Short term effect of ploughing a permanent pasture on N2O production from nitrification and denitrification

Soils are an important source of N₂O, which can be produced both in the nitrification and the denitrification processes. Grassland soils in particular have a high potential for mineralization and subsequent nitrification and denitrification. When ploughing long term grassland soils, the resulting high supply of mineral N may provide a high potential for N₂O losses. In this work, the short-term effect of ploughing a permanent grassland soil on gaseous N production was studied at different soil depths. Fertiliser and irrigation were applied in order to observe the effect of ploughing under a range of conditions. The relative proportions of N₂O produced from nitrification and denitrification and the proportion of N₂ gas produced from denitrification were determined using the methyl fluoride and acetylene specific inhibitors. Irrespectively to ploughing, fertiliser application increased the rates of N₂O production, N₂O production from nitrification, N₂O production from denitrification and total denitrification (N₂O + N₂). Application of fertiliser also increased the denitrification N₂O/N₂ ratio both in the denitrification potential and in the gaseous N productions by denitrification. Ploughing promoted soil organic N mineralization which led to an increase in the rates of N₂O production, N₂O production from nitrification, N₂O production from denitrification and total denitrification (N₂O + N₂). In both the ploughed and unploughed treatments the 0–10 cm soil layer was the major contributing layer to gaseous N production by all the above processes. However, the contribution of this layer decreased by ploughing, gaseous N productions from the 10 to 30 cm layer being significantly increased with respect to the unploughed treatment. Ploughing promoted both nitrification and denitrification derived N₂O production, although a higher proportion of N₂O lost by denitrification was observed as WFPS increased. Recently ploughed plots showed lower denitrification derived N₂O percentages than those ploughed before as a result of the lower soil water content in the former plots. Similarly, a lower mean nitrification derived N₂O percentage was found in the 10–30 cm layer compared with the 0–10 cm.     

Effect of Soil pH Increase by Biochar on NO,N2O and N2 Production during Denitrification in Acid Soils

Biochar (BC) application to soil suppresses emission of nitrous- (N₂O) and nitric oxide (NO), but the mechanisms are unclear. One of the most prominent features of BC is its alkalizing effect in soils, which may affect denitrification and its product stoichiometry directly or indirectly. We conducted laboratory experiments with anoxic slurries of acid Acrisols from Indonesia and Zambia and two contrasting BCs produced locally from rice husk and cacao shell. Dose-dependent responses of denitrification and gaseous products (NO, N₂O and N₂) were assessed by high-resolution gas kinetics and related to the alkalizing effect of the BCs. To delineate the pH effect from other BC effects, we removed part of the alkalinity by leaching the BCs with water and acid prior to incubation. Uncharred cacao shell and sodium hydroxide (NaOH) were also included in the study. The untreated BCs suppressed N₂O and NO and increased N₂ production during denitrification, irrespective of the effect on denitrification rate. The extent of N₂O and NO suppression was dose-dependent and increased with the alkalizing effect of the two BC types, which was strongest for cacao shell BC. Acid leaching of BC, which decreased its alkalizing effect, reduced or eliminated the ability of BC to suppress N₂O and NO net production. Just like untreated BCs, NaOH reduced net production of N₂O and NO while increasing that of N₂. This confirms the importance of altered soil pH for denitrification product stoichiometry. Addition of uncharred cacao shell stimulated denitrification strongly due to availability of labile carbon but only minor effects on the product stoichiometry of denitrification were found, in accordance with its modest effect on soil pH. Our study indicates that stimulation of denitrification was mainly due to increases in labile carbon whereas change in product stoichiometry was mainly due to a change in soil pH.     

Effects of oxygen concentration and moisture content of refuse on nitrification,denitrification and nitrous oxide production

The purposes of this study were to evaluate the potential production of nitrous oxide (N₂O), which is known as a greenhouse gas, to identify the reaction responsible for it and to examine the effects of oxygen and moisture content on nitrification, denitrification and N₂O production. Applying a tracer method using a ¹⁵N-isotope into an oxygen controllable reactor with artificial refuse proved that biological denitrification was a main source of released N₂O even when the oxygen of the bulk atmosphere was as high as 15%. Calculating the mass balance for nitrogenous compounds showed that only denitrification occurred as the sole microbial process when the bulk oxygen was 0–5%. With increasing oxygen above 5% nitrification also began to occur simultaneously with denitrification. As the bulk space of the refuse became aerobic, the total amount of N₂ produced from denitrification decreased but the proportion of N₂O in the (N₂ + N₂O) increased. Denitrification was the main source of released N₂O when the moisture content was between 40–60% and oxygen 10%. The amounts of nitrification, denitrification and N₂ production increased as the moisture content increased.     

Impacts of grazing intensity on denitrification and N<Subscript>2</Subscript>O production in a semi-arid grassland ecosystem

N₂O production from denitrification in soils contributes to the enhanced greenhouse effect and the destruction of the stratospheric ozone. Ungulate grazing affects denitrification and the production of N₂O. The short-term effect of grazing on denitrification and N₂O production has been examined in several grassland ecosystems. However, the effects of long-term grazing have rarely been studied. We measured denitrification and N₂O production during the 2005 and 2006 growing seasons in a long-term (17 years) experiment that had five grazing intensities (GI; 0.00, 1.33, 2.67, 4.00 and 5.33 sheep ha⁻¹). We found that denitrification and N₂O production rates were seasonally variable during the measurement period, with higher values observed in summer and lower values found in spring and autumn. The grazed treatments resulted in decreased denitrification and N₂O production, primarily due to the reduced soil nitrate concentration and organic N content under the long-term grazing. This supported our hypothesis that long-term over-grazing suppresses denitrification and N₂O production. Although significant differences in denitrification and N₂O production were not found between the four GI, there was a general trend that cumulative denitrification and N₂O production decreased as grazing intensity increased, especially in 2006. Lower N losses via denitrification and N₂O production in the grazed plots, to some extent, may contribute to the mitigation of greenhouse gas emission and help to preserve soil N and ameliorate the negative impacts of grazing on plant growth, productivity, and ecological restoration processes in the temperate steppe in northern China.     

Temporal Change in Nitrous Oxide and Dinitrogen from Denitrification Following Onset of Anaerobiosis

Similar temporal patterns were found in three mineral soils for the composition of the gaseous products of denitrification following the onset of anaerobic conditions. During the early period of anaerobiosis (0 up to 1 to 3 h), N₂ was the dominant product of denitrification. The NO₃⁻ → N₂O activity then increased, but was not accompanied by a corresponding increase in N₂O-reducing activity. This resulted in a relatively extended period of time (1 to 3 up to 16 to 33 h) during which N₂O was a major product. Eventually (after 16 to 33 h), an increase in N₂O-reducing activity occurred without a comparable increase in the N₂O-producing activity. The increase in the rate of N₂O reduction did not occur in the presence of chloramphenicol and required the presence of N₂O or NO₃⁻ during the preceding anaerobic incubation. During the final period (16 to 33, up to 48 h), N₂ was generally the sole product of denitrification, since the rate of N₂O reduction exceeded the rate of N₂O production. A similar sequential pattern was also found for a culture of a denitrifying Flavobacterium sp. shifted to anaerobic growth. A staggered synthesis of the enzymes in the denitrification sequence apparently occurred in response to anoxia, which caused first a net production of N₂O followed by consumption of N₂O.     

biological activity of ancient cultivated soil with buried horizons (the iverskii monastery, XVII century)

The biological activity of an ancient cultivated soil that has been in intense agricultural use since approximately the first half of the XVII century was studied. The potential biological activity of the buried horizon of the ancient cultivated soil was higher than that of its modern horizon or that of the noncultivated soil of an adjacent territory occurring under similar lithological and geomorphological conditions. A decreased rate of oxidative processes (decreased rates of CO₂ production and CH₄ oxidation) and an increased rate of reductive processes (denitrification and nitrogen fixation) were found in the buried horizon. A high potential denitrification activity (with predominant formation of nitrous oxide) was found in the buried horizon; in the upper horizon, the end product was molecular nitrogen.     

The effect of grass maturing and root decay on N2O production in soil

The N₂O flux from the surface of grass-covered pots was only significant following grass maturing. Removal of the above-ground plant material resulted in an immediate and long-lasting increase in N₂O production in the soil. The results suggest that easily available organic matter from the roots stimulates the denitrification when the plants are damaged. Grass cutting might therefore result in a marked nitrogen loss through denitrification. The quantitative effect was equal in soil with and without succinate added. The size of the anaerobic zone around the roots is therefore sufficient to allow for denitrification activity mediated by increased organic matter availability because of plant cutting.     

Dinitrogen and nitrous oxide produced by denitrification and nitrification in soil with and without barley plants

Summary To examine the effect of barley roots on denitrification, a pot experiment was designed to compare N₂O production and denitrification in soils with and without barley plants. Denitrification, N₂O resulting from denitrification and nitrification, and respiration were estimated by incubating pots with soil with and without intact plants in plastic bags at high moisture levels. C₂H₂-inhibition of nitrous oxide reductase (partial pressure of 10 kPa C₂H₂) was used to determine total denitrification rates while incubations with ambient air and with C₂H₂ at partial pressures of 2.5–5 Pa were used to estimate the amounts of N₂O released from autotrophic nitrification and from denitrification processes. Other sources of N₂O were presumed to be negligible. Potential denitrification, nitrification and root biomass were measured in subsamples collected from four soil depths. A positive correlation was found between denitrification rates and root biomass. N₂ was the predominant denitrification product found close to roots; N₂O formed by non autotrophic nitrifiers, assumed to be denitrifiers originated in soil not affected by growing roots. Apparently, roots promote denitrification because they consumed oxygen, thereby increasing the anaerobic volume of the soil. The ratio of actual to potential denitrification rates increased over time, especially in the presence of roots.     

Production and Loss of Nitric Oxide from Denitrification in Anaerobic Brookston Clay

Nitric oxide, nitrous oxide, and nitrite ion production was measured in a Brookston clay column undergoing anaerobic denitrification. A flow system method was used whereby argon carrier gas continuously stripped soil gases from the column, allowing steady-state rates to be obtained. Over several days the temporal change in rates of these gases and NO₂⁻ followed a pattern of increase and decay which may be expected of a reaction proceeding by several consecutive steps. The method permits observation of the relatively large net production rate of NO, which is normally not observed in static systems based on head space analysis of gaseous denitrification products. In the first several hours after the onset of anoxic conditions, the net rate of NO production, f_NO, increased sharply to a maximum (~1 × 10⁻¹⁰ mol of N/g of soil per min), paralleling the rapid increase in NO₂⁻ level, and then followed a more gradual decline extending over approximately 45 h. A similar but less pronounced pattern was observed for N₂O, with net rates of production being considerably less than for NO. The ratio [NO-N]/[N₂O-N] decreased with time from ~2.5 at 6 h to ~2.0 at 45 h. Estimated rates of N₂ production appeared to be initially high, decreased rapidly within a few hours, and then gradually increased with time after the establishment of anaerobic conditions.     

The potential effect of sustained hypoxia on nitrogen cycling in sediment from the southern North Sea: a mesocosm experiment

The potential effect of sustained hypoxia (up to 70 days) on the production of N₂ gas through denitrification and anammox, as well as sediment–water exchange of nitrite, nitrate and ammonia, oxygen consumption and penetration, were measured in mesocosms using sediment collected from the southern North Sea (north of Dogger Bank). As expected, both the penetration of oxygen into, and consumption of oxygen by, the sediment decreased by 42 and 46 %, respectively, once hypoxia was established. Importantly, the oxygen regime did not change significantly (P > 0.05) during the experiment, suggesting that organic carbon was not depleted. During the first 10 days, the exchange of NO₃ ^?, NO₂ ^? and NH₄ ⁺ between the sediment and water was erratic but once a steady state was established the sediment acted as either a sink for fixed nitrogen under hypoxia or as a source in the controls. Over the course of the mesocosm experiment the rate of both anammox and denitrification increased, with anammox increasing disproportionately under hypoxia relative to the controls, whereas the rate of increase in denitrification was the same for both. Under sustained hypoxia the production of N₂ gas increased by 72 % relative to the controls, with this increase in N₂ production remaining constant regardless of the duration of hypoxia. Longer periods of stratification and oxygen depletion are predicted to occur more regularly in the bottom waters of shallow coastal seas as one manifestation of climate change. Under sustained hypoxia the potential for nitrogen removal by the production of N₂ gas in this region of the southern North Sea was estimated to increase from 2.1 kt N 150 days^?1 to 3.6 kt 150 days^?1, while the efflux of dissolved inorganic nitrogen ceased altogether; both of which could down regulate the productivity of this region as a whole.     

Stochastic Models of Soil Denitrification

Soil denitrification is a highly variable process that appears to be lognormally distributed. This variability is manifested by large sample coefficients of variation for replicate estimates of soil core denitrification rates. Deterministic models for soil denitrification have been proposed in the past, but none of these models predicts the approximate lognormality exhibited by natural denitrification rate estimates. In this study, probabilistic (stochastic) models were developed to understand how positively skewed distributions for field denitrification rate estimates result from the combined influences of variables known to affect denitrification. Three stochastic models were developed to describe the distribution of measured soil core denitrification rates. The driving variables used for all the models were denitrification enzyme activity and CO₂ production rates. The three models were distinguished by the functional relationships combining these driving variables. The functional relationships used were (i) a second-order model (model 1), (ii) a second-order model with a threshold (model 2), and (iii) a second-order saturation model (model 3). The parameters of the models were estimated by using 12 separate data sets (24 replicates per set), and their abilities to predict denitrification rate distributions were evaluated by using three additional independent data sets of 180 replicates each. Model 2 was the best because it produced distributions of denitrification rate which were not significantly different (P > 0.1) from distributions of measured denitrification rates. The generality of this model is unknown, but it accurately predicted the mean denitrification rates and accounted for the stochastic nature of this variable at the site studied. The approach used in this study may be applicable to other areas of ecological research in which accounting for the high spatial variability of microbiological processes is of interest.     

Nitrous oxide production, its source and distribution in urine patches on grassland on peat soil

Urine patches are considered to be important sites for nitrous oxide (N₂O) production through nitrification and denitrification due to their high concentration of nitrogen (N). The aim of the present study was to determine the microbial source and size of production of N₂O in different zones of a urine patch on grassland on peat soil. Artificial urine was applied in elongated patches of 4.5 m. Four lateral zones were distinguished and sampled for four weeks using an intact soil core incubation method. Incubation of soil cores took place without any additions to the headspace to determine total N₂O production, with acetylene addition to determine total denitrification (N₂O+N₂), and with methyl fluoride to determine the N₂O produced through denitrification.Nitrous oxide production was largest in the centre and decreased towards the edge of the patch. Maximum N₂O production was about 50 mg N m^–2 d^–1 and maximum denitrification activity was 70 mg N m^–2 d^–1. Nitrification was the main N₂O producing process. Nitrous oxide production through denitrification was only of significance when denitrification activity was high. Total N loss through nitrification and denitrification over 31 days was 4.1 g N per patch which was 2.2% of the total applied urine-N.     

Denitrification and N2O emissions from a UK pasture soil following the early spring application of cattle slurry and mineral fertiliser

Total denitrification and nitrous oxide (N₂O) losses were measured from three contrasting dairy management systems representing good commercial practice (system 1), production maintained but with reduced N losses (system 2); and nitrate leaching less than 50 mg L^-1 but with reduced production (system 3). Measurements were made following mineral fertiliser application and from two plot experiments where four treatments were applied: control, NH₄NO₃ at 60 kg N ha^-1, cattle slurry applied to the surface (equivalent to 45 kg N ha^-1), and cattle slurry injected. Despite low soil temperatures (<6 °C) and low rainfall (<3 mm), total denitrification and N₂O losses peaked at 56 and 16 g N ha^-1 d^-1, respectively. Total denitrification losses decreased: system 1 system 2 > system 3, whereas N₂O losses decreased: system 2 > system 3 > system 1. Total denitrification losses tended to decrease with decreasing fertiliser application rate, whereas fertiliser application rate was not the sole determinant of the N₂O loss. The system 3 field was injected with cattle slurry for 2 yr, system 2 received some slurry by injection and system 1 received slurry to the surface. Thus, the amount, timing and method of previous cattle slurry application was important in determining the loss following subsequent fertiliser application. For the plot experiments, total denitrification and N₂O losses decreased in the order: slurry injected > mineral fertiliser > slurry applied to the surface > control for 5 days following application. However, 16 and 19 days after application, N₂O losses above the control were measured from plots that had received cattle slurry. It was inferred that the application of cattle slurry to the pasture soil stimulated greater N₂O production and increased losses over a longer time period compared with mineral fertiliser additions.     

Simultaneous di-oxygenation and denitrification in an internal circulation baffled bioreactor

An internal circulation baffled bioreactor was employed to realize simultaneous di-oxygenation of phthalic acid (PA) and denitrification of nitrate, which require aerobic and anoxic conditions, respectively. Adding a small concentration of succinate as an exogenous electron donor stimulated PA di-oxygenation, which produced readily oxidizable downstream products whose oxidation also enhanced denitrification of nitrate; succinate addition also stimulated denitrification. Depending on the concentration of PA, addition of 0.17 mM succinate increased the PA removal rate by 25 and 42%, while the corresponding nitrate removal rate was increased by 73 and 51%. UV/H₂O₂ advanced oxidation of PA had the same effects as adding succinate, since succinate is generated by UV/H₂O₂; this acceleration effect was approximately equivalent to adding 0.17 mM succinate.     

Nitrogen fluxes from marine sediments: quantification of the associated co-occurring bacterial processes

Different models for calculate on of di-nitrogen fluxes using ¹⁵NO₃ tracers were tested for their congruence with experimental data obtained with marine sediment samples. The co-occurence of nitrification as source of substrate and the simultaneous N₂ production from denitrification and/or Anammox were taken into account as well as nitrous oxide production in the total denitrification rate. The results highlighted that isotope technique provides a powerful tool to evaluate, in the same experimental set up, the rates of total N₂ fluxes: denitrification and/or Anammox if it is carefully applied and its limitations, mainly the range of ¹⁵NO₃ inputs are adapted to the studied samples and the linearity of the kinetics of the products checked.     

Effects of macrophyte-associated nitrogen cycling bacteria on denitrification in the sediments of the eutrophic Gonghu Bay, Taihu Lake

Integrated Elodea nuttallii-immobilized nitrogen cycling bacteria (INCB) technology was used for ecological restoration in the eutrophic Gonghu Bay, Taihu Lake. Sediment denitrification was investigated through microcosm incubations with four different treatments: bare sediment core as control without restoration, sediment + E. nuttallii, sediment + E. nuttallii + INCB, and sediment + INCB. The sediments with E. nuttallii-INCB assemblage (E-INCB) had the highest denitrification rates among all the treatments, and the E-INCB increased the denitrification rate by 162% in the sediments. The presence of macrophytes yielded a penetration depth of O₂ to more than 20 mm below the sediment–water interface (SWI), while the depth was only 4 mm in the sediments without macrophytes. The quantity of denitrifier in E-INCB sediments (within ~2 cm below the SWI) showed a significant increasing trend during one-month incubation, which was one order of magnitudes higher than that in the sediments without INCB. Macrophytes caused deeper O₂ penetration and increased oxic-anoxic interface, which could stimulate the coupled nitrification–denitrification. The high denitrification rate of the E-INCB treatment may result from the increased inorganic nitrogen content in the vicinity of the SWI, causing more nitrate to reach the anoxic denitrification zone. The results showed that E-INCB assemblage could increase benthic N removal by stimulating denitrification via combined O₂ penetration and enhanced microbial N cycling processes. E-INCB might be used as a potential restoration method for controlling fresh water system eutrophication.     

Carbon dioxide injection method for enhancing hydrogenotrophic denitrification of secondary wastewater effluent in fixed bed reactor

This study presents an optimal injection method for using carbon dioxide as a carbon source for the hydrogenotrophic denitrification of secondary wastewater effluent in a laboratory-scale fixed bed reactor (FBR). The FBR was operated under three conditions: a continuous CO₂ supply, periodic CO₂ supply, and without a CO₂ supply. The continuous operation of the FBR without carbon dioxide injection resulted in an increase in pH to 10 and a noticeable level of nitrite accumulation. The continuous co-injection of carbon dioxide and hydrogen gas decreased the pH to a range of 6 ～ 8, but the denitrification efficiency decreased to 29%. The co-injection of carbon dioxide decreased the maximum dissolved hydrogen concentration and hydrogen mass transfer rate by 25 and 61%, respectively. Compared to the continuous injection method, a periodic injection of carbon dioxide increased the denitrification efficiency from 28.6 to 85% as the hydrogen flow rate and hydraulic retention time (HRT) increased. With the periodic injection of carbon dioxide, the nitrite accumulation appeared to be insignificant as the hydrogen flow rate increased.     

The kinetics of denitrification in permeable sediments

Permeable sediments comprise the majority of shelf sediments, yet the rates of denitrification remain highly uncertain in these environments. Computational models are increasingly being used to understand the dynamics of denitrification in permeable sediments, which are complex environments to study experimentally. The realistic implementation of such models requires reliable experimentally derived data on the kinetics of denitrification. Here we undertook measurements of denitrification kinetics as a function of nitrate concentration in carefully controlled flow through reactor experiments on sediments taken from six shallow coastal sites in Port Phillip Bay, Victoria, Australia. The results showed that denitrification commenced rapidly (within 30 min) after the onset of anoxia and the kinetics could be well described by Michaelis–Menten kinetics with half saturation constants (apparent K_m) ranging between 1.5 and 19.8 μM, and maximum denitrification rate (V_max) were in the range of 0.9–7.5 nmol mL^?1 h^?1. The production of N₂ through anaerobic ammonium oxidation (anammox) was generally found to be less than 10 % of denitrification. V_max were in the same range as previously reported in cohesive sediments despite organic carbon contents one order of magnitude lower for the sediments studied here. The ratio of sediment O₂ consumption to V_max was in the range of 0.02–0.09, and was on average much lower than the theoretical ratio of 0.8. As a consequence, models implemented with the theoretical ratio of 0.8 are likely to overestimate denitrification by a factor of ~3. The most likely explanation for this is that the microbial community is not able to instantaneously shift or optimally use a particular electron acceptor in the highly dynamic redox environment experienced in permeable sediments. In contrast to previous studies, we did not observe any significant rates of oxic denitrification.     

Study the biocatalyzing effect and mechanism of cellulose acetate immobilized redox mediators technology (CE-RM) on nitrite denitrification

The biocatalyzing effect of a novel cellulose acetate immobilized redox mediators technology (CE-RM) on nitrite denitrification process was studied with anthraquinone, 1,8-dichloroanthraquinone, 1,5-dichloroanthraquinone and 1,4,5,8-tetrachloroanthraquinone. The results showed that the immobilized 1,4,5,8-tetrachloroanthraquinone presented the best biocatalyzed effect which increased nitrite denitrification rate to 2.3-fold with 12 mmol/L 1,4,5,8-tetrachloroanthraquinone. The unequal biocatalyzing effect was due to the quantity and position of –Cl substituent in anthraquinone-structure. Moreover, the nitrite denitrification rate was increased with the oxidation reduction potential (ORP) values becoming more negative during the biocatalyzing process. The stabilized ORP value with 12 mmol/L immobilized 1,4,5,8-tetrachloroanthraquinone were 81 mV lower than the control. At the same time, the more OH^? was produced with the higher nitrite removal rate achieved in the nitrite denitrification process. In addition, a positive linear correlation was found between the nitrite removal reaction constants k [gNO₂ ^?–N/(gVSS d)] and immobilized 1,4,5,8-tetrachloroanthraquinone concentration (C _{1,4,5,8-tetrachloroanthraquinone}), which was k = 1.8443 C _{1,4,5,8-tetrachloroanthraquinone} + 33.75(R ² = 0.9411). The initial nitrite concentration of 179 mgNO₂ ^?–N/L resulted in the maximum nitrite removal rate, which was 6.526[gNO₂ ^?–N/(gVSS d)]. These results show that the application of cellulose acetate immobilized redox mediators (CE-RM) can be valuable for increasing nitrite denitrification rate.