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1.
Effects of Specific Inhibitors on Anammox and Denitrification in Marine Sediments 总被引:1,自引:0,他引:1
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The effects of three metabolic inhibitors (acetylene, methanol, and allylthiourea [ATU]) on the pathways of N2 production were investigated by using short anoxic incubations of marine sediment with a 15N isotope technique. Acetylene inhibited ammonium oxidation through the anammox pathway as the oxidation rate decreased exponentially with increasing acetylene concentration; the rate decay constant was 0.10 ± 0.02 μM−1, and there was 95% inhibition at ~30 μM. Nitrous oxide reduction, the final step of denitrification, was not sensitive to acetylene concentrations below 10 μM. However, nitrous oxide reduction was inhibited by higher concentrations, and the sensitivity was approximately one-half the sensitivity of anammox (decay constant, 0.049 ± 0.004 μM−1; 95% inhibition at ~70 μM). Methanol specifically inhibited anammox with a decay constant of 0.79 ± 0.12 mM−1, and thus 3 to 4 mM methanol was required for nearly complete inhibition. This level of methanol stimulated denitrification by ~50%. ATU did not have marked effects on the rates of anammox and denitrification. The profile of inhibitor effects on anammox agreed with the results of studies of the process in wastewater bioreactors, which confirmed the similarity between the anammox bacteria in bioreactors and natural environments. Acetylene and methanol can be used to separate anammox and denitrification, but the effects of these compounds on nitrification limits their use in studies of these processes in systems where nitrification is an important source of nitrate. The observed differential effects of acetylene and methanol on anammox and denitrification support our current understanding of the two main pathways of N2 production in marine sediments and the use of 15N isotope methods for their quantification. 相似文献
2.
Simultaneous Measurement of Denitrification and Nitrogen Fixation Using Isotope Pairing with Membrane Inlet Mass Spectrometry Analysis 总被引:4,自引:1,他引:3
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A method for estimating denitrification and nitrogen fixation simultaneously in coastal sediments was developed. An isotope-pairing technique was applied to dissolved gas measurements with a membrane inlet mass spectrometer (MIMS). The relative fluxes of three N2 gas species (28N2, 29N2, and 30N2) were monitored during incubation experiments after the addition of 15NO3−. Formulas were developed to estimate the production (denitrification) and consumption (N2 fixation) of N2 gas from the fluxes of the different isotopic forms of N2. Proportions of the three isotopic forms produced from 15NO3− and 14NO3− agreed with expectations in a sediment slurry incubation experiment designed to optimize conditions for denitrification. Nitrogen fixation rates from an algal mat measured with intact sediment cores ranged from 32 to 390 μg-atoms of N m−2 h−1. They were enhanced by light and organic matter enrichment. In this environment of high nitrogen fixation, low N2 production rates due to denitrification could be separated from high N2 consumption rates due to nitrogen fixation. Denitrification and nitrogen fixation rates were estimated in April 2000 on sediments from a Texas sea grass bed (Laguna Madre). Denitrification rates (average, 20 μg-atoms of N m−2 h−1) were lower than nitrogen fixation rates (average, 60 μg-atoms of N m−2 h−1). The developed method benefits from simple and accurate dissolved-gas measurement by the MIMS system. By adding the N2 isotope capability, it was possible to do isotope-pairing experiments with the MIMS system. 相似文献
3.
Evidence for the Cooccurrence of Nitrite-Dependent Anaerobic Ammonium and Methane Oxidation Processes in a Flooded Paddy Field 总被引:1,自引:0,他引:1
Li-dong Shen Shuai Liu Qian Huang Xu Lian Zhan-fei He Sha Geng Ren-cun Jin Yun-feng He Li-ping Lou Xiang-yang Xu Ping Zheng Bao-lan Hu 《Applied and environmental microbiology》2014,80(24):7611-7619
Anaerobic ammonium oxidation (anammox) and nitrite-dependent anaerobic methane oxidation (n-damo) are two of the most recent discoveries in the microbial nitrogen cycle. In the present study, we provide direct evidence for the cooccurrence of the anammox and n-damo processes in a flooded paddy field in southeastern China. Stable isotope experiments showed that the potential anammox rates ranged from 5.6 to 22.7 nmol N2 g−1 (dry weight) day−1 and the potential n-damo rates varied from 0.2 to 2.1 nmol CO2 g−1 (dry weight) day−1 in different layers of soil cores. Quantitative PCR showed that the abundance of anammox bacteria ranged from 1.0 × 105 to 2.0 × 106 copies g−1 (dry weight) in different layers of soil cores and the abundance of n-damo bacteria varied from 3.8 × 105 to 6.1 × 106 copies g−1 (dry weight). Phylogenetic analyses of the recovered 16S rRNA gene sequences showed that anammox bacteria affiliated with “Candidatus Brocadia” and “Candidatus Kuenenia” and n-damo bacteria related to “Candidatus Methylomirabilis oxyfera” were present in the soil cores. It is estimated that a total loss of 50.7 g N m−2 per year could be linked to the anammox process, which is at intermediate levels for the nitrogen flux ranges of aerobic ammonium oxidation and denitrification reported in wetland soils. In addition, it is estimated that a total of 0.14 g CH4 m−2 per year could be oxidized via the n-damo process, while this rate is at the lower end of the aerobic methane oxidation rates reported in wetland soils. 相似文献
4.
Using a combination of process rate determination, microsensor profiling and molecular techniques, we demonstrated that denitrification, and not anaerobic ammonium oxidation (anammox), is the major nitrogen loss process in biological soil crusts from Oman. Potential denitrification rates were 584±101 and 58±20 μmol N m−2 h−1 for cyanobacterial and lichen crust, respectively. Complete denitrification to N2 was further confirmed by an 15NO3− tracer experiment with intact crust pieces that proceeded at rates of 103±19 and 27±8 μmol N m−2 h−1 for cyanobacterial and lichen crust, respectively. Strikingly, N2O gas was emitted at very high potential rates of 387±143 and 31±6 μmol N m−2 h−1 from the cyanobacterial and lichen crust, respectively, with N2O accounting for 53–66% of the total emission of nitrogenous gases. Microsensor measurements revealed that N2O was produced in the anoxic layer and thus apparently originated from incomplete denitrification. Using quantitative PCR, denitrification genes were detected in both the crusts and were expressed either in comparable (nirS) or slightly higher (narG) numbers in the cyanobacterial crusts. Although 99% of the nirS sequences in the cyanobacterial crust were affiliated to an uncultured denitrifying bacterium, 94% of these sequences were most closely affiliated to Paracoccus denitrificans in the lichen crust. Sequences of nosZ gene formed a distinct cluster that did not branch with known denitrifying bacteria. Our results demonstrate that nitrogen loss via denitrification is a dominant process in crusts from Oman, which leads to N2O gas emission and potentially reduces desert soil fertility. 相似文献
5.
Sang-Wan Kim Shinya Fushinobu Shengmin Zhou Takayoshi Wakagi Hirofumi Shoun 《Applied and environmental microbiology》2009,75(9):2652-2658
Although denitrification or nitrate respiration has been found among a few eukaryotes, its phylogenetic relationship with the bacterial system remains unclear because orthologous genes involved in the bacterial denitrification system were not identified in these eukaryotes. In this study, we isolated a gene from the denitrifying fungus Fusarium oxysporum that is homologous to the bacterial nirK gene responsible for encoding copper-containing nitrite reductase (NirK). Characterization of the gene and its recombinant protein showed that the fungal nirK gene is the first eukaryotic ortholog of the bacterial counterpart involved in denitrification. Additionally, recent genome analyses have revealed the occurrence of nirK homologs in many fungi and protozoa, although the denitrifying activity of these eukaryotes has never been examined. These eukaryotic homolog genes, together with the fungal nirK gene of F. oxysporum, are grouped in the same branch of the phylogenetic tree as the nirK genes of bacteria, archaea, and eukaryotes, implying that eukaryotic nirK and its homologs evolved from a single ancestor (possibly the protomitochondrion). These results show that the fungal denitrifying system has the same origin as its bacterial counterpart.Denitrification plays an important role in the global nitrogen cycle and reduces nitrate (NO3−) and/or nitrite (NO2−) to a gaseous form of nitrogen, generally to dinitrogen (N2) or nitrous oxide (N2O) (27). It typically follows four reduction stages, NO3− → NO2− → NO → N2O → N2, each of which is catalyzed by a specific reductase: dissimilatory NO3− reductase (dNaR), dissimilatory NO2− reductase (dNiR), nitric oxide (NO) reductase (NoR), and N2O reductase, respectively. These enzymes receive electrons from a respiratory chain functioning as a “terminal reductase.” Thus, denitrification exhibits a physiological significance in its ability to anaerobically respire through the processes of nitrate respiration, nitrite respiration, and so forth. Denitrification was previously thought to be a characteristic of bacteria; however, similar reactions have been found to occur in a few eukaryotes and archaea (6, 27). Eukaryotic nitrate respiration was first found in protozoa that reside in an anaerobic freshwater habitat (8). The organism particularly reduces NO3− to NO2− in a single step, a process which recovers dNaR activity in the mitochondrial fraction but does not result in denitrification. Eukaryotic denitrification was first found to occur among fungi (19, 20), which generally form N2O from NO3− or NO2−. Recently, eukaryotic denitrification was also found in a benthic foraminifer that forms N2 from NO3− (18). The fungal denitrification system localizes in the mitochondria and couples to the mitochondrial electron transport chain to produce ATP (12, 21), thus exhibiting properties similar to those of the bacterial systems in its ability to respire anaerobically. Moreover, the mechanism of anaerobic respiration in the “aerobic” organelle of eukaryotes (mitochondrion) evokes interest regarding the origin and evolution of the mitochondrion.The main components of the fungal denitrifying system, the dNaR, dNiR, and NoR proteins, were either completely or partially purified from Fusarium oxysporum. Fungal NoR of the cytochrome P450 (P450) type, referred to as P450nor (CYP55) (11, 16), is a distinct species of bacterial cytochrome cb-type NoR. By contrast, the previously isolated fungal dNiR protein is a copper-containing type (NirK) that closely resembles its bacterial counterpart (13). Furthermore, dNaR activity partially purified from the mitochondrial membrane fraction showed that fungal dNaR possibly resembles its bacterial counterpart, NarGHI (12, 23). Therefore, while a portion of the fungal system appears to resemble its bacterial counterpart, the phylogenetic relationship between the fungal and bacterial denitrification systems remained unclear because the genes of the fungal components (dNaR and dNiR) have not been sequenced.Recent genome analyses have revealed the presence of nirK homolog genes in many eukaryotes (fungi and protozoa), a finding consistent with our previous findings on the isolation of the fungal NirK protein (13). Therefore, whether these eukaryotes containing the nirK homolog gene exhibit denitrification activity and whether the denitrifying fungus F. oxysporum really contains a nirK gene deserve a great deal of attention. To address this issue, we used the suppression subtractive hybridization (SSH) technique (7) and succeeded in isolating the nirK gene from the denitrifying fungus F. oxysporum. 相似文献
6.
Settlement ponds are used to treat aquaculture discharge water by removing nutrients through physical (settling) and biological (microbial transformation) processes. Nutrient removal through settling has been quantified, however, the occurrence of, and potential for microbial nitrogen (N) removal is largely unknown in these systems. Therefore, isotope tracer techniques were used to measure potential rates of denitrification and anaerobic ammonium oxidation (anammox) in the sediment of settlement ponds in tropical aquaculture systems. Dinitrogen gas (N2) was produced in all ponds, although potential rates were low (0–7.07 nmol N cm−3 h−1) relative to other aquatic systems. Denitrification was the main driver of N2 production, with anammox only detected in two of the four ponds. No correlations were detected between the measured sediment variables (total organic carbon, total nitrogen, iron, manganese, sulphur and phosphorous) and denitrification or anammox. Furthermore, denitrification was not carbon limited as the addition of particulate organic matter (paired t-Test; P = 0.350, n = 3) or methanol (paired t-Test; P = 0.744, n = 3) did not stimulate production of N2. A simple mass balance model showed that only 2.5% of added fixed N was removed in the studied settlement ponds through the denitrification and anammox processes. It is recommended that settlement ponds be used in conjunction with additional technologies (i.e. constructed wetlands or biological reactors) to enhance N2 production and N removal from aquaculture wastewater. 相似文献
7.
San'an Nie Hu Li Xiaoru Yang Zhaoji Zhang Bosen Weng Fuyi Huang Gui-Bing Zhu Yong-Guan Zhu 《The ISME journal》2015,9(9):2059-2067
Anaerobic oxidation of ammonium (anammox) is recognized as an important process for nitrogen (N) cycling, yet its role in agricultural ecosystems, which are intensively fertilized, remains unclear. In this study, we investigated the presence, activity, functional gene abundance and role of anammox bacteria in rhizosphere and non-rhizosphere paddy soils using catalyzed reporter deposition–fluorescence in situ hybridization, isotope-tracing technique, quantitative PCR assay and 16S rRNA gene clone libraries. Results showed that rhizosphere anammox contributed to 31–41% N2 production with activities of 0.33–0.64 nmol N2 g−1 soil h−1, whereas the non-rhizosphere anammox bacteria contributed to only 2–3% N2 production with lower activities of 0.08–0.26 nmol N2 g−1 soil h−1. Higher anammox bacterial cells were observed (0.75–1.4 × 107 copies g−1 soil) in the rhizosphere, which were twofold higher compared with the non-rhizosphere soil (3.7–5.9 × 106 copies g−1 soil). Phylogenetic analysis of the anammox bacterial 16S rRNA genes indicated that two genera of ‘Candidatus Kuenenia'' and ‘Candidatus Brocadia'' and the family of Planctomycetaceae were identified. We suggest the rhizosphere provides a favorable niche for anammox bacteria, which are important to N cycling, but were previously largely overlooked. 相似文献
8.
Jessika Füssel Phyllis Lam Gaute Lavik Marlene M Jensen Moritz Holtappels Marcel Günter Marcel MM Kuypers 《The ISME journal》2012,6(6):1200-1209
Nitrite oxidation is the second step of nitrification. It is the primary source of oceanic nitrate, the predominant form of bioavailable nitrogen in the ocean. Despite its obvious importance, nitrite oxidation has rarely been investigated in marine settings. We determined nitrite oxidation rates directly in 15N-incubation experiments and compared the rates with those of nitrate reduction to nitrite, ammonia oxidation, anammox, denitrification, as well as dissimilatory nitrate/nitrite reduction to ammonium in the Namibian oxygen minimum zone (OMZ). Nitrite oxidation (⩽372 nM NO2− d−1) was detected throughout the OMZ even when in situ oxygen concentrations were low to non-detectable. Nitrite oxidation rates often exceeded ammonia oxidation rates, whereas nitrate reduction served as an alternative and significant source of nitrite. Nitrite oxidation and anammox co-occurred in these oxygen-deficient waters, suggesting that nitrite-oxidizing bacteria (NOB) likely compete with anammox bacteria for nitrite when substrate availability became low. Among all of the known NOB genera targeted via catalyzed reporter deposition fluorescence in situ hybridization, only Nitrospina and Nitrococcus were detectable in the Namibian OMZ samples investigated. These NOB were abundant throughout the OMZ and contributed up to ∼9% of total microbial community. Our combined results reveal that a considerable fraction of the recently recycled nitrogen or reduced NO3− was re-oxidized back to NO3− via nitrite oxidation, instead of being lost from the system through the anammox or denitrification pathways. 相似文献
9.
Vertical Distribution of Denitrification in an Estuarine Sediment: Integrating Sediment Flowthrough Reactor Experiments and Microprofiling via Reactive Transport Modeling
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Anniet M. Laverman Christof Meile Philippe Van Cappellen Elze B. A. Wieringa 《Applied microbiology》2007,73(1):40-47
Denitrifying activity in a sediment from the freshwater part of a polluted estuary in northwest Europe was quantified using two independent approaches. High-resolution N2O microprofiles were recorded in sediment cores to which acetylene was added to the overlying water and injected laterally into the sediment. The vertical distribution of the rate of denitrification supported by nitrate uptake from the overlying water was then derived from the time series N2O concentration profiles. The rates obtained for the core incubations were compared to the rates predicted by a forward reactive transport model, which included rate expression for denitrification calibrated with potential rate measurements obtained in flowthrough reactors containing undisturbed, 1-cm-thick sediment slices. The two approaches yielded comparable rate profiles, with a near-surface, 2- to 3-mm narrow zone of denitrification and maximum in situ rates on the order of 200 to 300 nmol cm−3 h−1. The maximum in situ rates were about twofold lower than the maximum potential rate for the 0- to 1-cm depth interval of the sediment, indicating that in situ denitrification was nitrate limited. The experimentally and model-derived rates of denitrification implied that there was nitrate uptake by the sediment at a rate that was on the order of 50 (± 10) nmol cm−2 h−1, which agreed well with direct nitrate flux measurements for core incubations. Reactive transport model calculations showed that benthic uptake of nitrate at the site is particularly sensitive to the nitrate concentration in the overlying water and the maximum potential rate of denitrification in the sediment. 相似文献
10.
11.
Nitrous Oxide Formation in the Colne Estuary, England: the Central Role of Nitrite 总被引:2,自引:1,他引:1
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Liang F. Dong David B. Nedwell Graham J. C. Underwood Daniel C. O. Thornton Iman Rusmana 《Applied microbiology》2002,68(3):1240-1249
Nitrate and nitrite concentrations in the water and nitrous oxide and nitrite fluxes across the sediment-water interface were measured monthly in the River Colne estuary, England, from December 1996 to March 1998. Water column concentrations of N2O in the Colne were supersaturated with respect to air, indicating that the estuary was a source of N2O for the atmosphere. At the freshwater end of the estuary, nitrous oxide effluxes from the sediment were closely correlated with the nitrite concentrations in the overlying water and with the nitrite influx into the sediment. Increases in N2O production from sediments were about 10 times greater with the addition of nitrite than with the addition of nitrate. Rates of denitrification were stimulated to a larger extent by enhanced nitrite than by nitrate concentrations. At 550 μM nitrite or nitrate (the highest concentration used), the rates of denitrification were 600 μmol N · m−2 · h−1 with nitrite but only 180 μmol N · m−2 · h−1 with nitrate. The ratios of rates of nitrous oxide production and denitrification (N2O/N2 × 100) were significantly higher with the addition of nitrite (7 to 13% of denitrification) than with nitrate (2 to 4% of denitrification). The results suggested that in addition to anaerobic bacteria, which possess the complete denitrification pathway for N2 formation in the estuarine sediments, there may be two other groups of bacteria: nitrite denitrifiers, which reduce nitrite to N2 via N2O, and obligate nitrite-denitrifying bacteria, which reduce nitrite to N2O as the end product. Consideration of free-energy changes during N2O formation led to the conclusion that N2O formation using nitrite as the electron acceptor is favored in the Colne estuary and may be a critical factor regulating the formation of N2O in high-nutrient-load estuaries. 相似文献
12.
Ronald S. Oremland Cindy Umberger Charles W. Culbertson Richard L. Smith 《Applied microbiology》1984,47(5):1106-1112
The acetylene block technique was employed to study denitrification in intertidal estuarine sediments. Addition of nitrate to sediment slurries stimulated denitrification. During the dry season, sediment-slurry denitrification rates displayed Michaelis-Menten kinetics, and ambient NO3− + NO2− concentrations (≤26 μM) were below the apparent Km (50 μM) for nitrate. During the rainy season, when ambient NO3− + NO2− concentrations were higher (37 to 89 μM), an accurate estimate of the Km could not be obtained. Endogenous denitrification activity was confined to the upper 3 cm of the sediment column. However, the addition of nitrate to deeper sediments demonstrated immediate N2O production, and potential activity existed at all depths sampled (the deepest was 15 cm). Loss of N2O in the presence of C2H2 was sometimes observed during these short-term sediment incubations. Experiments with sediment slurries and washed cell suspensions of a marine pseudomonad confirmed that this N2O loss was caused by incomplete blockage of N2O reductase by C2H2 at low nitrate concentrations. Areal estimates of denitrification (in the absence of added nitrate) ranged from 0.8 to 1.2 μmol of N2 m−2 h−1 (for undisturbed sediments) to 17 to 280 μmol of N2 m−2 h−1 (for shaken sediment slurries). 相似文献
13.
Microzonation of Denitrification Activity in Stream Sediments as Studied with a Combined Oxygen and Nitrous Oxide Microsensor 总被引:14,自引:6,他引:8
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Peter Bondo Christensen Lars Peter Nielsen Niels Peter Revsbech Jan Srensen 《Applied microbiology》1989,55(5):1234-1241
Microzonation of denitrification was studied in stream sediments by a combined O2 and N2O microsensor technique. O2 and N2O concentration profiles were recorded simultaneously in intact sediment cores in which C2H2 was added to inhibit N2O reduction in denitrification. The N2O profiles were used to obtain high-resolution profiles of denitrification activity and NO3− distribution in the sediments. O2 penetrated about 1 mm into the dark-incubated sediments, and denitrification was largely restricted to a thin anoxic layer immediately below that. With 115 μM NO3− in the water phase, denitrification was limited to a narrow zone from 0.7 to 1.4 mm in depth, and total activity was 34 nmol of N cm−2 h−1. With 1,250 μM NO3− in the water, the denitrification zone was extended to a layer from 0.9 to 4.8 mm in depth, and total activity increased to 124 nmol of N cm−2 h−1. Within most of the activity zone, denitrification was not dependent on the NO3− concentration and the apparent Km for NO3− was less than 10 μM. Denitrification was the only NO3−-consuming process in the dark-incubated stream sediment. Even in the presence of C2H2, a significant N2O reduction (up to 30% of the total N2O production) occurred in the reduced, NO3−-free layers below the denitrification zone. This effect must be corrected for during use of the conventional C2H2 inhibition technique. 相似文献
14.
Scrapings of decomposing Cladophora sp. mats (periphyton) covering stream bed rocks produced N2O when incubated under N2 plus 15% C2H2. Denitrification (N2O formation) was enhanced by NO3− and was inhibited by autoclaving, Hg2+, and O2. No N2O was formed in the absence of C2H2 (air or N2 atmosphere). Chloramphenicol did not block N2O formation, indicating that the enzymes were constitutive. In field experiments, incubation of periphyton scrapings in the light inhibited denitrification because of algal photosynthetic O2 production. The diurnal periphyton-associated denitrification rate was estimated to be 45.8 μmol of N2O·m−2·day−1, as determined by averaging light, aerobic plus dark, and anaerobic rates over a 24-h period. 相似文献
15.
Natural denitrification rates and activities of denitrifying enzymes were measured in an agricultural soil which had a 20-year past history of low pH (pH ca. 4) due to fertilization with acid-generating ammonium salts. The soil adjacent to this site had been limed and had a pH of ca. 6.0. Natural denitrification rates of these areas were of similar magnitude: 158 ng of N g−1 of soil day−1 for the acid soil and 390 ng of N g−1 of soil day−1 at the neutral site. Estimates of in situ denitrifying enzyme activity were higher in the neutral soil, but substantial enzyme activity was also detected in the acid soil. Rates of nitrous oxide reduction were very low, even when NO3− and NO2− were undetectable, and were ca. 400 times lower than the rates of N2O production from NO3−. Denitrification rates measured in slurries of the acid and neutral soil showed distinctly different pH optima (pH 3.9 and pH 6.3) which were near the pH values of the two soils. This suggests that an acid-tolerant denitrifying population had been selected during the 20-year period of low pH. 相似文献
16.
Correlation between Anammox Activity and Microscale Distribution of Nitrite in a Subtropical Mangrove Sediment 总被引:8,自引:2,他引:6
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Rikke Louise Meyer Nils Risgaard-Petersen Diane Elizabeth Allen 《Applied microbiology》2005,71(10):6142-6149
The distribution of anaerobic ammonium oxidation (anammox) in nature has been addressed by only a few environmental studies, and our understanding of how anammox bacteria compete for substrates in natural environments is therefore limited. In this study, we measure the potential anammox rates in sediment from four locations in a subtropical tidal river system. Porewater profiles of NOx− (NO2− plus NO3−) and NO2− were measured with microscale biosensors, and the availability of NO2− was compared with the potential for anammox activity. The potential rate of anammox increased with increasing distance from the mouth of the river and correlated strongly with the production of nitrite in the sediment and with the average concentration or total pool of nitrite in the suboxic sediment layer. Nitrite accumulated both from nitrification and from NOx− reduction, though NOx− reduction was shown to have the greatest impact on the availability of nitrite in the suboxic sediment layer. This finding suggests that denitrification, though using NO2− as a substrate, also provides a substrate for the anammox process, which has been suggested in previous studies where microscale NO2− profiles were not measured. 相似文献
17.
Fungal activity is a major driver in the global nitrogen cycle, and mounting evidence suggests that fungal denitrification activity contributes significantly to soil emissions of the greenhouse gas nitrous oxide (N2O). The metabolic pathway and oxygen requirement for fungal denitrification are different from those for bacterial denitrification. We hypothesized that the soil N2O emission from fungi is formate and O2 dependent and that land use and landforms could influence the proportion of N2O coming from fungi. Using substrate-induced respiration inhibition under anaerobic and aerobic conditions in combination with 15N gas analysis, we found that formate and hypoxia (versus anaerobiosis) were essential for the fungal reduction of 15N-labeled nitrate to 15N2O. As much as 65% of soil-emitted N2O was attributable to fungi; however, this was found only in soils from water-accumulating landforms. From these results, we hypothesize that plant root exudates could affect N2O production from fungi via the proposed formate-dependent pathway. 相似文献
18.
Environmental anaerobic ammonium oxidation (anammox) was demonstrated for the first time in 2002, using 15N labeling, in homogenized sediment from the Skagerrak, where it accounted for up to 67% of N2 production. We returned to some of these original sites in 2010 to make measurements of nitrogen and carbon cycling under conditions more representative of those in situ, quantifying anammox and denitrification, together with oxygen penetration and consumption, in intact sediment cores. Overall, oxygen consumption and N2 production decayed with water depth, as expected, but the drop in N2 production was relatively more pronounced. Whereas we confirmed the dominance of N2 production by anammox (72% and 77%) at the two deepest sites (∼700 m of water), anammox was conspicuously absent from two shallower sites (∼200 m and 400 m). At the shallower sites, we could measure no anammox activity with either intact or homogeneous sediment, and quantitative PCR (16S rRNA) gave a negligible abundance of anammox bacteria in the anoxic layers. Such an absence of anammox, especially at one locale where it was originally demonstrated, is hard to reconcile. Despite the dominance of anammox at the deepest sites, anammox activity could not make up for the drop in denitrification, and assuming Redfield ratios for the organic matter being mineralized, the estimated retention of fixed N actually increased to 90% to 97% of that mineralized, whereas it was 80% to 86% at the shallower sites. 相似文献
19.
A. F. Bouwman A. H. W. Beusen J. Griffioen J. W. Van Groenigen M. M. Hefting O. Oenema P. J. T. M. Van Puijenbroek S. Seitzinger C. P. Slomp E. Stehfest 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2013,368(1621)
Soil nitrogen (N) budgets are used in a global, distributed flow-path model with 0.5° × 0.5° resolution, representing denitrification and N2O emissions from soils, groundwater and riparian zones for the period 1900–2000 and scenarios for the period 2000–2050 based on the Millennium Ecosystem Assessment. Total agricultural and natural N inputs from N fertilizers, animal manure, biological N2 fixation and atmospheric N deposition increased from 155 to 345 Tg N yr−1 (Tg = teragram; 1 Tg = 1012 g) between 1900 and 2000. Depending on the scenario, inputs are estimated to further increase to 408–510 Tg N yr−1 by 2050. In the period 1900–2000, the soil N budget surplus (inputs minus withdrawal by plants) increased from 118 to 202 Tg yr−1, and this may remain stable or further increase to 275 Tg yr−1 by 2050, depending on the scenario. N2 production from denitrification increased from 52 to 96 Tg yr−1 between 1900 and 2000, and N2O–N emissions from 10 to 12 Tg N yr−1. The scenarios foresee a further increase to 142 Tg N2–N and 16 Tg N2O–N yr−1 by 2050. Our results indicate that riparian buffer zones are an important source of N2O contributing an estimated 0.9 Tg N2O–N yr−1 in 2000. Soils are key sites for denitrification and are much more important than groundwater and riparian zones in controlling the N flow to rivers and the oceans. 相似文献
20.
Estimation of Sediment Denitrification Rates at In Situ Nitrate Concentrations 总被引:1,自引:9,他引:1
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The denitrification rates in a marine sediment, estimated by using 15N-nitrate, Vmax, Km, and sediment nitrate concentrations, were 12.5 and 2.0 nmol of N2-N cm−3 day−1 at 0 to 1 and 1 to 3 cm, respectively, at 12°C. The total rate was 165 nmol of N2-N m−2 day−1. 相似文献