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To evaluate the sustainability of biomass plantations, effects on soil organic carbon (SOC) need to be quantified. Miscanthus × giganteus is increasingly used as a bioenergy plant, and it has been hypothesized that, after conversion from cropland, Miscanthus cropping increases SOC storage, whereas conversion from grassland to Miscanthus provides, on average, no sequestration. All field studies hitherto were carried out on mineral soils with topsoil SOC contents of below 3.3%. Here, we analyze in the temperate zone of Switzerland five sites that have been cultivated with Miscanthus for 19–24 years and of which four sites are higher in topsoil SOC content (4.7%–16.2%) and storage (188–262 t SOC) than any previously studied Miscanthus plantation in Europe. We used the difference in carbon isotopic signature between C4 (Miscanthus) and neighboring plots with C3 vegetation (grassland) to quantify the accumulation of new SOC from Miscanthus down to 0.75 m. Annual C4‐C accumulation rates were 1.66 (standard error ± 0.14) t C4‐C ha−1 year−1 (range: 1.26–2.01) in the upper 0.3 m of soil and 1.96 (±0.18) t C4‐C ha−1 year−1 (1.40–2.38) in 0–0.75 m. Average rates for 0–0.3 m were higher than those of mineral soils (n = 37) published previously (0.96 [±0.10] t C4‐C ha−1 year−1). However, high rates of C4‐C accumulation were also reported previously for some mineral soils. Nevertheless, the one mineral soil in our study did not reveal a systematically different accumulation of Miscanthus‐derived carbon compared with the four carbon‐rich soils. We therefore conclude that soils rich in organic matter do not show a different C4‐C accumulation pattern as compared with mineral soils. However, their C4‐C accumulation rates are at the upper end of the data ensemble. Our results further underpin that conversion to Miscanthus, despite C4‐C accumulation, provides no means to increase soil carbon stocks relative to grassland management.

Black carbon (BC) plays an important role in terrestrial carbon storage and can sustainably improve soil fertility. However, the accurate quantification of BC remains critical to fully unravelling the functions and dynamics of BC in soil. In this study, we explored the potential of differential scanning calorimetry (DSC) to identify, characterize and quantify charcoal in the soil of pre-industrial charcoal kiln sites from various forest and cropland areas in Belgium and Germany. Pre-industrial charcoals and uncharred soil organic matter (SOM) demonstrated a distinct thermal signature that could be used to distinguish between them, with charcoal being more thermally stable than SOM. The DSC pattern of charcoals was characterized by one to three specific exothermic peaks, varying in size and position depending on soil conditions. Our data suggest that the thermal moieties within charcoal depend on the strength of chemical bonds of C atoms (increasing with the degree of aromatic condensation and decreasing with weathering) and on the activation energy required to initiate combustion. Despite the specific thermal features of charcoal, its decomposition spans a wide range of temperatures that overlaps with the thermal signature of uncharred SOM. This stresses the challenge of BC quantification in soil and hinders the use of cut-off temperatures to accurately quantify charcoal in soil. Therefore, charcoal-C content was estimated from the relative height of exothermic peaks, attributed either to the combustion of charcoal or SOM. For a selection of 45 soil samples, charcoal-C content estimated by DSC was compared to benzene polycarboxylic acid (BPCA) abundance, a widely used method to quantify BC in soil. The two methods correlated strongly (R2=0.97), with BPCA C representing about one-fifth of DSC-derived charcoal C. This reinforces the view that operationally defined BC content has an absolute quantitative value only if the recovery rate is controlled, which is very complicated for many case studies. Overall, our results demonstrate that dynamic thermal analysis is largely under-exploited despite providing quantitatively interpretable information across the continuum of SOM.

The rapidly collapsing glacial systems of the Alps produced a large number of melt-water lakes and mires after the Last Glacial Maximum (LGM) in the Late Glacial period. The Rhone-Aare-glacier system gave rise to large moorlands and lakes in the region of the Three Lakes Region of Western Switzerland. When moorlands are formed, they are efficient sinks of atmospheric carbon, but when transformed to agricultural land they are significant C sources. In addition, mires can be used as archives for reconstructing landscape evolution. We explored in more detail the dynamics of the landscape of the Three Lakes Region with a particular focus on the formation and degradation of mires. The Bernese part of the Three Lakes Region developed to become—after the optimisation of the water-levels of the Swiss Jura—the vegetable belt of Switzerland. The situation for agriculture, however, has now become critical due to an overexploitation of the peatland. Until c. 13 ka BP the entire region was hydrologically connected. An additional lake existed at the western end of the plain receiving sediments from the Aare river. Around 13 ka BP, this lake was isolated from the Aare river and completely silted up until c. 10 ka BP when a mire started to form. In the valley floor (‘Grosses Moos’), the meandering Aare and the varying level of the nearby lake of Neuchâtel caused a spatio-temporally patchy formation of mires (start of formation: 10–3 ka BP). Strong morphodynamics having high erosion and sedimentation rates and a high variability of the chemical composition of the deposited material prevailed during the early Holocene until c. 7.5 ka BP. The situation remained relatively quiet between 5 and 2 ka BP. However, during the last 2000 years the hydrodynamic and geomorphic activities have increased again. The optimisation of the Swiss Jura water-levels during the nineteenth and twentieth centuries enabled the transformation of moorland into arable land. As a consequence, the moorland strongly degraded. Mean annual C-losses in agricultural land are c. 4.9 t ha−1 and c. 2.4 t ha−1 in forests. Because forests limit, but not stop, the degradation of mires, agroforestry might be tested and propagated in future as alternative land-use systems for such sensitive areas.

International audience; The climate impact of water-table drawdown in peatlands is unclear as carbon dioxide emissions increase and methane emissions decrease due to drying. This study shows decreasing water-table depth results in net greenhouse gas emissions from global peatlands, despite reducing methane emissions.Water-table drawdown across peatlands increases carbon dioxide (CO2) and reduces methane (CH4) emissions. The net climatic effect remains unclear. Based on global observations from 130 sites, we found a positive (warming) net climate effect of water-table drawdown. Using a machine-learning-based upscaling approach, we predict that peatland water-table drawdown driven by climate drying and human activities will increase CO2 emissions by 1.13 (95% interval: 0.88-1.50) Gt yr(-1) and reduce CH4 by 0.26 (0.14-0.52) GtCO(2)-eq yr(-1), resulting in a net increase of greenhouse gas of 0.86 (0.36-1.36) GtCO(2)-eq yr(-1) by the end of the twenty-first century under the RCP8.5 climate scenario. This drops to 0.73 (0.2-1.2) GtCO(2)-eq yr(-1) under RCP2.6. Our results point to an urgent need to preserve pristine and rehabilitate drained peatlands to decelerate the positive feedback among water-table drawdown, increased greenhouse gas emissions and climate warming.

International audience; Understanding the processes underlying carbon (C) stability in soils is of utmost importance in the context of climate change. In this setting, biochar is often studied for its persistence in soils and reported to have positive impacts on soil fertility. Whilst recent research has mostly focused on the short-term effects of biochar amendments to soil, a better understanding of its long-term persistence in soils is needed. Our study focuses on agricultural soils enriched in charcoal residues, produced in preindustrial kiln sites ca. 220 years ago, as a proxy for aged biochar. Our aim is to better understand the processes governing the long-term persistence of pyrogenic organic matter (PyOM) in cultivated soils. To achieve this, we focus on i) the effect of PyOM on soil aggregation, ii) its distribution amongst soil fractions and iii) its chemical and thermal properties. For this purpose, we combined a soil particle size-density fractionation with elemental and thermal analyses on topsoil samples collected in charcoal enriched (CHAR) and adjacent reference (REF) soils in a conventionally cropped field in Wallonia (Belgium). The presence of charcoal in soils resulted in a 91 ± 34% higher C content in CHAR soils than REF soils, of which 84 to 94% was PyOM and 6 to 16% was additional non-PyOM. In CHAR soils, macroaggregation was promoted at the expense of microaggregation (CHARMACRO = 48.9 ± 12.8; CHARMICRO = 25.5 ± 8.3 g 100 g−1 soil) whereas these were similar in REF soils (REFMACRO = 41.3 ± 9.5; REFMICRO = 36.0 ± 8.7 g 100 g−1 soil). Elemental and thermal analyses revealed that PyOM did not only occur as free light fractions but was also occluded in aggregates or sorbed onto mineral phases (56.4 ± 22.9% of total PyOM) suggesting PyOM may be further stabilized through organo-mineral associations. Century-old PyOM showed increased H:C and O:C atomic ratios compared to recently pyrolyzed OM, particularly in occluded as opposed to free light fractions, vouching for the functionalization of its surfaces. Furthermore, regardless of high C contents in CHAR soils, similar C:N ratios between studied soils in mineral dominated fractions suggested increased amounts of N-rich non-PyOM in charcoal rich soils. Our results demonstrate that, over centuries in cultivated soils, PyOM plays an active role in aggregation patterns. We conclude that century old PyOM is broken down from coarse to fine particles, and through functionalization of its surfaces contributes to organo-mineral associations. Beyond its intrinsic chemical recalcitrance, the long-term persistence of biochar is enhanced by occlusion and sorption processes.

The role of soils in the global carbon cycle and in reducing GHG emissions from agriculture has been increasingly acknowledged. The '4 per 1000' (4p1000) initiative has become a prominent action plan for climate change mitigation and achieve food security through an annual increase in soil organic carbon (SOC) stocks by 0.4%, (i.e. 4 parts per thousand per year). However, the feasibility of the 4p1000 scenario and, more generally, the capacity of individual countries to implement soil carbon sequestration (SCS) measures remain highly uncertain. Here, we evaluated country-specific SCS potentials of agricultural land for 24 countries in Europe. Based on a detailed survey of available literature, we estimate that between 0.1% and 27% of the agricultural greenhouse gas (GHG) emissions can potentially be compensated by SCS annually within the next decades. Measures varied widely across countries, indicating differences in country-specific environmental conditions and agricultural practices. None of the countries' SCS potential reached the aspirational goal of the 4p1000 initiative, suggesting that in order to achieve this goal, a wider range of measures and implementation pathways need to be explored. Yet, SCS potentials exceeded those from previous pan-European modelling scenarios, underpinning the general need to include national/regional knowledge and expertise to improve estimates of SCS potentials. The complexity of the chosen SCS measurement approaches between countries ranked from tier 1 to tier 3 and included the effect of different controlling factors, suggesting that methodological improvements and standardization of SCS accounting are urgently required. Standardization should include the assessment of key controlling factors such as realistic areas, technical and practical feasibility, trade-offs with other GHG and climate change. Our analysis suggests that country-specific knowledge and SCS estimates together with improved data sharing and harmonization are crucial to better quantify the role of soils in offsetting anthropogenic GHG emissions at global level.

Peatlands are impacted by climate and land-use changes, with feedback to warming by acting as either sources or sinks of carbon. Expert elicitation combined with literature review reveals key drivers of change that alter peatland carbon dynamics, with implications for improving models. The carbon balance of peatlands is predicted to shift from a sink to a source this century. However, peatland ecosystems are still omitted from the main Earth system models that are used for future climate change projections, and they are not considered in integrated assessment models that are used in impact and mitigation studies. By using evidence synthesized from the literature and an expert elicitation, we define and quantify the leading drivers of change that have impacted peatland carbon stocks during the Holocene and predict their effect during this century and in the far future. We also identify uncertainties and knowledge gaps in the scientific community and provide insight towards better integration of peatlands into modelling frameworks. Given the importance of the contribution by peatlands to the global carbon cycle, this study shows that peatland science is a critical research area and that we still have a long way to go to fully understand the peatland-carbon-climate nexus.

10 páginas. 1 figuras.- 2 tablas.- 134 referencias., To track changes in organic matter (OM) in peat soils, analytical techniques are needed that effectively characterize their chemical components. Pyrolysis-gas chromatography/mass spectrometry is a useful method for obtaining a chemical "fingerprint" of OM. To obtain representative fingerprints, the pyrolysis process should be highly reproducible and representative of the original sample; however, these key indicators for successful volatilization are underreported in the literature. We investigated the influence of instrumental parameters (temperatures, heating rates, sample mass), original organic C and nitrogen (N) content, and instrument type ("slow" vs "flash"), on volatilization of different peat samples by monitoring sample mass loss and changes in organic C and N content before and after pyrolysis. Average percent C by mass volatilized ("C pyrolysis efficiency") across all pyrolysis experiments conducted (mass, instrument types, and settings) was 47.8 +/- 1.8%. Sample mass was not a major driver; however, instrument temperatures, heating rate, and original N content had a significant influence on pyrolysis efficiency. N pyrolysis efficiency occurred at significantly higher rates (56.7-75.8%) than C pyrolysis efficiency (45.1-51.6%). N pyrolysis efficiency was also negatively influenced by decreasing concentrations of original sample N, suggesting that N-containing compounds may undergo preferential volatilization in high pyrolysis temperatures. Our data suggest that C pyrolysis efficiency is relatively insensitive to instrumental parameters; whereas when seeking to identify N-containing compounds, appropriate temperatures and heating rates must be chosen. These results provide an expected range for pyrolysis efficiency as a reference for peat samples analyzed with this technique., This work was supported by the Consejo Superior de Investigaciones Científicas [RYC2014-16338]; Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung [200021_169556].

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

Sustainable soil carbon sequestration practices need to be rapidly scaled up and implemented to contribute to climate change mitigation. We highlight that the major potential for carbon sequestration is in cropland soils, especially those with large yield gaps and/or large historic soil organic carbon losses. The implementation of soil carbon sequestration measures requires a diverse set of options, each adapted to local soil conditions and management opportunities, and accounting for site-specific trade-offs. We propose the establishment of a soil information system containing localised information on soil group, degradation status, crop yield gap, and the associated carbon-sequestration potentials, as well as the provision of incentives and policies to translate management options into region- and soil-specific practices., Reducing soil degradation and improving soil management could make an important contribute to climate change mitigation. Here the authors discuss opportunities and challenges towards implementing a global climate mitigation strategy focused on carbon sequestration in agricultural soils, and propose a framework for guiding region- and soil-specific management options.

Major common production activities on organic soils require drainage, which results in the loss of important ecosystem services such as carbon storage. This paper provides an overview of the farming situation on organic soils in a western region of Switzerland characterized by intensive vegetable farming and therefore by high opportunity costs of adopting sustainable practices on these soils. Based on a review of the academic and grey literature and interviews with regional experts, we find that the main challenges to a change in management practices include the profitability of the current land use, the difficult economic environment of farmers, the cultural background associated with the region, and the absence of systematic data on soil properties. We provide a comparative overview of policy options that could promote sustainable use of organic soils, and present the diverse economic, environmental, and social implications of potential future scenarios of the development on these soils, namely pursuing the current land use versus adopting peat-preserving land use. Based on a basic economic analysis, we find that considering the carbon benefits of preserving the soils, current offsetting-carbon policies cannot compensate the opportunity cost of switching land use on organic soils used for intensive vegetable farming. With the price of carbon offsetting options, only up to the half of the opportunity cost would be covered. We therefore stress the need for a long-term vision of the management decision on these soils and for eliciting society’s willingness to invest in preserving organic soils.

Metal-blending of biomass prior to pyrolysis is investigated in this work as a tool to modify biochar physico-chemical properties and its behavior as adsorbent. Six different compounds were used for metal-blending: AlCl3, Cu(OH)2, FeSO4, KCl, MgCl2 and Mg(OH)2. Pyrolysis experiments were performed at 400 and 700 °C and the characterization of biochar properties included: elemental composition, thermal stability, surface area and pore size distribution, Zeta potential, redox potential, chemical structure (with nuclear magnetic resonance) and adsorption behavior of arsenate, phosphate and nitrate. Metalblending strongly affected biochars' surface charge and redox potential. Moreover, it increased biochars' microporosity (per mass of organic carbon). For most biochars, mesoporosity was also increased. The adsorption behavior was enhanced for all metal-blended biochars, although with significant differences across species: Mg(OH)2-blended biochar produced at 400 °C showed the highest phosphate adsorption capacity (Langmuir Qmax approx. 250 mg g−1), while AlCl3-blended biochar produced also at 400 °C showed the highest arsenate adsorption (Langmuir Qmax approx. 14 mg g−1). Significant differences were present, even for the same biochar, with respect to the investigated oxyanions. This indicates that biochar properties need to be optimized for each application, but also that this optimization can be achieved with tools such as metal-blending. These results constitute a significant contribution towards the production of designer biochars.

Soil organic carbon (SOC) dynamics result from different interacting processes and controls on spatial scales from sub-aggregate to pedon to the whole ecosystem. These complex dynamics are translated into models as abundant degrees of freedom. This high number of not directly measurable variables and, on the other hand, very limited data at disposal result in equifinality and parameter uncertainty. Carbon radioisotope measurements are a proxy for SOC age both at annual to decadal (bomb peak based) and centennial to millennial timescales (radio decay based), and thus can be used in addition to total organic C for constraining SOC models. By considering this additional information, uncertainties in model structure and parameters may be reduced. To test this hypothesis we studied SOC dynamics and their defining kinetic parameters in the Zürich Organic Fertilization Experiment (ZOFE) experiment, a > 60-year-old controlled cropland experiment in Switzerland, by utilizing SOC and SO14C time series. To represent different processes we applied five model structures, all stemming from a simple mother model (Introductory Carbon Balance Model – ICBM): (I) two decomposing pools, (II) an inert pool added, (III) three decomposing pools, (IV) two decomposing pools with a substrate control feedback on decomposition, (V) as IV but with also an inert pool. These structures were extended to explicitly represent total SOC and 14C pools. The use of different model structures allowed us to explore model structural uncertainty and the impact of 14C on kinetic parameters. We considered parameter uncertainty by calibrating in a formal Bayesian framework. By varying the relative importance of total SOC and SO14C data in the calibration, we could quantify the effect of the information from these two data streams on estimated model parameters. The weighing of the two data streams was crucial for determining model outcomes, and we suggest including it in future modeling efforts whenever SO14C data are available. The measurements and all model structures indicated a dramatic decline in SOC in the ZOFE experiment after an initial land use change in 1949 from grass- to cropland, followed by a constant but smaller decline. According to all structures, the three treatments (control, mineral fertilizer, farmyard manure) we considered were still far from equilibrium. The estimates of mean residence time (MRT) of the C pools defined by our models were sensitive to the consideration of the SO14C data stream. Model structure had a smaller effect on estimated MRT, which ranged between 5.9 ± 0.1 and 4.2 ± 0.1 years and 78.9 ± 0.1 and 98.9 ± 0.1 years for young and old pools, respectively, for structures without substrate interactions. The simplest model structure performed the best according to information criteria, validating the idea that we still lack data for mechanistic SOC models. Although we could not exclude any of the considered processes possibly involved in SOC decomposition, it was not possible to discriminate their relative importance.

Biochar, a carbon-rich, porous pyrolysis product of organic residues may positively affect plant yield and can, owing to its inherent stability, promote soil carbon sequestration when amended to agricultural soils. Another possible effect of biochar is the reduction in emissions of nitrous oxide (N2O). A number of laboratory incubations have shown significantly reduced N2O emissions from soil when mixed with biochar. Emission measurements under field conditions however are more scarce and show weaker or no reductions, or even increases in N2O emissions. One of the hypothesised mechanisms for reduced N2O emissions from soil is owing to the increase in soil pH following the application of alkaline biochar. To test the effect of biochar on N2O emissions in a temperate maize cropping system, we set up a field trial with a 20t ha−1 biochar treatment, a limestone treatment adjusted to the same pH as the biochar treatment (pH 6.5), and a control treatment without any addition (pH 6.1). An automated static chamber system measured N2O emissions for each replicate plot (n = 3) every 3.6 h over the course of 8 months. The field was conventionally fertilised at a rate of 160 kg N ha−1 in three applications of 40, 80 and 40 kg N ha−1 as ammonium nitrate. Cumulative N2O emissions were 52 % smaller in the biochar compared to the control treatment. However, the effect of the treatments overall was not statistically significant (p = 0.27) because of the large variability in the data set. Limed soils emitted similar mean cumulative amounts of N2O as the control. There is no evidence that reduced N2O emissions with biochar relative to the control is solely caused by a higher soil pH.

Amount, stability, and distribution of black carbon (BC) were studied at four sites of a large peatland ("Witzwil") formerly used as a disposal for combustion residues from households to derive BC displacement rates in the profile. Possible artefacts from thermal oxidation with Differential Scanning Calorimetry (DSC) on BC quantification of C-rich deposits were inferred by choosing three sites from a second peatland with no historical record of waste disposal as a reference ("Seebodenalp"). All sites were under grassland at time of sampling, but were partially cropped in the past at Witzwil. Mean BC contents in topsoils of Witzwil ranged from 10.7 to 91.5 (0–30 cm) and from 0.44 to 51.3 (30–140 cm) mg BC g−1 soil, corresponding to BC/OC ratios of 0.04 to 0.3 (topsoil) and 0.02 to 0.18 (deeper soil). At three sites of Seebodenalp, BC was below the detection limit of 0.4 mg g−1 organic soil, indicating negligible formation of BC during thermal oxidation of peat. 13C NMR spectra corroborated the high BC contents at Witzwil. The data support a considerable vertical transport of BC given that soils were ploughed not deeper than 30 cm since abandonment of waste application about 50 years ago. The total amount of BC in the Witzwil profiles ranged from 3.2 to 7.5 kg BC m−2, with 21 to 69 percent of it stemming from below the former ploughing depth. Under the premise of negligible rates of BC consumption since abandonment of waste application, minimum BC transport rates in these peats are 0.6 to 1.2 cm a−1. The high mobility of BC might be explained by high macro-pore volumes in combination with occasional water saturation. By means of DSC peak temperatures, different types of BC could be distinguished, with deeper horizons containing BC of higher thermal stability. Application of combustion residues likely involved a mixture of various BC types, of which thermally more stable ones, most likely soots, were preferentially transported downwards.

Palsa peats are unique northern ecosystems formed under an arctic climate and characterized by a high biodiversity and sensitive ecology. The stability of the palsas are seriously threatened by climate warming which will change the permafrost dynamic and induce a degradation of the mires. We used stable carbon isotope depth profiles in two palsa mires of Northern Sweden to track environmental change during the formation of the mires. Soils dominated by aerobic degradation can be expected to have a clear increase of carbon isotopes (δ13C) with depth, due to preferential release of 12C during aerobic mineralization. In soils with suppressed degradation due to anoxic conditions, stable carbon isotope depth profiles are either more or less uniform indicating no or very low degradation or depth profiles turn to lighter values due to an enrichment of recalcitrant organic substances during anaerobic mineralisation which are depleted in 13C. The isotope depth profile of the peat in the water saturated depressions (hollows) at the yet undisturbed mire Storflaket indicated very low to no degradation but increased rates of anaerobic degradation at the Stordalen site. The latter might be induced by degradation of the permafrost cores in the uplifted areas (hummocks) and subsequent breaking and submerging of the hummock peat into the hollows due to climate warming. Carbon isotope depth profiles of hummocks indicated a turn from aerobic mineralisation to anaerobic degradation at a peat depth between 4 and 25 cm. The age of these turning points was 14C dated between 150 and 670 yr and could thus not be caused by anthropogenically induced climate change. We found the uplifting of the hummocks due to permafrost heave the most likely explanation for our findings. We thus concluded that differences in carbon isotope profiles of the hollows might point to the disturbance of the mires due to climate warming or due to differences in hydrology. The characteristic profiles of the hummocks are indicators for micro-geomorphic change during permafrost up heaving.

Drainage and land-use are key factors that trigger CO 2 emissions from cultivated organic soils. Drainage enhances aeration, and land-use might affect peat decomposition due to the input of fresh organic matter (FOM). The effect of FOM addition on peat decomposition of agriculturally used organic soils has seldom been quantified experimentally. In this study, we i) incubated soil samples taken from three adjacent former peatland sites that were drained and managed as cropland, perennial grassland and forest, respectively, and measured CO 2 release over 16 months at 20 °C. In a second experiment, ii) we incubated soil samples from the same three sites with and without adding corn straw as FOM (2% w/w) at 20 °C over three weeks. The 13 C and 14 C signatures of soil organic carbon (SOC) and emitted CO 2 enabled us to apportion the amount of decomposed corn, as well as to estimate relative effects of corn addition on the decomposition of SOC from old peat (SOC old ) and from young soil organic carbon (SOC young ). In the first experiment, samples lost between 0.03 and 0.09 mg CO 2 -C mg SOC − 1 in the order forest > grassland > cropland. The higher 14 C values of the emitted CO 2 vs. that of SOC indicated that SOC young was more easily decomposable. FOM addition induced negative (− 14.8 ± 5.2%), positive (+ 14.9 ± 4.6%) and neutral priming (− 14.2 ± 30.0%) of SOC decomposition in the forest, grassland and cropland samples, respectively. Most importantly, we find that the relative contribution of SOC old to the overall CO 2 release consistently decreased after FOM application, whereas decomposition of SOC young was rather stimulated. The latter finding is in line with previous studies on intact peat. Our results show that young and old C pools in managed organic soils respond differently to the addition of fresh plant residues, and FOM addition can effectively reduce the decomposition of old peat. Hitherto negative priming was never reported for agriculturally used organic soils and it might be caused by the overall poor decomposability of old peat.

Carbon (C) emissions from anthropogenic land use have accelerated climate change. To reduce C emissions, dynamic models can be used to assess the impact of human drivers on terrestrial C sequestration. Model accuracy requires correct initialisation, since incorrect initialisation can influence the results obtained. Therefore, we sought to improve the initialisation of a process-based SOC model, RothC, which can estimate the effect of climate and land-use change on SOC. The most common initialisation involves running the model until equilibrium (‘spin-up run’), when the SOC pools stabilise (method 1). However, this method does not always produce realistic results. At our experimental sites, the observed SOC was not at equilibrium after 10 years, suggesting that the commonly used spin-up initialisation method assuming equilibrium might be improved. In addition to method 1, we tested two alternative initialisations for RothC that involved adjusting the total or individual SOC pool equilibrium values by regulating the C input during the entire spin-up initialisation period (method 2) and initialising each SOC pool with recently measured SOC values obtained by SOC fractionation (method 3). Analysis of the simulation accuracy for each model initialisation, quantified using the root mean square error (RMSE), indicated that a variant of method 2 that involved adjusting the equilibrium total SOC to observed values (method 2-T) generally showed less variation in the individual SOC pools and total SOC. Furthermore, as total SOC is the sum of all SOC pools, and because total SOC data are more readily available than the individual SOC pool data, we conclude that method 2-T is best for initialising RothC.

International audience; 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.

Research networks provide a framework for review, synthesis and systematic testing of theories by multiple scientists across international borders critical for addressing global-scale issues. In 2012, a GHG research network referred to as MAGGnet (Managing Agricultural Greenhouse Gases Network) was established within the Croplands Research Group of the Global Research Alliance on Agricultural Greenhouse Gases (GRA). With involvement from 46 alliance member countries, MAGGnet seeks to provide a platform for the inventory and analysis of agricultural GHG mitigation research throughout the world. To date, metadata from 315 experimental studies in 20 countries have been compiled using a standardized spreadsheet. Most studies were completed (74%) and conducted within a 1–3-year duration (68%). Soil carbon and nitrous oxide emissions were measured in over 80% of the studies. Among plant variables, grain yield was assessed across studies most frequently (56%), followed by stover (35%) and root (9%) biomass. MAGGnet has contributed to modeling efforts and has spurred other research groups in the GRA to collect experimental site metadata using an adapted spreadsheet. With continued growth and investment, MAGGnet will leverage limited-resource investments by any one country to produce an inclusive, globally shared meta-database focused on the science of GHG mitigation. Inst. de Clima y Agua Fil: Liebig, M.A. United States Department of Agriculture. Agricultural Research Service; Estados Unidos Fil: Posse Beaulieu, Gabriela. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Clima y Agua; Argentina Fil: Lewczuk, Nuria. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Clima y Agua; Argentina Fil: Franzluebbers, A.J. United States Department of Agriculture. Agricultural Research Service; Estados Unidos. NC State University. Campus; Estados Unidos Fil: Alvarez, Carolina. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Manfredi; Argentina Fil: Chiesa, Tomás Della. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Piñeiro, Gervasio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Yahdjian, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Grace, P. Queensland University of Technology; Australia Fil: Cabral, Osvaldo Machado Rodrigues. Embrapa Environment; Brasil Fil: Martin-Neto, Ladislau. Embrapa. Departamento de Administração do Parque Estação Biológica; Brasil Fil: Rodrigues, Renato de Aragao Ribeiro. Embrapa Solos; Brasil Fil: Angers, D. Agriculture and Agri-Food Canada; Canadá Fil: Hao, X. Agriculture and Agri-Food Canada, Lethbridge; Canadá Fil: Oelbermann, M. University of Waterloo; Canadá Fil: Tenuta, M. University of Manitoba. Department of Soil Science; Canadá Fil: Munkholm, L.J. Aarhus University. Department. of Agroecology; Dinamarca Fil: Regina, K. Natural Resources Institute; Finlandia Fil: Cellier, Pierre. Institut National de la Recherche Agronomique; Francia Fil: Ehrhardt, Fiona. Institut National de la Recherche Agronomique; Francia Fil: Richard, G. Institut National de la Recherche Agronomique; Francia Fil: Dechow, R. Thünen Institute of Climate Smart Agriculture; Alemania Fil: Agus, F. Indonesian Soil Research Institute; Indonesia Fil: Widiarta, N. Indonesian Center for Food Crop Research and Development; Indonesia Fil: Spink, J. Oak Park Crops Research Centre; Irlanda Fil: Berti, Antonio. Università di Padova. Dipartimento di Agronomia Animali Alimenti Risorse Naturali e Ambiente; Italia Fil: Grignani, Carlo. Università degli Studi di Torino. Dipartimento di Scienze Agrarie, Forestali e Alimentari; Italia Fil: Mazzoncini, Marco. Università di Pisa. Dipartimento di Agronomia e Gestione dell'Agroecosistema; Italia Fil: Orsini, Roberto. Universita Politecnica delle Marche. Dipartimento di Scienze Agrarie Alimentari e Ambientali; Italia Fil: Roggero, Pier Paolo. Universita di Sassari. Dipartimento di Agraria. Nucleo di Ricerca sulla Desertificazione; Italia Fil: Seddaiu, Giovanna. Universita di Sassari. Dipartimento di Agraria. Nucleo di Ricerca sulla Desertificazione; Italia Fil: Tei, Francesco. Università di Perugia. Dipartimento di Scienze Agrarie, Alimentari ed Ambientali; Italia Fil: Ventrella, Domenico. Research Unit for Cropping Systems in Dry Environments; Italia Fil: Vitali, Giuliano. Universita di Bologna. Dipartimento di Scienze Agrarie, Alma Mater Studiorum; Italia Fil: Kishimoto-Mo, A. National Institute for Agro-Environmental Sciences; Japón Fil: Shirato, Y. National Institute for Agro-Environmental Sciences; Japón Fil: Sudo, S. National Institute for Agro-Environmental Sciences; Japón Fil: Shin, J. National Academy of Agricultural Science; Corea del Sur Fil: Schipper, L. University of Waikato. Environmental Research Institute; Nueva Zelanda Fil: Leifeld, J. Agroscope; Suiza Fil: Spadavecchia, L. Department for Environment, Food & Rural Affairs; Reino Unido Fil: Yeluripati, J. The James Hutton Institute; Escosia Fil: Del Grosso, Stephen J. United States Department of Agriculture. Agricultural Research Service; Estados Unidos Fil: Rice, Charles W. Kansas State University; Estados Unidos Fil: Sawchik, Jorge. Instituto Nacional de Investigación Agropecuaria; Uruguay

Land-use change (LUC) and management are among the major driving forces of soil carbon (C) storage. Abandonment of mountain grassland promotes accumulation of aboveground biomass and litter, but related responses of soil organic matter (SOM) dynamics are uncertain. To determine SOM-C turnover we sampled 0–10 cm of soils in the European Alps along two land-use gradients (hay meadows, grazed pastures and abandoned grasslands) of different management intensity. A first land-use gradient was located at Stubai Valley (MAT: 3 °C, MAP: 1097 mm) in Austria and a second at Matsch Valley (MAT: 6.6 °C, MAP: 527 mm) in Italy. We estimated C input and decomposition rates of water-floatable and free particulate organic matter (wPOM, fPOM −3) and aggregate-occluded particulate and mineral-associated organic matter (oPOM −3, mOM >1.6 g cm−3) using bomb radiocarbon. In mountain grasslands average C turnover increased from roots (3 yr) < wPOM (5 yr) < fPOM (80 yr) < oPOM (108 yr) < mOM (192 yr). Among SOM fractions the turnover of fPOM-C varied most in relation to management. Along both land-use gradients C input pathways shifted from root-derived towards litter-derived C. The C input rates of both wPOM-C and fPOM-C were affected by land management at both sites. In contrast, oPOM-C and mOM-C dynamics remained relatively stable in response to grassland abandonment. Carbon accumulation rates of free POM decreased strongly with time since LUC (10, 25 and 36 yr). For wPOM-C, for example, it decreased from 7.4 > 2.2> 0.8 g C m−2 yr−1. At both sites, most C was sequestered in the first years after LUC and free POM reached new steady state within 20–40 yr. We conclude that w-and fPOM-C vs. oPOM-C dynamics respond differently to grassland management change and thus POM does not represent a homogeneous SOM fraction. Sequestered C is stored in the labile POM and not stabilized in the long-term. Thus, it is unlikely that abandonment, the dominant form of LUC in the European Alps, provides a substantial net soil C sink.

15 páginas.-- 2 figuras.-- 1 tablas.-- 42 referencias.-- Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jafc.5b05055.-- Bachmann, Hans Jörg et al. (2016) Journal of Agricultural and Food Chemistry 64(2): 513–527, Biochar produced by pyrolysis of organic residues is increasingly used for soil amendment and many other applications. However, analytical methods for its physical and chemical characterization are yet far from being specifically adapted, optimized, and standardized. Therefore, COST Action TD1107 conducted an interlaboratory comparison in which 22 laboratories from 12 countries analyzed three different types of biochar for 38 physical–chemical parameters (macro- and microelements, heavy metals, polycyclic aromatic hydrocarbons, pH, electrical conductivity, and specific surface area) with their preferential methods. The data were evaluated in detail using professional interlaboratory testing software. Whereas intralaboratory repeatability was generally good or at least acceptable, interlaboratory reproducibility was mostly not (20% < mean reproducibility standard deviation < 460%). This paper contributes to better comparability of biochar data published already and provides recommendations to improve and harmonize specific methods for biochar analysis in the future., The biochar-producing companies Pyreg GmbH, Sonnenerde GmbH, and Swiss Biochar GmbH are acknowledged for sample donation. We are grateful to the IBI and the EBC for fruitful discussions about analytical method standardization. D.F., A.B., and A.G.R. thank the Universitàdi Bologna and Regione Emilia Romagna (Italy) APQ Ricerca Intervento a “Sostegno dello sviluppo dei Laboratori di ricerca nei campi della nautica e dell’energia per il Tecnopolo di Ravenna” and Denis Zannoni for laboratory assistance. F.Z. thanks the laboratory staff at the Institute of Soil Research, University of Natural Resources and Life Sciences (BOKU), Vienna, Austria., We thank the European Cooperation in Science and Technology (COST) for financial support

Biochar, a carbon-rich, porous pyrolysis product of organic residues, is evaluated as an option to tackle major problems of the global food system. Applied to soil, biochar can sequester carbon and have beneficial effects on nitrogen (N) cycling, thereby enhancing crop yields and reducing nitrous oxide (N2O) emissions. There is little understanding of the underlying mechanisms, but many experiments indicated increased yields and manifold changes in N transformation, suggesting an increase in N use efficiency. Biochar's effects can be positive in extensively managed tropical agriculture, however less is known about its use in temperate soils with intensive fertilisation. We tested the effect of slow pyrolysis wood chip biochar on N use efficiency, crop yields and N2O emissions in a lysimeter system with two soil types (sandy loamy Cambisol and silty loamy Luvisol) in a winter wheat—cover crop—sorghum rotation. 15N-labelled ammonium nitrate fertiliser (170 kg N ha−1 in 3 doses, 10% 15N) was applied to the first crop to monitor its fate in three ecosystem components (plants, soil, leachate). Green rye was sown as cover crop to keep the first year's fertiliser N for the second year's sorghum crop (fertilised with 110 kg N ha−1 in two doses and natural abundance 15N). We observed no effects of biochar on N fertiliser use efficiency, yield or N uptake for any crop. Biochar reduced leaching by 43 ± 19% but only towards the end of the experiment with leaching losses being generally low. For both soils N2O emissions were reduced by 15 ± 4% with biochar compared to the control treatments. Our results indicate that application of the chosen biochar induces environmental benefits in terms of N2O emission and N leaching but does not substantially affect the overall N cycle and hence crop performance in the analyzed temperate crop rotation. ISSN:1748-9326 ISSN:1748-9318

In order to evaluate the sustainability and efficiency of soil carbon sequestration measures and the impact of different management and environmental factors, information on soil organic matter (SOM) stability and mean residence time (MRT) is required. However, this information on SOM stability and MRT is expensive to determine via radiocarbon dating, precluding a wide spread use of stability measurements in soil science. In this paper, we test an alternative method, first developed by Conen et al. (2008) for undisturbed Alpine grassland systems, using C and N stable isotope ratios in more frequently disturbed agricultural soils. Since only information on carbon and nitrogen concentrations and their stable isotope ratios is required, it is possible to estimate the SOM stability at greatly reduced costs compared to radiocarbon dating. Using four different experimental sites located in various climates and soil types, this research proved the effectiveness of using the C/N ratio and δ15N signature to determine the stability of mOM (mineral associated organic matter) relative to POM (particulate organic matter) in an intensively managed agro-ecological setting. Combining this approach with δ13C measurements allowed discriminating between different management (grassland vs cropland) and land use (till vs no till) systems. With increasing depth the stability of mOM relative to POM increases, but less so under tillage compared to no-till practises. Applying this approach to investigate SOM stability in different soil aggregate fractions, it corroborates the aggregate hierarchy theory as proposed by Six et al. (2004) and Segoli et al. (2013). The organic matter in the occluded micro-aggregate and silt & clay fractions is less degraded than the SOM in the free micro-aggregate and silt & clay fractions. The stable isotope approach can be particularly useful for soils with a history of burning and thus containing old charcoal particles, preventing the use of 14C to determine the SOM stability. publisher: Elsevier articletitle: Predicting soil organic matter stability in agricultural fields through carbon and nitrogen stable isotopes journaltitle: Soil Biology and Biochemistry articlelink: http://dx.doi.org/10.1016/j.soilbio.2015.05.011 content_type: article copyright: Copyright © 2015 Elsevier Ltd. All rights reserved. ispartof: Soil Biology & Biochemistry vol:88 pages:29-38 status: published

Palsa peatlands are a significant carbon pool in the global carbon cycle and are projected to change by global warming due to accelerated permafrost thaw. Our aim was to use stable carbon isotopes as indicators of palsa degradation. Depth profiles of stable carbon isotopes generally reflect organic matter dynamics in soils with an increase of δ13C values during aerobic decomposition and stable or decreasing δ13C values with depth during anaerobic decomposition. Stable carbon isotope depth profiles of undisturbed and degraded sites of hummocks as well as hollows at three palsa peatlands in northern Sweden were used to investigate the degradation processes. The depth patterns of stable isotopes clearly differ between intact and degraded hummocks at all sites. Erosion and cryoturbation at the degraded sites significantly changes the stable carbon isotope depth profiles. At the intact hummocks the uplifting of peat material by permafrost is indicated by a turning in the δ13C depth trend, and this assessment is supported by a change in the C / N ratios. For hollows isotope patterns were less clear, but some hollows and degraded hollows in the palsa peatlands show differences in their stable carbon isotope depth profiles indicating enhanced degradation rates. We conclude that the degradation of palsa peatlands by accelerated permafrost thawing can be identified with stable carbon isotope depth profiles. At intact hummocks δ13C depth patterns display the uplifting of peat material by a change in peat decomposition processes.

Agricultural management strongly affects soil organic carbon (C), as shown by numerous long-term experiments (1). Practices known to increase soil C include adding organic manures and including grassland in crop rotations. Their effect on C is related to the net primary productivity of the agroecosystem and the fraction of organic matter remaining in the field or returned as residues.

Cette publication a fait l'objet d'une discussion : Conen, F., Morris, C. E., Leifeld, J., Yakutin, M. V., and Alewell, C. Biological residues define the ice nucleation properties of soil dust, Atmos. Chem. Phys. Discuss., 2011, 11, 16585-16598, doi:10.5194/acpd-11-16585-2011; International audience; Soil dust is a major driver of ice nucleation in clouds leading to precipitation. It consists largely of mineral particles with a small fraction of organic matter constituted mainly of remains of micro-organisms that participated in degrading plant debris before their own decay. Some micro-organisms have been shown to be much better ice nuclei than the most efficient soil mineral. Yet, current aerosol schemes in global climate models do not consider a difference between soil dust and mineral dust in terms of ice nucleation activity. Here, we show that particles from the clay and silt size fraction of four different soils naturally associated with 0.7 to 11.8 % organic carbon (w/w) can have up to four orders of magnitude more ice nucleation sites per unit mass active in the immersion freezing mode at −12 °C than montmorillonite, the nucleation properties of which are often used to represent those of mineral dusts in modelling studies. Most of this activity was lost after heat treatment. Removal of biological residues reduced ice nucleation activity to, or below that of montmorillonite. Desert soils, inherently low in organic content, are a large natural source of dust in the atmosphere. In contrast, agricultural land use is concentrated on fertile soils with much larger organic matter contents than found in deserts. It is currently estimated that the contribution of agricultural soils to the global dust burden is less than 20 %. Yet, these disturbed soils can contribute ice nuclei to the atmosphere of a very different and much more potent kind than mineral dusts.

Mechanisms leading to high mean residence times of organic matter in subsoil horizons are poorly understood. In lower parts of the soil profile root material contributes greatly to soil organic matter (SOM). The objective of this study was to elucidate the decomposition dynamics of root-derived C and N in different soil depths during a 3 year field experiment and to examine the importance of different protection mechanisms as well as abiotic factors for the decomposition dynamics. Additionally, we assessed the effect of root litter addition on native SOM. Our conceptual approach included the exposure of litterbags with (13)C and (15)N labeled wheat root material mixed to loamy agricultural soil at three different soil depths (30, 60 and 90 cm). During the incubation period, we monitored soil temperature, humidity and the incorporation of root derived C and N into the soil microbial biomass and physical SOM fractions. Our results showed that abiotic decay conditions were better in subsurface horizons compared to the topsoil. Root litter addition significantly increased the size of microbial biomass in all three soil horizons. In the topsoil, root-derived C decomposition was significantly higher in the first 6 months of incubation compared to subsoil horizons. In 60 and 90 cm depths, a lag phase with development of soil microbial biomass seemed to be prevailing before decomposition was activated. For root-derived N, similar decomposition kinetics could be observed in top- and subsoil horizons. Despite of higher SOM contents, better soil structure and higher microbial activity in the topsoil horizon compared to subsoil horizons, the amounts of root-derived C and N remaining after 3 years were similar for all three depths. Most of the root-derived C and N was present as organo-mineral complexes or occluded in soil aggregates (oPOM), illustrating similar importance of these two protection mechanisms in all three soil depths. Addition of fresh root litter caused small losses of native soil C whereas native N was retained. We conclude that despite of similar SOM protection mechanisms, there are distinct differences in decomposition dynamics of root litter between top- and subsoil horizons. In the long run, the better abiotic decay conditions prevailing in subsoil horizons may compensate for their poorer physico-chemical characteristics.

8 pages, 8 figures, 2 tables, 45 references., Vegetation fires profoundly alter the C cycle of terrestrial ecosystems, notably through the potential formation of highly stable pyrogenic structures. Fire-induced changes in the structure of organic matter (OM) have been studied mainly under controlled laboratory conditions. The objective of this work was to characterise changes in OM chemistry occurring in the litter layer of a scrub–oak ecosystem subjected to a prescribed fire. Maximum temperatures reached during the fire were monitored with thermo-sensitive paint. Litter samples collected before and after the fire were subjected to size fractionation, each size fraction being divided on the basis of visual observation into burnt and unburnt components, i.e. black and brown, respectively. All fractions were analysed for C and N contents and stable carbon isotopic composition. Shifts in the composition of >2 mm fraction components were evaluated using solid-state 13C nuclear magnetic resonance (NMR) spectroscopy and differential scanning calorimetry (DSC). The effects of charring were evaluated through comparisons of black vs. brown post-fire litter in >370 C plots. Comparison of bulk pre- vs. post-fire litter proved unreliable because of the complicating effect of fresh litter fall during the fire event. Charring significantly increased the litter C content by 115– 142 mg g 1 and significantly decreased the d13C value by an average of 0.8‰. The NMR and DSC analyses indicated that O-alkyl compounds were preferentially lost vs. aryl and alkyl compounds. This suggests a preferential loss of cellulose components and a relative preservation of lignin and lipids. However, the charred litter samples had a low degree of condensation vs. a graphitic-like model. The findings suggest that leaf-derived charcoal produced during natural vegetation fires does not contribute much to the highly stable fraction of pyrogenic OM., The project was financially supported by the Institut National des Sciences de l’Univers, a department of the Centre National de la Recherche Scientifique under the framework of the ECCO program, and by a grant from the Smithsonian Environmental Research Center.

Carbon dioxide concentrations were measured semi-continuously in soil pore space under permanent grassland for a 3-year period, using gas-permeable membrane tubes buried at various depths in the soil, in an attempt to quantify temporal variations of soil CO2 storage. Diurnal wavelike variations in CO2 concentration were observed systematically through the soil profile down to 50 cm, and the patterns and amplitude of mean diurnal waves depended on soil- and environmental conditions. For moderate to high soil water contents (SWC), soil CO2 concentrations were positively correlated with soil temperature on a diurnal basis, resulting from an exponential increase of soil respiration with temperature and a shift in thermodynamic gaseous/aqueous phase equilibria. In dry conditions, however, air-filled porosity CO2 concentrations tended to be lowest in the late afternoon and highest in the early morning, and thus negatively correlated with soil temperature. The storage of CO2 in soil was calculated in the air-filled and in the water-filled pore fractions using Henry's law and carbonate chemistry. Storage estimates were extremely sensitive to soil pH and a parametrisation of soil pH as a function of soil water content was derived from field measurements and used in the storage calculation scheme. Instantaneous rates of soil CO2 storage change with time were negatively correlated with atmospheric friction velocity in dry and moderately wet conditions, though in very wet conditions storage changes were dominated by vertical movements of soil water. The data suggest that CO2 can accumulate in the soil during the night when transport is restricted to molecular diffusion through soil layers, and that wind-induced pressure pumping results in a gradual daytime flushing out. These findings may help account for the oft-reported u*-dependence of night-time eddy covariance respiration fluxes.

Soil/atmosphere exchange fluxes of nitrous oxide were monitored for a 3-year period at 10 grassland sites in eight European countries (Denmark, France, Hungary, Ireland, Italy, The Netherlands, Switzerland and United Kingdom), spanning a wide range of climatic, environmental and soil conditions. Most study sites investigated the influence of one or several management practices on N2O exchange, such as nitrogen fertilization and grazing intensity. Fluxes were measured using non-steady state chambers at most sites, and alternative measurement techniques such as eddy covariance and fast-box using tunable diode laser spectroscopy were implemented at some sites. The overall uncertainty in annual flux estimates derived from chamber measurements may be as high as 50% due to the temporal and spatial variability in fluxes, which warrants the future use of continuous measurements, if possible at the field scale. Annual emission rates were higher from intensive than from extensive grasslands, by a factor 4 if grazed (1.77 versus 0.48 kg N2O-N ha(-1) year(-1)) and by a factor 3 if ungrazed (0.95 versus 0.32 kg N2O-N ha(-1) year(-1)). Annual emission factors for fertilized systems were highly variable, ranging from 0.01% to 3.56%. but the mean emission factor across all sites (0.75%) was substantially lower than the IPCC default value of 1.25%. Emission factors for individual fertilization events increased with soil temperature and were generally higher for water-filled pore space values in the range 60-90%, though precipitation onto dry soils was also shown to lead to high losses of N2O-N from applied fertilizer. An empirical, multiple regression model to predict N2O emission factors on the basis of soil temperature, moisture and rainfall is developed, explaining half of the variability in observed emission factors.

We used differential scanning calorimetry (DSC) to infer thermal properties of soil organic matter (SOM) in the static fertilization experiment in Bad Lauchstädt, Germany, which has been established in 1902. Four treatments (null N, change from null to manuring in 1978 NM, change from manuring to null in 1978 MN, and permanent manure and mineral fertilization since 1902 M) were sampled in 2004. Soil organic carbon contents were highest for M (2.4%), lowest for N (1.7%), and similar for MN and NM (2.2%). Three heat flow peaks at around 354°C, 430°C, and 520°C, which were assigned to as thermally labile and stable SOM and combustion residues from lignite, respectively, characterized DSC thermograms. DSC peak temperatures were relatively constant among treatments, but peak heights normalized to the organic C content of the soil were significantly different for labile and stable SOM. Labile C was higher for M>MN=NM=N, and stable C decreased in the order N=NM>MN=M, showing that agricultural depletion of SOM increases the share of thermally stable C. Lignite-derived C was not affected by management, suggesting a homogeneous deposition across treatments.

A substantial amount of the atmospheric carbon taken up on land through photosynthesis and chemical weathering is transported laterally along the aquatic continuum from upland terrestrial ecosystems to the ocean. So far, global carbon budget estimates have implicitly assumed that the transformation and lateral transport of carbon along this aquatic continuum has remained unchanged since pre-industrial times. A synthesis of published work reveals the magnitude of present-day lateral carbon fluxes from land to ocean, and the extent to which human activities have altered these fluxes. We show that anthropogenic perturbation may have increased the flux of carbon to inland waters by as much as 1.0 Pg C yr(-1) since pre-industrial times, mainly owing to enhanced carbon export from soils. Most of this additional carbon input to upstream rivers is either emitted back to the atmosphere as carbon dioxide (similar to 0.4 Pg C yr(-1)) or sequestered in sediments (similar to 0.5 Pg C yr(-1)) along the continuum of freshwater bodies, estuaries and coastal waters, leaving only a perturbation carbon input of similar to 0.1 Pg C yr(-1) to the open ocean. According to our analysis, terrestrial ecosystems store similar to 0.9 Pg C yr(-1) at present, which is in agreement with results from forest inventories but significantly differs from the figure of 1.5 Pg C yr(-1) previously estimated when ignoring changes in lateral carbon fluxes. We suggest that carbon fluxes along the land-ocean aquatic continuum need to be included in global carbon dioxide budgets.