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.     

Oxygen control prevents denitrifiers and barley plant roots from directly competing for nitrate

Abstract Two denitrifying bacteria ( Pseudomonas chlororaphis and P. aureofaciens ) and a plant (barley, Hordeum vulgare ) were used to study the effect of O₂ concentration on denitrification and NO₃⁻ uptake by roots under well-defined aeration conditions. Bacterial cells in the early stationary phase were kept in a chemostat vessel with vigorous stirring and thus a uniform O₂ concentration in the solution. Both Pseudomonads lacked N₂O reductase and so total denitrification could be directly measured as N₂O production.
Denitrification decreased to 6–13% of the anaerobic rate at 0.01% O₂ saturation (0.14 μM O₂) and was totally inhibited at 0.04% O₂ saturation (0.56 μM O₂). In this well-mixed system denitrification was 10-times more oxygen sensitive than stated in earlier reports. Uptake of nitrate by plants was measured in the same system under light. The NO₃⁻ uptake rate decreased gradually from a maximum in 21% O₂-saturated medium (air saturated) to zero at 1.6% O₂ saturation (22.4 μM O₂). Owing to the very different non-overlapping oxygen requirements of the two processes, direct competition for nitrate between plant roots and denitrifying bacteria cannot occur.     

Effects of photoperiod on growth of and denitrification by Pseudomonas chlororaphis in the root zone of Glyceria maxima,studied in a gnotobiotic microcosm

The emergent macrophyte Glyceria maxima was subjected to different photoperiods and grown with ammonium or nitrate as nitrogen source in presterilized microcosms with spatially separated root and non-root compartments. The microcosms were inoculated with the denitrifying bacterium Pseudomonas chlororaphis. The effect of the plant and the photoperiod on growth and denitrification by P. chlororaphis was assessed. The plant had a strong positive effect on the growth of the bacteria. The bacterial numbers in the root compartment of the planted microcosms were 19-32 times higher than found in the non-root sediment of the unplanted systems. Lengthening the photoperiod resulted in elevated bacterial numbers due to the higher carbon exudation of the plant. This effect was greater still with the nitrate-fed plants, where additional P. chlororaphis growth could proceed via denitrification, indicating oxygen-limiting conditions in the microcosms. Higher porewater N₂O concentrations in the root compartments as compared to the non-root compartments, which were highest for the long photoperiod, were also indicative of a plant-induced stimulation of denitrification. An effect of a diurnal oxygen release pattern of G. maxima on denitrification could not be detected. The gnotobiotic microcosm used in this study represents a potential system for the study of the behaviour and interactions of important bacterial groups, such as nitrifying and denitrifying bacteria where plant roots drive bacterial activity.     

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.     

Aerobic denitrification — old wine in new bottles?

The evidence concerning aerobic denitrification over the past 100 years has been reviewed and the conclusion reached that the denitrification systems of some bacteria are inhibited by oxygen, other species are capable of aerobic denitrification, or co-respiration of nitrate and oxygen. Possible mechanisms and ecological implications are discussed.     

好氧反硝化微生物学机理与应用研究进展

近年来,关于好氧反硝化过程的研究主要集中在三个方面:分别是好氧反硝化菌株的分离和脱氮性能表征,好氧反硝化微生物的应用潜力分析,以及好氧反硝化过程的机理研究。好氧反硝化菌株分布范围广泛,可从多种环境中分离得到,种属以Pseudomonas sp.、Alcaligenes sp.和Paracoccus sp.为主。好氧反硝化菌株及菌群在实验室条件下表现出优良的耐冷、耐盐特性,并具有可降解毒性有机物及N_2O减排的潜力。关于好氧反硝化过程的机理研究表明,虽然硝酸盐作为电子受体的竞争力比氧气弱,但反硝化作为辅助电子传递途径,可提高产能效率,防止NAD(P)H的过量积累。因此,硝酸盐可与氧气同时参与微生物的新陈代谢,即发生好氧反硝化现象。未来除了继续分离更新更好的好氧反硝化菌株外,应加强对好氧反硝化机理及实际生物强化方面的研究。     

Simultaneous nitrification and denitrification using an autotrophic membrane-immobilized biofilm reactor

AIMS: To develop a laboratory-scale autotrophic membrane-immobilized biofilm reactor to remove nitrogen from drinking water. METHODS AND RESULTS: A polyvinyl alcohol (PVA) immobilized biofilm, attached to the surface of a silicone tube, was used as the basis of a bioreactor for simultaneous nitrification and denitrification of water. The bioreactor was aerated with air to supply oxygen for nitrification. Pure hydrogen was supplied to the silicone tube and diffused through the membrane wall to feed the biofilm for autotrophic denitrification. The bioreactor was effective for the simultaneous nitrification and denitrification of water after a short period of acclimation, while the biofilm exhibited good resistance to the inhibition of denitrification by dissolved oxygen; the denitrification rate decreased by only 8% as the dissolved oxygen increased from 2 mg l(-1) to saturation. CONCLUSIONS: By using PVA crosslinked with sodium nitrate to entrap nitrifying and denitrifying sludge on the surface of a silicone tube, a novel bioreactor for simultaneous nitrification and denitrification was developed. In addition to performing as an immobilizing agent to strengthen the biofilm, PVA protected the denitrifying microorganisms to reduce the inhibition by dissolved oxygen under aerobic condition. Therefore, nitrification and denitrification occurred simultaneously within the biofilm. Furthermore, the immobilization technique shortened the acclimation period of the bioreactor. SIGNIFICANCE AND IMPACT OF THE STUDY: The described space saving and simple to operate bioreactor for nitrogen removal performed autotrophic denitrification to solve the problem of residual carbon in heterotrophic denitrification, and thus is suitable for removing nitrogen from drinking water.     

Modeling denitrification in aquatic sediments

Sediment denitrification is a major pathway of fixed nitrogen loss from aquatic systems. Due to technical difficulties in measuring this process and its spatial and temporal variability, estimates of local, regional and global denitrification have to rely on a combination of measurements and models. Here we review approaches to describing denitrification in aquatic sediments, ranging from mechanistic diagenetic models to empirical parameterizations of nitrogen fluxes across the sediment-water interface. We also present a compilation of denitrification measurements and ancillary data for different aquatic systems, ranging from freshwater to marine. Based on this data compilation we reevaluate published parameterizations of denitrification. We recommend that future models of denitrification use (1) a combination of mechanistic diagenetic models and measurements where bottom-waters are temporally hypoxic or anoxic, and (2) the much simpler correlations between denitrification and sediment oxygen consumption for oxic bottom waters. For our data set, inclusion of bottom water oxygen and nitrate concentrations in a multivariate regression did not improve the statistical fit.     

Influence of the Pseudomonas quinolone signal on denitrification in Pseudomonas aeruginosa

Denitrification is a well-studied respiratory system that is also important in the biogeochemical nitrogen cycle. Environmental signals such as oxygen and N-oxides have been demonstrated to regulate denitrification, though how denitrification is regulated in a bacterial community remains obscure. Pseudomonas aeruginosa is a ubiquitous bacterium that controls numerous genes through cell-to-cell signals. The bacterium possesses at least two N-acyl-L-homoserine lactone (AHL) signals. In our previous study, these quorum-sensing signals controlled denitrification in P. aeruginosa. In addition to the AHL signals, a third cell-to-cell communication signal, 2-heptyl-3-hydroxy-4-quinolone, referred to as the Pseudomonas quinolone signal (PQS), has been characterized. In this study, we examined the effect of PQS on denitrification to obtain more insight into the respiratory regulation in a bacterial community. Denitrification in P. aeruginosa was repressed by PQS, which was partially mediated by PqsR and PqsE. Measuring the denitrifying enzyme activities indicated that nitrite reductase activity was increased by PQS, whereas PQS inhibited nitric oxide reductase and the nitrate-respiratory chain activities. This is the first report to demonstrate that PQS influences enzyme activities, suggesting this effect is not specific to P. aeruginosa. Furthermore, when iron was supplied to the PQS-added medium, denitrifying activity was almost restored, indicating that the iron chelating property of PQS affected denitrification. Thus, our data indicate that PQS regulates denitrification primarily through iron chelation. The PQS effect on denitrification was relevant in a condition where oxygen was limited and denitrification was induced, suggesting its role in controlling denitrification where oxygen is present.     

Warming can boost denitrification disproportionately due to altered oxygen dynamics

Background

Global warming and the alteration of the global nitrogen cycle are major anthropogenic threats to the environment. Denitrification, the biological conversion of nitrate to gaseous nitrogen, removes a substantial fraction of the nitrogen from aquatic ecosystems, and can therefore help to reduce eutrophication effects. However, potential responses of denitrification to warming are poorly understood. Although several studies have reported increased denitrification rates with rising temperature, the impact of temperature on denitrification seems to vary widely between systems.

Methodology/Principal Findings

We explored the effects of warming on denitrification rates using microcosm experiments, field measurements and a simple model approach. Our results suggest that a three degree temperature rise will double denitrification rates. By performing experiments at fixed oxygen concentrations as well as with oxygen concentrations varying freely with temperature, we demonstrate that this strong temperature dependence of denitrification can be explained by a systematic decrease of oxygen concentrations with rising temperature. Warming decreases oxygen concentrations due to reduced solubility, and more importantly, because respiration rates rise more steeply with temperature than photosynthesis.

Conclusions/Significance

Our results show that denitrification rates in aquatic ecosystems are strongly temperature dependent, and that this is amplified by the temperature dependencies of photosynthesis and respiration. Our results illustrate the broader phenomenon that coupling of temperature dependent reactions may in some situations strongly alter overall effects of temperature on ecological processes.     

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.     

The expression of redox proteins of denitrification inThiosphaera pantotropha grown with oxygen,nitrate, and nitrous oxide as electron acceptors

The redox proteins and enzymes involved in denitrification inThiosphaera pantotropha exhibited a differential expression in response to oxygen. Pseudoazurin was completely repressed during batch or continuous culture under oxic conditions. Cytochromecd ₁ nitrite reductase was also heavily repressed after aerobic growth. Nitrite, nitric oxide, and nitrous oxide reductase activities were detected in intact cells under some conditions of aerobic growth, indicating that aerobic denitrification might occur in some circumstances. However, the rates of denitrification were much lower after aerobic growth than after anaerobic growth. Growth with nitrous oxide as sole electron acceptor mimicked aerobic growth in some respects, implying that expression of parts of the denitrification apparatus might be controlled by the redox state of a component of the electron transport chain rather than by oxygen itself. Nevertheless, the regulation of expression of nitrous oxide reductase was linked to the oxygen concentration.     

Production of NO, N2O and N2 by extracted soil bacteria, regulation by NO2(-) and O2 concentrations.

The oxygen control of denitrification and its emission of NO/N2O/N2 was investigated by incubation of Nycodenz-extracted soil bacteria in an incubation robot which monitors O2, NO, N2O and N2 concentrations (in He+O2 atmosphere). Two consecutive incubations were undertaken to determine (1) the regulation of denitrification by O2 and NO2(-) during respiratory O2 depletion and (2) the effects of re-exposure to O2 of cultures with fully expressed denitrification proteome. Early denitrification was only detected (as NO and N2O) at 相似文献   

Denitrification potential of a river floodplain during flooding with nitrate-rich water: grasslands versus reedbeds

Denitrification is a major mechanism for nitrogen removal from nitrogen-rich waters, but it requires oxygen-poor conditions. We assessed denitrification rates in nitrate-rich but also oxygen-rich river water during its stay in a floodplain. We measured diurnal oxygen fluctuations in floodwater along the river Rhine, and carried out an experiment to assess denitrification rates during day, evening and night. Denitrification in floodwater and flooded sediment were measured, comparing activity of periphyton and sediment from agricultural grasslands and reedbeds. Floodwater along the river Rhine was oxygen-saturated (> 10 mg O₂/L) during the day, but oxygen largely disappeared during the night (0.4–0.8 mg O₂/L). Independent of oxygen concentrations, denitrification in surface water alone hardly occurred. In flooded sediments, however, denitrification rates were much higher (1.1–1.5 mg N m^–2 h^–1), particularly at dark and oxygen-poor conditions (nighttime). In the experimental jars, reedbed-periphyton bacteria achieved similar denitrification rates as bacteria in sediment, but overall periphyton denitrification was of minor importance when calculated per square meter. Apart from oxygen levels, maximum denitrification appeared to be regulated by nitrate diffusion from water into the sediment, as the maximum quantity of N denitrified in the sediment equalled the quantity of N lossed from the surface water. Assessed 24-hr denitrification rates in the flooded floodplains (c. 15 mg N m^–2 d^–1) were similar in grasslands and reedbeds, and were rather low compared to rates in other floodplains.     

Denitrification in undisturbed cores from a solodized solonetz B horizon

Summary An electrolytic respirometer was used to study the effects of oxygen, moisture and glucose on denitrification in undisturbed cores from a solodized solonetz B horizon. Under the experimental conditions, nitrous oxide present after 144 h was a reasonable index of total denitrification. Nitrous oxide evolution was positively correlated with moisture, quantity of added glucose, and negatively correlated with per cent oxygen. With glucose present, denitrification proceeded at high oxygen and moderate moisture levels, but was most rapid at low oxygen and high moisture. At low oxygen content, denitrification increased with increasing water content. In horizons with high potential denitrifying activity, denitrification could occur under field conditions at moderate aeration and moderately high moisture contents.This work was supported by the Australian Wheat Industry Research Council as part of a programme of investigation of nitrogen conservation in Australian wheat soils.Formerly holder of an Australian Wheat Industry Research Council Studentship, and Associate Professor, respectively, Department of Agronomy, University of New England, Armidale, New South Wales, Australia. The senior author is now with CSIRO, P.O. Box 21, Katherine, N.T. 5780, Australia.     

细菌好氧反硝化研究进展

阐述了好氧反硝化细菌的种类及有关性质 ,并从电子理论、氧的浓度、反硝化酶系等方面对细菌好氧反硝化的作用机制进行了探讨 ,对细菌好氧反硝化的研究概况、进展及其研究意义和目前存在的问题作了较为详细的介绍。     

Diurnal variation of rates of denitrification and nitrogen fixation of periphyton associated with Oryza glumaepatula Steud in an Amazonian Lake

The rates of denitrification and biological nitrogen fixation of the periphyton communities associated with the culms and adventitious root of Oryza glumaepatula in Lake Batata, State of Pará, Brazilian Amazonia, were investigated over the course of 24 h. N₂O was not detected during the period, demonstrating that denitrification was not occurring. The low concentration of nitrate in the water column was indicated as the main factor limiting the denitrification process. The rates of biological nitrogen fixation (BNF) in culms were lowest at night and early morning, while the highest values were measured at 1200 h. BNF rates in periphyton associated with adventitious roots were lowest during the morning, while highest values were measured at 1600 h. The difference in the daily patterns of BNF rates in the periphyton of culms and roots of O. glumaepatula in the euphotic zone was attributed to defferences in the availability of organic carbon which supports this process. In the periphyton of the culms, the BNF process was carried out by heterocystous cyanobacteria, which was photoautotrophs. In the periphyton of the adventitious roots, BNF was carried out by periphytic bacteria, and is heterotrophically mediated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Biodegradation of aromatic compounds under mixed oxygen/denitrifying conditions: a review

Bioremediation of aromatic hydrocarbons in groundwater and sediments is often limited by dissolved oxygen. Many aromatic hydrocarbons degrade very slowly or not at all under anaerobic conditions. Nitrate is a good alternative electron acceptor to oxygen, and denitrifying bacteria are commonly found in the subsurface and in association with contaminated aquifer materials. Providing both nitrate and microaerophilic levels of oxygen may result in oxidation of the stable benzene rings in aromatic contaminants and allow for the intermediates of this oxidation to degrade via denitrification. The effects of using mixed electron acceptors on biodegradation of subsurface contaminants is unclear. Below some critical oxygen threshold, aerobic biodegradation is inhibited, however high levels of oxygen inhibit denitrification. The mechanisms which regulate electron transfer to oxygen and nitrate are complex. This review: 1) describes the factors which may affect the utilization of oxygen and nitrate as dual electron acceptors during biodegradation; 2) summarizes the incidence of dual use of nitrate and oxygen (aerobic denitrification); and 3) presents evidence of the effectiveness of bioremediation under mixed oxygen/nitrate conditions. Received 08 November 1995/ Accepted in revised form 09 June 1996