 emissions at a restored peatland is overtaken by the cumulative negative radiative forcing due to CO2 uptake, range from 398 to almost 798 years, depending on water table. Switchover can only be reached when the system is a net CO2 sink, i.e. at water table depths of -7 cm or less. Both metrics, the cumulative radiative forcing and the switchover time, reveal optimum water table depths of between -6 and -2 cm (i.e., below surface). However, relative to a business-as-usual scenario with a water table of -60 cm, any water table raise improves the overall radiative balance of the rewetted system from the very beginning.In case of non-permanence of rewetting (e.g., accidental drainage), radiative forcing calculations can be used to derive suitable, biophysically based risk buffer accounts for carbon markets. For example, keeping a peatland rewetted for only 30 instead of 100 years as contractually settled still yields a 51 % climate benefit relative to a business-as-usual. The implications of these findings are discussed in the light of the carbon farming schemes proposed by the EU. ReferencesEvans, C.D. et al., 2021, Nature 593, 548–552. Leifeld, J. & Keel, S.G., 2022, Geoderma 423, 115971. Tiemeyer, B. et al., 2020, Ecological Indicators 109, 105838.

Drainage for agriculture induces peatland decomposition, subsidence, and nitrogen (N) losess, thereby contributing to climate change. In order to maintain the productivity of agricultural managed peatland, and to counteract soil subsidence, mineral soil coverage is becoming an increasingly used practice in Switzerland and other European countries. Mineral soil coverage may change the N balance from the corronsponding organic soil. To explore the effect of this practice on the N flow within the plant – soil system and the N loss, we carried out a field experiment on a peatland in the Swiss Rhine Valley that was managed as an intensive meadow. The peatland was divided into two parts, either without (Ref) or with mineral soil coverage, thickness ~ 40 cm (Cov). In this experiment, 15NH415NO3 were applied on field plots to follow the recovery of 15N in grass, root, and soil over 11 months. The 15N that was not recovered was designated as lost via leaching or gaseous emissions. Soil N mineralization was measured in a laboratory incubation. And the gaseous N loss as N2O was determined by automatic time integrating chamber systems (ATIC) over two years. The experimental results showed that the total 15N loss from Cov was lower (p < 0.05) than from Ref, even though plant 15N uptake did not vary between the two sites. The lower net N loss from the Cov site was accompanied by higher soil 15N retention in the soil. The laboratory incubation revealed a ~2 times higher specific N release per unit soil N at Cov than at Ref, suggesting a faster SOM turnover rate at Cov. Regarding the N loss as N2O, emissions from Ref were at the upper end of previously measured fluxes in drained peatland. In contrast, N2O emissions from Cov were reduced by a factor of nine over two years. Overall, the mineral soil cover increased the retention of fertilizer-N in the soil, thus reducing the system N losses, especially N loss as N2O emissions. Our results indicate agricultural production on drained peatland is less harmful to the environment with mineral soil coverage than using drained peatland directly.

Anoxic wetland soils are the biggest natural source of methane (CH4) globally. Climate-driven changes to soil moisture regimes are expected to alter wetland CH4 production, consumption, and transport in a variety of different ways. At the same time, moisture changes also influence plants and their traits, especially belowground. Wetland plants provide key carbon substrates for methanogenesis, and transport CH4 to the atmosphere but also oxygen into the soils, which can promote CH4 consumption. We tested hypotheses on these complex abiotic and biotic interactions to understand how belowground plant traits influence net CH4 emissions in wetlands. Specifically, we address the following questions 1) which root traits are most important for wetland CH4 processes? 2) how does water table manipulation influence the link between root biomass and CH4? 3) how does soil moisture influence the amount of root-derived carbon emitted as CH4? First, using a literature review, we developed a conceptual framework describing root traits that would be most related to CH4 processes, highlighting trait categories regulating CH4 substrate provision and transport. Second, using a field manipulation in an experimental rice system, we found that root biomass and CH4 emissions are positively linked, but only under low moisture conditions. Lastly, in a lab incubation, we found that the amount of root-derived C-CH4 increases with increased fresh root litter, in water saturated peat soils. Overall, our studies identify root traits and their moisture interactions that should be considered in wetland CH4 measurements and models.

Peatlands store carbon in the form of dead organic residues. Climate change and human impact impose risks on the sustainability of the peatlands carbon balance due to increased peat decomposition. Here, we investigated molecular changes in the upper peat layers (0-40 cm), inferred from high-resolution vertical depth profiles, from a boreal peatland using two-dimensional H-1-C-13 nuclear magnetic resonance (NMR) spectroscopy, and comparison to delta C-13, delta N-15, and carbon and nitrogen content. Effects of hydrological conditions were investigated at respective sites: natural moist, drainage ditch, and natural dry. The molecular characterization revealed preferential degradation of specific side-chain linkages of xylan-type hemicelluloses within 0-14 cm at all sites, indicating organic matter losses up to 25%. In contrast, the xylan backbone, galactomannan-type hemicelluloses, and cellulose were more resistant to degradation and accumulated at the natural moist and drainage site. delta C-13, delta N-15, and carbon and nitrogen content did not correlate with specific hemicellulose structures but reflected changes in total carbohydrates. Our analysis provides novel insights into peat carbohydrate decomposition and indicates substantial organic matter losses in the acrotelm due to the degradation of specific hemicellulose structures. This suggests that variations in hemicellulose content and structure influence peat stability, which may have important implications with respect to climate change.

Biochar is obtained by pyrolyzing biomass and is, by definition, applied in a way that avoids its rapid oxidation to CO. Its use in agriculture includes animal feeding, manure treatment (e.g. as additive for bedding, composting, storage or anaerobic digestion), fertilizer component or direct soil application. Because the feedstock carbon is photosynthetically fixed CO from the atmosphere, producing and applying biochar is essentially a carbon dioxide removal (CDR) technology, which has a high-technology readiness level. However, for swift implementation of pyrogenic carbon capture and storage (PyCCS), biochar use in agriculture needs to deliver co-benefits, for example, by improving crop yields and ecosystem services and/or by improving climate change resilience by ameliorating key soil properties. Agronomic biochar research is a rapidly evolving field of research moving from less than 100 publications in 2010 to more than 15,000 by the end of 2020. Here, we summarize 26 rigorously selected meta-analyses published since 2016 that investigated a multitude of soil properties and agronomic performance parameters impacted by biochar application, for example, effects on yield, root biomass, water use efficiency, microbial activity, soil organic carbon and greenhouse gas emissions. All 26 meta-analyses show compelling evidence of the overall beneficial effect of biochar for all investigated agronomic parameters. One of the remaining challenges is the standardization of basic biochar analysis, still lacking in many studies. Incomplete biochar characterization increases uncertainty because adverse effects of individual studies included in the meta-analyses might be related to low-quality biochars, which would not qualify for certification and subsequent use (e.g. high content of contaminants, high salinity, incomplete pyrolysis, etc.). In summary, our systematic review suggests that biochar use in agriculture has the potential to combine CDR with significant agronomic and/or environmental co-benefits., German Federal Ministry of Education and Research; German Federal Ministry for Economy and Energy, Grant/ Award Number: ZF4203804SB8; Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Grant/Award Number: IZ08Zo_177346; Spanish Ministry of Science, Innovation and Universities, Grant/Award Number: RTI2018- 099417-B-I00

During the last centuries major parts of European peatlands were degraded along with drainage and land use changes. Peatland biodiversity and essential ecosystem functions (e.g. flood prevention, groundwater purification and CO2 sink) were dramatically impaired. Moreover, climate change threatens peatlands in the near future. Increasing pressure to peatland ecosystems calls for a more cost-efficient method to indicate the current state of peatlands and the success of restoration effort. Metabolism processes in peatland soils are imprinted in stable isotope signatures due to differences in microorganism communities and their metabolic pathways. Therefore we hypothesize that depth profiles of nitrogen stable isotope values provide a promising opportunity to detect peatland decomposition or restoration. We studied five peatlands: Degero Stormyr (Northern Sweden), Lakkasuo (Central Finland) and three mires in the Black Forest (Southern Germany). At all locations cores were taken from adjacent drained (or rewetted) and natural sites to identify δ15N trends that could indicate changes due to drainage and restoration. At all drained (and rewetted) sites we found a distinct peak ( turning point ) of the δ15N values in the center of the drained horizon. To verify our interpretation δ13C, the C / N ratio and the bulk density were measured and a microscopic analysis of the macro residuals in the peat cores was made. In addition we did a phospholipid fatty acid (PLFAs) analysis to link our results to microbial community composition. We distinguished between fungal and bacterial-derived PLFAs. In accordance with other studies, our results suggest, that fungi dominate the microbial metabolism in the upper, aerobic peat horizon. This is reflected by depleted δ15N values. Downwards the drained horizon conditions slowly switch to oxygen limitation. In consequence fungal-derived PLFAs decreases whereas bacterial-derived PLFAs are rising. The highest diversity of microbial-derived PLFAs is indicated by the δ15N turning point. Below the δ15N turning point, oxygen is increasingly limited and concentrations of all microbial-derived PLFAs are decreasing down to the onset of the permanently waterlogged, anaerobic horizon. Peatland cores with restoration success show, above the formerly drainage-affected horizon, again no depth trend of the isotopic values. Hence, we conclude that δ15N stable isotope values reflect microbial community composition, which differ between drained and natural peatlands.

Peatland degradation is tightly connected to hydrological changes and microbial metabolism. To better understand these metabolism processes, more information is needed on how microbial communities and substrate cycling are affected by changing hydrological regimes. These activities should be imprinted in stable isotope bulk values (δ

Peatlands drained for agriculture emit large amounts of nitrous oxide (N2O) and thereby contribute to global warming. In order to counteract soil subsidence and sustain agricultural productivity, mineral soil coverage of drained organic soil is an increasingly used practice. This management option may also influence soil-borne N2O emissions. Understanding the effect of mineral soil coverage on N2O emissions from agricultural peatland is necessary to implement peatland management strategies which not only sustain agricultural productivity but also reduce N2O emissions. In this study, we aimed to quantify the N2O emissions from an agriculturally managed peatland in Switzerland and to evaluate the effect of mineral soil coverage on these emissions. The study was conducted over two years on a grassland on drained nutrient-rich fen in the Swiss Rhine Valley which was divided into two parts, both with identical management. One site was not covered with mineral soil (reference “Ref”), and the other site had a ∼40 cm thick mineral soil cover (coverage “Cov”). The grassland was intensively managed, cut 5–6 times per year, and received c. 230 kg N ha−1 yr−1 of nitrogen fertilizer. N2O emissions were continuously monitored using an automatic time integrating chamber (ATIC) system. During the experimental period, site Ref released 20.5 ± 2.7 kg N ha−1 yr−1 N2O-N, whereas the N2O emission from site Cov was only 2.3 ± 0.4 kg N ha−1 yr−1. Peak N2O emissions were mostly detected following fertilizer application and lasted for 2–3 weeks before returning to the background N2O emissions. At both sites, N2O peaks related to fertilization events contributed more than half of the overall N2O emissions. However, not only the fertilization induced N2O peaks but also background N2O emissions were lower with mineral soil coverage. Our data suggest a strong and continued reduction in N2O emissions with mineral soil cover from the investigated organic soil. Mineral soil coverage, therefore, seems to be a promising N2O mitigation option for intensively used drained organic soils when a sustained use of the drained peatland for intensive agricultural production is foreseen, and potential rewetting and restoration of the peatland are not possible.

Globally, the intensive use of peatlands contributes substantially to greenhouse gas emissions. The intensification of peatland use has led to increasing carbon (C) losses over the last centuries, but without historical emissions data, these increases and cumulative emissions are difficult to quantify. To understand the magnitude and development of soil C losses through peatland drainage in Switzerland through time, and to relate the situation of peatlands today to this historical development. Historical records and a published estimate of the peatland extent are used to estimate peatlands’ original extent and C stocks, and to understand trends in the historical use of peatlands. Land use-specific emission factors are applied to estimate the C emission through drainage over the last 300 years. Ca. 15 to 55 Mt C have been lost through peatland drainage in Switzerland. Despite a decrease in the area of organic soils, annual C emissions have increased considerably especially since the mid-twentieth century due to intensification of their use, particularly for agriculture. This C loss is a magnitude greater than that lost through extracted peat. Remaining C stocks approximate those lost over the last 300 years. The rate of peatland surface loss in Switzerland is typical of European wetlands. Uncertainties in emission factors remain high and should be refined to justify any mitigation strategies. Although peat is no longer mined in Switzerland, future C emissions from peatlands will remain high as long as the effects of drainage networks and their current intensity of use persist.

Reducing greenhouse gas emissions from arable soil while maintaining productivity is a major challenge for agriculture. Biochar is known to reduce N₂O emissions from soil, but the underlying mechanisms are unclear. This study examined the impact of green waste biochar (20 Mg ha⁻¹) and lime (CaCO₃; 2 Mg ha⁻¹) application on soil gas transport properties and related changes in these to soil N₂O and CO₂ emissions measured using automated chambers in a field experiment cropped with maize. In situ soil water content monitoring was combined with laboratory measurements of relative soil gas diffusion coefficient (Dₚ/D₀) at different matric potentials, to determine changes in Dₚ/D₀ over time. Cumulative N₂O emissions were similar in the control and lime treatment, but much lower in the biochar treatment. Cumulative CO₂ emissions decreased in the order: lime treatment > biochar treatment > control soil. When N₂O emissions were not driven by excess N supply shortly after fertilisation, they were associated with Dₚ/D₀ changes, whereby decreases in Dₚ/D₀ corresponded to N₂O emissions peaks. No distinct pattern was observed between CO₂ emissions and Dₚ/D₀. Cumulative N₂O emissions were positively related to number of days with Dₚ/D₀ < 0.02, a critical limit for soil aeration. These results indicate that improved soil gas diffusivity, and hence improved soil aeration, may explain the effect of biochar in reducing N₂O emissions. They also suggest that knowledge of Dₚ/D₀ changes may be key to explaining N₂O emissions.

From a carbon sequestration perspective, peatland restoration projects could be considered successful when net primary productivity exceeds decomposition, resulting in net peat growth in the ecosystem. To demonstrate the effectiveness of peatland restoration projects with a carbon storage aim, analytical techniques are needed that can distinguish between natural/restored ecosystems undergoing (or transitioning to) net peat growth and degraded ecosystems experiencing increased rates of aerobic decomposition (carbon loss). Molecular analysis techniques able to relate changes in organic matter (OM) chemical composition to changes in degradation status occurring on the mechanistic level are especially needed.This study combined a molecular biomarker and chemical compound class approach to conduct a depth-based molecular comparison of natural (ON) and drained (OD) ombrotrophic peatland sites in Lakkasuo Finland. To explore how changes in hydrology impacted peat OM chemical composition, the relative abundance of various molecular biomarkers (Sphagnum marker p-isopropenylphenol, lignin vascular plant markers) and chemical compound classes (phenolics, polysaccharides, aromatics, N-containing compounds, lipids) was determined with depth from three replicate cores per site using pyrolysis gas chromatography tandem mass spectrometry (Py-GCMS). Py-GCMS results were compared with onsite vegetative assemblages and bulk elemental analysis conducted on the same cores. ON and OD were matched by age using radiocarbon dating at three depths per core.For OD relative to ON, significant reductions in average relative percent abundance were observed for p-isopropenylphenol, phenolics and polysaccharides, and corresponding increases in abundance were observed for lignin, aromatics, N-containing compounds, and lipid sterols. Differences in compound classes between sites were greatest in the drainage-affected upper acrotelm, and diminished with depth. Samples consistently below the depth of the water table (>20 cm) followed similar trends in both ON and OD, suggesting that deeper horizons remained unaffected by the onsite drainage activities. An increasing trend in the relative abundance of lignin-derived compounds was observed with depth - particularly in ON. As the plant macrofossil assessment did not suggest previous dominance of vascular plants, this trend was considered evidence for preservation of lignin in anaerobic conditions in organic soils. Overall, these findings indicate that differences in chemical composition between the two sites can be directly correlated to OM transformation occurring on a mechanistic level, and that observed shifts in chemical composition reflect the effect of altered hydrology in peatland ecosystems.

Drainage for agriculture has turned peatlands from a net sink to a net source of carbon (C). In order to reduce the environmental footprint of agricultural peatland drainage, and to counteract soil subsidence, mineral soil coverage is becoming an increasingly used practice in Switzerland. To explore the effect of mineral soil coverage on soil C loss and the source of CO2 from peatland drained for agriculture, we utilized the radiocarbon signature (F14C) of soil C and emitted CO2 in the field. The experiment, located in the Swiss Rhine Valley, was carried out on two adjacent drained organic soils, either without mineral soil cover (reference 'Ref'), or covered with mineral soil (thickness ~ 40 cm) (coverage 'Cov') 13 years ago. Drainage already commenced 130 years ago and the site was managed as meadow since the 1970ies. Drainage induced 41-75 kg C m-2 loss, which is equivalent to annual C loss rates of 0.49-0.58 kg C m-2 yr-1 and 0.31-0.63 kg C m-2 yr-1 for Cov and Ref, respectively. Mineral soil coverage had no significant effect on the amount of heterotrophic respiration, however, at Cov, the radiocarbon signature of heterotrophic CO2 was significantly (p

To meet the Paris Agreement goal of limiting average global warming to less than 1.5°C above pre-industrial temperatures, European Union (EU) aims to reduce by 40% its domestic greenhouse gas (GHG) emissions by 2030 and in the longer term to become the world’s first climate-neutral economy by 2050 (“Green Deal”). Today, 10% of the European GHG emissions derive directly from agriculture, and measures to decrease or compensate these emissions are required for achieving climatic goals. The role of soils in the global carbon cycle and the importance of reducing GHG emissions from agriculture has been increasingly acknowledged (IPCC, 2018, EEA report 2019). The “4 per 1000” initiative (4p1000) has become a prominent model for mitigating climate change and securing food security through an annual increase in soil organic carbon (SOC) stocks by 0.4 %, or 4‰ per year, in the first 0-40 cm of soil. However, the feasibility of the 4p1000 scenario and more generally the capacity of European countries to implement soil carbon sequestration (SCS) measures are highly uncertain.As part of the EJP Soil project, we collected country-specific informationonon on the available knowledge and data of achievable carbon sequestration in mineral agricultural soils (cropland and grassland) across Europe, under various farming systems and pedo-climatic conditions. With this bottom-up approach, we provide a reality check on weather European countries are on track in relation to GHG reductions targets and the “4p1000” initiative. First results showed that the availability of datasets on SCS is heterogeneous across Europe. While northern Europe and central Europe is relatively well studied, references are lacking for parts of Southern, Southeaster and Western Europe. Further, this stocktake highlighted that the current country-based knowledge and engagement is still poor; very few countries have an idea on their national-wide achievable SCS potential. Nevertheless, national SCS potentials that were estimated for 13 countries support the view that SCS can contribute significantly to climate mitigation, covering from 1 to 28, 5 % of the domestic GHG emissions from the agricultural sector, which underpins the importance of further investigations.

Intact peatlands serve as a globally important carbon sink. However, impacts from climate change, extraction, and drainage increase aerobic decomposition in these ecosystems—shifting their carbon flux from sink to source. A variety of projects are ongoing to restore peatlands to their natural or near-natural states; however, for carbon sequestration, net accumulation of peat relative to decomposition is of primary importance. Molecular analysis techniques provide information on peat growth and degradation trends dating from centuries to millennia. Pyrolysis coupled to gas chromatography mass spectrometry (Py-GC/MS) has been proposed for the rapid characterization of molecular biomarkers in organic matter. This paper reviews plant and microbial biomarkers analyzable via Py-GC/MS for peatland ecosystems, associated challenges, and future applications of the technique. It is noted that far fewer organism-specific biomarkers have been identified via Py-GC/MS for microbial communities in comparison to plant-based studies, and as a topic remains an area greatly needing additional research. In the future, through improved Py-GC/MS-derived fingerprinting of peatland molecular components, periods of degradation and growth could be more precisely distinguished and described, even in profiles where changes in contributing source material are not macroscopically visible.

Peatlands accumulate organic matter (OM) under anaerobic conditions. After drainage for forestry or agriculture, microbial respiration and peat oxidation induce OM losses and change the stoichiometry of the remaining organic material. Here, we (i) evaluate whether land use (cropland CL, grassland GL, forest FL, natural peatland NL) is associated with different peat stoichiometry, (ii) study how peat stoichiometry changes with OM content and (iii) infer the fate of nitrogen upon soil degradation. Organic C and soil N were measured for 1310 samples from 48 sites in Switzerland, and H and O for 1165. The soil OM content and C/N ratio were most sensitive to land use and are hence best suited as indicators for peatland degradation. OM contents (CL GL FL NL), H/C, O/C, C/N ratios, and OM oxidation states were significantly different between land use types in top- and subsoils. With decreasing bulk OM content, C was relatively depleted while H and particularly N were higher. The data suggest very high N mobilization rates from strongly decomposed peat in agricultural topsoil. A comparison to peat C and N from mostly intact peatlands of the Northern hemisphere reveals that agriculture and, to a lesser extent, forestry induce a progressed state of soil degradation.

Below ground carbon (BGC) inputs to soil, i.e. root biomass and rhizodeposition carbon (C), are among the most important variables driving soil C dynamics in agroecosystems. Hence, increasing BGC inputs to deep soil is a proposed strategy to sequester C in the long term. As BGC inputs are inherently difficult to measure in the field, they are usually estimated from yield in order to supply soil C models with input data. While fertilization intensity considerably affects above ground biomass, its influence on BGC inputs is largely unclear, especially with respect to the subsoil. Therefore, we determined net root biomass and rhizodeposition C of field-grown maize and wheat at harvest in different farming systems (bio-organic, conventional) and fertilization treatments (zero, manure, mineral) along an intensity gradient in two Swiss long-term field trials. Plants in microplots were repeatedly pulse-labelled with 13C-CO2 throughout the growing seasons and shoots, roots, and soil to 0.75 m depth were sampled at harvest. Despite a strong increase of above ground biomass with increasing fertilization intensity, BGC inputs were similar among treatments on both sites irrespective of soil depth. However, the proportions of rhizodeposition C of BGC inputs averaged 54 to 63% and were, therefore, much larger than the widely adopted 40% for field-grown cereals. They increased with soil depth and were highest under sole organic fertilization. The shift in whole-plant C allocation towards above ground biomass with increasing fertilization intensity entailed 10% higher C allocation below ground in organic than conventional farming for both maize and wheat. Our findings imply that yield-independent values provide closer estimates for BGC inputs to soil of cereals in different farming systems than yield-based functions. We further conclude that fertilization has only little potential to alter absolute amounts of BGC inputs to deep soil in order to sequester C in the long term.

N2O is a major greenhouse gas and the majority of anthropogenic N2O emissions originate from agriculturally managed soils. Therefore, developing N2O mitigation strategies is a key challenge for the agricultural sector and biochar soil treatment is one reported option. Biochar's capacity to increase soil pH and to foster activity of specialized N2O reducers has been proposed as possible mechanisms for N2O mitigation. An experiment was undertaken to investigate whether changes in the community composition of N2O reducers was observed under field conditions after biochar application. The study objective was to assess the abundance and taxonomic composition of the functional marker genes nosZ and nosZ –II across a vegetation period of Zea mays L. after biochar or lime addition compared to an untreated control. After fertilization, biochar amendment resulted in a significant increase of nosZ gene copy numbers compared to the control and the lime treatment. Simultaneously a shift in community composition of nosZ-II bearing bacteria was observed in the biochar treatment that went beyond the sole liming effect. This study broadens our understanding of the functional impact of biochar on N2O emissions and emphasizes the possibility to shape the functioning of the N2O reducing microbial community through the addition of biochar at a field scale.

Land-use change disturbs the function of peatland as a natural carbon sink and triggers high GHG emissions1. Nevertheless, historical trends and future trajectories of GHG budgets from soil do not explicitly include peatlands2,3. Here, we provide an estimate of the past and future role of global peatlands as either a source or sink of GHGs based on scenario timelines of land conversion. Between 1850 and 2015, temperate and boreal regions lost 26.7 million ha, and tropical regions 24.7 million ha, of natural peatland. By 2100, peatland conversion in tropical regions might increase to 36.3 million ha. Cumulative emissions from drained sites reached 80 ± 20 PgCO2e in 2015 and will add up to 249 ± 38 Pg by 2100. At the same time, the number of intact sites accumulating peat will decline. In 1960 the global peatland biome turned from a net sink into a net source of soil-derived GHGs. Annual back-conversion of most of the drained area would render peatlands GHG neutral, whereas emissions from peatland may comprise 12–41% of the GHG emission budget for keeping global warming below +1.5 to +2 °C without rehabilitation. Natural peatlands accumulate carbon but land-use change and drainage leads to emission of GHGs from peatlands. Loss of natural peatland area globally has shifted the peatland biome from a sink to a source of carbon, but restoration of drained peatlands could make them carbon neutral.

Root biomass is the most commonly studied root parameter to investigate below ground crop response to environmental conditions and carbon cycling in agroecosystems. Root growth is strongly regulated by site-specific growth conditions and resource availability, but only little is known about the extent to which root biomass, vertical distribution, and size class respond to fertilization intensity as compared to site. We determined coarse (> 2 mm) and fine (> 0.5 mm and ≤2 mm) root biomass of maize and wheat in three soil layers to 0.75 m depth in different farming systems (half and full organic, full conventional) and fertilization treatments (zero, manure, full mineral N plus half mineral PK, full mineral NPK) of the Swiss long-term field trials DOK and ZOFE, respectively, and evaluated the effects of fertilization intensity and site on root biomass, vertical distribution, and size class. In DOK, total root biomass was similar in organic and conventional farming systems. In ZOFE, wheat root biomass was 1.7-times higher under full mineral N plus half mineral PK fertilization than under zero or manure fertilization and intermediate under full NPK fertilization. Vertical root distribution and size class were only marginally affected by fertilization intensity on both sites. By contrast, total root biomass of maize and topsoil root biomass of both maize and wheat were higher but subsoil root biomass of wheat and fine root proportions of both maize and wheat were lower in DOK than in ZOFE. We conclude that roots respond more to site than to fertilization intensity and that absolute inputs of root biomass carbon to soil are similar in low- and high-intensity systems. Further, root-shoot ratios were inversely related to fertilization intensity, implying that estimations of below ground carbon inputs to soil from shoot biomass need to be differentiated by fertilization intensity. Deep (below 0.5 m) root biomass was 3-times higher for wheat than for maize, suggesting that crop choice is more important than fertilization intensity for carbon sequestration in deep soil.

Pyrogenic carbon (PyC) derives from incomplete combustion of organic matter and is ubiquitous in terrestrial and aquatic systems. Most PyC is inherently more stable against decomposition than plant residues, and PyC therefore forms an important component of the global carbon (C) cycle. During the Holocene, about 436 Pg organic C accumulated in northern peatlands, and we hypothesize that PyC may contribute substantially to that C stock. We studied 70 samples from 19 intact and degraded European peatland sites and analyzed their PyC content by 13C nuclear magnetic resonance spectroscopy and molecular modeling and peat age and accumulation by radiocarbon dating. Classification of a peatland as either intact or degraded was based on the comparison between apparent and expected long-term C accumulation rates. On average, PyC amounted for 13·5% of soil C across sites, and accounted for up to 50% at single sites. The amount of PyC increased significantly with peat age. Degraded peatlands had lost approximately 56 kg C m�2, half of their former C stock. However, degraded peat had higher PyC contents than intact one. Selective enrichment of PyC during both peat build-up and decomposition seems to be an important factor fostering PyC accumulation. Assignment of our results to peatlands of the northern hemisphere, stratified by age, revealed an estimated PyC stock of 62 (±22) Pg. Our estimate indicates a substantial and hitherto unquantified contribution of northern peatlands to global PyC storage. © 2017 The Authors. Land Degradation & Development Published by John Wiley & Sons Ltd.

Summary The application of dynamic models to report changes in soil organic carbon (SOC) stocks, for example as part of greenhouse gas inventories, is becoming increasingly important. Most of these models rely on input data from harvest residues or decaying plant parts and also organic fertilizer, together referred to as soil carbon inputs (C). The soil C inputs from plants are derived from measured agricultural yields using allometric equations. Here we compared the results of five previously published equations. Our goal was to test whether the choice of method is critical for modelling soil C and if so, which of these equations is most suitable for Swiss conditions. For this purpose we used the five equations to calculate soil C inputs based on yield data from a Swiss long-term cropping experiment. Estimated annual soil C inputs from various crops were averaged from 28 years and four fertilizer treatments; the average was 3.6 Mg C ha−1 and covered a surprisingly large range from 2.1 to 5.3 Mg C ha−1 year−1 among the five equations. For single crop species, differences reached 6.6 Mg C ha−1 year−1. The variation between estimated soil C inputs depended on crop type and increased with yield. Simulations with the model C-TOOL showed that calculated SOC stocks were affected strongly by the choice of the allometric equation. With four equations, a decrease in SOC stocks was simulated, whereas with one equation there was no change. This considerable uncertainty in modelled soil C is attributable solely to the allometric equation used to estimate the soil C input. We identify the evaluation and selection of allometric equations and associated coefficients as critical steps when setting up a model-based soil C inventory for agricultural systems. Highlights Uncertainty analyses in soil C modelling have focused mainly on model parameters and structures. The uncertainty related to estimation of soil C inputs from crop residues was calculated. Simulated soil C stocks and stock changes depend strongly on the method of estimating C input. The method to derive soil C inputs is critical for model-based soil C inventories.

We studied carbon and radiocarbon content in three historical time series of soil profiles from sites with different histories in the Parangalitsa biosphere, Rila mountains (Bulgaria). Our aim was to understand the consequences of forest regrowth in Eastern European forests for C stocks in the medium and long term. Disturbance history of the area has been studied in detail in recent decades, and we were therefore able to assess the impact of natural events such as windthrows and insect outbreaks on soil C stocks. By combining unique historical profile data with radiocarbon measurements, we obtained a picture of the kinetics at three different sites. These sites were 1) no land use change but an old (>120 years) forest subjected to decades old disturbances from the secondary consequences of a windthrow, 2) a forest site subjected to decades old disturbances from the direct consequences of a windthrow and 3) a grassland converted to forest. While the difference between direct and indirect disturbance did not have a relevant effect on C stocks, the ecological successions triggered either by afforestation or by disturbances caused similar dynamics of SOC decrease followed by accumulation, according to the pattern of primary productivity. The accumulation was marked in the conversion, and clearly involved the subsoil layers as well, leading to a C sequestration considered durable. The huge economic and social changes happening in Eastern Europe in the last two decades have generated a clear trend towards afforestation of lands that were formerly cultivated. The SOC changes from grassland to forest use in these areas (~50 t ha-1) represented a doubling in stocks in less than 40 years, and their impact on a global scale could represent an unexpected C sink.

Ongoing peatland degradation calls for an efficient method to indicate peatland hydrology and the success of restoration effort. In previous studies we found specific depth patterns of 13C and 15N depending on peatland hydrology (drained, rewetted or natural), but were unable to find an explanation of these patterns. As degradation is mostly connected to drainage we assumed an increase of microbial activity. This microbial activity should then be imprinted in stable isotope signatures (15N, 13C) due to differences in microorganism communities, their metabolic pathways and nutrient sources. We aimed to find a link between our investigated isotope depth patterns to microbial community composition. Therefore, we conducted a phospholipid fatty acid (PLFAs) analysis. As a marker for bacteria we used PLFAs i-C15:0 and a-C-15:0 as well as the C18:2,9c as a marker for fungi. We studied two nutrient poor peatlands in Northern Europe: Lakkasuo (Central Finland) and Degerö Stormyr (Northern Sweden). At all locations cores were taken from adjacent drained (or rewetted) and natural sites. At Lakkasuo drained site, we found a high humification index (HI, after van Post), shown by less plant residuals and a high amount of matrix. For Degerö Stormyr the picture looks different. Above the drained horizon (high HI) peat was light, with a smaller amount of matrix and lots of plant residuals (low HI), like it was also seen in the natural cores. At the drained (and rewetted) sites we found distinct peaks in microbial PLFA concentrations, which correlate to the stable isotope peaks ("turning point”) we found before. At the 15N turning point, in the center of the drained horizon, overall microbial-derived PLFA abundance is also the highest. Furthermore, the overall microbial-derived PLFA abundance is positively correlated with 15N values (r2=0.5). Fungi-derived PLFAs are negatively correlated (r2=0.4) to 13C. Fungi-derived PLFAs showed the highest amount at the uppermost part of the drained horizon and low amounts in the waterlogged conditions below the drained horizon, whereas 13C showed lowest values at the surface and high values below the drained horizon. Our results suggest, that fungi dominate microbial metabolism in the upper, aerobic peat horizon. Downwards the drained horizon conditions slowly switch to oxygen limitation. Thus, fungal-derived PLFAs decrease whereas bacterial-derived PLFAs are increasing. The highest diversity of microbial-derived PLFAs is indicated by the 15N turning point. Below this point, oxygen is increasingly limited and concentrations of all microbial-derived PLFAs are decreasing down to the 13C turning point and the onset of the permanently waterlogged, anaerobic horizon. Cores from rewetted peatlands show no depth trend of 15N values above the formerly drained horizon and a low amount of microbial-derived PLFAs. Hence, we conclude that stable isotope values reflect microbial metabolism processes, which differ between drained, rewetted and natural peatlands. Additionally, stable isotope patterns reflect a switch in the predominant communities from fungi to bacteria within a drained horizon. Summing up, the PLFA analysis approved that stable isotope measurements can serve as a cost and work efficient monitoring tool for peatland history as well as peatland restoration success.

Drainage for agriculture has converted peatlands from a carbon sink to one of the world’s major greenhouse gas (GHG) sources. In order to improve the sustainability of peatland management in agriculture, and to counteract soil subsidence, mineral soil coverage is becoming an increasingly used practice in Switzerland. Cover fills may change the GHG balance from the corresponding organic soil. To explore the effect of cover fill on soil N2O emissions, we carry out a field experiment in the Swiss Rhine Valley and measure the soil – borne N2O exchange from two adjacent sites: drained organic soil without mineral soil cover (DN), and drained organic soil with mineral soil cover (DC). Mineral soil material was applied 12 years ago and varies in thickness between 20 – 80 cm. Both sites have the identical farming practice (intensive permanent meadow). In our experiment, an automatic chamber system is used for collecting the N2O at an interval of 3 h. Soil moisture, expressd as volumetric water content (VWC), is recorded every 10 min. After ten month (303 days) of continous measurement, the data reveal that: (1) The average N2O emission from DN is higher than DC by a factor of 11 (11.24 ± 3.46 vs 0.97 ± 0.22 mg N2O-N m-2 day-1). Hence, mineral soil cover of organic soil seems to induce a strong reduction in N2O emissions. (2) Exogenous N inputs (mineral N fertilizer and cow slurry) are the main drivers of N2O emissions. N2O peaks occured shortly after the N application and lasted for 2 to 3 weeks before returning to background N2O emission. At the DC site post N- input N2O emissions accounted for 68 % of the total N2O emission over the whole measurement period. An equivalent of around 1 % of the exogenous N- input was emitted as N2O. At the DN site, emission peaks after fertilization accounted for 79 % of the total N2O emission, equivalent to around 13 % of the exogenous N- input. Background emissions between peak events shows no significant difference between DC (0.51± 0.15 mg N2O-N m-2 day-1) and DN (2.73± 2.44 mg N2O-N m-2 day-1). The comparison of peak and background fluxes tentatively indicates that higher average emission rates from the DN site are related directly to fertilization. Finally, surface soil characteristics (soil pH, bulk density, and soil N) changed after mineral soil cover, and soil moisture content differed between sites. During the experimental period, the mean daily soil moisture from DN site (24.1 % VWC – 60.18 % VWC) is higher than DC site (20.17 % VWC – 51.26 % VWC). In summary, our data from this first experimental period suggest that mineral soil cover fill could strongly reduce the N2O emission from drained organic soil, and may therefore be an interesting GHG mitigation option in agriculture.

During the last centuries major parts of European peatlands were degraded along with drainage and land use changes. Peatland biodiversity and essential ecosystem functions (e.g. flood prevention, groundwater purification and CO2 sink) were dramatically impaired. Moreover, climate change threatens peatlands in the near future. Increasing pressure to peatland ecosystems calls for a more cost-efficient method to indicate the current state of peatlands and the success of restoration effort. Metabolism processes in peatland soils are imprinted in stable isotope signatures due to differences in microorganism communities and their metabolic pathways. Therefore we hypothesize that depth profiles of nitrogen stable isotope values provide a promising opportunity to detect peatland decomposition or restoration. We studied five peatlands: Degerö Stormyr (Northern Sweden), Lakkasuo (Central Finland) and three mires in the Black Forest (Southern Germany). At all locations cores were taken from adjacent drained (or rewetted) and natural sites to identify δ15N trends that could indicate changes due to drainage and restoration. At all drained (and rewetted) sites we found a distinct peak (turning point) of the δ15N values in the center of the drained horizon. To verify our interpretation δ13C, the C / N ratio and the bulk density were measured and a microscopic analysis of the macro residuals in the peat cores was made. In addition we did a phospholipid fatty acid (PLFAs) analysis to link our results to microbial community composition. We distinguished between fungal and bacterial-derived PLFAs. In accordance with other studies, our results suggest, that fungi dominate the microbial metabolism in the upper, aerobic peat horizon. This is reflected by depleted δ15N values. Downwards the drained horizon conditions slowly switch to oxygen limitation. In consequence fungal-derived PLFAs decreases whereas bacterial-derived PLFAs are rising. The highest diversity of microbial-derived PLFAs is indicated by the δ15N turning point. Below the δ15N turning point, oxygen is increasingly limited and concentrations of all microbial-derived PLFAs are decreasing down to the onset of the permanently waterlogged, anaerobic horizon. Peatland cores with restoration success show, above the formerly drainage-affected horizon, again no depth trend of the isotopic values. Hence, we conclude that δ15N stable isotope values reflect microbial community composition, which differ between drained and natural peatlands.

The agricultural use of peatlands usually requires drainage, thereby transforming these organic soils from a net carbon sink into a net source. The Seeland region of Switzerland is characterised by fens that have been intensively used for agriculture for 150 years. Our site is a degraded fen with a remaining peat layer of 60 cm that had been used as cropland until 2009. In connection to a nature protection project it has been managed as extensive permanent grassland since then. The net ecosystem carbon balance (NECB) was determined for two years (2015-2016). For this purpose, the net ecosystem exchange of CO2 (NEE) and CH4 fluxes were measured by eddy covariance, and the carbon removed by harvest was quantified. Our degraded fen site was found to be a net carbon source of 477±73g C m−2 yr -1 and 434±51 g C m-2 yr−1 in 2015 and 2016, respectively. Annual CH4 emissions were marginal in both years with 0.4±0.8 g CH4-C m−2 yr -1 (2015) and 0.7±0.7 g CH4-C m−2 yr -1 (2016). In contrast to NECB, the NEE was considerably higher in 2015 than in 2016 (308±71 g C m−2 yr -1 vs 117±39 g C m−2 yr -1). The year 2015 was characterised by partial flooding of the grassland, followed by a dry and hot summer leading to lower CO2 uptake due to reduced growth, which was reflected in lower harvest compared to 2016. Thus, the short-term plant-induced carbon fluxes were altered, whereas total soil carbon loss remained rather constant. This was verified by an intra site comparison between the flooded and non-flooded part in 2015. Our results indicate that the soil carbon loss of this highly degraded peatland with a shallow peat layer is relatively moderate and hardly influenced by interannual weather variations.

Palsas develop as permafrost aggradation uplifts peat out of the zone influenced by groundwater. Here we relate δ15N values to C/N ratios along depth profiles through palsas in two peatlands near Abisko, northern Sweden, to identify perturbation of the peat. The perturbation by uplift as well as the potential nutrient input from the adjacent hollows can be detected in soil δ15N values when related to the C/N ratio at the same depth. Nine out of ten profiles show a perturbation at the depth where peat was uplifted by permafrost. Palsa uplift could be detected by the δ15N depth pattern, with the highest δ15N values at the so-called turning point. The δ15N values increase above and decrease below the turning point, when permafrost initiated uplift. Onset of permafrost aggradation calculated from peat accumulation rates was between 80 and 545 years ago, with a mean of 242 ( ±66) years for Stordalen and 365 ( ±53) years for Storflaket peatland. The mean ages of permafrost aggradation are within the Little Ice Age. Depth profiles of δ15N, when related to C/N ratio, seem to be a suitable tool to detect perturbation and uplift of palsas. Copyright © 2016 John Wiley & Sons, Ltd.

Research on biochar has increased, but its long-term effect on the fertility of temperate agricultural soil remains unclear. In Wallonia, Belgium, pre-industrial charcoal production affected former forested areas that were cleared for cultivation in the nineteenth century. The sites of traditional charcoal kilns, largely enriched in charcoal residues, are similar to soil amended with hardwood biochar more than 150 years ago. We sampled 17 charcoal kiln sites to characterize their effect on soil properties compared with adjacent reference soils. Charcoal-C content was estimated by differential scanning calorimetry. The kiln soil contains from 1.8 to 33.1 g kg−1 of charcoal-C, which markedly increases organic C:N and C:P ratios. It also contains slightly more uncharred soil organic carbon (SOC) than the reference soil, which accords with larger total N content. We measured a small increase in nitrates in the kiln soil that might relate to greater mineralization and nitrification of organic N. Frequent application of lime raised the pH to values close to neutral, which offset the residual effect of charcoal production on soil acidity. A cation exchange capacity (CEC) of 414 cmolc kg−1 was estimated for charcoal-C, whereas that of uncharred SOC was 213 cmolc kg−1. Despite the large CEC of the kiln soil, exchangeable K+ content was no different from the adjacent soil, whereas exchangeable Ca2+ and Mg2+ contents were considerably larger. Charcoal enrichment has little effect on available, inorganic and total P, but it can form strong complexes with Cu, which reduces the availability of the metal. Biochar is very persistent in soil; therefore, long-term implications should not be overlooked. Highlights Charcoal kiln soil contains from 1.8 to 33.1 g kg−1 of charcoal-C, which raises C:N and C:P ratios. Charcoal-C content was estimated by differential scanning calorimetry. We estimated a CEC of 414 cmolc kg−1 for charcoal-C and 213 cmolc kg−1 for uncharred SOC. Retention of exchangeable K+ remained unaffected by charcoal but that of Ca2+ and Mg2+ increased.

We have shown previously that soil with historical (>150 years) applications of charcoal had larger recent (C4-maize derived) carbon content than adjacent soil; however, we could not determine w ...

In the version of this Analysis originally published, the following affiliation for A. Lohila was missing: ‘Finnish Meteorological Institute, Climate System Research, Helsinki, Finland’. This affiliation has now been added, and subsequent affiliations renumbered accordingly, in the online versions of the Analysis.

While many studies have measured the CO2 and N2O exchange of grassland ecosystems and analysed the influence of relevant drivers, only few reported the entire carbon budget over multiple years, which is most relevant for the net greenhouse gas (GHG) source or sink effect. When analysing eddy-covariance-based flux measurements for management and weather related drivers, this is commonly done by comparing either different measurement years at one site or data from different sites distributed regionally or globally. However this procedure makes it usually difficult to clearly attribute observed differences in the carbon exchange to management effects or meteorological drivers. In this study we present results of the carbon and GHG budget of a 10-year paired grassland field experiment in Switzerland comparing intensive and extensive management. We focus on the inter-annual variability of the entire 10-year dataset and especially on the effect of a renovation activity in the intensive field after seven years. By comparing the results of the paired plots, we attempted to disentangle the effects of management including renovation from the effect of seasonal weather conditions on the carbon and greenhouse gas budget. The annual carbon budgets of the two paired fields showed clear systematic differences attributable to the different management. The inter-annual variation (IAV) of the carbon budget was determined as residuals from linear trends. Due to the high correlation of the IAV between the two parallel fields, it was assigned mainly to variations in seasonal weather conditions. The total range of weather attributed variations of annual NECB values was similar in magnitude to the systematic management induced difference between the two fields (100–200 gC m−2 yr-1). In contrast to previous studies on grassland renovation, a large net carbon loss and enhanced N2O emission over 2–3 years was observed here. The excess N2O emission after renovation could be well explained by the IPCC default emission factor approach when considering the additional N input by plant residues and the net soil organic matter mineralisation. Concerning the total GHG budget effect the cumulated GHG uptake by the INT field in the first six years of the experiment was more than compensated by the release in the three post-renovation years.

Land-use changes and afforestation activities are widely recognized as possible measures for mitigating climate change through carbon sequestration. The present study was conducted to evaluate the effect of afforestation on (i) soil physical and chemical properties and soil carbon stocks in four mountain ecosystems and (ii) whole ecosystem carbon storage. The four experimental sites, situated in the Western Rhodope Mountains (Bulgaria) were characterized by typical forest-related land-use conversions. The four sites were a Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) plantation (Rd1) established on former cropland, a mixed black pine (Pinus nigra Arn.) with Scots pine (Pinus sylvestris L.) plantation (Rd2) established on former cropland, a cropland (RdA1) and an abandoned land with uncontrolled extensive grazing (RdA2) historically used as cropland. Soil parameters, i.e., sand content, pH, organic C and N contents, C/N ratio and soil organic carbon (SOC) stocks, were significantly affected by land use and land-use history. Conversion from cropland into forestland significantly reduced soil bulk density and coarse fragments at 0-10 cm depth. Compared with adjacent cropland and abandoned land, soils in coniferous plantations were acidified in their upper layers. Sites Rd2 and RdA2 contained the least SOC owing to the previous long-term arable cultivation (>100 years). Analysis of the ecosystem C stock distribution revealed that most of C in forests was stored in the aboveground tree biomass. Our study confirmed that afforestation of cropland turned the soil into a C sink for the selected mountain region, but showed conflicting results when afforestation occurred on abandoned cropland.

In mountainous areas of Europe, the abandonment of grasslands followed by forest expansion is the dominant land-use change. Labile (i.e. easily decomposable) litter represents the major source for soil microbial products, which promote soil aggregation and long-term C stabilization. Our objective was to investigate changes in the content and origin of soil C components involved into aggregate stabilization (i.e. carbohydrates) following forest expansion on abandoned grassland in the Alps, where only few studies have been conducted. Changes in carbohydrates and thermally labile C were assessed along a land-use gradient in the Southern Alps (Italy) following analysis of carbohydrate monomers and thermal analysis of mineral soil and physical soil fractions. The land-use gradient comprised managed grassland, two transitional phases in which grassland abandonment led to colonization by Picea abies (L.) Karst., and an old forest dominated by Fagus sylvatica L. and P. abies. Grassland abandoned for 10 years tended to have higher levels of carbohydrate and thermally labile soil C than managed grassland and old forest, presumably caused by differences in the quality and amount of litter input. Carbohydrates and thermally labile C showed similar patterns in bulk soil, suggesting that thermal analysis can be used to complement chemical analysis although a straightforward relationship could not be established. Following forest expansion on abandoned grassland, ratios of microbially to plant-derived carbohydrates and thermally labile to resistant components decreased in bulk soil and soil fractions. Forest expansion entailed decreasing amounts of microbially derived compounds known to be important for aggregate stability, and corresponded to decreased soil C allocation to stable aggregates. The combination of carbohydrate and thermal analyses revealed a lower abundance of microbially derived C components after forest colonization on abandoned grasslands, thus resulting in lower physical protection of soil C considering that carbohydrates of microbial origin actively promote soil aggregation.

Organic soils in peatlands store a great proportion of the global soil carbon pool and can lose carbon via the atmosphere due to degradation. In Germany, most of the greenhouse gas (GHG) emissions from organic soils are attributed to sites managed as grassland. Here, we investigated a land use gradient from near-natural wetland (NW) to an extensively managed (GE) to an intensively managed grassland site (GI), all formed in the same bog complex in northern Germany. Vertical depth profiles of δ13C, δ15N, ash content, C / N ratio and bulk density as well as radiocarbon ages were studied to identify peat degradation and to calculate carbon loss. At all sites, including the near-natural site, δ13C depth profiles indicate aerobic decomposition in the upper horizons. Depth profiles of δ15N differed significantly between sites with increasing δ15N values in the top soil layers paralleling an increase in land use intensity owing to differences in peat decomposition and fertilizer application. At both grassland sites, the ash content peaked within the first centimetres. In the near-natural site, ash contents were highest in 10–60 cm depth. The ash profiles, not only at the managed grassland sites, but also at the near-natural site indicate that all sites were influenced by anthropogenic activities either currently or in the past, most likely due to drainage. Based on the enrichment of ash content and changes in bulk density, we calculated the total carbon loss from the sites since the peatland was influenced by anthropogenic activities. Carbon loss at the sites increased in the following order: NW < GE < GI. Radiocarbon ages of peat in the topsoil of GE and GI were hundreds of years, indicating the loss of younger peat material. In contrast, peat in the first centimetres of the NW was only a few decades old, indicating recent peat growth. It is likely that the NW site accumulates carbon today but was perturbed by anthropogenic activities in the past. Together, all biogeochemical parameters indicate a degradation of peat due to (i) conversion to grassland with historical drainage and (ii) land use intensification.

Black carbon (BC) from incomplete combustion of organic materials is abundant in many soils. Its age is often higher than that of thermally unaltered soil organic carbon (SOC) owing to the presence of BC from fossil sources or to a high recalcitrance against microbial decomposition compared to that of plant residues. For a meaningful application of radiocarbon as an indicator for soil carbon age and turnover, the relative contribution of BC needs to be quantified, but BC is difficult to separate physically from soil. However, BC is thermally more stable than SOC, and hence thermal stability may provide a quantitative BC indicator. Here, we analyzed 30 light particulate organic carbon (POC) soil fractions for their thermal stability and for their 14C signature. POC is particularly sensitive to “contamination” with BC, because it is obtained by combined size and density fractionation. A steady-state “bomb” 14C model was used to derive mean POC ages. Soils from four sample sets, each consisting of six to eight individual POC samples and representing different field sites and POC types, were analyzed. Samples from one of the sets were virtually BC free, and their mean POC ages ranged from 60 to 100 yr. The 14C signature of samples from the other three sets indicated the presence of very old carbon, with mean POC ages of several hundred and up to 3500 yr. Two indicators for thermal stability—(1) the amount of heat released at temperatures >450°C and (2) the amount of heat released at 500°C (the latter representing the peak temperature of heat released from charcoal isolated from soil)—correlated both significantly and nonlinearly with POC age, indicating that samples with high BC content were older than those with low BC content. It can be concluded that at an individual site with increasing abundance of BC, both the age and the thermal stability of POC increase. However, thermal stability proved to be a reliable predictor for BC in only one sample set, whereas thermal signals of the other two BC-containing sample sets were not significantly different from those of BC-free samples. Thermal stability thus gives no unequivocal indication for the presence of BC in POC across different sites.

Nitrous oxide (N2O) contributes substantially to greenhouse gas (GHG) emissions in the agricultural and land-use sectors. Owing to the high effort needed for measuring N2O emissions and the resulting lack of sufficient field measurements to apply at country-wide scale, soil-borne N2O emissions are often estimated by applying published IPCC default emission factors. To examine the data reported in the national GHG inventory, the current study utilizes a large data set of soil C/N ratios to predict N2O emissions and their distribution from drained organic soils in Switzerland. Calculated emission rates increase in the order of forest

Organic soils comprise a large yet fragile carbon (C) store in the global C cycle. Drainage, necessary for agriculture and forestry, triggers rapid decomposition of soil organic matter (SOM), typically increasing in the order forest, Biogeosciences, 15 (3), ISSN:1726-4170