Production Of Dinitrogen Research Articles

Soil CH4 and N2O response diminishes during decadal soil warming in a temperate mountain forest

Global warming is considered to impact the fluxes of methane (CH4) and nitrous oxide (N2O) between forest soils and the atmosphere, but it is unclear whether the responses change over time. In this study the response of soil CH4 and N2O fluxes to field soil warming (+4 °C) were determined during years 2–5 and 14–16 in a soil warming experiment in a temperate forest. In the second and sixteenth year of soil warming, temperature sensitivities of CH4 and N2O fluxes were assessed in-situ by gradually rising field soil temperatures to ∼10 °C above ambient within a short period of three to four days. Production of dinitrogen (N2) was measured ex-situ in the sixteenth year of warming. Soil warming significantly reduced CH4 uptake (-19.5%) and increased N2O emissions (+41.6%) during the first years of warming, whereas no warming effects on soil CH4 and N2O fluxes were observed during the later years. Dinitrogen production was up to ten times higher than N2O production, though the high spatiotemporal variability masked any significant effects of soil warming on soil N2 fluxes. Temperature sensitivities (Q10) for CH4 uptake and N2O emissions were 2.07 and 4.06, respectively, in the second year of warming and 1.52 and 1.79, respectively, in the sixteenth year of soil warming. The diminishing warming response of the soil N2O fluxes likely were caused by longer-term changes in soil N availability and/or simultaneous acclimation of the soil microbial community to soil warming. Soil moisture was largely unaffected by soil warming, and soil temperature alone was only a weak predictor of soil CH4 fluxes. Methane fluxes therefore can be expected to be generally less affected than N2O fluxes. Overall, our results suggest that soil warming has only limited and transient effects on soil CH4 and N2O fluxes in this type of temperate forest.

(Invited, Digital Presentation) Mechanistic Insight into the Electrocatalytic Reduction of Nitrate to Ammonia

The excessive use of nitrogenous fertilizers has thrown the nitrogen cycle out of balance. As a result, nitrate contamination in our water resources is pervasive, creating severe environmental and health consequences. The electrocatalytic reduction of nitrate to ammonia is an attractive strategy for addressing this issue, as it would treat nitrate contamination while simultaneously recovering the active nitrogen component. Several examples in the literature demonstrate the electrocatalytic reduction of nitrate, yet the water treatment industry has not adopted catalysis as a general strategy for nitrate removal and resource recovery. Catalyst selectivity has been a key roadblock to the adoption of electrocatalytic nitrate reduction technology, as the nitrate reduction mechanism is complex and highly sensitive to catalyst composition, structure, and operating environment. In this work, we apply density functional theory (DFT) to understand key factors that influence the nitrate reduction mechanism. We find that elementary reactions on the catalyst surface are highly sensitive to surface coverage. For example, metals that exhibit high coverage of adsorbed NO* promote N-N coupling and the production of dinitrogen over ammonia. Our results also show that nitrate adsorption and dissociation is sensitive to the structure of the exposed catalyst facet, and thus the morphology of the catalyst particle heavily influences reaction selectivity. In particular, we find that the triangular arrangement of atoms on (111) facets yield a lower nitrate dissociation barrier compared to the square arrangement of atoms on (100) facets. This behavior explains trends observed by our experimentalist collaborators, who found enhanced nitrate activation rates on octahedron particles that predominantly expose the (111) facet. These two examples illustrate how mechanistic insight from DFT can be used to guide strategies for tailoring catalyst composition and structure to achieve active and selective nitrate reduction to ammonia.

ANAMMOX MICROBIAL ACTIVITY IN SODIUM SALINE SOIL OF FORMER LAKE TEXCOCO, MEXICO

The Anammox process, involving transformation of ammonium to dinitrogen, is well known in aquatic ecosystems. However, this anaerobic process in soil has been little explored, even less in extremophile soils. The saline-sodic soil of the former Lake Texcoco exposed to desertification with irrigation projects using wastewater of Mexico City, is a unique environment, yet little is known about its microbial ecology. The objective of this study was to examine the presence of Anammox microorganisms and their microcosm activity after a period of Anammox enrichment (229 days). Microcosm kinetics monitored after the 229 days enrichment experiment, showed a significant removal of ammonium and nitrite, with a significant production of dinitrogen. The stoichiometric conversion of NO2– and NH4+ to N2 gas is complete in the studied soils, based on an Anammox process where 1 mole of NH4+ resulted in 1.02 moles of N2. The presence of the Anammox functional gene hzoA was observed in saline-sodic soils of the former Lake Texcoco. The Anamx1 and Anamx2 operational taxonomic units (OTU) are phylogenetically close to a bacterium of the phylum Planctomycetes from a wastewater treatment reactor and marine environment (AB257585.1 and HE654780.1, respectively). Those two OTU represent indigenous or exogenous Anammox microorganisms phylotypes. The existence of microorganisms with Anammox activity in a saline-sodic alkaline soil is of great interest for the understanding of the nitrogen cycle in extremophile soils.

Amphipods’ grazing and excretion loop facilitates Chara contraria persistence in a eutrophic lagoon

Charophyte stands represent valuable ecosystems threatened by eutrophication-related phytoplankton and epiphyte blooms. The mechanisms allowing the persistence of charophytes in eutrophic environments are important but poorly studied. We analyzed the benthic primary production and respiration, and inorganic nitrogen (N) fluxes in a Chara contraria stand within a eutrophic estuarine system (Curonian Lagoon) via light and dark intact core incubations. Rates were contrasted with those measured in adjacent unvegetated sediments. Additionally, O2 production was measured in fragments of C. contraria and in the associated community of epiphytes, whereas O2 respiration and ammonium (NH4+) excretion rates were measured in incubation of amphipods (Pontogammarus robustoides) alone. The results from core incubations suggest high primary production and respiration within charophyte stands, resulting in pronounced daily O2 variations in the overlaying water. The incubations of charophyte fragments and associated epiphytes indicate that the latter supports a major fraction of the benthic primary production. The large production of dinitrogen in the dark indicates the occurrence of denitrification, which is suppressed in the light due to primary producers-bacteria competition. On a daily basis, the charophyte stand was a sink for inorganic N via assimilative NH4+ uptake and a dark nitrate sink via denitrification. Interestingly, active NH4+ excretion by the abundant amphipods supported nearly 40 % of the N uptake by the primary producers. We speculate that amphipods continuously feed on epiphytes growing on charophytes, favouring C. contraria persistence and recycling large amounts of N via herbivory and excretion that are immediately re-used by benthic primary producers. This grazing, excretion and assimilation loop may represent an example of macrofauna-macrophyte mutual facilitation and a mechanism easing C. contraria competition under eutrophic conditions.

The Effect of Chironomid Larvae on Nitrogen Cycling and Microbial Communities in Soft Sediments

The combination of biogeochemical methods and molecular techniques has the potential to uncover the black-box of the nitrogen (N) cycle in bioturbated sediments. Advanced biogeochemical methods allow the quantification of the process rates of different microbial processes, whereas molecular tools allow the analysis of microbial diversity (16S rRNA metabarcoding) and activity (marker genes and transcripts) in biogeochemical hot-spots such as the burrow wall or macrofauna guts. By combining biogeochemical and molecular techniques, we analyzed the role of tube-dwelling Chironomus plumosus (Insecta, Diptera) larvae on nitrification and nitrate reduction processes in a laboratory experiment with reconstructed sediments. We hypothesized that chironomid larvae stimulate these processes and host bacteria actively involved in N-cycling. Our results suggest that chironomid larvae significantly enhance the recycling of ammonium (80.5 ± 48.7 µmol m−2 h−1) and the production of dinitrogen (420.2 ± 21.4 µmol m−2 h−1) via coupled nitrification–denitrification and the consumption of water column nitrates. Besides creating oxygen microniches in ammonium-rich subsurface sediments via burrow digging and ventilation, chironomid larvae serve as hot-spots of microbial communities involved in N-cycling. The quantification of functional genes showed a significantly higher potential for microbial denitrification and nitrate ammonification in larvae as compared to surrounding sediments. Future studies may further scrutinize N transformation rates associated with intimate macrofaunal–bacteria associations.

Ruthenium-catalysed oxidative conversion of ammonia into dinitrogen.

Conversion of ammonia into dinitrogen has attracted broad scientific interest in relation to molecular models of the heterogeneous nitrogen fixation process, environmental treatment for denitrification and utilization of ammonia as an energy carrier. Here we show that some ruthenium complexes bearing 2,2'-bipyridyl-6,6'-dicarboxylate ligands work as catalysts for the ammonia oxidation reaction. Production of dinitrogen is observed when ammonium salts are treated with a triarylaminium radical as an oxidant and 2,4,6-collidine as a base in the presence of the ruthenium catalysts. Based on the characterization of some intermediates, we propose a reaction pathway via a bimetallic nitride-nitride coupling process. The proposed reaction pathway is supported by density functional theory calculations. Further investigation of the ammonia oxidation reaction under the electrochemical conditions revealed that the ruthenium complex works as a new anode catalyst for ammonia oxidation.

Electrodes Donate Electrons for Nitrate Reduction in a Soil Matrix via DNRA and Denitrification.

Microbial strains and indigenous microbiota in soil slurries have been reported to use electrons from electrodes for nitrate (NO3-) reduction. However, few studies have confirmed this in a soil matrix hitherto. This study investigated if, and how, an electric potential affected NO3- reduction in a soil matrix. The results showed that, compared to a control treatment, applying an electric potential of -0.5 V versus the standard hydrogen electrode (SHE) significantly increased the relative abundance of NO3--reducing microbes (e.g., Alcaligenaceae and Pseudomonadaceae) and the abundances of the nrfA, nirK, nirS, and nosZ genes in soil matrices. Meanwhile, the electric potential treatment doubled the NO3- reduction rate and significantly increased the rates of production of ammonium (NH4+), dinitrogen (N2), and nitrous oxide (N2O). The amount of NO3--N reduced under the electric potential treatment was comparable to the sum of the amounts of N observed in the increased N2O, N2, NH4+, and nitrite (NO2-) pools. An open-air experiment showed that the electric potential treatment promoted soil NO3- reduction with a spatial scale of at least 38 cm. These results demonstrated that an electric potential treatment could enhance NO3- reduction via both denitrification and dissimilatory NO3- reduction to ammonium (DNRA) in the soil matrix. The mechanisms revealed in this study have implications for the future development of potential techniques for enhancing NO3- reduction in the vadose zone and consequently reducing the risk of NO3- leaching.

Antibiotic Effects on Microbial Communities Responsible for Denitrification and N2O Production in Grassland Soils.

Antibiotics in soils may affect the structure and function of microbial communities. In this study, we investigated the acute effects of tetracycline on soil microbial community composition and production of nitrous oxide (N2O) and dinitrogen (N2) as the end-products of denitrification. Grassland soils were pre-incubated with and without tetracycline for 1-week prior to measurements of N2O and N2 production in soil slurries along with the analysis of prokaryotic and fungal communities by quantitative polymerase chain reaction (qPCR) and next-generation sequencing. Abundance and taxonomic composition of bacteria carrying two genotypes of N2O reductase genes (nosZ-I and nosZ-II) were evaluated through qPCR and metabolic inference. Soil samples treated with tetracycline generated 12 times more N2O, but N2 production was reduced by 84% compared to the control. In parallel with greater N2O production, we observed an increase in the fungi:bacteria ratio and a significant decrease in the abundance of nosZ-II carrying bacteria; nosZ-I abundance was not affected. NosZ-II-carrying Bacillus spp. (Firmicutes) and Anaeromyxobacter spp. (Deltaproteobacteria) were particularly susceptible to tetracycline and may serve as a crucial N2O sink in grassland soils. Our study indicates that the introduction of antibiotics to agroecosystems may promote higher N2O production due to the inhibitory effects on nosZ-II-carrying communities.

Compound driven differences in N2 and N2O emission from soil; the role of substrate use efficiency and the microbial community

Organic C is an important control on the process of denitrification, a process that can result in the production and reduction of the potent greenhouse gas nitrous oxide (N2O). This study identified the influence of different low molecular weight C (LMW-C) compounds on the production of nitrous oxide (N2O) and dinitrogen (N2) and the associated role of the size and structure of the microbial community. We examined this following application of glucose, glutamine or citric acid (250 mg C kg−1 dry soil) and 15N-KNO3 (100 mg N kg−1 dry soil) to a sandy loam soil and measured the production of N2 and N2O by denitrifiers using 15N labeling techniques, changes in the bacterial community as measured by T-RFLP on 16SrDNA fragments and changes in the gene copy number of 16SrDNA, nirK, nirS and nosZ over 144 h. Addition of glucose, citric acid and glutamine all increased emissions of 15N-N2 above that found in the control (P < 0.05) while the addition of glucose and glutamine resulted in higher emissions of 14+15N-N2O (P < 0.001) than the addition of citric acid, resulting in a lower 15N-N2O to 15N-N2 ratio in the citric acid treatment. The 16SrDNA gene copy number increased after addition of citric acid and glutamine, whilst 16SrDNA showed significant shifts in community composition in all C treatments although over different time periods. The gene copy number of nosZ only significantly increased at 120 h in the glutamine treatment (P < 0.05) and nirS at 120 h in the citric acid and glutamine treatments (P < 0.05). This suggests that where C is added as a single input, differences in N2 and N2O emissions between LMW-C compounds were not caused by selection for denitrifiers but likely driven by differences in substrate use efficiency and subsequent differences in C partitioning between growth and respiration. The differing influence of the three selected C compounds on denitrification indicates the potential for lowering net N2O emissions through regulation of C compound availability.

Stable isotopes and iron oxide mineral products as markers of chemodenitrification.

When oxygen is limiting in soils and sediments, microorganisms utilize nitrate (NO3-) in respiration--through the process of denitrification--leading to the production of dinitrogen (N2) gas and trace amounts of nitrous (N2O) and nitric (NO) oxides. A chemical pathway involving reaction of ferrous iron (Fe2+) with nitrite (NO2-), an intermediate in the denitrification pathway, can also result in production of N2O. We examine the chemical reduction of NO2- by Fe(II)--chemodenitrification--in anoxic batch incubations at neutral pH. Aqueous Fe2+ and NO2- reacted rapidly, producing N2O and generating Fe(III) (hydr)oxide mineral products. Lepidocrotite and goethite, identified by synchrotron X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopy, were produced from initially aqueous reactants, with two-line ferrihydrite increasing in abundance later in the reaction sequence. Based on the similarity of apparent rate constants with different mineral catalysts, we propose that the chemodenitrification rate is insensitive to the type of Fe(III) (hydr)oxide. With stable isotope measurements, we reveal a narrow range of isotopic fractionation during NO2- reduction to N2O. The location of N isotopes in the linear N2O molecule, known as site preference, was also constrained to a signature range. The coexistence of Fe(III) (hydr)oxide, characteristic 15N and 18O fractionation, and N2O site preference may be used in combination to qualitatively distinguish between abiotic and biogenically emitted N2O--a finding important for determining N2O sources in natural systems.

Migrant solution to the anammox mystery

Every night a massive migration takes place in ocean waters. Zooplankton and micronekton, a diverse group of organisms <1 mm to 10 cm in size, swim up from midwater depths (200–700 m) to the surface ocean to feed and return down to resting depths before daybreak. The importance of this diel vertical migration to marine biogeochemical cycles has been recognized for some time. Research has primarily focused on the migrant-mediated movement of elements including nitrogen (N) from the surface ocean to midwaters. Such an “active transport” involves feeding at night in the upper ocean and the consequent excretion of ammonium (1) and dissolved organic N (2, 3) at midwater depths during the day. However, within the midwater realm, the effect of such migratory behavior on elemental cycles is less well understood. This “twilight zone” hosts many of the reactions that drive global biogeochemical cycles, including the remineralization of particulate organic matter into nutrients such as nitrate and the production of dinitrogen (N2) gas. In PNAS, Bianchi et al. (4) significantly advance our knowledge of the role of animals in midwater biogeochemistry by linking the activity of migrant zooplankton and micronekton to an important N transformation pathway, anammox.

Nitrogen loss from soil through anaerobic ammonium oxidation coupled to iron reduction

The oxidation of ammonium is a key step in the nitrogen cycle, regulating the production of nitrate, nitrous oxide and dinitrogen. In marine and freshwater ecosystems, anaerobic ammonium oxidation coupled to nitrite reduction, termed anammox, accounts for up to 67% of dinitrogen production 1‐3 . Dinitrogen production through anaerobic ammonium oxidation has not been observed in terrestrial ecosystems, but the anaerobic oxidation of ammonium to nitrite has been observed in wetland soils under iron-reducing conditions 4,5 . Here, we incubate tropical upland soil slurries with isotopically labelled ammonium and iron(III) to assess the potential for anaerobic ammonium oxidation coupled to iron(III) reduction, otherwise known as Feammox 6 , in these soils. We show that Feammox can produce dinitrogen, nitrite or nitrate in tropical upland soils. Direct dinitrogen production was the dominant Feammox pathway, short-circuiting the nitrogen cycle and resulting in ecosystem nitrogen losses. Rates were comparable to aerobic nitrification 7,8 and to denitrification 9 , the latter being the only other process known to produce dinitrogen in terrestrial ecosystems. We suggest that Feammox could fuel nitrogen losses in ecosystems rich in poorly crystalline iron minerals, with low or fluctuating redox conditions.

Denitrification and total nitrogen gas production from forest soils of Eastern China

Reactive forms of nitrogen (Nr) are accumulating at local, regional and global levels largely due to human activities, particularly N-fertilizer production and use as well as fossil fuel combustion. This has resulted in a change in the nitrogen (N) cycle and excess Nr in the environment, which has negative environmental effects. Therefore, characterizing denitrification and the edaphic variables controlling denitrification and its products is the first step in predicting the long-term effects of Nr accumulation. In the present study, six forest soil types in different climatic zones were collected from East China and evaluated for denitrification products following a K 15NO 3 amendment and subsequent incubation. The results showed that denitrification, indicated by production of nitric oxide (NO), nitrous oxide (N 2O) and dinitrogen (N 2), was higher in the studied temperate forest soils than in the studied subtropical and tropical forest soils and was negatively correlated with soil redox potential at the beginning of incubation ( r = −0.94, P < 0.01), but not with soil pH. The ratios of NO/total N gas and N 2O/total N gas produced during denitrification varied among the soils, and were generally higher in the subtropical and tropical soils. Spearman's correlation analysis showed that the NO ratio was positively correlated with soil oxidation capacity (OXC) ( r = 0.94, P < 0.01) and redox potential at the beginning of incubation ( r = 0.86, P < 0.05), but negatively correlated with soil pH ( r = −0.83, P < 0.05). The N 2O ratio was not significantly correlated with these edaphic variables, but showed a significant correlation to NO ratio ( r = 0.83, P < 0.05). These results suggested that the OXC value might be the key factor affecting denitrification rates in soils. One possible explanation for these effects is that large OXC values would result in a higher level soil redox potential, thus suppressing denitrification and enhancing NO and N 2O ratios during denitrification.

Dinitrogen production from ammonia by Nitrosomonas europaea

In this study, the conversion efficiency and optimal conditions of successive nitrification and denitrification were assessed for Nitrosomonas europaea, which uses ammonia monooxygenase (AMO), nitrite reductase and nitrous oxide reductase. In aerobic conditions, the first step of nitrification (i.e. NH 4 +→NO 2 −) occurred; under oxygen-limiting or oxygen free-conditions, however, there was denitrification, whereby nitrous oxide and dinitrogen were produced from nitrite (NO 2 −). About 7% of the total ammonium was converted to dinitrogen following the successive nitrification and denitrification by N. europaea. During nitrification and denitrification, the optimal pH range for the production of nitrite and dinitrogen was found to be 7.0–8.0. A low partial oxygen pressure or oxygen-free conditions were favorable for the production of dinitrogen.

Conversion of ammonia to dinitrogen in wastewater by Nitrosomonas europaea.

Because Nitrosomonas europaea contains ammonia-oxidizing enzyme, nitrite reductase, and nitrous oxide reductase, the conversion of ammonia to dinitrogen was tried with different reaction conditions. In aerobic reaction conditions, ammonium was converted to nitrite (NO2-), while under oxygen-limiting or oxygen-free conditions, NO2(-)-N formed from ammonia oxidation by N. europaea was reduced to N2O and dinitrogen with 22% conversion. During denitrification, optimal pH for the production of N2O and dinitrogen was found to be 7.0-8.0. Dinitrogen was not produced in acidic pH <7.0. A low partial oxygen pressure as well as oxygen-free conditions are favorable for high production of dinitrogen.

Effect of oxygen on denitrification in continuous chemostat culture withComamonas sp SGLY2

Continuous cultures ofComamonas sp SGLY2 were grown anaerobically prior to establishing steady states at different oxygen flow rates. At a low oxygen transfer rate, no dissolved oxygen accumulated in the medium and all nitrate was reduced to dinitrogen. Concurrently with the increase of dissolved oxygen concentration in the liquid phase, the rate of denitrification decreased. However, at a dissolved oxygen concentration near saturation (33 mg L−1), a part of the electron flow always diverted to nitrate with production of dinitrogen: the aerobic denitrification rate was equivalent to 35% of that calculated under anaerobic conditions. These experiments reflected the co-utilization of oxygen and N-oxides and the production of dinitrogen, up to saturated conditions, which implied synthesis and activity of the four denitrifying enzymes under various aeration conditions.

Nitrogen gas flux from sediments: insights from simulation modelling

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 10:209-211 (1996) - doi:10.3354/ame010209 Nitrogen gas flux from sediments: insights from simulation modelling Blackburn TH Direct measurements of dinitrogen efflux from continental shelf sediments indicated that denitrification (mean 3.2 mmol N m-2 d-1) was very important in nitrogen cycling. Most dinitrogen came from sediment-nitrate. All ammonium produced in these sediments was probably nitrified and then denitrified. In a closed incubation, the linear production of dinitrogen, as oxygen decreased, was unexpected as was the low ratio of oxygen consumption to denitrification (3.6:1). Simulation modelling suggests the following explanation: Most carbon is oxidised anoxically, but nitrogen (ammonium) diffuses to the oxygen zone relatively deep in the sediment, where high rates of coupled nitrification-denitrification result. As oxygen decreases, the zones of nitrification and denitrification move upward. The nitrate initially present in the enclosed overlying water decreases, but due to the decreasing diffusional path to the zone of denitrification, its rate of denitrification remains constant. The concentration of nitrate from sediment nitrification increases in the overlying water, but due to the decreasing rates of sediment nitrification, its rate of denitrification is also constant. Nitrification . Denitrification . Model . Diffusion . Nitrate . Ammonium Full text in pdf format PreviousExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 10, No. 2. Publication date: May 09, 1996 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1996 Inter-Research.

Production of dinitrogen and nitrous oxide in soil suspensions as affected by redox potential

The effect of soil redox potential on N2O and N2 emission from soil suspensions was studied under laboratory conditions. Crowley silt loam soil suspensions were equilibrated under controlled (−200, −100, 0, +100, +200, +300, and +400 mV) redox levels, and the amounts of N2 and N2O evolved quantified. At higher redox levels (+300, and +400 mV) nitrification was the dominant soil biological process controlling N chemistry. A small amount of N2O evolved during nitrification. A redox value between +300 and +200 mV was found critical for denitrification to occur. Both N2 and N2O were produced during denitrification. The maximum amount of N2O evolved at a redox value of 0 mV. Dinitrogen emission increased at lower redox levels. The highest N2/N2O evolution ratio was observed at −200 mV and the ratio decreased with increasing redox. A lack of N-balance during denitrification at redox levels of +100, and +200 mV is also reported.

Denitrification by extremely halophilic bacteria

Extremely halophilic bacteria were isolated from widely separated sites by anaerobic enrichment in the presence of nitrate. The anaerobic growth of several of these isolates was accompanied by the production of nitrite, nitrous oxide, and dinitrogen. These results are a direct confirmation of the existence of extremely halophilic denitrifying bacteria, and suggest that such bacteria may be common inhabitants of hypersaline environments.

Denitrification by extremely halophilic bacteria.

Extremely halophilic bacteria were isolated from widely separated sites by anaerobic enrichment in the presence of nitrate. The anaerobic growth of several of these isolates was accompanied by the production of nitrate, nitrous oxide, and dinitrogen. These results are a direct confirmation of the existence of extremely halophilic denitrifying bacteria, and suggest that such bacteria may be common inhabitants of hypersaline environments.