Component-specific oyster-mediated modular nitrous oxide turnover

n this Note we prove that in one space dimension, the symmetric discontinuous Galerkin method for second order elliptic problems is stable for polynomial orders p2 without using any stabilization parameter. The method yields optimal convergence rates in both the energy norm (L2-norm of broken gradient plus jump terms) and the L2-norm and can be written in conservative form with fluxes independent of any stabilization parameter.

Exotic Spartina alterniflora invasion resulting from anthropogenic activities significantly affects microbial nitrogen (N) transformation and associated nitrous oxide (N2O) emission in coastal wetland soils. However, the responses of soil N2O emission dynamics to plant invasion remain unclear. This study assesses the effects of S. alterniflora invasion on soil N2O potential production and consumption processes. We used natural isotope tracing technique to investigate potential N2O production and consumption rates in S. alterniflora invaded and native saltmarsh zones (Phragmites australis, Scirpus mariqueter and bare mudflat) in the Yangtze Estuary. Soil potential net N2O production rates in summer were lower in S. alterniflora stands than in S. mariqueter and bare mudflat stands, but no significant differences among these saltmarsh habitats occurred during winter. Potential gross N2O production and consumption rates were higher in S. alterniflora and P. australis stands compared to S. mariqueter and bare mudflat stands. The gross consumption proportion in S. alterniflora and P. australis stands was higher, which affected net N2O production. Hydroxylamine (NH2OH) oxidation and nitrifier denitrification contributed 4.52–12.62% and 13.87–21.58% of soil N2O source, respectively, but denitrification was the dominant pathway (69.83–80.09%). S. alterniflora invasion increased the contributions of NH2OH oxidation and nitrifier denitrification to N2O source slightly, but decreased the contribution of denitrification to N2O source. Soil potential N2O production and consumption processes were influenced by water-filled pore space, pH, sulfide, and carbon and N substrates. Exotic S. alterniflora invasion affected soil N2O dynamics by increasing substrates and altering microenvironments, thus mediating N2O emission from coastal saltmarsh soils.

Net N2O production from soil particle size fractions and its response to changing temperature

Nitrous oxide production and consumption by denitrification in a grassland: Effects of grazing and hydrology

The ocean is estimated to contribute up to ~20% of global fluxes of atmospheric nitrous oxide (N2O), an important greenhouse gas and ozone depletion agent. Marine oxygen minimum zones contribute disproportionately to this flux. To further understand the partition of nitrification and denitrification and their environmental controls on marine N2O fluxes, we report new relationships between oxygen concentration and rates of N2O production from nitrification and denitrification directly measured with 15N tracers in the Eastern Tropical Pacific. Highest N2O production rates occurred near the oxic‐anoxic interface, where there is strong potential for N2O efflux to the atmosphere. The dominant N2O source in oxygen minimum zones was nitrate reduction, the rates of which were 1 to 2 orders of magnitude higher than those of ammonium oxidation. The presence of oxygen significantly inhibited the production of N2O from both nitrification and denitrification. These experimental data provide new constraints to a multicomponent global ocean biogeochemical model, which yielded annual oceanic N2O efflux of 1.7–4.4 Tg‐N (median 2.8 Tg‐N, 1 Tg = 1012 g), with denitrification contributing 20% to the oceanic flux. Thus, denitrification should be viewed as a net N2O production pathway in the marine environment.

Abundance for subgroups of denitrifiers in soil aggregates asscociates with denitrifying enzyme activities under different fertilization regimes

Core Ideas We quantified N 2 O production and reduction for cultivated intermittently flooded peatland soils. Labile organic C limited N 2 O production and reduction. High residual NO 3 − in soils inhibited N 2 O reduction. N 2 O emissions were inversely proportional to land management intensity and decreased in the order of uncultivated, turfgrass, vegetable, and sugarcane soils. Biogeochemical controls of N 2 O production and reduction during denitrification in cultivated and intermittently flooded peatland soils are poorly understood. Soils from sugarcane ( Saccharum spp.), vegetable, turfgrass, and uncultivated subtropical peatlands in the Everglades Agricultural Area (EAA) were studied to elucidate influence of land use on N 2 O production and reduction. Under ambient soil conditions, intensively managed, tilled soils (sugarcane and vegetable) had 1.5 to 4 times lower N 2 O production and reduction than turfgrass soils. Uncultivated soils had 130 to 270% higher N 2 O production than tilled soils but had similar N 2 O reduction compared with tilled soils. A lower ratio of N 2 O reduction to production was observed for uncultivated soils compared to other land uses. Net N 2 O production was highest for uncultivated soils and decreased in the order of turfgrass, vegetable, and sugarcane soils. For all land uses, N 2 O production was limited by electron donors (labile organic C) but not by electron acceptors (NO 3 − ). Depletion of labile organic C through long‐term soil oxidation after drainage resulted in limited availability of this energy source for denitrifying microorganisms. In addition, high residual NO 3 − resulting from organic N mineralization and inorganic fertilizer additions inhibited N 2 O reduction. Our results suggest that sugarcane production is likely to reduce N 2 O emissions from the EAA compared with other current land uses. Management practices with addition of labile organic C to the EAA soils may possibly result in N 2 O emission pulses because of the greater stimulation of labile organic C on N 2 O production than on N 2 O reduction.

Abstract. Nitrous oxide (N2O) is a greenhouse gas and an ozone depletion agent. Estuaries that are subject to seasonal anoxia are generally regarded as N2O sources. However, insufficient understanding of the environmental controls on N2O production results in large uncertainty about the estuarine contribution to the global N2O budget. Incubation experiments with nitrogen stable isotope tracer were used to investigate the geochemical factors controlling N2O production from denitrification in the Chesapeake Bay, the largest estuary in North America. The highest potential rates of water column N2O production via denitrification (7.5±1.2 nmol-N L−1 h−1) were detected during summer anoxia, during which oxidized nitrogen species (nitrate and nitrite) were absent from the water column. At the top of the anoxic layer, N2O production from denitrification was stimulated by addition of nitrate and nitrite. The relative contribution of nitrate and nitrite to N2O production was positively correlated with the ratio of nitrate to nitrite concentrations. Increased oxygen availability, up to 7 µmol L−1 oxygen, inhibited both N2O production and the reduction of nitrate to nitrite. In spring, high oxygen and low abundance of denitrifying microbes resulted in undetectable N2O production from denitrification. Thus, decreasing the nitrogen input into the Chesapeake Bay has two potential impacts on the N2O production: a lower availability of nitrogen substrates may mitigate short-term N2O emissions during summer anoxia; and, in the long-run (timescale of years), eutrophication will be alleviated and subsequent reoxygenation of the bay will further inhibit N2O production.

Effects of hydraulic retention time on nitrous oxide production rates during nitrification in a laboratory-scale biological aerated filter reactor

In flooded paddy fields, peak greenhouse gas nitrous oxide (N2O) emission after rewetting the dry soils is widely recognised. However, the relative contribution of biotic and abiotic factors to this emission remains uncertain. In this study, we used the isotope technique (δ18O and δ15NSP) and molecular-based microbial analysis in an anoxic incubation experiment to evaluate the contributions of bacterial, fungal, and chemical denitrification to N2O emissions. We collected eight representative paddy soils across southern China for an incubation experiment. Results show that during the 10-day incubation period, the net N2O emissions were mainly produced by fungal denitrification, which accounted for 58–77% in six of the eight investigated flooded paddy soils. In contrast, bacterial denitrification contributed 6–15% of the net N2O emissions. Moreover, around 11–35% of the total N2O emissions were derived from chemical denitrification in all soil types. Variation partitioning analysis (VPA) and principal component analysis (PCA) demonstrated that initial soil organic carbon (OC) concentrations were the primary regulator of N2O source patterns. Soils with relatively lower OC concentration (7–15 mg g−1) tend to be dominated by fungal denitrification, which accounted for the net N2O production at the end of the incubation period. Overall, these findings highlight the dominance of the fungal denitrification pathway for N2O production in flooded paddy soils, which predominates in soils with relatively lower OC content. This suggests that fungal contribution should be considered when optimizing agricultural management system timing to control N2O emissions in flooded paddy soil ecosystems, and for the relevant establishment of predictive numerical models in the future.

Temperature differentially regulates estuarine microbial N2O production along a salinity gradient

C:N ratio is not a reliable predictor of N2O production in acidic soils after a 30-day artificial manipulation

Abstract. Nitrous oxide (N2O) has significant global warming potential as a greenhouse gas. Estuarine and coastal regimes are the major zones of N2O production in the marine system. However, knowledge on biological sources of N2O in estuarine ecosystems remains controversial but is of great importance for understanding global N2O emission patterns. Here, we measured concentrations and isotopic compositions of N2O as well as distributions of ammonia-oxidizing bacterial and archaeal amoA and denitrifier nirS genes by quantitative polymerase chain reaction along a salinity gradient in the Pearl River estuary, and we performed in situ incubation experiments to estimate N2O yields. Our results indicated that nitrification predominantly occurred, with significant N2O production during ammonia oxidation. In the hypoxic waters of the upper estuary, strong nitrification resulted in the observed maximum N2O and ΔN2Oexcess concentrations, although minor denitrification might be concurrent at the site with the lowest dissolved oxygen. Ammonia-oxidizing β-proteobacteria (AOB) were significantly positively correlated with all N2O-related parameters, although their amoA gene abundances were distinctly lower than ammonia-oxidizing archaea (AOA) throughout the estuary. Furthermore, the N2O production rate and the N2O yield normalized to amoA gene copies or transcripts estimated a higher relative contribution of AOB to the N2O production in the upper estuary. Taken together, the in situ incubation experiments, N2O isotopic composition and concentrations, and gene datasets suggested that the high concentration of N2O (oversaturated) is mainly produced from strong nitrification by the relatively high abundance of AOB in the upper reaches and is the major source of N2O emitted to the atmosphere in the Pearl River estuary.

Composting is widely used for organic waste management and is also a major source of nitrous oxide (N2O) emission. New insight into microbial sources and sinks is essential for process regulation to reduce N2O emission from composting. This study used genome-resolved metagenomics to decipher the genomic structures and physiological behaviors of individual bacteria for N2O sources and sinks during composting. Results showed that several nosZ-lacking denitrifiers in feedstocks drove N2O emission at the beginning of the composting. Such emission became negligible at the thermophilic stage, as high temperatures inhibited all denitrifiers for N2O production except for those containing nirK. The nosZ-lacking denitrifiers were notably enriched to increase N2O production at the cooling stage. Nevertheless, organic biodegradation limited energy availability for chemotaxis and flagellar assembly to restrain nirKS-containing denitrifiers for nitrate reduction toward N2O sources but insignificantly interrupt norBC- and nosZ-containing bacteria (particularly nosZ-containing nondenitrifiers) for N2O sinks by capturing N2O and nitric oxide (NO) for energy production, thereby reducing N2O emission at the mature stage. Furthermore, nosZII-type bacteria included all nosZ-containing nondenitrifiers and dominated N2O sinks. Thus, targeted strategies can be developed to restrict the physiological behaviors of nirKS-containing denitrifiers and expand the taxonomic distribution of nosZ for effective N2O mitigation in composting.

NO production rates, NO uptake rate constants, NO compensation points, and different soil variables were determined for various soil types and different soil horizons, and checked for mutual correlations. NO production was detected in all, and NO comsuption in most soils tested. Only soils in a very early state of soil genesis showed no NO consumption activity. NO consumption was positively correlated with soil water and NH 4 + contents. NO production rates were not correlated with any soil variable. Both NO production and NO consumption tended to decrease from the upper organic to the deeper mineral horizons in different climax soils. The seasonal variation of NO production and NO consumption in a calcic cambisol and a luvisol showed highest rates in summer. The rates of NO production and NO consumption were correlated with a few of the soil variables, but showed no uniform, theoretically comprehensible pattern. However, NO production in samples of the calcic cambisol was stimulated by fertilization with NH 4 + , but not with NO 3 − and was inhibited by nitrapyrin, indicating that NO was produced by nitrification. NO production made up about 3% of the nitrification rates. In the luvisol, in contrast, NO production was not affected by the addition of NH 4 + or NO 3 − . Nitrification was also undetectable in this acidic soil, except for a few patches where NO production was also detected.