Sulfide Alleviation of the Acetylene Inhibition of Nitrous Oxide Reduction in Soil

The alleviation of the acetylene blockage of nitrous oxide reduction by sulfide was studied in anaerobically incubated Brookston soil to better characterize the process. Removal of nitrate-derived nitrous oxide from soil amended with acetylene and sulfide occurred earlier in the presence of glucose than it did in its absence. This was attributed to the influence of glucose on nitrous oxide production rather than reduction during the early stages of the soil incubation. Glucose was found to have no effect on reduction of injected nitrous oxide in the presence of acetylene- and sulfide-amended soil, whereas carbon dioxide significantly stimulated reduction. It is suggested that the microorganism(s) involved may use carbon dioxide as a cellular carbon source. The sulfide added to the soil probably did not act solely as an electron donor, as the number of electrons required to reduce the added nitrous oxide in our systems was greater than the amount supplied by the sulfide. The soil pH at which the alleviation occurred was 6.7 and was not affected by the sulfide treatment.     

Fluxes of CO2, CH4 and N2O from a Welsh peatland following simulation of water table draw-down: Potential feedback to climatic change

A potential effect of climatic change was simulated by manipulating the water table height within intact peat monoliths. The treatment decreased methane flux (maximum –80%) and increased both carbon dioxide flux (maximum 146%) and nitrous oxide flux maximum 936%). Returning the water table height to its original level caused both nitrous oxide and carbon dioxide flux to rapidly return to control levels. However, methane flux remained at its experimentally induced low levels.     

Continuous measurement of gas uptake and elimination in anesthetized patients using an extractable marker gas.

Measurement of pulmonary gas uptake and elimination is often performed, using nitrogen as marker gas to measure gas flow, by applying the Haldane transformation. Because of the inability to measure nitrogen with conventional equipment, measurement is difficult during inhalational anesthesia. A new method is described, which is compatible with any inspired gas mixture, in which fresh gas and exhaust gas flows are measured using carbon dioxide as an extractable marker gas. A system was tested in eight patients undergoing colonic surgery for automated measurement of uptake of oxygen, nitrous oxide, isoflurane, and elimination of carbon dioxide with this method. Its accuracy and precision were compared with simultaneous measurements made with the Haldane transformation and corrected for predicted nitrogen excretion by the lungs. Good agreement was obtained for measurement of uptake or elimination of all gases studied. Mean bias was -0.003 l/min for both oxygen and nitrous oxide uptake, -0.0002 l/min for isoflurane uptake, and 0.003 l/min for carbon dioxide elimination. Limits of agreement lay within 30% of the mean uptake rate for nitrous oxide, within 15% for oxygen, within 10% for isoflurane, and within 5% for carbon dioxide. The extractable marker gas method allows accurate and continuous measurement of gas uptake and elimination in an anesthetic breathing system with any inspired gas mixture.     

Nitrous oxide emissions from a gully mire in mid-Wales, UK, under simulated summer drought

Certain general circulation models predict that a doubling of atmospheric carbon dioxide concentrations will increase the frequency of summer drought in northern wetlands due to hotter, drier summers. There is currently much uncertainty as to how drought will affect emissions of the greenhouse gas, nitrous oxide, from wetlands. We have demonstrated that an eight centimetre drawdown of the water table in a gully mire does not significantly affect nitrous oxide emissions from this site. However, under a more extreme drought scenario carried out on peat monoliths, nitrous oxide emissions increased exponentially with a linear decrease in water table height. Drought caused a significant increase in nitrous oxide productionbelow the water table but most of the total increase could be attributed to increased emissionsabove the water table. Results from an acetylene block experiment suggested that increased emissions were caused by increased nitrous oxide production from denitrification, rather than by increased production from nitrification. In the laboratory study, drought severity had no effect on peatwater nitrate concentrations below the water table, however, increasing drought severity decreased ammonium concentrations.     

Residual effect of organic carbon as a tool for mitigating nitrogen oxides emissions in semi-arid climate

Residual effects of different fertilizers (mineral and organic) on the first pulses of carbon dioxide (CO₂), nitric oxide (NO), and nitrous oxide (N₂O) after rewetting dry soil with or without application of a mineral N fertilizer were studied in a laboratory experiment. Six months before this study was conducted the fields had received either manure + urea, manure, urea or no fertilizer. In the first phase the soil was rewetted with water simulating a summer shower (heavy rainfall in short time) and in the second phase with a urea solution simulating a mineral fertilization. There were not significant differences in trace gas emissions between earlier field treatments after soil was rewetted with water addition. However, after urea addition, plots that had received manure 6 months earlier showed smaller total emissions of N₂O and NO compared to plots that had only received urea. The residual effect of manure can play an important role in carbon poor soils under arid-semiarid climate in mitigating atmospheric pollutants such us NO and N₂O.     

Physiological Impacts of Elevated CO2 Concentration Ranging from Molecular to Whole Plant Responses

The dynamics of the terrestrial ecosystems depend on interactions between a number of biogeochemical cycles (i.e. carbon, nutrient, and hydrological cycles) that may be modified by human actions. Conversely, terrestrial ecosystems are important components of these cycles that create the sources and sinks of important greenhouse gases (e.g. carbon dioxide, methane, nitrous oxide). Especially, carbon is exchanged naturally among these ecosystems and the atmosphere through photosynthesis, respiration, decomposition, and combustion processes. Continuous increase of atmospheric carbon dioxide (CO₂) concentration has led to extensive research over the last two decades, during which more then 1 400 scientific papers describing impacts of elevated [CO₂] (EC) on photosynthesis have been published. However, the degree of response is very variable, depending on species, growing conditions, mineral nutrition, and duration of CO₂ enrichment. In this review, I have summarised the major physiological responses of plants, in particular of trees, to EC including molecular and primary, especially photosynthetic, physiological responses. Likewise, secondary (photosynthate translocation and plant water status) and tertiary whole plant responses including also plant to plant competition are shown.     

Elevated CO<Subscript>2</Subscript> and nitrogen addition accelerate net carbon gain in a brackish marsh

Wetlands have an inordinate influence on the global greenhouse gas budget, but how global changes may alter wetland contribution to future greenhouse gas fluxes is poorly understood. We determined the greenhouse gas balance of a tidal marsh exposed to nine years of experimental carbon dioxide (CO₂) and nitrogen (N) manipulation. We estimated net carbon (C) gain rates by measuring changes in plant and soil C pools over nine years. In wetland soils that accrete primarily through organic matter inputs, long-term measurements of soil elevation, along with soil C density, provide a robust estimate of net soil C gain. We used net soil C gain along with methane and nitrous oxide fluxes to determine the radiative forcing of the marsh under elevated CO₂ and N addition. Nearly all plots exhibited a net gain of C over the study period (up to 203 g C m^?2 year^?1), and C gain rates were greater with N and CO₂ addition. Treatment effects on C gain and methane emissions dominated trends in radiative forcing while nitrous oxide fluxes in all treatments were negligible. Though these soils experience salinities that typically suppress methane emissions, our results suggest that elevated CO₂ can stimulate methane emissions, overcoming positive effects of elevated CO₂ on C gain, converting brackish marshes that are typically net greenhouse gas sinks into sources. Adding resources, either CO₂ or N, will likely increase “blue carbon” accumulation rates in tidal marshes, but importantly, each resource can have distinct influences on the direction of total greenhouse forcing.     

Turning, compacting and the addition of water as factors affecting gaseous emissions in farm manure composting

Composting allows simple management of animal manure but excessive aeration can increase emissions of polluting gases such as ammonia or nitrous oxide. The aim of the present work was to determine the effect of three techniques--turning, compacting and the addition of water--on gaseous emissions. One ton of cattle manure and 3 tons of turkey manure were composted in two and four cells for 46 and 51 days respectively. The manure was either turned, wetted, or compacted. Emissions of carbon dioxide, water vapor, ammonia and nitrous oxide were monitored. The results show that turning did not alter the free air space. Compacting can be used specifically to reduce the water loss. A reduction of free air space by 20-60%, either by compacting or adding water (or both), reduced the ammonia and nitrous oxide emissions by 30-70%.     

Divergent Controls on Stream Greenhouse Gas Concentrations Across a Land-Use Gradient

Ecosystems - Inland waters can be significant sources of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) to the atmosphere. However, considerable uncertainty remains in regional and...     

On fertilizer‐induced soil carbon sequestration in China's croplands

Applications of fertilizer, often thought to enhance carbon sequestration in agricultural soils, are of no value to the mitigation of climate change if the carbon dioxide released during the production and distribution of nitrogen fertilizer exceeds the incremental carbon storage in soils from its use. Nitrogen fertilizer is also a source of the greenhouse gas nitrous oxide. The recent analysis of carbon sequestration in cropland soils of China does not apply these ‘discounts’ to the global warming mitigation expected from greater use of fertilizer; doing so would likely eliminate all the climate benefits of the postulated enhanced carbon sequestration.     

Greenhouse Gas Balance of Sphagnum Farming on Highly Decomposed Peat at Former Peat Extraction Sites

Ecosystems - For two years, we quantified the exchange of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) at two different large-scale Sphagnum farming sites. At both, peat extraction...     

Effect of carbon source and competition for electrons on nitrous oxide reduction in a mixed denitrifying microbial community

The competition for electrons has been recently demonstrated to affect the reduction rates of the nitrogen oxides in a methanol enriched denitrifying community. The aim of this study was to test if electron competition also occurred when other substrates were used for denitrification and if that could have an effect on the potential nitrous oxide (N₂O) production and subsequent consumption. A denitrifying culture was developed in a sequencing batch reactor using nitrate as electron acceptor and a combination of acetate, ethanol and methanol as carbon sources. Four sets of batch tests were conducted using acetate, ethanol, methanol and a combination of the three carbon sources respectively. For each set the effect of nitrate, nitrite and nitrous oxide on each other reduction rates when present individually or in combination was assessed. Results show that reduction rates are affected by the type of substrate added, probably due to different microbial populations specialized with consuming a particular substrate. Also, N₂O reduction rate is the most reduced under the different electron competition scenarios tested, which results in N₂O accumulation in some cases. The effect of substrate limitation on N₂O reduction was also assessed.     

A field enclosure apparatus for measuring crop photosynthesis

The field enclosure is a transparent box covering a soil area of 1.5 m². It is a semi-closed system in which concentrations of water vapour and carbon dioxide are maintained constant: the required rate of input of carbon dioxide being a measure of the photosynthesis rate, and the rate of condensation of water, on cooling coils, a measure of transpiration. The air within the enclosure is circulated rapidly by fans to decrease concentration gradients, and under steady radiation inputs the air temperature is controlled to ±0.5 °C. Both photosynthesis and transpiration rates are corrected for air exchange with the surroundings, as measured through the injection of the inert gas, nitrous oxide.     

On a sporeforming bacterium causing the swelling of cans containing cured ham

Summary An investigation has been carried out on a type of spoilage of canned cured ham which is characterised by a swelling of the cans, whilst at the same time there are no evident symptoms of a putrefactive decomposition of the contents of the can. From these contents a facultative aerobic, thermophilic, sporeforming rod was isolated. Earlier investigators, notablyJensen and collaborators had undoubtedly also encountered this organism in their studies. These authors attempted to explain the swelling of the cans by assuming that under certain conditions the fermentation of sugar by the bacterium was deviated from its normal course so that carbon dioxide is formed in considerable quantities.In contrast hereto it has been shown that the bacterium in question is an actively denitrifying organism, and that the swelling of the cans is due to the formation of the gaseous products of denitrification, amongst which — next to carbon dioxide —nitrogen and nitrous oxide are always present and under certain conditions may prevail.     

Earthworm effects on gaseous emissions during vermifiltration of pig fresh slurry

Treatment of liquid manure can result in the production of ammonia, nitrous oxide and methane. Earthworms mix and transform nitrogen and carbon without consuming additional energy. The objective of this paper is to analyse whether earthworms modify the emissions of NH₃, N₂O, CH₄ and CO₂ during vermifiltration of pig slurry.The experiment used mesocosms of around 50 L, made from a vermifilter treating the diluted manure of a swine house. Three levels of slurry were added to the mesocosms, with or without earthworms, during one month, in triplicate. Earthworm abundance and gas emissions were measured three and five times, respectively.There was a decrease in emissions of ammonia and nitrous oxide and a sink of methane in treatments with earthworms. We suggest that earthworm abundance can be used as a bioindicator of low energy input, and low greenhouse gas and ammonia output in systems using fresh slurry with water recycling.     

Kinetic Explanation for Accumulation of Nitrite, Nitric Oxide, and Nitrous Oxide During Bacterial Denitrification

The kinetics of denitrification and the causes of nitrite and nitrous oxide accumulation were examined in resting cell suspensions of three denitrifiers. An Alcaligenes species and a Pseudomonas fluorescens isolate characteristically accumulated nitrite when reducing nitrate; a Flavobacterium isolate did not. Nitrate did not inhibit nitrite reduction in cultures grown with tungstate to prevent formation of an active nitrate reductase; rather, accumulation of nitrite seemed to depend on the relative rates of nitrate and nitrite reduction. Each isolate rapidly reduced nitrous oxide even when nitrate or nitrite had been included in the incubation mixture. Nitrate also did not inhibit nitrous oxide reduction in Alcaligenes odorans, an organism incapable of nitrate reduction. Thus, added nitrate or nitrite does not always cause nitrous oxide accumulation, as has often been reported for denitrifying soils. All strains produced small amounts of nitric oxide during denitrification in a pattern suggesting that nitric oxide was also under kinetic control similar to that of nitrite and nitrous oxide. Apparent K_m values for nitrate and nitrite reduction were 15 μM or less for each isolate. The K_m value for nitrous oxide reduction by Flavobacterium sp. was 0.5 μM. Numerical solutions to a mathematical model of denitrification based on Michaelis-Menten kinetics showed that differences in reduction rates of the nitrogenous compounds were sufficient to account for the observed patterns of nitrite, nitric oxide, and nitrous oxide accumulation. Addition of oxygen inhibited gas production from ¹³NO₃⁻ by Alcaligenes sp. and P. fluorescens, but it did not reduce gas production by Flavobacterium sp. However, all three isolates produced higher ratios of nitrous oxide to dinitrogen as the oxygen tension increased. Inclusion of oxygen in the model as a nonspecific inhibitor of each step in denitrification resulted in decreased gas production but increased ratios of nitrous oxide to dinitrogen, as observed experimentally. The simplicity of this kinetic model of denitrification and its ability to unify disparate observations should make the model a useful guide in research on the physiology of denitrifier response to environmental effectors.     

Carbon, nitrogen and Greenhouse gases budgets over a four years crop rotation in northern France

Croplands mainly act as net sources of the greenhouse gases carbon dioxide (CO₂) and nitrous oxide (N₂O), as well as nitrogen oxide (NO), a precursor of troposheric ozone. We determined the carbon (C) and nitrogen (N) balance of a four-year crop rotation, including maize, wheat, barley and mustard, to provide a base for exploring mitigation options of net emissions. The crop rotation had a positive net ecosystem production (NEP) of 4.4?±?0.7 Mg C ha^-1 y^-1 but represented a net source of carbon with a net biome production (NBP) of -1.3?±?1.1 Mg C?ha^-1 y^-1. The nitrogen balance of the rotation was correlated with the carbon balance and resulted in net loss (?24?±?28 kg N ha^-1 y^-1). The main nitrogen losses were nitrate leaching (?11.7?±1.0 kg N ha^-1 y^-1) and ammonia volatilization (?9 kg N ha^-1 y^-1). Dry and wet depositions were 6.7?±?3.0 and 5.9?±0.1 kg N ha^-1 y^-1, respectively. Fluxes of nitrous (N₂O) and nitric (NO) oxides did not contribute significantly to the N budget (N₂O: -1.8?±?0.04; NO: -0.7?±?0.04 kg N ha^-1 y^-1) but N₂O fluxes equaled 16% of the total greenhouse gas balance. The link between the carbon and nitrogen balances are discussed. Longer term experiments would be necessary to capture the trends in the carbon and nitrogen budgets within the variability of agricultural ecosystems.     

Interactions among substrates and inhibitors of nitrogenase.

Examination of interactions among various substrates and inhibitors reacting with a partially purified nitrogenase from Azotobacter vinelandii has shown that: nitrous oxide is competitive with N2; carbon monixide and acetylene are noncompetitive with N2; carbon monoxide, cyanide, and nitrous oxide are noncompetitive with acetylene, whereas N2 is competitive with acetylene; carbon monoxide is noncompetitive with cyanide, whereas azide is competitive with cyanide; acetylene and nitrous oxide increase the rate of reduction of cyanide. The results are understandable if nitrogenase serves as an electron sink and substrates and inhibitors bind at multiple modified sites on reduced nitrogenase. It is suggested that substrates such as acetylene may be reduced by a less completely reduced electron sink than is required for the six-electron transfer necessary to reduce N2.     

Nitrous oxide reduction by members of the family Rhodospirillaceae and the nitrous oxide reductase of Rhodopseudomonas capsulata.

After growth in the absence of nitrogenous oxides under anaerobic phototrophic conditions, several strains of Rhodopseudomonas capsulata were shown to possess a nitrous oxide reductase activity. The enzyme responsible for this activity had a periplasmic location and resembled a nitrous oxide reductase purified from Pseudomonas perfectomarinus. Electron flow to nitrous oxide reductase was coupled to generation of a membrane potential and inhibited by rotenone but not antimycin. It is suggested that electron flow to nitrous oxide reductase branches at the level of ubiquinone from the previously characterized electron transfer components of R. capsulata. This pathway of electron transport could include cytochrome c', a component hitherto without a recognized function. R. capsulata grew under dark anaerobic conditions in the presence of malate as carbon source and nitrous oxide as electron acceptor. This confirms that nitrous oxide respiration is linked to ATP synthesis. Phototrophically and anaerobically grown cultures of nondenitrifying strains of Rhodopseudomonas sphaeroides, Rhodopseudomonas palustris, and Rhodospirillum rubrum also possessed nitrous oxide reductase activity.