Search

Nitrous oxide, a greenhouse gas, is mainly emitted from soils during the denitrification process. Nitrogen stable-isotope investigations can help to characterise the N(2)O source and N(2)O production mechanisms. The stable-isotope approach is increasingly used with (15)N natural abundance or relatively low (15)N enrichment levels and requires a good knowledge of the isotopic fractionation effect inherent to this biological mechanism. This paper reports the measurement of the net and instantaneous isotopic fractionation factor (alpha(s/p) (i)) during the denitrification of NO(3) (-) to N(2)O over a range of (15)N substrate enrichments (0.37 to 1.00 atom% (15)N). At natural abundance level, the isotopic fractionation effect reported falls well within the range of data previously observed. For (15)N-enriched substrate, the value of alpha(s/p) (i) was not constant and decreased from 1.024 to 1.013, as a direct function of the isotopic enrichment of the labelled nitrate added. However, for enrichment greater than 0.6 atom% (15)N, the value of alpha(s/p) (i) seems to be independent of substrate isotopic enrichment. These results suggest that for isotopic experiments applied to N(2)O emissions, the use of low (15)N-enriched tracers around 1.00 atom% (15)N is valid. At this enrichment level, the isotopic effect appears negligible in comparison with the enrichment of the substrate., (Copyright (c) 2007 John Wiley & Sons, Ltd.)

Nitrous oxide (N2O) emission estimates from forest ecosystems are based currently on emission measurements using soil enclosures. Such enclosures exclude emissions via tall plants and trees and may therefore underestimate the whole-ecosystem N2O emissions. Here, we measured plant-mediated N2O emissions from the leaves of potted beech (Fagus sylvatica) seedlings after fertilizing the soil with 15N-labelled ammonium nitrate (15NH4(15)NO3), and after exposing the roots to elevated concentrations of N2O. Ammonium nitrate fertilization induced N2O + 15N2O emissions from beech leaves. Likewise, the foliage emitted N2O after beech roots were exposed to elevated concentrations of N2O. The average N2O emissions from the fertilization and the root exposure experiments were 0.4 and 2.0 microg N m(-2) leaf area h(-1), respectively. Higher than ambient atmospheric concentrations of N2O in the leaves of the forest trees indicate a potential for canopy N2O emissions in the forest. Our experiments demonstrate the existence of a previously overlooked pathway of N2O to the atmosphere in forest ecosystems, and bring about a need to investigate the magnitude of this phenomenon at larger scales.

The combination of nitrogen (N) fertilization and straw incorporation has complex influences on soil N transformations and derived nitrous oxide (N2O) emissions. This study aimed to reveal the coupled effects of straw returning forms and N fertilizer management on soil N2O emissions. Here, carbon (C) sources with varied availabilities were supplied by different straw returning forms, including straw, charred straw, and combined application of straw and charred straw. The time gaps between additions of exogenous N and C sources were carried out by managing the timing of N fertilization, including N application simultaneous with or delayed after straw return. Soil N2O emissions under different straw returning forms and their response relationships to soil C, N, microbial biomass, as well as soil pH and oxygen (O2) were explored. Co‐application of straw and N fertilizer provided sufficient C and N sources, enhanced the microbial biomass, and consequently increased N2O emissions. Delayed N fertilization could decouple the response of N2O emissions to straw addition, because of constrained N availability and limited pH decline, which decreased the cumulative N2O emissions significantly. Possibly due to straw induced N immobilization coupled with charred straw induced pH elevation, the combined application of straw and charred straw constrained soil N2O emissions compared with straw only application, regardless of N fertilizer management. By shaping the microbial biomass and soil C, N, and O2 dynamics, delayed application of N fertilizer could further enhance the inhibition effect of the charred straw and straw combination on soil N2O emissions. Therefore, the varied straw returning forms and the timing of N fertilization could affect the supply of available C and N, influencing the hot moments of N2O emissions, and the joint addition of straw and charred straw with a few weeks delayed N application could possibly reduce the risk of soil N2O emissions from straw return systems. Such mitigation potential should be evaluated further under field conditions. Highlights: Delayed N fertilization attenuated the magnitude of N2O emissions after straw additions.Combination of charred straw with straw mitigated N2O emissions, further enhanced by delayed N fertilization.Soil pH was the chief regulator for N2O emissions under different straw returning forms and N application. [ABSTRACT FROM AUTHOR]

Wildfire frequency and expanse in the Arctic have increased in recent years and are projected to increase further with changes in climatic conditions due to warmer and drier summers. Yet, there is a lack of knowledge about the impacts such events may have on the net greenhouse gas (GHG) balances in Arctic ecosystems. We investigated in situ effects of an experimental fire in 2017 on carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) surface fluxes in the most abundant tundra ecosystem in West Greenland in ambient and warmer conditions. Measurements from the growing seasons 2017 to 2019 showed that burnt areas became significant net CO2 sources for the entire study period, driven by increased ecosystem respiration (ER) immediately after the fire and decreased gross ecosystem production (GEP). Warming by open‐top chambers significantly increased both ER and GEP in control, but not in burnt plots. In contrast to CO2, measurements suggest that the overall sink capacity of atmospheric CH4, as well as net N2O emissions, were not affected by fire in the short term, but only immediately after the fire. The minor effects on CH4 and N2O, which was surprising given the significantly higher nitrate availability observed in burnt plots. However, the minor effects are aligned with the lack of significant effects of fire on soil moisture and soil temperature. Net uptake and emissions of all three GHG from burnt soils were less temperature‐sensitive than in the undisturbed control plots. Overall, this study highlights that wildfires in a typical tundra ecosystem in Greenland may not lead to markedly increased net GHG emissions other than CO2. Additional investigations are needed to assess the consequences of more severe fires. [ABSTRACT FROM AUTHOR]

• Low vs. high fire intensity lead to opposite responses of an Arctic soil microbiome. • Low fire intensity did not reduce tested genes while it promoted genes involved in N mineralization and archaeal nitrification. • High fire intensity reduced genes involved in N fixation/mineralization, P solubilization and denitrification. • Fire intensity is crucial for predictions of permafrost nutrient-climate feedbacks. Arctic tundra fires have been increasing in extent, frequency and intensity and are likely impacting both soil nitrogen (N) and phosphorus (P) cycling and, thus, permafrost ecosystem functioning. However, little is known on the underlying microbial mechanisms, and different fire intensities were neglected so far. To better understand immediate influences of different fire intensities on the soil microbiome involved in nutrient cycling in permafrost-affected soil, we deployed experimental fires with low and high intensity on an Arctic tundra soil on Disko Island, Greenland. Soil sampling took place three days postfire and included an unburned control. Using quantitative real-time PCR, copy numbers of 16S and ITS as well as of 17 genes coding for functional microbial groups catalyzing major steps of N and P turnover were assessed. We show that fires change the abundance of microbial groups already after three days with fire intensity as key mediating factor. Specifically, low-intensity fire significantly enhanced the abundance of chiA mineralizers and ammonia-oxidizing archaea, while other groups were not affected. On the contrary, high-intensity fire decreased the abundance of chiA mineralizers and of microbes that fix dinitrogen, indicating a dampening effect on N cycling. Only high-intensity fires enhanced ammonium concentrations (by an order of magnitude). This can be explained by burned plant material and the absence of plant uptake, together with impaired further N processing. Fire with high intensity also decreased nirK -type denitrifiers. In contrast, after fire with low intensity there was a trend for a decreased nosZ : (nirK + nirS) ratio, indicating – together with increased nitrate concentrations – an enhanced potential for nitric oxide and nitrous oxide emissions. Concerning P transformation, only gcd was affected in the short term which is important for P solubilization. Changes in gene numbers consistently showed the same contrasting pattern of elevated abundance with low fire intensity and decreased abundance with high fire intensity. Differentiating fire intensities is therefore crucial for further, longer-term studies of fire-induced changes in N and P transformations and potential nutrient-climate feedbacks of permafrost-affected soils. [ABSTRACT FROM AUTHOR]

Abstract: Fire is a major factor controlling global carbon (C) and nitrogen (N) cycling. While direct C and N losses caused by combustion have been comparably well established, important knowledge gaps remain on postfire N losses. Here, we quantified both direct C and N combustion losses as well as postfire gaseous losses (N2O, NO and N2) and N leaching after a high‐intensity experimental fire in an old shrubland in central Spain. Combustion losses of C and N were 9.4 Mg C/ha and 129 kg N/ha, respectively, representing 66% and 58% of initial aboveground vegetation and litter stocks. Moreover, fire strongly increased soil mineral N concentrations by several magnitudes to a maximum of 44 kg N/ha 2 months after the fire, with N largely originating from dead soil microbes. Postfire soil emissions increased from 5.4 to 10.1 kg N ha−1 year−1 for N2, from 1.1 to 1.9 kg N ha−1 year−1 for NO and from 0.05 to 0.2 kg N ha−1 year−1 for N2O. Maximal leaching losses occurred 2 months after peak soil mineral N concentrations, but remained with 0.1 kg N ha−1 year−1 of minor importance for the postfire N mass balance. 15N stable isotope labelling revealed that 33% of the mineral N produced by fire was incorporated in stable soil N pools, while the remainder was lost. Overall, our work reveals significant postfire N losses dominated by emissions of N2 that need to be considered when assessing fire effects on ecosystem N cycling and mass balance. We propose indirect N gas emissions factors for the first postfire year, equalling to 7.7% (N2‐N), 2.7% (NO‐N) and 5.0% (N2O‐N) of the direct fire combustion losses of the respective N gas species. [ABSTRACT FROM AUTHOR]

Recent advances in laser spectrometry offer new opportunities to investigate soil-atmosphere exchange of nitrous oxide. During two field campaigns conducted at a grassland site and a willow field, we tested the performance of a quantum cascade laser (QCL) connected to a newly developed automated chamber system against a conventional gas chromatography (GC) approach using the same chambers plus an automated gas sampling unit with septum capped vials and subsequent laboratory GC analysis. Through its high precision and time resolution, data of the QCL system were used for quantifying the commonly observed non-linearity in concentration changes during chamber deployment, making the calculation of exchange fluxes more accurate by the application of exponential models. As expected, the curvature in the concentration increase was higher during long (60 min) chamber closure times and under high flux conditions (FN2O > 150 µg N m-2 h-1) than those that were found when chambers were closed for only 10 min and/or fluxes were in a typical range of 2 to 50 µg N m-2 h-1. Extremely low standard errors of fluxes, i.e. ~0.1% of the flux value, were observed regardless of linear or exponential flux calculation when using QCL data. Thus, we recommend reducing chamber closure times to a maximum of 10 min when high-frequency measurements are available to keep soil disturbance low and conditions around the chamber plot as natural as possible. If instrumentation with high-frequency resolution is available, sampling times from 1 to 5 s proved to be sufficient for robust flux determination assuring standard errors of N2O fluxes still being on a relatively low level. Despite low signal to noise ratios, GC was still found to be a useful method to determine soil-atmosphere exchange of N2O at longer time scales, i.e. seasons to years, e.g., when the main focus of the study is to investigate site budgets. Intriguingly, the consistency between GC and QCL-based campaign averages was better under low than under high N2O efflux conditions, although single flux values were highly scattered during the low efflux campaign. Furthermore, the QCL technology provides a useful tool to accurately investigate the highly debated topic of diurnal courses of N2O fluxes and its controlling factors. Our new chamber design reduces the disturbance of the soil and complies with high quality requirements of long-term observation studies and research infrastructures. [ABSTRACT FROM AUTHOR]

One way of reducing the emissions of fossil fuel-derived carbon dioxide ( CO2) is to replace fossil fuels with biofuels produced from agricultural biomasses or residuals. However, cultivation of soils results in emission of other greenhouse gases ( GHGs), especially nitrous oxide ( N2O). Previous studies on biofuel production systems showed that emissions of N2O may counterbalance a substantial part of the global warming reduction, which is achieved by fossil fuel displacement. In this study, we related measured field emissions of N2O to the reduction in fossil fuel-derived CO2, which was obtained when agricultural biomasses were used for biofuel production. The analysis included five organically managed feedstocks (viz. dried straw of sole cropped rye, sole cropped vetch and intercropped rye-vetch, as well as fresh grass-clover and whole crop maize) and three scenarios for conversion of biomass into biofuel. The scenarios were (i) bioethanol, (ii) biogas and (iii) coproduction of bioethanol and biogas. In the last scenario, the biomass was first used for bioethanol fermentation and subsequently the effluent from this process was utilized for biogas production. The net GHG reduction was calculated as the avoided fossil fuel-derived CO2, where the N2O emission was subtracted. This value did not account for fossil fuel-derived CO2 emissions from farm machinery and during conversion processes that turn biomass into biofuel. The greatest net GHG reduction, corresponding to 700-800 g CO2 m−2, was obtained by biogas production or coproduction of bioethanol and biogas on either fresh grass-clover or whole crop maize. In contrast, biofuel production based on lignocellulosic crop residues (i.e. rye and vetch straw) provided considerably lower net GHG reductions (≤215 g CO2 m−2), and even negative numbers sometimes. No GHG benefit was achieved by fertilizing the maize crop because the extra crop yield, and thereby increased biofuel production, was offset by enhanced N2O emissions. [ABSTRACT FROM AUTHOR]

Abstract: In temperate regions, climate change is predicted to increase annual mean temperature and intensify the duration and frequency of summer droughts, which together with elevated atmospheric carbon dioxide (CO2) concentrations, may affect the exchange of nitrous oxide (N2O) and methane (CH4) between terrestrial ecosystems and the atmosphere. We report results from the CLIMAITE experiment, where the effects of these three climate change parameters were investigated solely and in all combinations in a temperate heathland. Field measurements of N2O and CH4 fluxes took place 1–2 years after the climate change manipulations were initiated. The soil was generally a net sink for atmospheric CH4. Elevated temperature (T) increased the CH4 uptake by on average 10 μg C m−2 h−1, corresponding to a rise in the uptake rate of about 20%. However, during winter elevated CO2 (CO2) reduced the CH4 uptake, which outweighed the positive effect of warming when analyzed across the study period. Emissions of N2O were generally low (<10 μg N m−2 h−1). As single experimental factors, elevated CO2, temperature and summer drought (D) had no major effect on the N2O fluxes, but the combination of CO2 and warming (TCO2) stimulated N2O emission, whereas the N2O emission ceased when CO2 was combined with drought (DCO2). We suggest that these N2O responses are related to increased rhizodeposition under elevated CO2 combined with increased and reduced nitrogen turnover rates caused by warming and drought, respectively. The N2O flux in the multifactor treatment TDCO2 was not different from the ambient control treatment. Overall, our study suggests that in the future, CH4 uptake may increase slightly, while N2O emission will remain unchanged in temperate ecosystems on well-aerated soils. However, we propose that continued exposure to altered climate could potentially change the greenhouse gas flux pattern in the investigated heathland. [Copyright &y& Elsevier]

In recent years, wildfire frequency and severity has increased in the Arctic tundra regions due to climate change. Pyrogenic organic matter (PyOM) is a product of incomplete combustion of biomass containing nutrients such as nitrogen (N), and is expected to affect ecosystem N cycling during a post-fire recovery period. We investigated effects of fire on soil biogeochemical cycles with a focus on pyrogenic N turnover over two subsequent growing seasons, combined with and without summer warming, in an Arctic heath tundra, West Greenland. The summer warming was achieved by deployment of open top chambers (OTCs). We simulated an in situ tundra fire by removing vegetation and litter, and scorching/heating soil surface followed by the addition of 15N-labelled PyOM (derived from aboveground biomass and litter) to the soil surface in plots with and without summer warming. A darker surface after the simulated fire resulted in an increase of 1.3 °C in soil temperature at 5-cm depth over the growing seasons. The fire also caused a nine-fold increase in soil NH 4 +-N and three-fold increase in soil NO 3 −-N concentrations at 7-cm depth after two years. Tracing the fate of 15N-labelled PyOM, 21 days after its application, showed low 15N recovery in microbial biomass (0.4%) and total dissolved N (TDN) pools (0.01%). Microbial and root 15N recovery increased two-fold and 15-fold after one year, respectively, and TDN 15N recovery increased two-fold after two years, suggesting that relatively recalcitrant N of PyOM can be partly transformed into plant-available forms over time. Root and TDN 15N recovery was also significantly higher after two years of summer warming than under ambient temperature conditions, suggesting that summer warming can enhance availability of PyOM-N for recovering plants after the fire. Hence, we conclude that fire-induced PyOM can act as an N source for plant recovery in this Arctic tundra ecosystem for years after the fire, and this N source will become increasingly important in a future warmer climate. • Pyrogenic organic matter (PyOM) turnover after fire in an Arctic dry tundra. • There was a large loss of 15N-PyOM (30%) after 21 days. • The PyOM-N provided a N source to soil microbes and plants. • Summer warming enhanced availability of PyOM-N for plant re-growth. [ABSTRACT FROM AUTHOR]

Climate change is profound in the Arctic where increased snowfall during winter and warmer growing season temperatures may accelerate soil nitrogen (N) turnover and increase inorganic N availability. Nitrous oxide (N 2 O) is a potent greenhouse gas formed by soil microbes and in the Arctic, the production is seen as limited mainly by low inorganic N availability. Hence, it can be hypothesized that climate change in the Arctic may increase total N 2 O emissions, yet this topic remains understudied. We investigated the combined effects of variable snow depths and experimental warming on soil N cycling in a factorial field study established along a natural snowmelt gradient in a low Arctic heath ecosystem. The study assessed N 2 O surface fluxes, gross N mineralization and nitrification rates, potential denitrification activity, and the pools of soil microbial, soil organic and soil inorganic N, carbon (C) and phosphorus (P) during two growing seasons. The net fluxes of N 2 O averaged 1.7 μg N 2 O–N m−2 h−1 (range −3.6 to 10.5 μg N 2 O–N m−2 h−1), and generally increased from ambient (1 m) to moderate (2–3 m) snow depths. At the greatest snow depth (4 m) where snowmelt was profoundly later, N 2 O fluxes decreased, likely caused by combined negative effects of low summer temperatures and high soil moisture. Positive correlations between N 2 O and nitrate (NO 3 −) and dissolved organic N (DON) suggested that the availability of N was the main controlling variable along the snowmelt gradient. The maximum N 2 O fluxes were observed in the second half of August associated with high NO 3 − concentrations. The effect of growing season experimental warming on N 2 O surface flux varied along the snowmelt gradient and with time. Generally, the experimental warming stimulated N 2 O fluxes under conditions with increased concentrations of inorganic N. In contrast, warming reduced N 2 O fluxes when inorganic N was low. Experimental warming had no clear effects on soil inorganic N. The study suggests that if increased winter precipitation leads to a deeper snow cover and a later snowmelt, total emissions of N 2 O from low Arctic heath ecosystems may be enhanced in the future and, dependent on dissolved N availability, summer warming may stimulate or reduce total emissions. [Display omitted] • We studied effects of warming on tundra N 2 O emissions along a snowmelt gradient. • The N 2 O emissions peaked with late snowmelt, likely due to high dissolved soil N. • Areas with highest snow depth (4 m) exhibited low N 2 O emissions (low temperature). • Experimental warming enhanced N 2 O emissions, where soil N was high (late snowmelt). • We conclude that low Arctic heath is a source to N 2 O regulated by dissolved soil N. [ABSTRACT FROM AUTHOR]

There is a need of proper nitrogen management in agricultural systems, which would enhancecrop productivity, while reduce the negative consequences resulting from fertilization.Application of biochars is gaining popularity because of its potential to sequester carbon (C)in soil. Because of their high porosity and large surface area, biochars have been reported tobe capable of adsorbing mineral N in their surfaces making it more available to plants,while reducing nitrogen (N) leaching and nitrous oxide (N2O) emissions. However,its mechanism is not fully understood yet. To enhance the surface properties ofbiochar, various techniques of preparing biochars are being explored and one ofthe techniques is hot activation with nutrient enrichment. In the current study, ourgoal was to test the effectiveness of such hot-activated biochar in comparison withnon-activated biochar in enhancing ryegrass growth while reducing N leaching and N2Oemission. A 15N-tracing pot experiment was conducted using two types of wood-based biochars: acommercially produced biochar (RPK Hilli Oy, BC1) and other produced with Kon-Tikiflame curtain pyrolysis of hardwood followed by activation with cattle slurry (BC2). Theexperiment consisted 11 treatments: control, 2 fertilized controls (15NH4+ and 15NO3−) and8 biochar treatments [2 biochar types x 2 biochar application rates (1% and 5%) x 2fertilization] with 5 replicates each. Ryegrass was sown in the pots and all the pots exceptcontrol ones received N-fertilizer as either 15NH4NO3 or NH415NO3 corresponding to 110kg N ha−1. During the experiment, N leaching and N2O emissions were measured weekly.At the end of the 33-day experiment, plant above ground and root biomass weremeasured. N2O emissions were measured using gas chromatography. N-NH4+and N-NO3− in leachate (after micro-diffusion) and 15N content in plant biomassand soil were measured from isotope ratio mass spectrometer (Thermo Scientific,Bremen, Germany). Compared to fertilized control, 1% biochar treatment pots had nodifferences while 5% biochar treatments had significantly higher above ground biomassirrespective of biochar type. The volume of leachate and N leaching was significantlyhigher in fertilized control compared to all biochar treatments, and 5% biochartreatments were better in reducing leaching compared to 1% biochar treatments. Inaddition, the biochar treatments reduced N2O emission by around 60% comparedto fertilized control but among the biochar treatments, there was no difference.The results suggest that wood-based biochar application helps in minimizing Nleaching and N2O emission. Also, in our short-term test, irrespective of biochartype, amount of biochar applied had significant impact on ryegrass biomass yield. [ABSTRACT FROM AUTHOR]

Abstract Colonies of mammals and sea birds are known hotspots for biogeochemical cycles with potentially large element stocks and fast turnover in the soil. Although penguin and seal colonies are sites with potentially extremely fast biogeochemical turnover, these sites as potential sources of GHG have largely been neglected. This study aims to quantify magnitudes and environmental drivers of GHG fluxes effected by the activity of Antarctic fur seal (Arctocephalus gazella) and King penguin (Aptenodytes patagonicus) in South Georgia, sub-Antarctica. In-situ CO 2 and CH 4 gas flux measurements were combined with laboratory incubations of intact soil cores collected from sites along two transects away from a seal and a penguin colony. Variations in laboratory incubations were consistent with the in-situ fluxes measured in February 2017, and showed high ecosystem respiration rates at colonies (mean 44.3 μg CO 2 cm−3 h−1 for seal colony, and 52.9–159 μg CO 2 cm−3 h−1 for penguin colony) and a marked decrease away from these hotspots. Moderate methane production rates were found within the colonies (mean 0.1 ng CH 4 cm−3 h−1 for seal colony, 44–145.5 ng CH 4 cm−3 h−1 for penguin colony), while relatively high consumption rates (mean −1.8 ng CH 4 cm−3 h−1) occurred outside the colonies. Incubations also included N 2 O production rates, which were highly variable within the colonies (1.1–293 ng N 2 O cm−3 h−1 for seal colony, 0.8–594.7 ng N 2 O cm−3 h−1 for penguin colony) and decreased markedly to near zero away from the colonies. Bacterial and pmoA communities and drivers of GHG turnover and microbe community along both transects varied according to the sea animal activity intensity gradient. This is the first study at these latitudes to quantify the overall capacity of in-situ soil methane uptake at hot spots linked to sea animal colonies versus ambient conditions. All colony sites in this study were net sources of N 2 O, while sites beyond colonies, which dominate the ice-free areas in South Georgia, were sinks of methane. Highlights • High CH 4 uptake rates are observed in bare soil areas but decreased towarsds seal and penguin colonies. • Colonies were hotspots for CO 2 , CH 4 and N 2 O emissions due to large excreta deposits. • Spatial trends in gas rates were correlated to microbial community distribution. • Dominate methanotrophs differed between sites. [ABSTRACT FROM AUTHOR]

Intensive vegetable fields, characterized by extremely high nitrogen (N) application rates, emit a large amount of the potent greenhouse gas nitrous oxide (N 2 O). Short-term substitution of organic fertilizers for chemical fertilizers may mitigate N 2 O emissions from vegetable fields. However, the long-term impacts, particularly on soil background N 2 O emissions (excluding effects caused by newly applied fertilizers) in vegetable fields, remain poorly elucidated. Thus, we conducted an 11-year experiment to investigate the long-term fertilization effects on soil background N 2 O emissions and the abundance of N-cycling genes in a greenhouse vegetable field. The soil capacity for potential denitrification activity (PDA) was further measured to evaluate denitrification potential. The field experiment comprised of four treatments: no fertilization (control, CK), only chemical N fertilizers (CF), 50 % of chemical N fertilizers substituted by organic fertilizers (OL), and 87.5 % of chemical fertilizers substituted by organic fertilizers (OH). The long-term application of chemical fertilizers alone (CF) and organic fertilizer substitutions (OL and OH) increased soil background N 2 O emissions 30-fold and 10-fold, respectively, with average N 2 O fluxes of 1.2 ± 3.8, 33.8 ± 5.1, 9.4 ± 2.3 and 10.2 ± 2.7 μg N 2 O-N m−2 h−1 in the CK, CF, OL and OH treatment, respectively. The CF treatment significantly decreased the abundance of AOA amoA , nirS and nosZ genes, while both the OL and OH treatments increased the abundance of AOB amoA , and the OH treatment also increased nosZ gene abundance. Soil pH was a key determinant of the contrasting responses of N-cycling genes to different fertilizer types. Compared with low fertilizer substitutions (OL), high organic fertilizer substitutions (OH) did not result in more soil background N 2 O emissions, despite higher potential denitrification activities and soil total N contents. This was due to increased abundance of nosZ gene and likely enhanced N 2 O consumption activities. Soil NO 3 −-N concentrations, soil pH, and the abundance of nosZ gene were three main factors in controlling the responses of soil background N 2 O emissions to long-term fertilization. Overall, this study suggests that in the long-term perspective organic fertilizer substitution is a beneficial practice to mitigate N 2 O emissions from intensive greenhouse vegetable cropping systems. • We compared long-term chemical and organic fertilization effects in a vegetable field. • Long-term organic fertilizer substitutions increased AOB amoA and nosZ gene abundance. • Soil N 2 O emissions were controlled by soil NO 3 −-N, soil pH, and nosZ gene abundance. • Long-term organic fertilizer substitutions mitigated soil background N 2 O emissions. [ABSTRACT FROM AUTHOR]

Impacts of increased winter snowfall and warmer summer air temperatures on nitrous oxide (N 2 O) dynamics in arctic tundra are uncertain. Here we evaluate surface N 2 O dynamics in both wet and dry tundra in West Greenland, subjected to field manipulations with deepened winter snow and summer warming. The potential denitrification activity (PDA) and potential net N 2 O production (N 2 O net) were measured to assess denitrification and N 2 O consumption potential. The surface N 2 O fluxes averaged 0.49 ± 0.42 and 2.6 ± 0.84 μg N 2 O–N m−2 h−1, and total emissions were 212 ± 151 and 114 ± 63 g N 2 O–N scaled to the entire study area of 0.15 km2, at the dry and wet tundra, respectively. The experimental summer warming, and in combination with deepened snow, significantly increased N 2 O emissions at the dry tundra, but not at the wet tundra. The deepened snow increased winter soil temperatures and growing season soil N availability (DON, NH 4 +-N or NO 3 −-N), but no main effect of deepened snow on N 2 O fluxes was found at either tundra ecosystem. The mean PDA was 5- and 121-fold higher than the N 2 O net at the dry and wet tundra, respectively, suggesting that N 2 O might be reduced and emitted as dinitrogen (N 2). Overall, this study reveals modest but evident surface N 2 O fluxes from tundra ecosystems in Western Greenland, and suggests that projected increases in winter precipitation and summer air temperatures may increase N 2 O emissions, particularly at the dry tundra dominating in this region. • We studied climate change effects on N 2 O fluxes in dry and wet tundra West Greenland. • Generally, N 2 O fluxes were relatively modest in both types of vegetation. • Summer warming combined with deepened snow enhanced N 2 O emissions in dry tundra. • Climate change did not affect N 2 O fluxes in wet tundra. [ABSTRACT FROM AUTHOR]

A three-season field experiment was established and repeated twice with spring barley used as cover crop for different perennial grass-legume intercrops followed by a full year pasture cropping and winter wheat after sward incorporation. Two fertilization regimes were applied with plots fertilized with either a high or a low rate of mineral nitrogen (N) fertilizer. Life cycle assessment (LCA) was used to evaluate the carbon footprint (global warming potential) of the grassland management including measured nitrous oxide (N 2 O) emissions after sward incorporation. Without applying any mineral N fertilizer, the forage legume pure stand, especially red clover, was able to produce about 15 t aboveground dry matter ha − 1 year − 1 saving around 325 kg mineral N fertilizer ha − 1 compared to the cocksfoot and tall fescue grass treatments. The pure stand ryegrass yielded around 3 t DM more than red clover in the high fertilizer treatment. Nitrous oxide emissions were highest in the treatments containing legumes. The LCA showed that the low input N systems had markedly lower carbon footprint values than crops from the high N input system with the pure stand legumes without N fertilization having the lowest carbon footprint. Thus, a reduction in N fertilizer application rates in the low input systems offsets increased N 2 O emissions after forage legume treatments compared to grass plots due to the N fertilizer production-related emissions. When including the subsequent wheat yield in the total aboveground production across the three-season rotation, the pure stand red clover without N application and pure stand ryegrass treatments with the highest N input equalled. The present study illustrate how leguminous biological nitrogen fixation (BNF) represents an important low impact renewable N source without reducing crop yields and thereby farmers earnings. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N 2 O) is an important long-lived greenhouse gas and precursor of stratospheric ozone-depleting mono-nitrogen oxides. The atmospheric concentration of N 2 O is persistently increasing; however, large uncertainties are associated with the distinct source strengths. Here we investigate for the first time N 2 O emission from terrestrial vegetation in response to natural solar ultra violet radiation. We conducted field site measurements to investigate N 2 O atmosphere exchange from grass vegetation exposed to solar irradiance with and without UV-screening. Further laboratory tests were conducted with a range of species to study the controls and possible loci of UV-induced N 2 O emission from plants. Plants released N 2 O in response to natural sunlight at rates of c. 20–50 nmol m −2 h −1 , mostly due to the UV component. The emission response to UV-A is of the same magnitude as that to UV-B. Therefore, UV-A is more important than UV-B given the natural UV-spectrum at Earth's surface. Plants also emitted N 2 O in darkness, although at reduced rates. The emission rate is temperature dependent with a rather high activation energy indicative for an abiotic process. The prevailing zone for the N 2 O formation appears to be at the very surface of leaves. However, only c. 26% of the UV-induced N 2 O appears to originate from plant-N. Further, the process is dependent on atmospheric oxygen concentration. Our work demonstrates that ecosystem emission of the important greenhouse gas, N 2 O, may be up to c. 30% higher than hitherto assumed. [ABSTRACT FROM AUTHOR]

Abstract: Conventional cropping systems rely on targeted short-term fertility management, whereas organic systems depend, in part, on long-term increase in soil fertility as determined by crop rotation and management. Such differences influence soil nitrogen (N) cycling and availability through the year. The main objective of this study was to compare nitrous oxide (N2O) emissions from soil under winter wheat (Triticum aestivum L.) within three organic and one conventional cropping system that differed in type of fertilizer, presence of catch crops and proportion of N2-fixing crops. The study was replicated in two identical long-term crop rotation experiments on sandy loam soils under different climatic conditions in Denmark (Flakkebjerg—eastern Denmark and Foulum—western Denmark). The conventional rotation received 165–170kgNha−1 in the form of NH4NO3, while the organic rotations received 100–110kgNha−1 as pig slurry. For at least 11 months, as from September 2007, static chambers were used to measure N2O emissions at least twice every calendar month. Mean daily N2O emissions across the year ranged from 172 to 438μg N m−2 d−1 at Flakkebjerg, and from 173 to 250μg N m−2 d−1 at Foulum. A multiple linear regression analysis showed inter-seasonal variations in emissions (P <0.001), but annual N2O emissions from organic and conventional systems were not significantly different despite the lower N input in organic rotations. The annual emissions ranged from 54 to 137mgNm−2, which corresponded to 0.5–0.8% of the N applied in manure or mineral fertilizer. Selected soil attributes were monitored to support the interpretation of N2O emission patterns. A second multiple linear regression analysis with potential drivers of N2O emissions showed a negative response to soil temperature (P =0.008) and percent water-filled pore space (WFPS) (P =0.052) at Foulum. However, there were positive interactions of both factors with NO3-N, i.e., high N2O emissions occurred during periods when high soil nitrate levels coincided with high soil temperature (P =0.016) or high soil water content (P =0.056). A positive effect (P =0.03) of soil temperature was identified at Flakkebjerg, but the number of soil samplings was limited. Effects of cropping system on N2O emissions were not observed. [Copyright &y& Elsevier]

• Exposure time since glacier retreat enhanced soil development, CO 2 production and CH 4 consumption. • Soil labile C and moisture were key limiting factors for CO 2 production. • Fresh penguin guano deposition stimulated CO 2 and N 2 O production and decreased CH 4 consumption. • N 2 O production was not influenced by exposure time but increased strongly due to penguin activity. The effects of soil succession after glacial retreat and fertilisation by marine animals are known to have major impacts on soil greenhouse gas (GHG) fluxes in polar terrestrial ecosystems. While in many polar coastal areas retreating glaciers open up new ground for marine animals to colonise, little is known about the combination of both factors on the local GHG budget. We studied the magnitude of GHG fluxes (CO 2 , CH 4 and N 2 O) on the combined effect of glacial retreat and penguin-induced fertilisation along a transect protruding into the world's largest King Penguin (Aptenodytes patagonicus) colony at Saint Andrews Bay on sub-Antarctic South Georgia. GHG production and consumption rates were assessed based on laboratory incubations of intact soil cores and nutrients and water additional experimental incubations. The oldest soils along the transect show significant higher contents of soil carbon, nutrients and moisture and were strongly influenced by penguin activity. We found a net CH 4 consumption along the entire transect with a marked decrease within the penguin colony. CO 2 production strongly increased along the transect, while N 2 O production rates were low near the glacier front and increased markedly within the penguin colony. Controlled applications of guano resulted in a significant increase in CO 2 and N 2 O production, and decrease in CH 4 consumption, except for sites already strongly influenced by penguin activity. The results show that soil microbial activity promptly catalyses a turnover of soil C and atmospheric methane oxidation in de-glaciated forelands. The methane oxidizers, however, may increase relatively slowly in their capacity to oxidise atmospheric CH 4. Results show also that the increase of nutrients by penguins reduces CH 4 oxidation whereas N 2 O production is greatly increased. A future expansion of penguins into newly available ice-free polar coastal areas may therefore markedly increase the local GHG budget. [ABSTRACT FROM AUTHOR]