N2O is a potent greenhouse gas involved in the destruction of the protective ozone layer in the stratosphere and contributing to global warming. The ecological processes regulating its emissions from ...soil are still poorly understood. Here, we show that the presence of arbuscular mycorrhizal fungi (AMF), a dominant group of soil fungi, which form symbiotic associations with the majority of land plants and which influence a range of important ecosystem functions, can induce a reduction in N2O emissions from soil. To test for a functional relationship between AMF and N2O emissions, we manipulated the abundance of AMF in two independent greenhouse experiments using two different approaches (sterilized and re-inoculated soil and non-mycorrhizal tomato mutants) and two different soils. N2O emissions were increased by 42 and 33% in microcosms with reduced AMF abundance compared to microcosms with a well-established AMF community, suggesting that AMF regulate N2O emissions. This could partly be explained by increased N immobilization into microbial or plant biomass, reduced concentrations of mineral soil N as a substrate for N2O emission and altered water relations. Moreover, the abundance of key genes responsible for N2O production (nirK) was negatively and for N2O consumption (nosZ) positively correlated to AMF abundance, indicating that the regulation of N2O emissions is transmitted by AMF-induced changes in the soil microbial community. Our results suggest that the disruption of the AMF symbiosis through intensification of agricultural practices may further contribute to increased N2O emissions.
Peatlands drained for agriculture emit large amounts of nitrous oxide (N
2
O) 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 N
2
O emissions. Understanding the effect of mineral soil coverage on N
2
O emissions from agricultural peatland is necessary to implement peatland management strategies which not only sustain agricultural productivity but also reduce N
2
O emissions. In this study, we aimed to quantify the N
2
O 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. N
2
O 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
N
2
O-N, whereas the N
2
O emission from site Cov was only 2.3 ± 0.4 kg N ha
−1
yr
−1
. Peak N
2
O emissions were mostly detected following fertilizer application and lasted for 2–3 weeks before returning to the background N
2
O emissions. At both sites, N
2
O peaks related to fertilization events contributed more than half of the overall N
2
O emissions. However, not only the fertilization induced N
2
O peaks but also background N
2
O emissions were lower with mineral soil coverage. Our data suggest a strong and continued reduction in N
2
O emissions with mineral soil cover from the investigated organic soil. Mineral soil coverage, therefore, seems to be a promising N
2
O 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.
•Two grazed pasture fields with different cow feeding strategies were compared.•Field-scale and small-scale exchange of CO2, CH4 and N2O was measured.•Full annual GHG budgets showed that both ...pastures were GHG neutral.•Maize supplements in the feed led to an improved GHG budget.•Annual N2O emissions were dominated by emissions from fertilization.
Increasing the soil carbon stock by optimizing the grassland management is seen as a potential cost-effective mitigation strategy to counteract greenhouse gas (GHG) emissions from pasture fields associated with the application of fertilizer or cattle excreta. This study presents results of GHG flux measurements in a paired field experiment of two neighboring grazing systems over a full year. Each pasture was grazed by 12 dairy cows in a rotational grazing management. Different feeding strategies (system G: grazing only; system M: grazing with supplement of maize silage) resulted in different nitrogen excretion rates. The field scale emissions of CO2, methane (CH4) and nitrous oxide (N2O) were quantified using the eddy covariance (EC) technique on both parallel pasture fields excluding the direct emissions by the animals. Small-scale CH4 emissions from excreta patches and background areas were also measured using the ‘fast-box’ chamber technique. The fast-box measurements dominated by dung patch emissions were up-scaled to the field and compared to the EC measurements revealing some discrepancies between the two measurement approaches. N2O emissions resulted mainly from slurry and mineral fertilization (44 ± 17%) while both animal excreta and background emissions contributed each about 28% to the annual emissions. Total N2O emissions amounted to 3.8 ± 1.1 kg N2O-N ha−1 yr−1 and 3.7 ± 1.4 kg N2O-N ha−1 yr−1 for the pasture fields M and G, respectively. In order to determine the net ecosystem carbon budget (NECB) of the pasture fields, additional non-gaseous carbon fluxes were either measured (harvest, slurry application) or estimated based on an animal feeding model (grazing intake, excreta). For the investigated year, the NECB (negative sign indicating sequestration) resulted in –103 ± 74 g C m−2 yr−1 and –63 ± 67 g C m−2 yr−1 for pastures M and G, respectively, indicating the tendency of carbon storage especially in the pasture M soil. However, the emissions of CH4 and N2O almost balanced the NECB resulting in non-significant (near-neutral) net GHG budgets for the pasture soils (field M:–144 ± 277 g CO2-eq. m−2 yr−1, field G:–9 ± 256 g CO2-eq. m−2 yr−1). Due to the paired plot design of the experiment, the difference between the two pasture fields was significant with pasture M showing a reduction in net GHG emissions by 135 ± 89 g CO2-eq. m−2 yr−1 compared to pasture G.
•The carbon and GHG budgets of a 10-year grassland field experiment are presented.•The paired plot design allowed separation of management and weather induced effects.•Grassland renovation in one ...field led to a large carbon loss and N2O emissions.•In contrast to other studies, a multi-annual GHG effect of renovation was observed.•Effects of management and weather on annual NECB were of similar magnitude.
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.
Grazed pastures are strong sources of the greenhouse gas nitrous oxide (N2O). The quantification of N2O emissions is challenging due to the strong spatial and temporal variabilities of the emission ...sources and so N2O emission estimates are very uncertain. This study presents N2O emission measurements from two grazing systems in western Switzerland over the grazing season of 2016. The 12 dairy cows of each herd were kept in an intensive rotational grazing management. The diet for the two herds of cows consisted of different protein-to-energy ratios (system G: grass only diet; system M: grass with additional maize silage) resulting in different nitrogen (N) excretion rates. The N in the excretion was estimated by calculating the animal nitrogen budget taking into account the measurements of feed intake, milk yield, and body weight of the cow herds. Directly after the rotational grazing phases, background and urine patches were identified based on soil electric conductivity measurements while fresh dung patches were identified visually. The magnitude and temporal pattern of these different emission sources were measured with a fast-box (FB) chamber and the field-scale fluxes were quantified using two eddy covariance (EC) systems. The FB measurements were finally upscaled to the field level and compared to the EC measurements for quality control by using EC footprint estimates of a backward Lagrangian stochastic dispersion model. The comparison between the two grazing systems was performed during emission periods that were not influenced by fertilizer applications. This allowed the calculation of the excreta-related N2O emissions per cow and grazing hour and resulted in considerably higher emissions for system G compared to system M. Relating the found emissions to the excreta N resulted in excreta-related emission factors (EFs) of 0.74±0.26 % for system M and 0.83±0.29 % for system G. These EF values were thus significantly smaller compared to the default EF of 2 % provided by the IPCC guidelines for cattle excreta deposited on pasture. The measurements showed that urine patch emission dominated the field-scale fluxes (57 %), followed by significant background emissions (38 %), and only a small contribution of dung patch emission (5 %). The resulting source-specific EFs exhibited a clear difference between urine (1.12±0.43 %) and dung (0.16±0.06 %), supporting a disaggregation of the grazing-related EFs by excreta type in emission inventories. The study also highlights the advantage of a N-optimized diet, which resulted in reduced N2O emissions from animal excreta.
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<0.01) younger than at Ref, indicating that mineral soil coverage moved the source of decomposition of soil organic carbon (SOC) from a higher share of old peat towards a higher share of relatively younger material. In summary, our study lends support to the hypothesis that mineral soil coverage might reduce the decomposition of old peat underneath, and may therefore be a promising peatland management technique for the future use of drained peatland for agriculture.
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•Sustained use of drained peatland requires halting the decline of peatland carbon stocks.•Mineral soil coverage has become an increasingly used management in drained peatland.•Mineral soil coverage does not reduce heterotrophic respiration from drained peatland.•Decomposition of relatively old peat carbon is reduced after mineral soil coverage.
Loss of ammonia (NH3) after field application of livestock slurry contributes between 30% and 50% of agricultural NH3 emissions from European countries. The objectives of this study were to ...re-evaluate NH3 emissions following application of cattle and pig slurry to grassland in Switzerland and to investigate the effectiveness of abatement techniques. In 17 field experiments, NH3 emissions were determined with a micrometeorological approach, relating the emission to the measured concentration by means of atmospheric dispersion modelling. The cattle slurry applied exhibited an average dry matter content of 3.3% (range between 1.0% and 6.7% dry matter). The emission after application of cattle slurry spread with a splash plate (referred to as reference technique) ranged from 10% to 47% of applied Total Ammoniacal Nitrogen (% of TAN) and averaged to 25% of TAN. This range of losses is lower by approx. a factor of two compared to measurements from earlier Swiss experiments. Applications with trailing hose and trailing shoe systems yielded an average reduction of 51% and 53%, respectively, relative to the reference technique. A regression analysis showed that the dry matter content of the slurry and the air temperature are important drivers for NH3 emission.
•We conducted 17 field experiments on NH3 emission after slurry application.•Emissions after slurry broadcast application ranged from 10% to 47% of TAN.•Examined abatement techniques proofed to be efficient in reducing emissions.•A regression analysis was performed.•Air temperature and slurry dry matter were important predictor parameters.
The quantification of ammonia (NH3) emissions is still a challenge and the corresponding emission factor for grazed pastures is uncertain. This study presents NH3 emission measurements of two pasture ...systems in western Switzerland over the entire grazing season 2016. During the measurement campaign, each pasture system was grazed by 12 dairy cows in an intensive rotational management. The cow herds on the two pastures differed in the energy to protein balance of the diet. NH3 concentrations were measured upwind and downwind of a grazed subplot with line-integrating open path instruments that were able to retrieve small horizontal concentration differences (< 0.2 µg NH3 m−3). The NH3 emission fluxes were calculated by applying a backward Lagrangian stochastic (bLS) dispersion model to the difference of paired concentration measurements and ranged from 0 to 2.5 µg N–NH3 m−2 s−1. The fluxes increased steadily during a grazing interval from previous non-significant values to reach maximum emissions at the end of the grazing interval. Afterwards they decreased exponentially to near zero-values within 3–5 days. A default emission curve was calculated for each of the two systems and adopted to each rotation in order to account for missing data values and to estimate inflow disturbances due to grazing on upwind paddocks. Dung and cow location were monitored to account for the non-negligible inhomogeneity of cow excreta on the pasture. The average emission (± SD of individual rotation values) per grazing hour was calculated as 0.64±0.11 g N–NH3 cow−1 h−1 for the herd with the N-balanced diet (system M) and 1.07±0.06 g N–NH3 cow−1 h−1 for the herd with the protein-rich grass-only diet (system G). Surveys of feed intake, body weight and milk yield of the cow herds were used to estimate the nitrogen (N) excretion by an animal N budget model. Based on that, mean relative emission factors of 6.4±2.0 % and 8.7±2.7 % of the applied urine N were found for the systems M and G, respectively. The results can be used to validate the Swiss national emission inventory and demonstrate the positive effect of an N-balanced diet on pasture NH3 emissions.
Nitrogen (N) is one of the most limited nutrients of terrestrial ecosystems, whose losses are prevented in tightly coupled cycles in finely tuned systems. Global change-induced N enrichment through ...atmospheric deposition and application of vast amounts of fertilizer are now challenging the terrestrial N cycle. Arbuscular mycorrhizal fungi (AMF) are known drivers of plant-soil nutrient fluxes, but a comprehensive assessment of AMF involvement in N cycling under global change is still lacking. Here, we simulated N enrichment by fertilization (low/high) in experimental grassland microcosms under greenhouse conditions in the presence or absence of AMF and continuously monitored different N pathways over nine months. We found that high N enrichment by fertilization decreased the relative abundance of legumes and the plant species dominating the plant community changed from grasses to forbs in the presence of AMF, based on aboveground biomass. The presence of AMF always maintained plant N:phosphorus (P) ratios between 14 and 16, no matter how the soil N availability changed. Shifts in plant N:P ratios due to the increased plant N and P uptake might thus be a primary pathway of AMF altering plant community composition. Furthermore, we constructed a comprehensive picture of AMF's role in N cycling, highlighting that AMF reduced N losses primarily by mitigating N leaching, while N2O emissions played a marginal role. Arbuscular mycorrhizal fungi reduced N2O emissions directly through the promotion of N2O-consuming denitrifiers. The underlying mechanism for reducing N leaching is mainly the AMF-mediated improved nutrient uptake and AMF-associated microbial immobilization. Our results indicate that synergies between AMF and other soil microorganisms cannot be ignored in N cycling and that the integral role of AMF in N cycling terrestrial ecosystems can buffer the upcoming global changes.
We present a differential optical absorption spectroscopy (DOAS) instrument, called "miniDOAS", optimised for optical open-path field-measurements of ambient ammonia (NH3) alongside nitrogen oxide ...(NO) and sulfur dioxide (SO2). The instrument is a further development of the miniDOAS presented by Volten et al. (2012). We use a temperature-controlled spectrometer, a deuterium light source and a modified optical arrangement. The system was set up in a robust, field-deployable, temperature-regulated housing. For the evaluation of light spectra we use a new high-pass filter routine based upon robust baseline extraction with local regression. Multiple linear regression including terms of an autoregressive–moving-average model is used to determine concentrations. For NH3 the random uncertainty is about 1.4 % of the concentration, and not better than 0.2 µg m−3. Potential biases for the slope of the calibration are given by the precision of the differential absorption cross sections (±3 %) and for the offset by the precision of the estimation of concentration offsets (cref) introduced by the reference spectrum Iref. Comparisons of miniDOAS measurements to those by NH3 acid trap devices showed good agreement. The miniDOAS can be flexibly used for a wide range of field trials, such as micrometeorological NH3 flux measurements with approaches based upon horizontal or vertical concentration differences. Results from such applications covering concentration dynamics of less than one up to several hundreds of µg m−3 are presented.
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