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1.
The intramolecular distribution of nitrogen isotopes in N 2O is an emerging tool for defining the relative importance of microbial sources of this greenhouse gas. The application of intramolecular isotopic distributions to evaluate the origins of N 2O, however, requires a foundation in laboratory experiments in which individual production pathways can be isolated. Here we evaluate the site preferences of N 2O produced during hydroxylamine oxidation by ammonia oxidizers and by a methanotroph, ammonia oxidation by a nitrifier, nitrite reduction during nitrifier denitrification, and nitrate and nitrite reduction by denitrifiers. The site preferences produced during hydroxylamine oxidation were 33.5 ± 1.2‰, 32.5 ± 0.6‰, and 35.6 ± 1.4‰ for Nitrosomonas europaea, Nitrosospira multiformis, and Methylosinus trichosporium, respectively, indicating similar site preferences for methane and ammonia oxidizers. The site preference of N 2O from ammonia oxidation by N. europaea (31.4 ± 4.2‰) was similar to that produced during hydroxylamine oxidation (33.5 ± 1.2‰) and distinct from that produced during nitrifier denitrification by N. multiformis (0.1 ± 1.7‰), indicating that isotopomers differentiate between nitrification and nitrifier denitrification. The site preferences of N 2O produced during nitrite reduction by the denitrifiers Pseudomonas chlororaphis and Pseudomonas aureofaciens (−0.6 ± 1.9‰ and −0.5 ± 1.9‰, respectively) were similar to those during nitrate reduction (−0.5 ± 1.9‰ and −0.5 ± 0.6‰, respectively), indicating no influence of either substrate on site preference. Site preferences of ~33‰ and ~0‰ are characteristic of nitrification and denitrification, respectively, and provide a basis to quantitatively apportion N 2O. 相似文献
2.
N 2O gas is involved in global warming and ozone depletion. The major sources of N 2O are soil microbial processes. Anthropogenic inputs into the nitrogen cycle have exacerbated these microbial processes, including nitrification. Ammonia-oxidizing archaea (AOA) are major members of the pool of soil ammonia-oxidizing microorganisms. This study investigated the isotopic signatures of N 2O produced by soil AOA and associated N 2O production processes. All five AOA strains (I.1a, I.1a-associated and I.1b clades of Thaumarchaeota) from soil produced N 2O and their yields were comparable to those of ammonia-oxidizing bacteria (AOB). The levels of site preference (SP), δ 15N bulk and δ 18O -N 2O of soil AOA strains were 13–30%, −13 to −35% and 22–36%, respectively, and strains MY1–3 and other soil AOA strains had distinct isotopic signatures. A 15N-NH 4+-labeling experiment indicated that N 2O originated from two different production pathways (that is, ammonia oxidation and nitrifier denitrification), which suggests that the isotopic signatures of N 2O from AOA may be attributable to the relative contributions of these two processes. The highest N 2O production yield and lowest site preference of acidophilic strain CS may be related to enhanced nitrifier denitrification for detoxifying nitrite. Previously, it was not possible to detect N 2O from soil AOA because of similarities between its isotopic signatures and those from AOB. Given the predominance of AOA over AOB in most soils, a significant proportion of the total N 2O emissions from soil nitrification may be attributable to AOA. 相似文献
3.
Nitrous oxide (N 2O) in soils is produced through nitrification and denitrification. The N 2O produced is considered as a nitrogen (N) loss because it will most likely escape from the soil to the atmosphere as N 2O or N 2. Aim of the study was to quantify N 2O production in grassland on peat soils in relation to N input and to determine the relative contribution of nitrification and denitrification to N 2O production. Measurements were carried out on a weekly basis in 2 grasslands on peat soil (Peat I and Peat II) for 2 years (1993 and 1994) using intact soil core incubations. In additional experiments distinction between N 2O from nitrification and denitrification was made by use of the gaseous nitrification inhibitor methyl fluoride (CH 3F).Nitrous oxide production over the 2 year period was on average 34 kg N ha -1 yr -1 for mown treatments that received no N fertiliser and 44 kg N ha -1 yr -1 for mown and N fertilised treatments. Grazing by dairy cattle on Peat I caused additional N 2O production to reach 81 kg N ha -1 yr -1. The sub soil (20–40 cm) contributed 25 to 40% of the total N 2O production in the 0–40 cm layer. The N 2O production:denitrification ratio was on average about 1 in the top soil and 2 in the sub soil indicating that N 2O production through nitrification was important. Experiments showed that when ratios were larger than l, nitrification was the major source of N 2O. In conclusion, N 2O production is a significant N loss mechanism in grassland on peat soil with nitrification as an important N 2O producing process. 相似文献
4.
Sulfur dioxide (SO 2) in the atmosphere has been demonstrated to have many adverse impacts on the environment and human health. In this study, deposition of SO 2 ranging from 9.0 to 127.8 mg kg ?1 with an average of 35.7 mg S kg ?1 was found to substantially stimulate NO and N 2O emissions from soils in the humid subtropical areas of Hainan, Fujian, Jiangxi, and Yunnan provinces of China under field conditions. Laboratory tests indicated that the stimulations were mediated biologically as the effects were not observed in sterilized soils. Acidification of soil resulting from SO 2 deposition was not responsible for the stimulated NO and N 2O emissions alone as the stimulation did not occur by acidifying soil with HNO 3 treatment. By using the 15N tracing method, we found that the N 2O emissions stimulated by SO 2 deposition were from either denitrification, heterotrophic nitrification or both, but not from autotrophic nitrification. Therefore, atmospheric SO 2 deposition would most likely stimulate NO and N 2O emissions in acidic soils in which heterotrophic nitrification dominates NO and N 2O production and waterlogged soils in which denitrification dominates NO and N 2O production. 相似文献
5.
Soils are an important source of N 2O, 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 N 2O 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 N 2O produced from nitrification and denitrification and the proportion of N 2 gas produced from denitrification were determined using the methyl fluoride and acetylene specific inhibitors. Irrespectively to ploughing, fertiliser application increased the rates of N 2O production, N 2O production from nitrification, N 2O production from denitrification and total denitrification (N 2O + N 2). Application of fertiliser also increased the denitrification N 2O/N 2 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 N 2O production, N 2O production from nitrification, N 2O production from denitrification and total denitrification (N 2O + N 2). 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 N 2O production, although a higher proportion of N 2O lost by denitrification was observed as WFPS increased. Recently ploughed plots showed lower denitrification derived N 2O percentages than those ploughed before as a result of the lower soil water content in the former plots. Similarly, a lower mean nitrification derived N 2O percentage was found in the 10–30 cm layer compared with the 0–10 cm. 相似文献
6.
Global warming effects have drawn more and more attention to studying all sources and sinks of nitrous oxide (N2O). Sludge bio-drying, as an effective sludge treatment technology, is being adopted worldwide. In this study, two aeration strategies (piles I and II) were compared to investigate the primary contributors to N2O emission during sludge bio-drying through studying the evolution of functional genes involved in nitrification (amoA, hao, and nxrA) and denitrification (narG, nirS, nirK, norB, and nosZ) by quantitative PCR (qPCR). Results showed that the profile of N2O emission can be divided into three stages, traditional denitrification contributed largely to N2O emission at stage I (days 1–5), but N2O emission mainly happened at stage II (days 5–14) due to nitrifier denitrification and NH2OH accumulation by ammonia-oxidizing bacteria (AOB), accounting for 51.4% and 58.2% of total N2O emission for piles I and II, respectively. At stage III (days 14–21), nitrifier denitrification was inhibited because sludge bio-drying proceeded mainly by the physical aeration, thus N2O emission decreased and changed little. The improved aeration strategy availed pile I to reduce N2O emission much especially at stages II and III, respectively. These results indicated that nitrifier denitrification by AOB and biological NH2OH oxidation due to AOB made more contribution to N2O emission, and aeration strategy was crucial to mitigate N2O emission during sludge bio-drying. 相似文献
7.
Many lacustrine systems, despite management efforts to control eutrophication, are hypoxic during stratified periods. Hypoxia is a major concern, not only for its impact on aquatic life but also for its potential to stimulate production of the greenhouse gases, methane (CH 4) and nitrous oxide (N 2O). We investigated the drivers of hypoxia in Muskegon Lake, a temperate dimictic freshwater estuary that experiences frequent hypolimnetic mixing due to atmospheric forces, riverine inputs, and intrusion of oxic water from coastal upwelling in Lake Michigan. Primary production and respiration (R) rates obtained from a δ 18O mass balance model were similar to other mesotrophic environments (0.56–26.31 and 0.57–13.15 mmol O 2 m ?3 day ?1, respectively), although high P/R (≥2 in mid-summer) indicated there is sufficient autochthonous production to support hypoxia development and persistence. The isotopic enrichment factor for respiration (ε obs) varied markedly and was least negative in August of both sampling years, consistent with high R rates. Hypoxic conditions were associated with accumulation of N 2O but not CH 4, and emissions of N 2O are among the highest reported from lakes. The average N 2O site preference value of 25.4‰ indicates that the majority of N 2O was produced by nitrification via hydroxylamine oxidation, despite the presence of resilient hypoxia. While it has been hypothesized that denitrification acts as a sink for N 2O in hypoxic lakes, it is clear that Muskegon Lake functions as a strong source of N 2O via nitrification. Further considerations of lakes as global sources of N 2O thus warrant a closer evaluation of nitrification-fueled N 2O production. 相似文献
8.
Fungi are capable of both nitrification and denitrification and dominate the microbial biomass in many soils. Recent work
suggests that fungal rather than bacterial pathways dominate N transformation in desert soils. We evaluated this hypothesis
by comparing the contributions of bacteria and fungi to N 2O production at control and N fertilized sites within a semiarid grassland in central New Mexico (USA). Soil samples were
taken from the rhizosphere of blue grama ( B. gracilus) and the microbiotic crusts that grow in open areas between the bunch grasses. Soils incubated at 30% or 70% water holding
capacity, were exposed to one of three biocide treatments (control, cycloheximide or streptomycin). After 48 h, N 2O and CO 2 production were quantified along with the activities of several extracellular enzymes. N 2O production from N fertilized soils was higher than that of control soils (165 vs. 41 pmol h −1 g −1), was higher for crust soil than for rhizosphere soil (108 vs. 97 pmol h −1 g −1), and increased with soil water content (146 vs. 60 pmol h −1 g −1). On average, fungicide (cycloheximide) addition reduced N 2O production by 85% while increasing CO 2 production by 69%; bactericide (streptomycin) reduced N 2O by 53% with mixed effects on CO 2 production. N 2O production was significantly correlated with C and N mineralization potential as measured by assays for glycosidic and proteolytic
enzymes, and with extractable nitrate and ammonium. Our data indicate that fungal nitrifier denitrification and bacterial
autotrophic nitrification dominate N transformation in this ecosystem and that N 2O production is highly sensitive to soil cover, N deposition and moisture. 相似文献
9.
The intramolecular distribution of nitrogen isotopes in N2O is an emerging tool for defining the relative importance of microbial sources of this greenhouse gas. The application of intramolecular isotopic distributions to evaluate the origins of N2O, however, requires a foundation in laboratory experiments in which individual production pathways can be isolated. Here we evaluate the site preferences of N2O produced during hydroxylamine oxidation by ammonia oxidizers and by a methanotroph, ammonia oxidation by a nitrifier, nitrite reduction during nitrifier denitrification, and nitrate and nitrite reduction by denitrifiers. The site preferences produced during hydroxylamine oxidation were 33.5 +/- 1.2 per thousand, 32.5 +/- 0.6 per thousand, and 35.6 +/- 1.4 per thousand for Nitrosomonas europaea, Nitrosospira multiformis, and Methylosinus trichosporium, respectively, indicating similar site preferences for methane and ammonia oxidizers. The site preference of N2O from ammonia oxidation by N. europaea (31.4 +/- 4.2 per thousand) was similar to that produced during hydroxylamine oxidation (33.5 +/- 1.2 per thousand) and distinct from that produced during nitrifier denitrification by N. multiformis (0.1 +/- 1.7 per thousand), indicating that isotopomers differentiate between nitrification and nitrifier denitrification. The site preferences of N2O produced during nitrite reduction by the denitrifiers Pseudomonas chlororaphis and Pseudomonas aureofaciens (-0.6 +/- 1.9 per thousand and -0.5 +/- 1.9 per thousand, respectively) were similar to those during nitrate reduction (-0.5 +/- 1.9 per thousand and -0.5 +/- 0.6 per thousand, respectively), indicating no influence of either substrate on site preference. Site preferences of approximately 33 per thousand and approximately 0 per thousand are characteristic of nitrification and denitrification, respectively, and provide a basis to quantitatively apportion N2O. 相似文献
10.
This study examines the role of tree canopies in processing atmospheric nitrogen (N dep) for four forests in the United Kingdom subjected to different N dep: Scots pine and beech stands under high N dep (HN, 13–19 kg N ha ?1 yr ?1), compared to Scots pine and beech stands under low N dep (LN, 9 kg N ha ?1 yr ?1). Changes of NO 3‐N and NH 4‐N concentrations in rainfall (RF) and throughfall (TF) together with a quadruple isotope approach, which combines δ 18O, Δ 17O and δ 15N in NO 3? and δ 15N in NH 4+, were used to assess N transformations by the canopies. Generally, HN sites showed higher NH 4‐N and NO 3‐N concentrations in RF compared to the LN sites. Similar values of δ 15N‐NO 3? and δ 18O in RF suggested similar source of atmospheric NO 3? (i.e. local traffic), while more positive values for δ 15N‐NH 4+ at HN compared to LN likely reflected the contribution of dry NH x deposition from intensive local farming. The isotopic signatures of the N‐forms changed after interacting with tree canopies. Indeed, 15N‐enriched NH 4+ in TF compared to RF at all sites suggested that canopies played an important role in buffering dry N dep also at the low N dep site. Using two independent methods, based on δ 18O and Δ 17O, we quantified for the first time the proportion of NO 3? in TF, which derived from nitrification occurring in tree canopies at the HN site. Specifically, for Scots pine, all the considered isotope approaches detected biological nitrification. By contrast for the beech, only using the mixing model with Δ 17O, we were able to depict the occurrence of nitrification within canopies. Our study suggests that tree canopies play an active role in the N cycling within forest ecosystems. Processing of N dep within canopies should not be neglected and needs further exploration, with the combination of multiple isotope tracers, with particular reference to Δ 17O. 相似文献
11.
The source of N 2O produced in soil is often uncertain because denitrification and nitrification can occur simultaneously in the same soil aggregate. A technique which exploits the differential sensitivity of these processes to C 2H 2 inhibition is proposed for distinguishing among gaseous N losses from soils. Denitrification N 2O was estimated from 24-h laboratory incubations in which nitrification was inhibited by 10-Pa C 2H 2. Nitrification N 2O was estimated from the difference between N 2O production under no C 2H 2 and that determined for denitrification. Denitrification N 2 was estimated from the difference between N 2O production under 10-kPa C 2H 2 and that under 10 Pa. Laboratory estimates of N 2O production were significantly correlated with in situ N 2O diffusion measurements made during a 10-month period in two forested watersheds. Nitrous oxide production from nitrification was most important on well-drained sites of a disturbed watershed where ambient NO 3− was high. In contrast, denitrification N 2O was most important on poorly drained sites near the stream of the same watershed. Distinction between N 2O production from nitrification and denitrification was corroborated by correlations between denitrification N 2O and water-filled pore space and between nitrification N 2O and ambient NO 3−. This technique permits qualitative study of environmental parameters that regulate gaseous N losses via denitrification and nitrification. 相似文献
12.
In forests of the humid subtropics of China, chronically elevated nitrogen (N) deposition, predominantly as ammonium (NH 4+), causes significant nitrate (NO 3?) leaching from well‐drained acid forest soils on hill slopes (HS), whereas significant retention of NO 3? occurs in near‐stream environments (groundwater discharge zones, GDZ). To aid our understanding of N transformations on the catchment level, we studied spatial and temporal variabilities of concentration and natural abundance (δ 15N and δ 18O) of nitrate (NO 3?) in soil pore water along a hydrological continuum in the N‐saturated Tieshanping (TSP) catchment, southwest China. Our data show that effective removal of atmogenic NH 4+ and production of NO 3? in soils on HS were associated with a significant decrease in δ 15N‐NO 3?, suggesting efficient nitrification despite low soil pH. The concentration of NO 3? declined sharply along the hydrological flow path in the GDZ. This decline was associated with a significant increase in both δ 15N and δ 18O of residual NO 3?, providing evidence that the GDZ acts as an N sink due to denitrification. The observed apparent 15N enrichment factor ( ε) of NO 3? of about ?5‰ in the GDZ is similar to values previously reported for efficient denitrification in riparian and groundwater systems. Episode studies in the summers of 2009, 2010 and 2013 revealed that the spatial pattern of δ 15N and δ 18O‐NO 3? in soil water was remarkably similar from year to year. The importance of denitrification as a major N sink was also seen at the catchment scale, as largest δ 15N‐NO 3? values in stream water were observed at lowest discharge, confirming the importance of the relatively small GDZ for N removal under base flow conditions. This study, explicitly recognizing hydrologically connected landscape elements, reveals an overlooked but robust N sink in N‐saturated, subtropical forests with important implications for regional N budgets. 相似文献
13.
Combined measurements of nitrification activity and N 2O emissions were performed in a lowland and a montane tropical rainforest ecosystem in NE-Australia over a 18 months period from October 2001 until May 2003. At both sites gross nitrification rates, measured by the BaPS technique, showed a strong seasonal pattern with significantly higher rates of gross nitrification during wet season conditions. Nitrification rates at the montane site (1.48?±?0.24–18.75?±?2.38 mg N kg ?1 day ?1) were found to be significantly higher than at the lowland site (1.65?±?0.21–4.54?±?0.27 mg N kg ?1 day ?1). The relationship between soil moisture and gross nitrification rates could be described best by O’Neill functions having a soil moisture optimum of nitrification at app. 65% WFPS. At the lowland site, for which continuous measurements of N 2O emissions were available, nitrification was positively correlated with N 2O emission. Nitrification contributed significantly to N 2O formation during dry season (app.85%) but less (app. 30%) during wet season conditions. In average 0.19‰ of the N metabolized by nitrification was released as N 2O. The N 2O fraction loss for nitrification was positively correlated with changes in soil moisture and varied slightly between 0.15 and 0.22‰. Our results demonstrate that combined N 2O emission and microbial N turnover studies covering prolonged observation periods are needed to clarify and quantify the role of the microbial processes nitrification and denitrification for annual N 2O emissions from soils of terrestrial ecosystems. 相似文献
14.
Production of NO and N 2 O by the heterotrophic nitrifier Alcaligenes faecalis subsp. parafaecalis was studied during growth in batch and continuous culture on peptone-meat extract medium. Depending on oxygen saturation level, medium redox status and amount of substrate supplied, the microorganisms produced 0.002–0.25 mg NO-N h - 1 (g protein) - 1 and 0.16–2.4 mg N 2 O-N h - 1 (g protein) - 1 . Maximum rates of nitrogen oxides production were observed during peak events initiated by sudden changes of oxygen supply in the medium and were due to combined nitrification/denitrification taking place simultaneously within the cells. Based on model simulations of enzymatic kinetics of denitrification, possible mechanisms of increased nitrogen oxides production during periods of changes in oxygen supply are suggested. 相似文献
15.
The rapid expansion of intensively farmed vegetable fields has substantially contributed to the total N 2O emissions from croplands in China. However, to date, the mechanisms underlying this phenomenon have not been completely understood. To quantify the contributions of autotrophic nitrification, heterotrophic nitrification, and denitrification to N 2O production from the intensive vegetable fields and to identify the affecting factors, a 15N tracing experiment was conducted using five soil samples collected from adjacent fields used for rice-wheat rotation system (WF), or for consecutive vegetable cultivation (VF) for 0.5 (VF1), 6 (VF2), 8 (VF3), and 10 (VF4) years. Soil was incubated under 50% water holding capacity (WHC) at 25°C for 96 h after being labeled with 15NH 4NO 3 or NH 4 15 NO 3. The average N 2O emission rate was 24.2 ng N?kg ?1 h ?1 in WF soil, but it ranged from 69.6 to 507 ng N?kg ?1 h ?1 in VF soils. Autotrophic nitrification, heterotrophic nitrification and denitrification accounted for 0.3–31.4%, 25.4–54.4% and 22.5–57.7% of the N 2O emissions, respectively. When vegetable soils were moderately acidified (pH, 6.2 to ?≥?5.7), the increased N 2O emissions resulted from the increase of both the gross autotrophic and heterotrophic nitrification rates and the N 2O product ratio of autotrophic nitrification. However, once severe acidification occurred (as in VF4, pH?≤?4.3) and salt stress increased, both autotrophic and heterotrophic nitrification rates were inhibited to levels similar to those of WF soil. The enhanced N 2O product ratios of heterotrophic nitrification (4.84‰), autotrophic nitrification (0.93‰) and denitrification processes were the most important factors explaining high N 2O emission in VF4 soil. Data from this study showed that various soil conditions (e.g., soil salinity and concentration of NO 3 - or NH 4 + ) could also significantly affect the sources and rates of N 2O emission. 相似文献
16.
The availability of O 2 is believed to be one of the main factors regulating nitrification and denitrification and the release of NO and N 2O. The availability of O 2 in soil is controlled by the O 2 partial pressure in the gas phase and by the moisture content in the soil. Therefore, we investigated the influence of O 2 partial pressures and soil moisture contents on the NO and N 2O release in a sandy and a loamy silt and differentiated between nitrification and denitrification by selective inhibition of nitrification with 10 Pa acetylene. At 60% whc (maximum water holding capacity) NO and N 2O release by denitrification increased with decreasing O 2 partial pressure and reached a maximum under anoxic conditions. Under anoxic conditions NO and N 2O were only released by denitrification. NO and N 2O release by nitrification also increased with decreasing O 2 partial pressure, but reached a maximum at 0.1–0.5% O 2 and then decreased again. Nitrification was the main source of NO and N 2O at O 2 partial pressures higher than 0.1–0.5% O 2. At lower O 2 partial pressures denitrification was the main source of NO and N 2O. With decreasing O 2 partial pressure N 2O release increased more than NO release, indicating that the N 2O release was more sensitive against O 2 than the NO release. At ambient O 2 partial pressure (20.5% O 2) NO and N 2O release by denitrification increased with increasing soil moisture content. The maximum NO and N 2O release was observed at soil moisture contents of 65–80% whc and 100% whc, respectively. NO and N 2O release by nitrification also increased with increasing soil moisture content with a maximum at 45–55% whc and 90% whc, respectively. Nitrification was the main source of NO and N 2O at soil moisture contents lower than 90% whc and 80% whc, respectively. Higher soil moisture contents favoured NO and N 2O release by denitrification. Soil texture had also an effect on the release of NO and N 2O. The coarse-textured sandy silt released more NO than N 2O compared with the fine-textured loamy silt. At high soil moisture contents (80–100% whc) the fine-textured soil showed a higher N 2O release by denitrification than the coarse-textured soil. We assume that the fine-textured soil became anoxic at a lower soil moisture content than the coarse-textured soil. In conclusion, the effects of O 2 partial pressure, soil moisture and soil texture were consistent with the theory that denitrification increasingly contributes to the release of NO and in particular N 2O when conditions for soil microorganisms become increasingly anoxic. 相似文献
17.
Ammonia conversion processes are essential for most soil and aquatic systems. Under natural conditions, the many possible reactions are difficult to analyze. For example, nitrification and denitrification have long been regarded as separate phenomena performed by different groups of bacteria in segregated areas of soils, sediments or aquatic systems sequentially in time. It has now been established that strict segregation in place and time of the two processes is not necessary and that both denitrifiers and nitrifiers have versatile metabolisms. However, the rates described for aerobic denitrifiers are very low compared to the rates observed under anoxic conditions. Also the rates of nitrifier denitrification are quite low, indicating that these conversions may not play an important role under natural conditions. In addition, these processes often result in the emission of quite large amounts of undesirable products, NO and N 2O. Heterotrophic nitrification might be of relevance for systems, that contain a high carbon to nitrogen ratio. Recently, a novel process (Anammox) has been discovered in which ammonium serves as the electron donor for denitrification of nitrite into dinitrogen gas. 15N labeling studies showed that hydrazine and hydroxylamine were important intermediates in this process. Enrichment cultures on ammonium, nitrite and bicarbonate resulted in the dominance of one morphotypical microorganism. The growth rate of the cultures is extremely low (doubling time 11 days), but the affinity for ammonium and nitrite and the conversion rates (9.2 10 –4 mol kg –1 s –1) are quite high. Some of the reported high nitrogen losses in soil and aquatic systems might be attributed to anaerobic ammonium oxidation. In addition, this conversion offers new opportunities for nitrogen removal, when it is combined with recently developed processes for partial nitrification. 相似文献
18.
Summary To examine the effect of barley roots on denitrification, a pot experiment was designed to compare N 2O production and denitrification in soils with and without barley plants. Denitrification, N 2O 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. C 2H 2-inhibition of nitrous oxide reductase (partial pressure of 10 kPa C 2H 2) was used to determine total denitrification rates while incubations with ambient air and with C 2H 2 at partial pressures of 2.5–5 Pa were used to estimate the amounts of N 2O released from autotrophic nitrification and from denitrification processes. Other sources of N 2O 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. N 2 was the predominant denitrification product found close to roots; N 2O 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. 相似文献
19.
The purposes of this study were to evaluate the potential production of nitrous oxide (N 2O), 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 N 2O 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 N 2O 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 N 2 produced from denitrification decreased but the proportion of N 2O in the (N 2 + N 2O) increased. Denitrification was the main source of released N 2O when the moisture content was between 40–60% and oxygen 10%. The amounts of nitrification, denitrification and N 2 production increased as the moisture content increased. 相似文献
20.
Nitrous oxide (N 2O) emissions from inland waters remain a major source of uncertainty in global greenhouse gas budgets. N 2O emissions are typically estimated using emission factors (EFs), defined as the proportion of the terrestrial nitrogen (N) load to a water body that is emitted as N 2O to the atmosphere. The Intergovernmental Panel on Climate Change (IPCC) has proposed EFs of 0.25% and 0.75%, though studies have suggested that both these values are either too high or too low. In this work, we develop a mechanistic modeling approach to explicitly predict N 2O production and emissions via nitrification and denitrification in rivers, reservoirs and estuaries. In particular, we introduce a water residence time dependence, which kinetically limits the extent of denitrification and nitrification in water bodies. We revise existing spatially explicit estimates of N loads to inland waters to predict both lumped watershed and half‐degree grid cell emissions and EFs worldwide, as well as the proportions of these emissions that originate from denitrification and nitrification. We estimate global inland water N 2O emissions of 10.6–19.8 Gmol N year ?1 (148–277 Gg N year ?1), with reservoirs producing most N 2O per unit area. Our results indicate that IPCC EFs are likely overestimated by up to an order of magnitude, and that achieving the magnitude of the IPCC's EFs is kinetically improbable in most river systems. Denitrification represents the major pathway of N 2O production in river systems, whereas nitrification dominates production in reservoirs and estuaries. 相似文献
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