Article

Influence of O2 availability on NO and N2O release by nitrification and denitrification in soils

March 2004
Global Change Biology 4(4):387 - 396

March 2004
4(4):387 - 396

DOI:10.1046/j.1365-2486.1998.00161.x

Authors:

Miami University

The availability of O2 is believed to be one of the main factors regulating nitrification and denitrification and the release of NO and N2O. The availability of O2 in soil is controlled by the O2 partial pressure in the gas phase and by the moisture content in the soil. Therefore, we investigated the influence of O2 partial pressures and soil moisture contents on the NO and N2O release in a sandy and a loamy silt and differentiated between nitrification and denitrification by selective inhibition of nitrification with 10 Pa acetylene. At 60% whc (maximum water holding capacity) NO and N2O release by denitrification increased with decreasing O2 partial pressure and reached a maximum under anoxic conditions. Under anoxic conditions NO and N2O were only released by denitrification. NO and N2O release by nitrification also increased with decreasing O2 partial pressure, but reached a maximum at 0.1–0.5% O2 and then decreased again. Nitrification was the main source of NO and N2O at O2 partial pressures higher than 0.1–0.5% O2. At lower O2 partial pressures denitrification was the main source of NO and N2O. With decreasing O2 partial pressure N2O release increased more than NO release, indicating that the N2O release was more sensitive against O2 than the NO release. At ambient O2 partial pressure (20.5% O2) NO and N2O release by denitrification increased with increasing soil moisture content. The maximum NO and N2O release was observed at soil moisture contents of 65–80% whc and 100% whc, respectively. NO and N2O release by nitrification also increased with increasing soil moisture content with a maximum at 45–55% whc and 90% whc, respectively. Nitrification was the main source of NO and N2O at soil moisture contents lower than 90% whc and 80% whc, respectively. Higher soil moisture contents favoured NO and N2O release by denitrification. Soil texture had also an effect on the release of NO and N2O. The coarse-textured sandy silt released more NO than N2O compared with the fine-textured loamy silt. At high soil moisture contents (80–100% whc) the fine-textured soil showed a higher N2O release by denitrification than the coarse-textured soil. We assume that the fine-textured soil became anoxic at a lower soil moisture content than the coarse-textured soil. In conclusion, the effects of O2 partial pressure, soil moisture and soil texture were consistent with the theory that denitrification increasingly contributes to the release of NO and in particular N2O when conditions for soil microorganisms become increasingly anoxic.

Isotopomeric Peak Assignment for N2O in Cross-Labeling Experiments by Fiber-Enhanced Raman Multigas Spectroscopy

Article

Full-text available

Feb 2024
ANAL CHEM

Human intervention in nature, especially fertilization, greatly increased the amount of N2O emission. While nitrogen fertilizer is used to improve nitrogen availability and thus plant growth, one negative side effect is the increased emission of N2O. Successful regulation and optimization strategies require detailed knowledge of the processes producing N2O in soil. Nitrification and denitrification, the main processes responsible for N2O emissions, can be differentiated using isotopic analysis of N2O. The interplay between these processes is complex, and studies to unravel the different contributions require isotopic cross-labeling and analytical techniques that enable tracking of the labeled compounds. Fiber-enhanced Raman spectroscopy (FERS) was exploited for sensitive quantification of N2O isotopomers alongside N2, O2, and CO2 in multigas compositions and in cross-labeling experiments. FERS enabled the selective and sensitive detection of specific molecular vibrations that could be assigned to various isotopomer peaks. The isotopomers ¹⁴N¹⁵N¹⁶O (2177 cm–1) and ¹⁵N¹⁴N¹⁶O (2202 cm–1) could be clearly distinguished, allowing site-specific measurements. Also, isotopomers containing different oxygen isotopes, such as ¹⁴N¹⁴N¹⁷O, ¹⁴N¹⁴N¹⁸O, ¹⁵N¹⁵N¹⁶O, and ¹⁵N¹⁴N¹⁸O could be identified. A cross-labeling showed the capability of FERS to disentangle the contributions of nitrification and denitrification to the total N2O fluxes while quantifying the total sample headspace composition. Overall, the presented results indicate the potential of FERS for isotopic studies of N2O, which could provide a deeper understanding of the different pathways of the nitrogen cycle.

Gross nitrification in soils - Contribution of nitrification to N-gas emission from soils Der naturwissenschaftlichen Fakultät der Gottfried Wilhelm Leibniz Universität Hannover zur Erlangung der venia legendi im Fach Bodenkunde vorgelegte, kumulative Habilitationsschrift

Thesis

Nov 2023

C. Florian Stange

This work contributes to developing a better understanding of nitrification in soils as an important source of N gas emissions from soils. Therefore, the nitrification process as well as N gas produced by nitrification are considered. The work described the common methods and new developed approach for determining the gross nitrification rate. Both measuring and quantifying nitrification in soils have been shown to achieve the objective. One focus is to differentiate the sources of N gases and to quantify the contribution of nitrification to N gas emission from soils. The separation of N gas production into source-related pathways that simultaneously operate in soils requires comprehensive experiments with complex analyses. Therefore a new analytical approach and calculates the fractions of ammonia oxidation, Norg oxidation and denitrification for total soil NO and N2O released from a soil probes at different oxygen states (2.5, 1.2 and 0 % O2) is presented and tested for a five loamy Spanish forest soils. Whereas the relation between ammonia oxidation and denitrification as sources of soil N2O gas release appear to be consistent, which is commonly accepted, the contribution of Norg oxidation was unexpectedly high (up to 76%). Also two model approaches to model the N-gas production in soils are parametrised on experimental data from laboratory studies. The findings are discussed in view of choosing the best approach to predict N2O production during nitrification. and an approach to combine response functions in modelling is presented and tested on field data. The advantage against the conventional combining approaches (multiplicative or min/max approaches) is discussed. N2O production data related to nitrification and nitrification rates were collected and multiple linear regression analysis between the soil properties and N2O product ratios were applied to this dataset to identify functional relationships. Future works to support the development of sufficient model approaches are needed, and in particular, the nitrite and oxygen concentrations in soils are the most important factors for N2O production. ZUSAMMENFASSUNG Diese Arbeit möchte zu einem besseren Verständnis über den Prozess der Nitrifikation als eine wichtige Quelle der N-Gasemission aus Böden beitragen. Daher werden einleitend die verschiedenen Prozesspfade der Nitrifikation und der Spurengasbildung beschrieben und bildlich dargestellt. Verfahren zur Messung der Nitrifikation und Versuche zu Bestimmung der Umsatzraten werden in der Arbeit vorgestellt. Dabei liegt der Fokus auf der Separation der verschiedenen Quellen von NO und N2O und beschreibt die dafür notwendigen komplexen Versuche inclusive mathematischer Verfahren zu deren Analyse. Mit Hilfe dieser Tools werden die Anteile der Ammoniakoxidation (erster Schritt der autotrophen Nitrifikation), der direkten Oxidation von organischem Stickstoff und der Denitrifikation bei unterschiedlichen Sauerstoffpartialdrücken (2.5, 1.2 und 0 % O2) bestimmt und in einem weiteren Schritt die Methoden auf fünf spanische Waldstandorte angewendet. Interessanterweise sind die Anteile der direkten Oxidation von organischem Stickstoff sehr hoch und auch relativ konstant bei verschiedenen Sauerstoffpartialdrücken. Zwei verschiedene Modellansätze zu Beschreibung der N-Spurengasproduktion in Böden werden vorgestellt und an Labordaten parametrisiert. Die beiden Ansätze und ihre Implikationen für die Bildungswege der N-Spurengasproduktion werden ausgiebig diskutiert. Zusätzlich wird für die Anwendung in Ökosystemmodellen ein auf dem harmonischen Mittel beruhenden Ansatz vorgeschlagen, um verschiedene Responsefunktionen (z.B. die für die Temperatur-und die für die Bodenfeuchteabhängigkeit) miteinander zu verbinden. Im letzten Abschnitt der Arbeit werden die Daten der zuvor beschriebenen Experimente sowie in der Literatur verfügbare Daten zur Bruttonitrifikation und der nitrifikatorischen N2O-Produktion systematisch zusammengetragen, daraus das N2O-Produktion/Nitrifikation-Verhältnis (N2O product ratio) berechnet und dieses mittels multipler lineare Regression gegenüber den Bodeneigenschaften analysiert. Es deutet sich an, dass besonders der aktuelle Sauerstoffpartialdruck und die Nitritkonzentration starken Einfluss auf die N-Spurengasproduktion haben könnten, aber um kausale Zusammenhänge zu bestätigen, gibt es zu wenige insitu Messungen dieser beiden Faktoren in bisherigen Experimenten. Daher endet die Arbeit mit der Aufforderung zukünftig in N-Gasexperimenten immer auch Nitrit und Sauerstoff im Boden zu messen. CONTENT

Dose effect of polyethylene microplastics on nitrous oxide emissions from paddy soils cultivated for different periods

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J HAZARD MATER

The presence of microplastics (MPs) under flooded conditions is beneficial for nitrifiers and denitrifiers to produce nitrous oxide (N2O), but their dose effect remains unclear. This study evaluated the impact of different doses of polyethylene (PE) MPs on the release of N2O from paddy soils cultivated for different years. Compared with unpolluted soils, low doses of MPs (≤ 0.1%) had a negligible influence on N2O emissions, and high amounts of MPs (≥ 0.5%) significantly (p < 0.05) increased N2O emissions from the paddy soils cultivated for 3, 15 and 40 years by 2.5-4.3, 3.9-8.5 and 8.9-27.7 times, respectively. Moreover, an exponential model indicated that a 0.2% concentration of PE MPs appeared to be the dose threshold that accelerated the release of N2O from the all soils. Increased MP concentrations accelerated N2O emissions by affecting microbial functional genes involved in N2O production and reduction, but microbial taxonomic attributes involved in nitrogen cycling played an insignificant role in controlling N2O emissions. Overall, our results indicated that high doses (≥ 0.5%) of PE MPs essentially accelerated the emission of N2O from rice soils, and a longer cultivation period (40 years) enhanced the positive effect of MPs on N2O emissions.

Evaluation of the Plant's Role in Greenhouse Gas Emissions in Furrow-irrigated Rice

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Soil pore architecture and rhizosphere legacy define N2O production in root detritusphere

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SOIL BIOL BIOCHEM

Root detritusphere is one of the most important sources of N2O, however, understanding of how N2O emission from the detritusphere is influenced by soil properties remains elusive. Here, we evaluated the effects of pore architecture and soil moisture on N2O emission during the decomposition of in-situ grown roots of switchgrass, an important bioenergy crop. We combined dual isotope labeling (¹⁵C and ¹⁵N) with zymography to gain insights into the location of the microbial N2O production in soils with contrasting pore architectures. In the studied soil, the effect of soil pore architecture on N2O emissions was 6 times greater than that of soil moisture. Soil dominated by > 30 μm Ø pores (i.e., large-pore soil) had higher chitinase activity than the soil dominated by < 10 μm Ø pores (i.e., small-pore soil), especially near the decomposing roots. The chitinase activity on the decomposing roots was positively correlated with emission of root-derived N2O, indicating that N released from root decomposition was an important source of N2O. Greater N2O and N2 emission was induced by switchgrass roots in soils dominated by the large-compared to the small-pore soils. The microenvironment developed near decomposing roots of the large-pore soil also resulted in positive N2O priming. Our study challenged the traditional view on soil moisture as the main factor of N2O production. Production and emission of N2O was most intensive in microbial activity hotspots (i.e., rhizosphere legacy) in the large pores, where decomposed roots release mineral N as the main N2O source.

Oxygen-depletion by rapid ammonia oxidation regulates kinetics of N2O, NO and N2 production in an ammonium fertilised agricultural soil

Article

Nov 2021
SOIL BIOL BIOCHEM

Oxygen (O 2) is a key factor driving the expression of N-cycle-related functional genes and regulating nitrogenous gas production in the soil. However, how and to what extent the associated gene transcription and corresponding gas kinetics interact with the transition of soil O 2 status caused by N fertilisation, remains poorly understood. In this context, we conducted a robotized incubation experiment using a He/O 2 atmosphere with different amounts of ammonium-based fertiliser (0 (control), 60 (AS 60) and 200 mg N kg − 1 (NH 4) 2 SO 4 (AS 200)) applied to an agricultural soil with a strong nitrification potential under three different initial O 2 levels (oxic 21%, sub-oxic 3%, and anoxic 0%) over 14 days. Through repeated measurements of N 2 O, NO, and N 2 concentrations and kinetics of mineral N following the decline of O 2 concentrations, we found that higher ammonium addition (200 vs. 60 mg N kg − 1) caused faster O 2 consumption in the headspace and induced up to 238 times higher net accumulation of N 2 O under initially oxic headspace condition. We speculate that this was due to: 1) the rapid transition of O 2 status from oxic to anoxic due to vigorous ammonia oxidation; and 2) the increased N 2 O/(N 2 O + NO + N 2) ratio of denitrification with higher N addition. The amoA and nosZ gene transcript numbers changed significantly in response to ammonium addition and decreasing O 2 concentration, whereas high-throughput sequencing revealed a significant structural alteration of the soil microbiota along with the transition of O 2 status. Our results highlight that the vigorousness of oxygen depletion in the soil matrix driven by rapid ammonia oxidation is the proximal factor that regulates gas kinetics in high nitrification-potential soil when O 2 diffusion is limited. This implies that practices which reduce hotspots of ammonia oxidation have the potential to mitigate N 2 O emissions from nitrifier denitrification and denitrification in agricultural soil.

Exploring temporal and spatial variation of nitrous oxide flux using several years of peatland forest automatic chamber data

Article

Full-text available

Apr 2024
BG

The urgent need to mitigate climate change has evoked a broad interest in better understanding and estimating nitrous oxide (N2O) emissions from different ecosystems. Part of the uncertainty in N2O emission estimates still comes from an inadequate understanding of the temporal and small-scale spatial variability of N2O fluxes. Using 4.5 years of N2O flux data collected in a drained peatland forest with six automated chambers, we explored temporal and small-scale spatial variability of N2O fluxes. A random forest with conditional inference trees was used to find immediate and delayed relationships between N2O flux and environmental conditions across seasons and years. The spatiotemporal variation of the N2O flux was large, with daily mean N2O flux varying between −10 and +1760 µgN2Om-2h-1 and annual N2O budgets of different chambers between +60 and +2110 mgN2Om-2yr-1. Spatial differences in fluxes persisted through years of different environmental conditions. Soil moisture, water table level, and air temperature were the most important variables explaining the temporal variation of N2O fluxes. N2O fluxes responded to precipitation events with peak fluxes measured on average 4 d after peaks in soil moisture and water table level. The length of the time lags varied in space and between seasons indicating possible interactions with temperature and other soil conditions. The high temporal variation in N2O flux was related to (a) temporal variation in environmental conditions, with the highest N2O fluxes measured after summer precipitation events and winter soil freezing, and (b) to annually varying seasonal weather conditions, with the highest N2O emissions measured during wet summers and winters with discontinuous snow cover. Climate change may thus increase winter N2O emissions, which may be offset by lower summer N2O emissions in dry years. The high sensitivity of N2O fluxes to seasonal weather conditions suggests increasing variability in annual peatland forest N2O budgets as the frequency of extreme weather events, such as droughts, is predicted to increase.

Short-Term Nitrous Oxide Emissions from Cattle Slurry for Silage Maize: Effects of Placement and the Nitrification Inhibitor 3,4-Dimethylpyrazole Phosphate (DMPP)

Article

Full-text available

Nov 2023

Cattle slurry is an important nitrogen source for maize on dairy farms. Slurry injection is an effective measure to reduce ammonia emissions after field application, but with higher risk of nitrous oxide emission than surface application. This study compared soil mineral nitrogen dynamics and nitrous oxide emissions with two ways of application. First, traditional injection at 25 cm spacing between rows followed by ploughing (called "non-placed slurry"), and second, injection using a new so-called goosefoot slurry injector that placed the slurry in ploughed soil as a 30 cm broad band at 10 cm depth below maize crop rows with 75 cm spacing (named "placed slurry"). Furthermore, the effect of treating slurry with the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) in Vizura ® was tested with both application methods. The field experiment was conducted on a sandy loam soil in a temperate climate. Both nitrous oxide emissions, and the dynamics of soil mineral nitrogen, were monitored for eight weeks after slurry application and seeding of maize using static chambers. The level of nitrous oxide emissions was higher with non-placed compared to placed slurry (p < 0.01), mainly due to higher emissions during the first four weeks. This might be due to higher rates of nitrification and in turn stimulation of denitrification. In both placed and non-placed slurry treatments, Vizura ® caused higher soil ammonium concentrations and lower nitrate concentrations (p < 0.001), particularly from 3 to 8 weeks after slurry application. The final level of soil nitrate was similar with and without the nitrification inhibitor, but higher with placed compared to non-placed slurry. Adding Vizura ® to non-placed slurry reduced nitrous oxide emissions by 70% when compared to untreated slurry. Surprisingly, there was a non-significant trend towards higher cumulative emissions from placed slurry with the nitrification inhibitor compared to untreated slurry, which was due to higher emissions in the last part of the monitoring period (5-7 weeks after slurry application). Possibly, degradation of the nitrification inhibitor and nitrification activity inside the slurry band as the soil dried promoted nitrous oxide emissions by this time. In summary, placement of untreated slurry in a broad band under maize seeds reduced nitrous oxide emissions compared to non-placed slurry with more soil contact. A comparable reduction was achieved by adding a nitrification inhibitor to non-placed slurry. The pattern of nitrous oxide emissions from placed slurry treated with the inhibitor was complex and requires more investigation. The emission of nitrous oxide was highest when nitrate accumulated in soil around decomposing cattle slurry, and mitigation strategies should aim to prevent this. This study demonstrated a potential for mitigation of nitrous oxide emission by placement of cattle slurry, which may be an alternative to the use of a nitrification inhibitor.

The effect of ecological farming techniques on nitrogen cycling microorganisms in soils with coffee plantations

Article

Full-text available

Dec 2023

Ecological agriculture promotes an interactive system for the sustainability of soil and agroecosystems, leveraging and optimizing available resources to improve the quality of the cultivated soil. This research aims at evaluating the physical, chemical, and microorganism changes in the nitrogen cycle of the soil after applying ecological farming techniques such as liquid humus, solid humus, efficient microorganisms, biol, poultry manure, phosphites, polyculture stimulation and green manures, in coffee plantations of different ages. For this evaluation, we collected soil samples in plots cultivated with zero-, two-, and four-year-old coffee trees during months zero, four, and ten. We determined the physical and chemical parameters and abundance of microorganisms associated with the nitrogen cycle (ammonifiers (AMO), proteolytic (PRO), ammonium oxidizing (BOA), nitrite oxidizing (BON) and denitrifiers (DEN). The results showed statistically significant changes in soil organic carbon, nitrogen, and phosphorus content as a result of applying ecological farming techniques, which were applied sequentially and evaluated as a set over time. These statistically significant differences occurred in the different months evaluated and in month 10 in contrast to month zero of application of techniques. However, no statistically significant changes were found in the abundance of microorganisms in the nitrogen cycle. In addition, direct relationships were obtained between variables such as P and %OC; pH and DEN; and BON and AMO. It can be concluded that although the application of organic farming techniques improves the physical and chemical properties of soils, there are no statistically significant differences in the abundance of nitrogen cycle microorganisms.

Diversity of the Hydroxylamine Oxidoreductase (HAO) Gene and Its Enzyme Active Site in Agricultural Field Soils

Article

Dec 2023

Nitrification is a key process in the biogeochemical nitrogen cycle and a major emission source of the greenhouse gas nitrous oxide (N2O). The periplasmic enzyme hydroxylamine oxidoreductase (HAO) is involved in the oxidation of hydroxylamine to nitric oxide in the second step of nitrification, producing N2O as a byproduct. Its three-dimensional structure demonstrates that slight differences in HAO active site residues have inhibitor effects. Therefore, a more detailed understanding of the diversity of HAO active site residues in soil microorganisms is important for the development of novel nitrification inhibitors using structure-guided drug design. However, this has not yet been examined. In the present study, we investigated hao gene diversity in beta-proteobacterial ammonia-oxidizing bacteria (β-AOB) and complete ammonia-oxidizing (comammox; Nitrospira spp.) bacteria in agricultural fields using a clone library analysis. A total of 1,949 hao gene sequences revealed that hao gene diversity in β-AOB and comammox bacteria was affected by the fertilizer treatment and field type, respectively. Moreover, hao sequences showed the almost complete conservation of the six HAO active site residues in both β-AOB and comammox bacteria. The diversity of nitrifying bacteria showed similarity between hao and amoA genes. The nxrB amplicon sequence revealed the dominance of Nitrospira cluster II in tea field soils. The present study is the first to reveal hao gene diversity in agricultural soils, which will accelerate the efficient screening of HAO inhibitors and evaluations of their suppressive effects on nitrification in agricultural soils.

Effects of extra-extreme precipitation variability on multi-year cumulative nitrous oxide emission in a semiarid grassland Author links open overlay panel

Article

Nov 2023
AGR FOREST METEOROL

Driving force of tidal pulses on denitrifiers-dominated nitrogen oxide emissions from intertidal wetland sediments

Article

Oct 2023
WATER RES

Intertidal wetland sediments are an important source of atmospheric nitrogen oxides (NOx), but their contribution to the global NOx budget remains unclear. In this work, we conducted year-round and diurnal observations in the intertidal wetland of Jiaozhou Bay to explore their regional source-sink patterns and influence factors on NOx emissions (initially in the form of nitric oxide) and used a dynamic soil reactor to further extend the mechanisms underlying the tidal pulse of nitric oxide (NO) observed in our investigations. The annual fluxes of NOx in the vegetated wetland were significantly higher than those in the wetland without vegetation. Their annual variations could be attributed to changes in temperature and the amount of organic carbon in the sediment, which was derived from vegetated plants and promoted the carbon-nitrogen cycle. Anaerobic denitrifiers had advantages in the intertidal wetland sediment and accounted for the major NO production (63.8%) but were still limited by nitrite and nitrate concentrations in the sediment. Moreover, the tidal pulse was likely a primary driver of NOx emissions from intertidal wetlands over short periods, which was not considered in previous investigations. The annual NO exchange flux considering the tide pulse contribution (8.93 ± 1.72 × 10–2 kg N ha–1 yr–1) was significantly higher than that of the non-pulse period (4.14 ± 1.13 × 10–2 kg N ha–1 yr–1) in our modeling result for the fluxes over the last decade. Therefore, the current measurement of NOx fluxes underestimated the actual gas emission without considering the tidal pulse.

Exploring temporal and spatial variation of nitrous oxide flux using several years of peatland forest automatic chamber data

Preprint

Full-text available

Sep 2023

The urgent need to mitigate climate change has evoked a broad interest in better understanding and estimating nitrous oxide (N2O) emissions from different ecosystems. Part of the uncertainty in N2O emission estimates still comes from an inadequate understanding of the temporal and small-scale spatial variability of N2O fluxes. Using 4.5 years of N2O flux data collected in a drained peatland forest with six automated chambers, we explored temporal and small-scale spatial variability of N2O fluxes. A Random forest with conditional inference trees was used to find immediate and time-lagged relationships between N2O flux and environmental conditions across seasons and years with different environmental conditions. The temporal variation of N2O flux was large, and the daily mean flux varied between –11 and 1760 µg N2O m⁻² h⁻¹. Three of the six measurement chambers had a maximum N2O flux of less than 400 µg N2O m⁻² h⁻¹, while the fluxes in the other three chambers exceeded 1000 µg N2O m⁻² h⁻¹. Spatial differences in the flux persisted over time, and despite the high small-scale spatial variability, the temporal patterns of the fluxes were relatively similar across the chambers. Soil moisture as well as air and soil surface temperature were the most important variables in the random forest, with lagged soil moisture also considered important. N2O flux responded to soil wetting with a time lag of 1–7 days, but the length of the time lag varied spatially and between seasons indicating interactions with other spatially and temporally variable environmental conditions. The high temporal variation in N2O flux was related to a) seasonally variable environmental conditions, with the highest N2O fluxes measured after summer dry-wet cycles and winter soil freezing, and b) to annually variable seasonal weather conditions, which lead to high year-to-year variability in N2O budget. Changes especially in the frequency of summer precipitation events and in winter temperature and snow conditions may increase the variability of annual N2O emissions if the variability in summer and winter weather conditions increases due to climate change.

Article

Full-text available

Sep 2023

Climate change and nutrient pollution are among the most urgent environmental issues. Enhancing the abundance and/or the activity of beneficial organisms is an attractive strategy to counteract these problems. Dissimilatory nitrate reduction to ammonium (DNRA), which theoretically improves nitrogen retention in soils, has been suggested as a microbial process that may be harnessed, especially since many DNRA-catalyzing organisms have been found to possess nosZ genes and the ability to respire N 2 O. However, the selective advantage that may favor these nosZ -harboring DNRA-catalyzing organisms is not well understood. Here, the effect of N 2 O on Nrf-mediated DNRA was examined in a soil isolate, Bacillus sp. DNRA2, possessing both nrfA and nosZ genes. The DNRA metabolism of this bacterium was observed in the presence of C 2 H 2, a NosZ inhibitor, with or without N 2 O, and the results were compared with C 2 H 2 -free controls. Cultures were also exposed to repeated oxic-anoxic transitions in the sustained presence of N 2 O. The NO 2 ⁻ -to-NH 4 ⁺ reduction following oxic-to-anoxic transition was significantly delayed in NosZ-inhibited C 2 H 2 -amended cultures, and the inhibition was more pronounced with repeated oxic-anoxic transitions. The possibility of C 2 H 2 involvement was dismissed since the cultures continuously flushed with C 2 H 2 /N 2 mixed gas after initial oxic incubation did not exhibit a similar delay in DNRA progression as that observed in the culture flushed with N 2 O-containing gas. The findings suggest a possibility that the oft-observed nosZ presence in DNRA-catalyzing microorganisms secures an early transcription of their DNRA genes by scavenging N 2 O, thus enhancing their capacity to compete with denitrifiers at oxic-anoxic interfaces. IMPORTANCE Dissimilatory nitrate/nitrite reduction to ammonium (DNRA) is a microbial energy-conserving process that reduces NO 3 ⁻ and/or NO 2 ⁻ to NH 4 ⁺ . Interestingly, DNRA-catalyzing microorganisms possessing nrfA genes are occasionally found harboring nosZ genes encoding nitrous oxide reductases, i.e., the only group of enzymes capable of removing the potent greenhouse gas N 2 O. Here, through a series of physiological experiments examining DNRA metabolism in one of such microorganisms, Bacillus sp. DNRA2, we have discovered that N 2 O may delay the transition to DNRA upon an oxic-to-anoxic transition, unless timely removed by the nitrous oxide reductases. These observations suggest a novel explanation as to why some nrfA -possessing microorganisms have retained nosZ genes: to remove N 2 O that may otherwise interfere with the transition from O 2 respiration to DNRA.

Short-Term Nitrous Oxide Emissions from Cattle Slurry for Silage Maize: Effects of Placement and the Nitrification Inhibitor 3,4-Dimethylpyrazole Phosphate (DMPP)

Preprint

Full-text available

Sep 2023

Cattle slurry is an important nitrogen source for maize on dairy farms. Slurry injection is an effective measure to reduce ammonia emissions after field application, but with higher risk of nitrous oxide emission than surface application. This study compared soil mineral nitrogen dynamics and nitrous oxide emissions with two ways of application. First, traditional injection at 25 cm spacing between rows followed by ploughing (called “non-placed slurry”), and second, injection using a new so-called goosefoot slurry injector that placed the slurry in ploughed soil as a c. 30 cm broad band at 10 cm depth below maize crop rows with 75 cm spacing (named “placed slurry”). Furthermore, the effect of treating slurry with the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) in Vizura® was tested with both application methods. The field experiment was conducted on a sandy loam soil in a temperate climate. Both nitrous oxide emissions, and the dynamics of soil mineral nitrogen, were monitored for eight weeks after slurry application and seeding of maize using static chambers. The level of nitrous oxide emissions was higher with non-placed compared to placed slurry, mainly due to higher emissions during the first four weeks. That might be due to higher rates of nitrification rate and in turn stimulation of denitrification process. In both placed and non-placed slurry treatments, Vizura® caused higher soil ammonium concentrations and lower nitrate concentrations, particularly from 3 to 8 weeks after slurry application. The final level of soil nitrate was similar with and without the nitrification inhibitor, but higher with placed compared to non-placed slurry. Adding Vizura® to non-placed slurry reduced nitrous oxide emissions by 70 % when compared to placed slurry. Surprisingly, there was a non-significant trend towards higher cumulative emissions from placed slurry with the nitrification inhibitor compared to untreated slurry, which were due to higher emissions in the last part of the monitoring period (5-7 weeks after slurry application). Possibly degradation of the nitrification inhibitor, and nitrification activity inside the slurry band as the soil dried, promoted nitrous oxide emissions by this time. In summary, placement of untreated slurry in a broad band under maize seeds reduced nitrous oxide emissions compared to non-placed slurry with more soil contact. A comparable reduction was achieved by adding a nitrification inhibitor to non-placed slurry. The pattern of nitrous oxide emissions from placed slurry treated with the inhibitor was complex and requires more investigation.

Interaction of Filth Flies and Epigeal Arthropods with Soil Nitrogen and Gas Emissions in Grazing Systems under a Legacy of Low Fertilization

Article

Full-text available

Aug 2023

During the summers of 2021 and 2022, we conducted a study in four Georgia Piedmont pastures to assess the effect of the presence of filth flies and epigeal arthropods on carbon and nitrogen emissions and soil nitrogen retention from lax rotational grazing systems under a legacy of low fertilization. Carbon dioxide (CO2), nitrous oxide (N2O), and ammonia (NH3) emissions were measured from dung on days 0, 4, 8, and 15 following depositions. Soil and manure samples were collected on days 0 and 16 and analyzed for ammonium (NH4+), nitrate (NO3−), plant-available nitrogen (PAN), and potentially mineralizable nitrogen (PMN). Manure samples were analyzed for total Kjeldahl nitrogen (TKN). The numbers of filth flies ovipositing and emerging from manure, fire ants, and epigeal arthropods around the manure were determined. Our results indicated that more than 12 ovipositing filth flies per manure pat can reduce PMN by up to 14.7 kg of nitrogen per hectare, while an increase in the biodiversity and abundance of predators may help to increase PAN and PMN in grazing systems, as well as decrease the number of emerging filth flies.

Effects of long-term organic and inorganic fertilization on greenhouse gas emissions and soil nutrient stoichiometry in a rice-rice-fallow cropping system

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AGR ECOSYST ENVIRON

Changes in soil pore structure generated by the root systems of maize, sorghum and switchgrass affect in situ N2O emissions and bacterial denitrification

Article

Full-text available

Aug 2023
BIOL FERT SOILS

Due to the heterogeneous nature of soil pore structure, processes such as nitrification and denitrification can occur simultaneously at microscopic levels, making prediction of small-scale nitrous oxide (N2O) emissions in the field notoriously difficult. We assessed N2O+N2 emissions from soils under maize (Zea mays L.), switchgrass (Panicum virgatum L.), and energy sorghum (Sorghum bicolor L.), three potential bioenergy crops in order to identify the importance of different N2O sources to microsite production, and relate N2O source differences to crop-associated differences in pore structure formation. The combination of isotopic surveys of N2O in the field during one growing season and X-ray computed tomography (CT) enabled us to link results from isotopic mappings to soil structural properties. Further, our methodology allowed us to evaluate the potential for in situ N2O suppression by biological nitrification inhibition (BNI) in energy sorghum. Our results demonstrated that the fraction of N2O originating from bacterial denitrification and reduction of N2O to N2 is largely determined by the volume of particulate organic matter occluded within the soil matrix and the anaerobic soil volume. Bacterial denitrification was greater in switchgrass than in the annual crops, related to changes in pore structure caused by the coarse root system. This led to high N-loses through N2 emissions in the switchgrass system throughout the season a novel finding given the lack of data in the literature for total denitrification. Isotopic mapping indicated no differences in N2O-fluxes or their source processes between maize and energy sorghum that could be associated with the release of BNI by the investigated sorghum variety. The results of this research show how differences in soil pore structures among cropping systems can determine both N2O production via denitrification and total denitrification N losses in situ.

Nitrous oxide emissions from trees planted on a closed landfill site

Article

Full-text available

Apr 2023

Trees growing in natural and managed environments have the capacity to act as conduits for the transport of greenhouse gases produced belowground to the atmosphere. Nitrous oxide (N2O) emissions have been observed from tree stems in natural ecosystems but have not yet been measured in the context of forested former landfill sites. This research gap was addressed by an investigation quantifying stem and soil N2O emissions from a closed UK landfill and a comparable natural site. Measurements were made by using flux chambers and gas chromatography over a four-month period. Analyses showed that the average N2O stem fluxes from the landfill and non-landfill sites were 0.63 ± 0.06 μg m–2 h–1 and 0.26 ± 0.05 μg m–2 h–1, respectively. The former landfill site showed seasonal patterns in N2O stem emissions and decreasing N2O fluxes with increased stem sampling position above the forest floor. Tree stem emissions accounted for 1% of the total landfill N2O surface flux, which is lower than the contribution of stem fluxes to the total surface flux in dry and flooded boreal forests.

Non-native Brachiaria humidicola with biological nitrification inhibition capacity stimulates in situ grassland N2O emissions

Article

Full-text available

Mar 2023

Introduction: Brachiaria humidicola, a tropical grass, could release root exudates with biological nitrification inhibition (BNI) capacity and reduce soil nitrous oxide (N2O) emissions from grasslands. However, evidence of the reduction effect in situ in tropical grasslands in China is lacking. Methods: To evaluate the potential effects of B. humidicola on soil N2O emissions, a 2-year (2015-2017) field experiment was established in a Latosol and included eight treatments, consisting of two pastures, non-native B. humidicola and a native grass, Eremochloa ophiuroide, with four nitrogen (N) application rates. The annual urea application rates were 0, 150, 300, and 450 kg N ha-1. Results: The average 2-year E. ophiuroides biomass with and without N fertilization were 9.07-11.45 and 7.34 t ha-1, respectively, and corresponding values for B. humidicola increased to 31.97-39.07 and 29.54 t ha-1, respectively. The N-use efficiencies under E. ophiuroide and B. humidicola cultivation were 9.3-12.0 and 35.5-39.4%, respectively. Annual N2O emissions in the E. ophiuroides and B. humidicola fields were 1.37 and 2.83 kg N2O-N ha-1, respectively, under no N fertilization, and 1.54-3.46 and 4.30-7.19 kg N2O-N ha-1, respectively, under N fertilization. Discussions: According to the results, B. humidicola cultivation increased soil N2O emissions, especially under N fertilization. This is because B. humidicola exhibited the more effective stimulation effect on N2O production via denitrification primarily due to increased soil organic carbon and exudates than the inhibition effect on N2O production via autotrophic nitrification. Annual yield-scaled N2O emissions in the B. humidicola treatment were 93.02-183.12 mg N2O-N kg-1 biomass, which were significantly lower than those in the E. ophiuroides treatment. Overall, our results suggest that cultivation of the non-native grass, B. humidicola with BNI capacity, increased soil N2O emissions, while decreasing yield-scaled N2O emissions, when compared with native grass cultivation.

Brachiaria humidicola Cultivation Enhances Soil Nitrous Oxide Emissions from Tropical Grassland by Promoting the Denitrification Potential: A 15N Tracing Study

Article

Full-text available

Nov 2022

Biological nitrification inhibition (BNI) in the tropical grass Brachiaria humidicola could reduce net nitrification rates and nitrous oxide (N2O) emissions in soil. To determine the effect on gross nitrogen (N) transformation processes and N2O emissions, an incubation experiment was carried out using 15N tracing of soil samples collected following 2 years of cultivation with high-BNI Brachiaria and native non-BNI grass Eremochloa ophiuroide. Brachiaria enhanced the soil ammonium (NH4+) supply by increasing gross mineralization of recalcitrant organic N and the net release of soil-adsorbed NH4+, while reducing the NH4+ immobilization rate. Compared with Eremochloa, Brachiaria decreased soil gross nitrification by 37.5% and N2O production via autotrophic nitrification by 14.7%. In contrast, Brachiaria cultivation significantly increased soil N2O emissions from 90.42 μg N2O-N kg−1 under Eremochloa cultivation to 144.31 μg N2O-N kg−1 during the 16-day incubation (p < 0.05). This was primarily due to a 59.6% increase in N2O production during denitrification via enhanced soil organic C, notably labile organic C, which exceeded the mitigated N2O production rate during nitrification. The contribution of denitrification to emitted N2O also increased from 9.7% under Eremochloa cultivation to 47.1% in the Brachiaria soil. These findings confirmed that Brachiaria reduces soil gross nitrification and N2O production via autotrophic nitrification while efficiently stimulating denitrification, thereby increasing soil N2O emissions.

Partial substitution of manure reduces nitrous oxide emission with maintained yield in a winter wheat crop

Article

Jan 2023
J ENVIRON MANAGE

Conventional fertilization of agricultural soils results in increased N2O emissions. As an alternative, the partial substitution of organic fertilizer may help to regulate N2O emissions. However, studies assessing the effects of partial substitution of organic fertilizer on both N2O emissions and yield stability are currently limited. We conducted a field experiment from 2017 to 2021 with six fertilizer regimes to examine the effects of partial substitution of manure on N2O emissions and yield stability. The tested fertilizer regimes, were CK (no fertilizer), CF (chemical fertilizer alone, N 300 kg ha⁻¹, P2O5 150 kg ha⁻¹, K2O 90 kg ha⁻¹), CF + M (chemical fertilizer + organic manure), CFR (chemical fertilizer reduction, N 225 kg ha⁻¹, P2O5 135 kg ha⁻¹, K2O 75 kg ha⁻¹), CFR + M (chemical fertilizer reduction + organic manure), and organic manure alone (M). Our results indicate that soil N2O emissions are primarily regulated by soil mineral N content in arid and semi-arid regions. Compared with CF, N2O emissions in the CF + M, CFR, CFR + M, and M treatments decreased by 16.8%, 23.9%, 42.0%, and 39.4%, respectively. The highest winter wheat yields were observed in CF, followed by CF + M, CFR, and CFR + M. However, the CFR + M treatment exhibited lower N2O emissions while maintaining high yield, compared with CF. Four consecutive years of yield data from 2017 to 2021 illustrated that a single application of organic fertilizer resulted in poor yield stability and that partial substitution of organic fertilizer resulted in the greatest yield stability. Overall, partial substitution of manure reduced N2O emissions while maintaining yield stability compared with the synthetic fertilizer treatment during the wheat growing season. Therefore, partial substitution of manure can be recommended as an optimal N fertilization regime for alleviating N2O emissions and contributing to food security in arid and semi-arid regions.

Effects of liming on oxic and anoxic N2O and CO2 production in different horizons of boreal acid sulfate soil and non-acid soil under controlled conditions

Article

Full-text available

Oct 2022

In acid sulfate (AS) soils, organic rich topsoil and subsoil horizons with highly variable acidity and moisture conditions and interconnected reactions of sulfur and nitrogen make them potential sources of greenhouse gases (GHGs). Subsoil liming can reduce the acidification of sulfidic subsoils in the field. However, the mitigation of GHG production in AS subsoils by liming, and the mechanisms involved, are still poorly known. We limed samples from different horizons of AS and non-AS soils to study the effects of liming on the N2O and CO2 production during a 56-day oxic and subsequent 72-h anoxic incubation. Liming to pH ≥ 7 decreased oxic N2O production by 97-98 % in the Ap1 horizon, 38-50 % in the Bg1 horizon, and 34-36 % in the BC horizon, but increased it by 136-208 % in the C horizon, respectively. Liming decreased anoxic N2O production by 86-94 % and 78-91 % in Ap1 and Bg1 horizons, but increased it by 100-500 % and 50-162 % in BC and C horizons, respectively. Liming decreased N2O/(N2O + N2) in anoxic denitrification in most horizons of both AS and non-AS soils. Liming significantly increased the cumulative oxic and anoxic CO2 production in AS soil, but less so in non-AS soil due to the initial high soil pH. Higher carbon and nitrogen contents in AS soil compared to non-AS soil agreed with the respectively higher cumulative oxic N2O production in all horizons, and the higher CO2 production in the subsoil horizons of all lime treatments. Overall, liming reduced the proportion of N2O in the GHGs produced in most soil horizons under oxic and anoxic conditions but reduced the total GHG production (as CO2 equivalents) only in the Ap1 horizon of both soils. The results suggest that liming of subsoils may not always effectively mitigate GHG emissions due to concurrently increased CO2 production and denitrification.

Simulated warming and low O2 promote N2O and N2 emissions in subtropical montane forest soil

Article

Full-text available

Jun 2022
J SOIL SEDIMENT

Purpose The montane subtropical forest soils contain huge nitrogen stocks, and climate warming might drive its volatilization due to the promotion of gaseous losses of nitrous oxide (N2O) and dinitrogen (N2), contributing a positive feedback to promote further warming. However, it is unclear how temperature increase in subtropical forests affects the loss of gaseous N and the mediated microbial mechanisms. Methods In this study, we employed the acetylene inhibition technique and molecular method to quantify N2O and N2 emissions as well as its microbial pathways under simulated warming and oxygen (O2) conditions in a subtropical forest (> 300 years old) soil. Results During the aerobic incubation, short-term increase of temperature of 2 ℃ caused an increase in N2O emission by a factor of 4.8, while under anaerobic conditions, N2O and N2 emissions increased 18- and 1.9-fold, respectively, thus leading to a significant increase of the ratio of N2O/(N2O + N2). Structural equation modeling showed that the increased potential of N2O loss under simulated warming could be explained by the reduction of nosZ-I gene abundance and thus the less N2O reduction to N2, as well as the promotion on SOC mineralization by the temperature increase, which provides more substrate DOC and nitrate for denitrification. Conclusion These findings suggest the nitrate substrate concentration and availability, together with the abundance variation of denitrifiers to produce and emit N2O, resulted the consequence of the increased N2O in response to the temperature increasing. Results contribute to the accurately establish models of N2O and N2 emissions in the subtropical montane forest soils and the budgets of global greenhouse gas.

Identification of nosZ-expressing microorganisms consuming trace N2O in microaerobic chemostat consortia dominated by an uncultured Burkholderiales

Article

Full-text available

Jun 2022
ISME J

Microorganisms possessing N2O reductases (NosZ) are the only known environmental sink of N2O. While oxygen inhibition of NosZ activity is widely known, environments where N2O reduction occurs are often not devoid of O2. However, little is known regarding N2O reduction in microoxic systems. Here, 1.6-L chemostat cultures inoculated with activated sludge samples were sustained for ca. 100 days with low concentration (<2 ppmv) and feed rate (<1.44 µmoles h−1) of N2O, and the resulting microbial consortia were analyzed via quantitative PCR (qPCR) and metagenomic/metatranscriptomic analyses. Unintended but quantified intrusion of O2 sustained dissolved oxygen concentration above 4 µM; however, complete N2O reduction of influent N2O persisted throughout incubation. Metagenomic investigations indicated that the microbiomes were dominated by an uncultured taxon affiliated to Burkholderiales, and, along with the qPCR results, suggested coexistence of clade I and II N2O reducers. Contrastingly, metatranscriptomic nosZ pools were dominated by the Dechloromonas-like nosZ subclade, suggesting the importance of the microorganisms possessing this nosZ subclade in reduction of trace N2O. Further, co-expression of nosZ and ccoNO/cydAB genes found in the metagenome-assembled genomes representing these putative N2O-reducers implies a survival strategy to maximize utilization of scarcely available electron acceptors in microoxic environmental niches.

Field response of N2O emissions, microbial communities, soil biochemical processes and winter barley growth to the addition of conventional and biodegradable microplastics

Article

Full-text available

Sep 2022
AGR ECOSYST ENVIRON

Microplastic contamination in agroecosystems is becoming more prevalent due to the direct use of plastics in agriculture (e.g., mulch films) and via contamination of amendments (e.g., compost, biosolids application). Long-term use of agricultural plastics and microplastic pollution could lead to soil degradation and reduced crop health due to the slow degradation of conventional plastics creating legacy plastic. Biodegradable plastics are more commonly being used, both domestically and in agriculture, to minimise plastic pollution due to their biodegradable nature. However, the influence of a biodegradable plastics on soil function at the field scale is largely unknown. We investigated the effect of conventional (polyethylene) and biodegradable (PHBV) microplastics on N2O emissions and soil biochemical processes in a field trial of winter barley. Microplastic was added to the soil at realistic levels (100 kg ha⁻¹) for both conventional and biodegradable treatments. N2O emissions were measured throughout the growing season alongside key soil quality indicators (microbial community composition, ammonium, nitrate, moisture content, pH and EC). Overall, microplastic addition had no observable effect on crop yield, microbial communities or soil biochemical properties. Yet, we found cumulative N2O emissions were reduced by two-thirds following conventional microplastic addition compared to the no-plastic and biodegradable microplastic treatments. We believe this response is due to the lower soil moisture levels over the winter in the conventional microplastic treatment. Overall, the response of key soil parameters to microplastic addition show fewer negative effects to those seen in high dose laboratory mesocosm experiments. Thus, it is imperative that long-term field experiments at realistic dose rates be undertaken to quantify the real risk that microplastics pose to agroecosystem health.

Yield and water productivity of crops, vegetables and fruits under subsurface drip irrigation: A global meta-analysis

Article

Jul 2022
AGR WATER MANAGE

The rapid population growth and economic development, climate change and irregular rainfall will inevitably intensify the competition of water resources, resulting in the reduction of agricultural irrigation water. In recent years, subsurface drip irrigation (SSDI), as an efficient water-saving irrigation technology, has been widely used in crop production, but its effects on crop yield, irrigation water productivity (IWP) and water productivity (WP) vary with field managements, climatic conditions and soil properties. Here, a global meta-analysis of 984 comparisons from 109 publications was carried out to systematically and quantitatively analyze the responses of yield, IWP and WP of crops, vegetables and fruits to SSDI. The results showed that SSDI significantly increased yield, IWP and WP by 5.39%, 6.75% and 3.97% relative to surface drip irrigation (SDI), respectively. The largest percentage increase in yield was observed in crops (6.42%), followed by vegetables (5.29%) and fruits (3.37%). SSDI performed best when crops, vegetables and fruits were planted in the open field, under film mulching, in arid regions (<200 mm) and in regions with mean annual temperature ≥ 12 ℃. Besides, the emitter spacing < 25 cm, emitter discharge rate of 2.5–3.5 L h⁻¹ and buried depth of drip pipe < 10 cm were beneficial to obtaining higher increases of yield, IWP and WP. In addition, yield was significantly affected by fertilization rate, and the maximum percentage increase in yield was obtained with 100–200 kg N ha⁻¹, < 50 kg P ha⁻¹ and < 100 kg K ha⁻¹. Yield, IWP and WP were also significantly affected by soil factors. The percentage changes in yield and IWP in soils with higher bulk density (≥ 1.4 g cm⁻³) and in acid soils (pH < 7) were significantly higher than those in soils with lower bulk density (<1.4 g cm⁻³) and in neural and alkaline soils (pH ≥ 7). In conclusion, SSDI can improve yield and WP, but the application of SSDI should be site-specific.

Functional N-cycle genes in soil and N2O emissions in tropical grass-maize intercropping systems

Article

Apr 2022
SOIL BIOL BIOCHEM

There is evidence that forage grasses such as Megathyrsus and Urochloa can suppress nitrification, with direct or indirect consequences on soil inorganic N dynamics and N2O emissions. However, the influence of soil chemical properties on the dynamics of functional N-genes and losses of N in maize (Zea mays L.) intercropped with forage grasses under N fertilization is poorly understood. In this study, soil samples and N2O emissions were analyzed from a field experiment in which maize (fertilized or not with ammonium-based fertilizer) was intercropped with Guinea grass (M. maximus cv. Tanzânia), palisade grass (U. brizantha cv. Marandu), and ruzigrass (U. ruziziensis cv. Comum). Soil N-cycle microorganisms [16S rRNA of bacteria and archaea, nifH (gene encoding N2-fixing bacteria), ammonia-oxidizing bacteria (AOB) and archaea (AOA), nirS (encoding nitrite reductase), and nosZ (encoding nitrous oxide reductase)] were influenced by forage grass, N fertilization, and sampling time, but no evidence of biological nitrification inhibition was found. Palisade grass was associated with a higher abundance of nifH (7.0 × 10⁵ gene copies g⁻¹ soil, on average) in the absence of N compared with the other grasses (4.3 × 10⁵ gene copies g⁻¹ soil, on average). Nitrogen fertilization increased the abundance of AOB but not AOA. Furthermore, N2O flux was influenced by AOB, water-filled pore space, and N fertilization, whereas the cumulative N2O emission and fertilizer-induced emission factor (0.36%, on average) were not affected by the grasses. In conclusion, this study reveals the strong dominance of AOB under ammonium supply, potentially stimulating N2O emissions in maize-forage grass intercropping systems.

Grazing Reduces the Soil-Atmosphere Exchange of Greenhouse Gases During Freeze-Thaw Cycles in Meadow Steppes in Inner Mongolia

Article

Full-text available

Dec 2021

Both livestock grazing and soil freeze-thaw cycles (FTCs) can affect the soil-atmosphere exchange of greenhouse gases (GHGs) in grasslands. However, the combined effects of grazing and FTCs on GHG fluxes in meadow steppe soils remain unclear. In this study, we collected soils from paired grazing and enclosed sites and conducted an incubation experiment to investigate the effect of grazing on soil GHG fluxes in the meadow steppes of Inner Mongolia during three FTCs. Our results showed that FTCs substantially stimulated the emissions of soil N2O and CO2 and the uptake of CH4 in the meadow steppes. However, compared with enclosure treatments, grazing significantly reduced the cumulative N2O, CO2 and CH4 fluxes by 13.3, 14.6, and 26.8%, respectively, during the entire FTCs experiment. The soil dissolved organic carbon (DOC) and nitrogen (DON), NH4+-N and NO3–-N, significantly increased after three FTCs and showed close correlations with N2O and CO2 emissions. Structural equation modeling (SEM) revealed that the increase in NO3–-N induced by FTCs dominated the variance in N2O emissions and that DOC strongly affected CO2 emissions during thawing periods. However, long-term grazing reduced soil substrate availability and microbial activity and increased soil bulk density, which in turn decreased the cumulative GHG fluxes during FTCs. In addition, the interaction between grazing and FTCs significantly affected CO2 and CH4 fluxes but not N2O fluxes. Our results indicated that livestock grazing had an important effect on soil GHG fluxes during FTCs. The combined effect of grazing and FTCs should be taken into account in future estimations of GHG budgets in both modeling and experimental studies.

Eight years organic amendment application alters N2O emission potential by increasing soil O2 consumption rate

Article

Sep 2021
SCI TOTAL ENVIRON

Organic amendments are efficient measures that can be employed to increase both nitrogen use efficiency and soil organic carbon (SOC) content. However, the long-term effects of such measures on soil N2O emission and the associated underlying mechanisms are still unclear. Here, we sampled soils that were part of two long-term trials after eight years of different amounts and types of organic amendment addition, and investigated the response of soil N2O emissions to different types of mineral N addition under oxic condition. Further, we selected two soil samples with a large difference in SOC content and investigated the responses of soil CO2, N2O, NO, and N2 emissions as well as O2 consumption to NH4⁺, NO3⁻, and nitrification inhibitor addition under limited O2 diffusion condition and anoxic condition. Results showed that long-term organic amendments significantly increased SOC content, while the stimulated effect on N2O and N2 emissions owing to increased SOC contents was more pronounced with NH4⁺ addition under limited O2 diffusion condition than under oxic or anoxic conditions. Further, in all treatments under limited O2 diffusion condition, soil O2 concentration and N2O production showed significant inverse relationships, suggesting that O2 directly regulates N2O production. We speculated that the decrease in O2 availability with higher SOC contents owing to enhanced soil respiration, instead of the increased supply of electron donors, is primarily responsible for the stimulated N2O emissions. This implied that practices which reduce limited O2 diffusion conditions might help to minimize the stimulated N2O emissions from increased SOC content.

Evaluation of variation in background nitrous oxide emissions: A new global synthesis integrating the impacts of climate, soil and management conditions

Article

Full-text available

Sep 2021

Robust global simulation of soil background N2O emissions (BNE) is a challenge due to the lack of a comprehensive system for quantification of the variations in their magnitude and location. We mapped global BNE based on 1,353 field observations from globally distributed sites and high‐resolution climate and soil data. We then calculated global and national total BNE budgets and compared them to the IPCC estimated values. The average BNE was 1.10, 0.92, and 0.84 kg N ha‐1 yr‐1 with variations from 0.18 to 3.47 (5–95th percentile, hereafter), 0.20 to 3.44, and ‐1.16 to 3.70 kg N ha‐1 yr‐1 for cropland, forestland, and grassland, respectively. Soil pH, soil N mineralization, atmospheric N deposition, soil volumetric water content, and soil temperature were the principle significant drivers of BNE. The total BNE of three land use types was lower than IPCC estimated total BNE by 0.83 Tg (10^12g) N yr‐1, ranging from ‐47% to 94% across countries. The estimated BNE with cropland values were slightly higher than the IPCC estimates by 0.11 Tg N yr‐1, and forestland and grassland lower than the IPCC estimates by 0.4 and 0.54 Tg N yr‐1, respectively. Our study underlined the necessity for detailed estimation of the spatial distribution of BNE to improve estimates of global N2O emissions and enable the establishment of more realistic and effective mitigation measures.

Seasonal Effluxes of Greenhouse Gases Under Different Tillage and N Fertilizer Management in a Dryland Maize Mono-crop

Article

Full-text available

Aug 2021

There are few studies that have assessed greenhouse gas (GHG) effluxes under dryland agriculture, especially in South Africa. Subsequently, limited data in the sub-Saharan region impedes the formulation of policies on GHG mitigation and adaptation. Therefore, the need to study effluxes of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) was salient. The objective of the study was to assess GHG effluxes across seasons in conventional tillage (CT) and no-till (NT) systems under nitrogen (N) fertilizer management. Gases were sampled using static PVC chambers and sampling was done by inserting a 25-mL polypropylene syringe into the chamber septa and slowly removing the gas. Samples were analysed for CO2, CH4 and N2O using gas chromatography. In winter, CH4 effluxes were higher under NT than CT for each application rate (p < 0.05). N2O efflux was higher (p < 0.05) under CT at 120 and 240 kg N ha−1 compared to NT in summer. The CO2 effluxes of CT were higher (p < 0.05) than NT at all N application rates and seasons. Higher GHG effluxes in summer than winter was attributed to higher soil temperature and moisture. CO2 and N2O emissions were positively correlated to tillage with CH4 negatively correlated, but it has to be noted that not only the intensity of tillage influenced effluxes, but also climatic conditions played a huge role in determining the direction of effluxes. Conservation tillage is climate smart and, in this case NT at 120 kg N ha−1, can be recommended because it sustained less effluxes especially during summer.

N2O emission and its influencing factors in subtropical streams, China

Article

Full-text available

Aug 2021

Background Rivers and streams are one of the primary sources of nitrous oxide (N 2 O) which is an important greenhouse gas with great global warming potential. Yet, over the past century, human activities have dramatically increased reactive nitrogen loadings into and consequently led to increased N 2 O emission from the river ecosystems. Here, we carried out a study in two subtropical rivers, i.e., Jinshui River and Qi River with slight and intense human disturbance in their respective catchments in China. The study intended to explore spatial variability and seasonality in N 2 O emissions, and the relative importance of physicochemical variables, nitrification and denitrification potentials, and functional genes abundance influencing N 2 O emissions. Results N 2 O concentration, N 2 O saturation, and N 2 O flux of Jinshui River peaked in high flow season. N 2 O concentration, N 2 O saturations, and N 2 O flux in Qi River and downstream of Jinshui River were significantly higher than that in other areas in normal and low flow seasons. N 2 O concentration was positively correlated with water temperature, water NO 3 ⁻ , and DOC, negatively correlated with water NH 4 ⁺ and DOC/NO 3 ⁻ (the ratio of dissolved organic carbon to NO 3 ⁻ in water), and positively correlated with potential nitrification rate in high flow season, but not correlated with functional genes abundance. Both rivers had lower N 2 O saturation and flux than many freshwater systems, and their EFr-5 (N 2 O emission factor for river) was lower than the recommended values of IPCC. Conclusions While the two rivers were moderate sources of N 2 O and N 2 O emissions in river systems were normally elevated in the summer, areas with intense human disturbance had higher N 2 O concentration, N 2 O saturations, and N 2 O flux than those with slight human disturbance. Physicochemical variables were good indicators of N 2 O emissions in the river ecosystems.

Comprehensive multi-gas study by means of fiber-enhanced Raman spectroscopy for the investigation of nitrogen cycle processes

Article

Feb 2024
ANALYST

Fiber-enhanced Raman spectroscopy allows for simultaneous quantification of multiple gases and enables the comprehensive analysis of processes of the nitrogen cycle with the aim to reduce the emission of reactive nitrogen species in agriculture.

Increased N2O emissions by the soil nematode community cannot be fully explained by enhanced mineral N availability

Article

Jan 2024
SOIL BIOL BIOCHEM

Soil nematodes are the most abundant soil fauna, with a potential great impact on soil N mineralization via interaction with soil microorganisms. As a consequence, nematodes likely also influence soil N2O production and emission but the very few studies on this matter were carried out in simplified setups with single nematode species and in (highly) disturbed soil conditions. Here we measured soil N2O emission in a 74-day incubation experiment in the presence or absence of the entire soil nematode community with minimal disturbance of the soil microbial community and soil nutrients. This was e.g. evidenced by readily recovery of nitrifiers after the mild and selective sterilization and soil powder inoculation. N2O emission increased in the presence of nematodes, varying between soils +747.7 % in a loamy sand, +55.8 % in a loam, and +51.9 % in a silt loam cropland topsoil, in line with nematode abundance in these soils. In particular, the loamy sand soil showed an atypical N2O emission peak at the time of high nematode abundance. Soil nematodes also increased net N mineralization by +8.4, +6.8 and +4.75 %, in these respective soils and to a smaller extent C mineralization as well. The extra soil nitrate buildup and the overall net stimulation of N mineralization by nematodes could not or just slightly explain the observed increased N2O emission. This research revealed the important role of soil nematodes in regulating N2O emission, and further stresses the need to consider the change in community composition and activity of denitrifiers, and connectivity of soil pores, rather than the stimulation of N mineralization as potential explanations for this role of nematodes.

Threshold-like effect of soil NO3− concentrations on denitrification product N2O/(N2O+N2) ratio is mediated by soil pH

Article

Oct 2023
SOIL BIOL BIOCHEM

Plant communities can attenuate flooding induced N2O fluxes by altering nitrogen cycling microbial communities and plant nitrogen uptake

Article

Aug 2023
SOIL BIOL BIOCHEM

Soil pore structure mediates the effects of soil oxygen on the dynamics of greenhouse gases during wetting–drying phases

Article

Jun 2023
SCI TOTAL ENVIRON

The timing and magnitude of greenhouse gas (GHG) production depend strongly on soil oxygen (O2) availability, and the soil pore geometry characteristics largely regulate O2 and moisture conditions relating to GHG biochemical processes. However, the interactions between O2 dynamics and the concentration and flux of GHGs during the soil moisture transitions under various soil pore conditions have not yet been clarified. In this study, a soil-column experiment was conducted under wetting-drying phases using three pore-structure treatments, FINE, MEDIUM, and COARSE, with 0 %, 30 %, and 50 % coarse quartz sand applied to soil, respectively. The concentrations of soil gases (O2, nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4)) were monitored at a depth of 15 cm hourly, and their surface fluxes were measured daily. Soil porosity, pore size distribution, and pore connectivity were quantified using X-ray computed microtomography. The soil O2 concentrations were found to decline sharply as soil moisture increased to the water holding capacities of 0.46, 0.41, and 0.32 cm cm-3 in the FINE, MEDIUM, and COARSE, respectively. The dynamic patterns of the O2 concentrations varied across the soil pore structures, decreasing to anaerobic in FINE (<0.01 %) and MEDIUM (0.02 %), and to hypoxic (4.42 %) in COARSE. Correspondingly, the soil N2O concentration was the highest in FINE (101 μL L-1) and the lowest in COARSE (10 μL L-1), whereas the highest surface N2O flux was observed in MEDIUM (131 μg N m-2 h-1). As soil CO2 concentrations declined, CO2 fluxes increased from FINE to MEDIUM to COARSE. Most pores of FINE, MEDIUM, and COARSE were 15-80 μm, 85-100 μm, and 105-125 μm, respectively, in terms of diameter. The X-ray CT visible (>15 μm) porosity in FINE, MEDIUM and COARSE were 0.09, 0.17, and 0.28 mm3 mm-3, respectively. The corresponding Euler-Poincaré numbers were 180,280, 76,705, and -10,604, respectively, indicating higher connectivity in COARSE than in MEDIUM or FINE. In soil dominated by small air-filled porosity which limits gas diffusion and result in low soil O2 concentration, N2O concentration was increased and CO2 flux was inhibited as the moisture content increased. The turning point in the sharp decrease in O2 concentration was found to correspond with a moisture content, and a pore diameter of 95-110 μm was associated with the critical turning point between holding water and O2 depletion in soil. These findings suggest that O2-regulated biochemical processes are key to the production and flux of GHGs, which in turn are dependent on the soil pore structure and a coupling relationship between N2O and CO2. Improved understanding of the intense effect of soil physical properties provided an empirical foundation for the future development of mechanistic prediction models for how pore-space scale processes with high temporal (hourly) resolution up to GHGs fluxes at larger spatial and temporal scales.

Preprint

Full-text available

Feb 2023

Climate change and nutrient pollution are among the most urgent environmental issues. Enhancing the abundance and/or the activity of beneficial organisms is an attractive strategy to counteract these problems. Dissimilatory nitrate reduction to ammonium (DNRA), which theoretically improves nitrogen retention in soils, has been suggested as a microbial process that may be harnessed, especially since many DNRA-catalyzing organisms have been found to possess clade II nosZ genes and the ability to respire N 2 O. However, the selective advantages that may favor these nosZ -harboring DNRA-catalyzing organisms is not well understood. Here, the effect of N 2 O on Nrf-mediated DNRA was examined in a recently isolated soil bacterium, Bacillus sp. DNRA2, possessing both nrfA and nosZ genes. The DNRA metabolism of this bacterium was observed in the presence of C 2 H 2 , a NosZ inhibitor, with or without N 2 O, and the results were compared with C 2 H 2 -free controls. Cultures were also exposed to repeated oxic-anoxic transitions in the sustained presence of N 2 O. The NO 2 ⁻ -to-NH 4 ⁺ reduction following oxic-to-anoxic transition was significantly delayed in NosZ-inhibited C 2 H 2 -amended cultures, and the inhibition was more pronounced with repeated oxic-anoxic transitions. The possible involvement of C 2 H 2 was dismissed since the cultures continuously flushed with C 2 H 2 /N 2 mixed gas after initial oxic incubation did not exhibit a similar delay in DNRA progression as that observed in the culture flushed with N 2 O-containing gas. The findings provide novel ecological and evolutionary insights into the oft-observed presence of nosZ genes in DNRA-catalyzing microorganisms. Importance Dissimilatory nitrate/nitrite reduction to ammonium (DNRA) is a microbial energy-conserving process that reduces NO 3 ⁻ and/or NO 2 ⁻ to NH 4 ⁺ . Interestingly, many DNRA-catalyzing microorganisms possessing nrfA genes harbor nosZ genes encoding nitrous oxide reductases, i.e., the only group of enzymes capable of removing the potent greenhouse gas N 2 O. Here, through a series of physiological experiments examining DNRA metabolism in one of such microorganisms, Bacillus sp. DNRA2, we have discovered that N 2 O may delay transition to DNRA upon an oxic-to-anoxic transition, unless timely removed by the nitrous oxide reductases. These observations suggest a novel explanation as to why some nrfA -possessing microorganisms have retained nosZ genes that had probably been acquired via horizontal gene transfers: to remove N 2 O that may otherwise interfere with the transition from O 2 respiration to DNRA.

Interactive Effects of Soil Ph and No3- Availability Managements on the Magnitude and Stoichiometry of Denitrification Products from Subtropical Acidic Agricultural Soil

Article

Jan 2022

Why overgrazing promotes nitrifiers and denitrifiers abundance and the resultant soil N 2 O emissions?

Article

May 2022

Livestock overgrazing is a global environmental problem, influencing global warming via soil N2O emissions. However, it remains unknown why overgrazing leads to increased N2O emissions. Here, we used a paired design of subalpine meadows in undisturbed and overgrazed sites at four different elevations (from 3000 to 3600 m) located over an area of ~200 km2 in the Qinghai‐Tibetan Plateau (QTP), China, to evaluate relationships among plant diversity, soil ammonium and nitrate N, the abundance of soil nitrifiers (AOA and AOB) and denitrifiers (nirK, nirS and the N2O reductase gene [nosZ]) and soil N2O emissions. Using a generalized linear mixed effects modeling framework with Poisson error, we found that the influence of overgrazing on increased abundance of soil nitrifiers and denitrifiers and associated increased soil N2O emission was a general phenomenon in QTP. More importantly, by using forward selection analysis and structural equation models, we showed overgrazing decreased plant richness, and this resulted in decreased ammonium N, but increased nitrate N at all elevations. Accordingly, decreased ammonium N, but increased nitrate N led to increased abundance of soil nitrifiers (AOA and AOB) and denitrifiers (nirK and nirS), but decreased nosZ abundance, which finally gave rise to increased soil N2O emission at all the elevations. Our results highlight the key role of plant diversity in regulating soil N2O emissions from soils. Thus, performing active ecological restoration to recover native plant species in overgrazed sites may help mitigate the influence of overgrazing on global warming. This article is protected by copyright. All rights reserved.

Managing Agricultural Nitrogen Losses in Crop Production and Mitigation of Climate Change Effects

Chapter

Apr 2022

Nitrogen (N) losses from cropping systems negatively affect soil quality/fertility, crop yield, and the environment through its contribution to climate change and water pollution. İt possesses oil-water-atmospheric system challenges to both the too much and the too little N application countries. Soil and climatic factors are the critical drivers of N loss from agricultural systems as they influence major processes like nitrification and denitrification. Other N loss pathways include leaching, runoff, and volatilization. Nitrous oxide (N2O) and ammonia (NH3) gases are the two pollutants resulting from N fertilizers in crop production and represent N loss’ significant pathway. Nitrous oxide is 300 times more a potent greenhouse gas than carbon dioxide, and it also depletes the ozone layer. Developing and adopting key strategies to mitigate N loss’s extent will be critical for crop productivity and environmental management. İn this chapter, we highlight the potential solutions that can be adopted at a global and local level to manage N in the agricultural system. A linkage between N and climate change has also been reviewed.KeywordsNitrogen lossMitigationAgricultureClimate change

Nitrogenous fertilizers: impact on environment sustainability, mitigation strategies, and challenges

Article

Apr 2022

The world has changed revolutionary for the last few decades owing to the surge in population. A consequence of this exponential increase in population is the high demand for food, water, and energy resources. The application of nitrogenous fertilizers is one of the solutions to accomplish the pressure of food security that the world has already seen in the second half of the century. However, the excessive use of chemical nitrogenous fertilizers has a negative impact on all the segments of the environment, namely soil, water, and air. Environment sustainability is at risk because of the loss of biodiversity in soil and water due to nitrogen pollution. The intense application of these fertilizers also affected the health of humans and livestock. Several strategies have been employed to mitigate the damaging impact of nitrogenous fertilizers. For example, the use of organic manure, compost, slow-release fertilizers or controlled-release fertilizers, and nano-enabled fertilizers is being promoted. Enhancing nitrogen assimilation of crops provides another solution to reduce the excessive use of chemical fertilizers. Although adopting these strategies faces some challenges, such as food security, lack of latest information on agricultural developments, and income of small-scale farmers. At present, the world has arrived at a situation to rethink, and the ‘need’ for nitrogenous fertilizers should be changed into ‘need to replace’ to preserve environmental sustainability.

Variance and main drivers of field nitrous oxide emissions: A global synthesis

Article

Apr 2022
J CLEAN PROD

The precise estimation of global nitrous oxide (N2O) emissions in nitrogen cycling will facilitate improved projections of future climate change. However, the geographical variations and the primary controlling factors of N2O emissions remain elusive at the global scale. What is lacking is their specific evaluation based on field data. We compiled a new dataset of soil N2O emission rates, including 6016 field observations from 219 articles, to synthesize N2O emission rates for different ecosystems and to explore the key determinants of N2O emission variations. The global mean soil N2O emission rate was 1111.8 ± 26.6 μg N m⁻² day⁻¹, with the largest one from humid subtropical regions and the smallest one from semi-arid areas. The soil N2O emission rates were positively correlated with the mean air annual temperature, soil pH, cation exchange capacity, soil moisture, soil organic carbon (C), total soil nitrogen (N), dissolved organic N, ammonium, nitrate, available phosphorus concentrations, microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) at a global scale. Conversely, the soil N2O rates were negatively correlated with soil bulk density, C:N ratio, and MBC:MBN ratio. The results of structural equation models revealed that the joint direct effects of soil nitrate, ammonium, and total N (combined standard coefficient = 0.45) accounted for most of the variability in global soil N2O emissions (total standard coefficient = 0.84), while climate factors and other soil physicochemical properties accounted for less. This study highlights the critical roles of soil N substrates on N2O emissions, which will facilitate the optimization of process-models for soil N2O emissions.

Mechanism of biochar on nitrification and denitrification to N2O emissions based on isotope characteristic values

Article

Apr 2022
ENVIRON RES

To clarify the mechanism of biochar on nitrification and denitrification to N2O emissions in farmland soil, the effects of combined application of biochar and different nitrogen sources on the contributions of nitrification and denitrification to N2O emissions were studied using isotope characteristic values. The results showed that the soil N2O emissions from ammonium nitrogen fertilizer treatments were significantly higher than that from nitrate nitrogen fertilizer treatments. The biochar combined with ammonium nitrogen fertilizer reduced soil N2O emissions by 31.0%–30.8%, and biochar combined with nitrate nitrogen fertilizer reduced soil N2O emissions by 70.6%–63.0%. The isotope model showed that the application of ammonium nitrogen fertilizer was more favorable for soil nitrification in the early stage of the experiment (0–2 d), and more favorable for denitrification in the middle and later stages of the experiment (3–17 d). Application of nitrate nitrogen fertilizer enhanced the nitrification of soil nitrifying bacteria in the early and middle stages of the experiment (0–8 d), and the denitrification of soil denitrifying bacteria in the later stage of the experiment (9–17 d). The effects of biochar on N2O emissions were mainly in the middle and later stages of the experiment by promoting the nitrification of nitrifying bacteria and inhibiting denitrification of denitrifying bacteria, so as to reduce N2O emission in soil. These results may help to understand the mitigation mechanism of biochar on N2O emission in upland soil.

Non-Native Marsh Grass (Phragmites australis) Enhances Both Storm and Ambient Nitrogen Removal Capacity in Marine Systems

Article

Mar 2022

Marshes play a key role in global nitrogen cycling at the land–water margin. Invasive species are generally considered detrimental as they alter ecosystems they invade, but recent studies have shown some established invasive species can enhance certain ecosystem functions. The European haplotype of Phragmites australis is an aggressive and widespread invasive plant species in North America. We hypothesized that P. australis may play an important role in marsh nitrogen cycling by promoting higher rates of sediment denitrification compared with native marsh species. Seasonal measurements of sediment dissolved gas (N2 and O2) fluxes at three sites within the Albemarle-Pamlico Region of North Carolina compared sediments from invasive P. australis, native Spartina alterniflora, and/or Juncus roemarianus, and unvegetated sediments. In a marine tidal site, annual net denitrification in sediments associated with upland P. australis was highest compared to lower elevation marsh species or unvegetated sediments under ambient (139 μmol N2-N m−2 h−1) and nitrate enriched (219 μmol N2-N m−2 h−1) conditions. N2 fluxes were lower in sediments from two brackish marshes and did not differ between associated species, unvegetated sediments, or between high or low organic matter sites. Treatments with elevated nitrate showed enhanced net denitrification in most sediments at the marine site, suggesting the capacity to remove additional nitrate delivered episodically. Additionally, N2 fluxes measured before and after Hurricane Florence showed an increase in denitrification in P. australis sediments after the hurricane. Ecosystem value for this nitrogen removal service in the marine tidal site was estimated at US$ 266–426 *ha−1*yr−1. These results demonstrate an important role for invasive P. australis in coastal nitrogen cycling in marine environments and provide landscape context for potential biogeochemical impacts of this invasion.

Changes in precipitation regime lead to acceleration of the N cycle and dramatic N2O emission

Article

Dec 2021
SCI TOTAL ENVIRON

Alpine meadows on the Qinghai-Tibetan Plateau are sensitive to climate change. The precipitation regime in this region has undergone major changes, “repackaging” precipitation from more frequent, smaller events to less frequent, larger events. Nitrous oxide (N2O) is an important indicator of responses to global change in alpine meadow ecosystems. However, little information is available describing the mechanisms driving the response of N2O emissions to changes in the precipitation regime. In this study, a manipulative field experiment was conducted to investigate N2O flux, soil properties, enzyme activity, and gene abundance in response to severe and moderate changes in precipitation regime over two years. Severe changes in precipitation regime led to a 12.6-fold increase in N2O fluxes (0.0068 ± 0.0018 mg m⁻² h⁻¹) from Zoige alpine meadows relative to natural conditions (0.0005 ± 0.0029 mg m⁻² h⁻¹). In addition, severe changes in precipitation regime significantly suppressed the activities of leucine amino peptidase (LAP) and peroxidase (PEO), affected ecoenzymatic stoichiometry, and increased the abundances of gdhA, narI and nirK genes, which significantly promoted organic nitrogen (N) decomposition, denitrification, and anammox processes. The increase in abundance of these genes could be ascribed to changes in the abundance of several dominant bacterial taxa (i.e., Actinobacteria and Proteobacteria) as a result of the altered precipitation regime. Decreases in nitrate and soil moisture caused by severe changes in precipitation may exacerbate N limitation and water deficit, lead to a suppression of soil enzyme activity, and change the structure of microorganism community. The N cycle of the alpine meadow ecosystem may accelerate by increasing the abundance of key N functional genes. This would, in turn, lead to increased N2O emission. This study provided insights into how precipitation regimes changes affect N cycling, and may also improve prediction of N2O fluxes in response to changes in precipitation regime.

Hierarchical feedbacks of vegetation and soil carbon pools to climate constraints in Brazilian ecosystems

Article

Full-text available

Nov 2021
REV BRAS CIENC SOLO

It remains unclear whether temperature and precipitation exert independent control on tropical vegetation and soil C pools. Likewise, it is unknown whether the feedbacks of tropical C pools to climate constraints vary with nutrient availability. These aspects are critical to improving our ability to predict the response of tropical C pools to climate dynamics. This review aimed to assess climate data and the spatial distribution of vegetation and soil C pools across the Brazilian territory to investigate i) whether mean annual precipitation (MAP) and temperature (MAT) exert independent effects on tropical C pools; ii) whether vegetation and soil C pools exhibit hierarchical feedbacks to climate; and iii) how these feedbacks reflect soil nutrient availability. To account for MAP and MAT effects on tropical C cycling, we calculated Ecosystem Effective Moisture (EEM), i.e., the difference between MAP and potential evapotranspiration. We gathered substantial evidence suggesting that under high MAT and MAP controlling EEM, plants exchange more C for water and resorb more nutrients (especially P), which limitations in plant litter reduce microbial-derived C inputs into soil organic matter. Frequent soil saturation under high EEM favors denitrification rates ("open" N cycle), allowing continuous mineralization of litter and shallow soil C pools to release nutrients, sustaining high plant C pools. With decreasing MAP levels, ecosystem C pools depend on MAT controlling evapotranspiration and EEM. Accordingly, decreasing MAP under high MAT reduces EEM, with vegetation and soil C pools co-limited by low net primary productivity (NPP), frequent fire and/or nutrient losses. Otherwise, decreasing MAP and coupled to cool temperatures allow EEM to remain positive, forcing plants to increase deep-rooting and/or shed their leaves, which nutrients are immobilized with microbial-derived C into mineral-organic associations, favoring high soil C pools. Combined, the evidence gathered suggests that the sensitivity of tropical ecosystems to global increases in temperature should not be overlooked, especially if coupled to reductions in precipitation. Overall, the horizontal distribution of vegetation and soil C pools is best described by EEM rather than temperature or precipitation alone, whereas the vertical partition of C in plant-soil systems reflects biotic responses to climate-nutrient constraints.

Agricultural Fertilization Aggravates Air Pollution by Stimulating Soil Nitrous Acid Emissions at High Soil Moisture

Article

Oct 2021

Soil nitrous oxide emissions after the introduction of integrated cropping systems in subtropical condition

Article

Full-text available

Jan 2022
AGR ECOSYST ENVIRON

The assessment of impacts of GHG to mitigate emissions in Brazil is a significant challenge for the expansion of integrated cropping systems. In Brazil, most studies on integrated cropping systems were conducted in tropical regions and evaluated N2O fluxes, important GHG due to its global warming potential. However, the dynamics of N2O fluxes of these systems in subtropical climate conditions in Brazil are still unclear. Thus, we investigated N2O emissions under integrated cropping systems and monoculture systems and evaluated N2O fluxes in five consolidated systems: cropland, integrated crop-forest (ICF), pasture, integrated livestock-forest (ILF), and eucalyptus. N2O emissions were monitored weekly using six manual static chambers for each agricultural system. Soil-weather variables were observed consecutively during N2O sampling. We assessed the relation between soil moisture, water-filled porous space (WFPS), rainfall, soil NO3-, and soil NH4+ with N2O. Our results showed that seasonal water availability influenced N2O fluxes in all five systems. Fertilization with N increased N2O daily fluxes in cropland and ICF (N2O maximum from 30 to 50 μg N m−2 h−1). However, cumulative N2O in the second season was lower than the first season to all evaluated systems. Cropland, ICF, and eucalyptus showed an increase of more than 50% of cumulative N2O emissions compared to the dry to the rainy season, while pasture and ILF presented an increase of more than 200% of cumulative N2O from one season to another. However, the absolute cumulative value was higher for cropland, ICF, and eucalyptus than pasture systems. Thus, the use of annual crops or just monoculture could increase N2O fluxes due to the influence of weather-soil variables. The results showed that N2O emissions were similar between ICF and ILF systems and between cropland, pasture, and eucalyptus. Therefore, integrated cropping systems offer potential for reduced N2O losses to the atmosphere and may support national and international climate change initiatives to reduce GHG emissions in agriculture.

Global analysis of the potential for N 2 O production in natural soils

Article

Full-text available

Sep 1993

A simple global model of the production potential of nitrous oxide (N2O) in natural soils is developed to analyze the relative importance, both geographically and seasonally, of the different controls on N2O production at the global scale. Five major controls on N2O production are included: (1) input of organic matter, (2) soil fertility, (3) soil moisture status, (4) temperature, and (5) soil oxygen status. Indices for the controls are derived from global gridded (1°×1° resolution) data bases of soil type, soil texture, NDVI and climate. The model explains close to 60% of the variability found in measurements reported at about 30 sites in six different ecosystems throughout the world. Although this result is reasonable for global analyses, the correlation is considered insufficient to make global estimates of nitrous oxide emission with confidence. The model confirms conclusions from earlier studies that the major source regions of nitrous oxide are in the tropics.

Processes Regulating Soil Emissions of NO and N^2O in a Seasonally Dry Tropical Forest

Article

Full-text available

Jan 1993

While much is known about control of production of NO and N[sub 2]O by nitrifying and denitrifying bacteria at the cellular level, application of this knowledge to field studies has not yielded unifying concepts that are widely applicable and that foster understanding of global sources of these atmospheric trace gases. We applied a simple conceptual model to the investigation of sources of NO and N[sub 2]O and the environmental factors affecting fluxes in a drought-deciduous forest of Mexico. Fluxes of NO and N[sub 2]O were higher in the wet season than the dry season, but addition of water to dry soil caused large pulses of CO[sub 2], NO, and N[sub 2]O emissions. Immediate increases of extractable soil NH[sub 4][sup +] and high rates of gross N mineralization and gross nitrification also were observed following wetting of dry soil. Soil NO[sub 2][sup [minus]] had accumulated during the dry season, and that NO[sub 2][sup [minus]] plus the pulse of increased soil NH[sub 4][sup +] were mostly consumed within 24 hours of wetting. This dynamic microbial processing of soil inorganic N coincided with the pulses of NO and N[sub 2]O production following wetting of dry soil. Acetylene inhibition experiments indicated that NO production was dependent on nitrification, that nitrification was the dominant source of N[sub 2]O when the soil was wetted at the end of the dry season, and that denitrification might be an important source of N[sub 2]O during the wet season. Post-wetting soil moisture was correlated negatively with NO fluxes and positively with N[sub O] fluxes. These results support a conceptual model in which N trace gas production is generally constrained by the rates of N mineralization and nitrification, while the specific ratios of NO and N[sub 2]O fluxes and the contributions from nitrifying and denitrifying bacteria are controlled largely by soil moisture. 42 refs., 5 figs., 4 tabs.

Nitric Oxide and Nitrous Oxide Production from Soil: Water and Oxygen Effects

Article

Full-text available

May 1992

In this two-soil study the total amount of NO plus N2O produced increased with increasing water content for the Brookston clay loam (Typic Argiaguoll), whereas it peaked at 15% water content with the Fox sandy loam, (Typical Hapludalf). The decrease in NO plus N2O at higher water contents was probably the result of the subsequent reduction of N2O to N2 in the Fox sandy loam soil. The residence time of the denitrification gases in the soils increased with increasing water content, hence facilitating subsequent conversions. In the sandy loam soil, O2 content and soil water affected both the amount and species of evolved denitrification gases. -from Authors

Direct Measurement of Oxygen Profiles and Denitrification Rates in Soil Aggregates1

Article

Full-text available

May 1985

An oxygen microelectrode was modified to measure O//2 concentrations in wet aggregates of a silt loam soil. The microelectrode tip had an O//2-permeable membrane opening 3 mu m in diameter, and O//2 measurements could be made in as little as 0. 1-mm increments to a depth of 12mm. When aggregates were incubated in air, steep O//2 gradients usually occurred over very small distances from the aggregate surface. The smallest aggregate exhibiting an anaerobic center had a radius of 4 mm, although small aggregates (radius less than equivalent to 6 mm) were generally oxic. Larger aggregates (radius less than equivalent to 10 mm) often had measurable anaerobic centers, with the exception of those from a native prairie soil which exhibited irregular O//2 profiles and had aerobic centers, apparently due to O//2 intrusion caused by old root channels. Oxygen profiles obtained in 45 degree increments around an aggregate circumference were used to construct contour maps of O//2 concentrations within the aggregate. Refs.

Oxidation of atmospheric methane in soil: Measurements in the field, in soil cores and in soil samples

Article

Full-text available

Mar 1993

Methane fluxes and vertical profiles of CH4 mixing ratios were measured in different German soils both in situ and in soil cores. Atmospheric CH4 was oxidized in the soil by microorganisms resulting in an average CH4 flux of -1.39+/-1.5 mumol-CH4 m-2 h-1. Methane deposition showed only a weak positive correlation (r2=0.38) with soil temperature but a relatively strong negative correlation (r2=0.61) with soil moisture indicating limitation of the CH4 flux by gas transport. Diffusion experiments in soil cores showed that gas transport between atmosphere and soil was faster than microbial CH4 oxidation. However, the diffusion from the gas-filled soil pores to the CH4 oxidizing microorganisms may have been limiting. The main CH4-oxidizing activity was located in a few centimeter thick subsurface soil layer at the top of the Ah horizon, whereas no activity was found in the overlying O horizons and in deep soil below about 20-cm depth. In contrast, the highest CO2 production was found in the topmost O horizon. The effective diffusion coefficient of CH4 in soil was determined using a method based on relaxation experiments with argon. The diffusion coefficient was used to model the CH4 oxidation in soil cores from the vertical profiles of CH4 mixing ratios. The thus calculated CH4 oxidation rates and their localization in the soil profile compared fairly well with those determined directly from incubated soil samples. Fluxes were similar within a factor of 2-4 whether derived from the model, calculated from the measured CH4 oxidation rates of soil samples, or measured directly.

Microbiological Basis of NO and N2O Production and Consumption in Soil

Article

Full-text available

Jan 1989

Soil-atmosphere exchange of nitrous oxide, nitric oxide, and methane under secondary succession of pasture to forest in the Atlantic lowlands of Costa Rica

Article

Full-text available

Dec 1994
GLOBAL BIOGEOCHEM CY

We investigated changes in soil-atmosphere flux of CH4, N2O, and NO resulting from the succession of pasture to forest in the Atlantic lowlands of Costa Rica. We studied a dozen sites intensively for over one year in order to measure rates and to understand controlling mechanisms for gas exchange. CH4 flux was controlled primarily by soil moisture content. Soil consumption of atmospheric CH4 was greatest when soils were relatively dry. Forest soils consumed CH4 while pasture soils which had poor drainage generally produced CH4. The seasonal pattern of N2O emissions from forest soils was related exponentially to soil water-filled pore space. Annual average N2O emissions correlated with soil exchangeable NO3- concentrations. Soil-atmosphere NO flux was greatest when soils were relatively dry. We found the largest NO emissions from abandoned pasture sites. Combining these data with those from another study in the Atlantic lowlands of Costa Rica that focused on deforestation, we present a 50-year chronosequence of trace gas emissions that extends fr5om natural conditions, through disturbance and natural recovery. The soil-atmosphere fluxes of CH4 and N2O and of NO may be restored to predisturbance rates during secondary succession. The changes in trace gas emissions following deforestation, through pasture use and secondary succession, may be explained conceptually through reference to two major controlling factors, nitrogen availability and soil-atmosphere diffusive exchange of gases as it is influenced by soil moisture content and soil compaction.

Short-Term Assay of Soil Urease Activity Using Colorimetric Determination of Ammonium

Article

Full-text available

Jan 1988

A rapid assay for soil urease in the absence of bacteriostatic agents has been developed. The method comprises incubation of soil with an aqueous or buffered urea solution, extraction of ammonium with 1 N KCl and 0.01 NHCl and colorimetric NH4 + determination by a modified indophenol reaction. The method is characterized by high sensitivity and stability of the coloured complex formed. Measurements obtained by this method showed that no change in urease activity occurred when field-moist samples of soils were stored at –20C for as long as 5 months. Air-drying of field-moist soil samples may lead to an increase in urease activity.

Denitrification: Production and consumption of nitric oxide

Article

Full-text available

May 1994

A comparison of NO and N2O production by the autotrophic nitrifier Nitrosomonas europaea and the heterotrophic nitrifier Alcaligenes faecalis

Article

Full-text available

Dec 1993

Soil microorganisms are important sources of the nitrogen trace gases NO and N2O for the atmosphere. Present evidence suggests that autotrophic nitrifiers such as Nitrosomonas europaea are the primary producers of NO and N2O in aerobic soils, whereas denitrifiers such as Pseudomonas spp. or Alcaligenes spp. are responsible for most of the NO and N2O emissions from anaerobic soils. It has been shown that Alcaligenes faecalis, a bacterium common in both soil and water, is capable of concomitant heterotrophic nitrification and denitrification. This study was undertaken to determine whether heterotrophic nitrification might be as important a source of NO and N2O as autotrophic nitrification. We compared the responses of N. europaea and A. faecalis to changes in partial O2 pressure (pO2) and to the presence of typical nitrification inhibitors. Maximal production of NO and N2O occurred at low pO2 values in cultures of both N. europaea (pO2, 0.3 kPa) and A. faecalis (pO2, 2 to 4 kPa). With N. europaea most of the NH4+ oxidized was converted to NO2-, with NO and N2O accounting for 2.6 and 1% of the end product, respectively. With A. faecalis maximal production of NO occurred at a pO2 of 2 kPa, and maximal production of N2O occurred at a pO2 of 4 kPa. At these low pO2 values there was net nitrite consumption. Aerobically, A. faecalis produced approximately the same amount of NO but 10-fold more N2O per cell than N. europaea did. Typical nitrification inhibitors were far less effective for reducing emissions of NO and N2O by A. faecalis than for reducing emissions of NO and N2O by N. europaea.(ABSTRACT TRUNCATED AT 250 WORDS)

Production of NO2- and N2O by Nitrifying Bacteria at Reduced Concentrations of Oxygen

Article

Full-text available

Oct 1980

Pure cultures of the marine ammonium-oxidizing bacterium Nitrosomonas sp. were grown in the laboratory at oxygen partial pressures between 0.005 and 0.2 atm (0.18 to 7 mg/liter). Low oxygen conditions induced a marked decrease in the rate for production of NO(2), from 3.6 x 10 to 0.5 x 10 mmol of NO(2) per cell per day. In contrast, evolution of N(2)O increased from 1 x 10 to 4.3 x 10 mmol of N per cell per day. The yield of N(2)O relative to NO(2) increased from 0.3% to nearly 10% (moles of N in N(2)O per mole of NO(2)) as the oxygen level was reduced, although bacterial growth rates changed by less than 30%. Nitrifying bacteria from the genera Nitrosomonas, Nitrosolobus, Nitrosospira, and Nitrosococcus exhibited similar yields of N(2)O at atmospheric oxygen levels. Nitrite-oxidizing bacteria (Nitrobacter sp.) and the dinoflagellate Exuviaella sp. did not produce detectable quantities of N(2)O during growth. The results support the view that nitrification is an important source of N(2)O in the environment.

Metabolism of nitric oxide and nitrous oxide during nitrification and denitrification in soil at different incubation conditions

Article

Jul 1992

M Schuster

Anaerobic Zones and Denitrification in Soil: Modelling and Measurement

Chapter

Jan 1990

Keith A. Smith

The general requirements for denitrification are (i) the presence of microorganisms possessing the metabolic capacity, (ii) suitable electron donors, (iii) anaerobic conditions or at least restricted oxygen availability, and (iv) nitrate, nitrite, nitric oxide (NO), and/or nitrous oxide (N2O) as terminal electron acceptor (Firestone, 1982). In terms of the spatial distribution and extent of anaerobic conditions in soils and sediments, it is convenient to consider soil environments in three broad categories.

Metabolism of Nitric Oxide in Soil and Soil Microorganisms and Regulation of Flux into the Atmosphere

Chapter

Jan 1996

Ralf Conrad

Nitric oxide plays a central role in the photochemistry of the atmosphere (Crutzen 1979; Logan 1983; Singh 1987). There are several reviews which summarize our knowledge on the emission of NO from soils (Johansson 1989; Conrad, 1990; Davidson 1991; Williams et al. 1992; Meixner 1994). They all agree that emissions from soils are a major source and, with a source strength of about 20 Tg N yr-1 , may contribute as much as 40% to the total budget of atmospheric NO. Because of the short atmospheric lifetime most of the emitted NO will soon be deposited again so that the nitrogen loss from one ecosystem may result in unintended fertilization of downwind ecosystems (Conrad 1990; Williams et al. 1992; Meixner 1994).

Chemodenitrification

Article

Jan 1983

It has long been suspected that the poor efficiency of N fertilizers was due in part to conversion to gaseous forms of N which were then evolved from the soil. It was generally assumed that the important pathways of loss were volatilization of NH3, and reduction of nitrate to N2O and N2 by soil microorganisms (biological denitrification). There was little direct evidence to support the assumption of significant losses via these pathways, despite intensive study of the factors affecting the processes. However, recent advances in the methodology for the collection of samples and measurement of gaseous forms of N, have stimulated research on gaseous-N losses from soil. Investigations have shown that several gaseous forms of N may be evolved from soils which are actively nitrifying. The nature of the processes which cause these losses is currently the subject of much investigation and speculation. There is evidence that nitrite produced by nitrifying or denitrifying microorganisms may react chemically to form gaseous N compounds (chemical denitrification).

Soil emissions of nitric oxide and nitrous oxide from no-till corn

Article

Jan 1996

Fertilized agricultural soils can be a significant source of emissions of NO and N2O into the atmosphere. This study was conducted to determine the influence of N rate on the emissions of these gases in a no-till corn (Zea mays L.) crop grown in western Tennessee. The influence of N rate was assessed for a 210-d period on replicated plots receiving 0, 140, and 252 kg N ha-1 (0N, 140N, and 252N) as ammonium nitrate (AN). Plots were located on a Routon silt loam (fine-silty, mixed, thermic Typic Ochraqualf) at the West Tennessee Agricultural Experiment Station in Jackson, TN. Gas fluxes were measured by static chamber boxes located on plots. The measurement technique was automated and replicate chamber estimates were made eight times daily for the entire study period. Fertilizer application significantly affected both NO and N2O emission rates. The cumulative N2O- N lost from the fertilizer treatments was from 10 to 20-fold that of NO. On an areal basis, the 140N treatment emitted 4.23 kg N2O-N and 0.19 kg ha-1 of NO-N whereas the 252N treatment emitted 6.56 kg N2O-N and 0.50 kg ha-1 NO-N. Soil parameters of water-filled pore space (WFPS), NO3- and NH4+, were correlated with N2O emissions but only soil NO3- was correlated with NO flux. Our data, and more recent data in the literature, suggest that N2O emissions from fertilized soil may be considerably higher than previously thought. Emissions of N2O were 2.6 to 3.0% of the fertilizer amounts applied. These higher emissions may, in part, explain some of the reason for the shortfall in the global N2O budget.

Nitrous and nitric oxide emissions during nitrification and denitrification from manure-amended soil in the laboratory

Article

Nov 1993

Denitrification and nitrification processes in soil produce significant amounts of atmospheric N2O and NO. Laboratory experiments were designed to measure N2O and NO emissions from an agricultural soil shortly after manure addition. Nitrous oxide emissions were higher from soil following addition of manure slurries than following addition of composted manure. Emissions of both N2O and NO were highest between 1 and 4 d after manure addition. Nitrous oxide emission following manure application was the result of both denitrification and nitrification, which occurred simultaneously in soil. Denitrification was a major producer of N2O because both denitrification rates and N2O emission increased dramatically at higher soil-moisture contents and increased manure concentration. Nitric oxide production occurred during nitrification. Nitrous oxide emitted during the 6 d after manure addition ranged from 0.025 to 0.85% of the manure N. Nitric oxide emissions were approximately 0.26% of the amount of added manure N....

Application of a soil core method to investigate the effect of oxygen concentration on denitrifcation

Article

Dec 1984
SOIL BIOL BIOCHEM

The effect of O2 concentration on denitrification rate was investigated in sandy loam and clay loam soils. Oxygen at different concentrations and acetylene were recirculated through freshly-collected soil cores. Denitrification rates under anaerobic conditions with argon as the recirculating gas were also determined. The effect of O2 on denitrification rate among cores could then be normalized by expressing the data as percent of the anaerobic rate. Denitrification rates were less than 2% of the anaerobic rate for O2 concentrations greater than 3%, but greatly increased at concentrations below 0.5% O2. For individual cores the denitrification rate increased 2- and 4-fold as the O2 content of the recirculating gas was decreased from 20 to 5%. The pattern of denitrification rate versus O2 concentration was very similar to that generated from the theoretical model of K. A. Smith, which describes the proportional anaerobic volume of soil aggregates as a function of O2 concentration. A soil gas sampling probe is described which uses porous Gortcx tubing buried in horizontal soil layers. The recirculating gas in the denitrificating assay 4system could then be adjusted to match the soil O2 content measured at the time of sampling.

Process modeling of controls on nitrogen trace gas emissions from soils worldwide

Article

Jan 1996

We report on an ecosystem modeling approach that integrates global satellite, climate, vegetation, and soil data sets to (1) examine conceptual controls on nitrogen trace gas (NO, N2O, and N2) emissions from soils and (2) identify weaknesses in our bases of knowledge and data for these fluxes. Nitrous and nitric oxide emissions from well-drained soils were estimated by using an expanded version of the Carnegie-Ames-Stanford (CASA) Biosphere model, a coupled ecosystem production and soil carbon-nitrogen model on a 1° global grid. We estimate monthly production of NO, N2O, and N2 based on predicted rates of gross N mineralization, together with an index of transient water-filled pore space in soils. Analyses of model performance along selected climate gradients support the hypothesis that low temperature restricts predicted N mineralization and trace gas emission rates in moist northern temperate and boreal forest ecosystems, whereas in tropical zones, seasonal patterns in N mineralization result in emission peaks for N2O that coincide with wetting and high soil moisture content. The model predicts the annual N2O:NO flux ratio at a mean value of 1.2 in wet tropical forests, decreasing to around 0.6 in the seasonally dry savannas. Global emission estimates at the soil surface are 6.1 Tg N and 9.7 Tg N yr-1 for N2O and NO, respectively. Tropical dry forests and savannas are identified by using this formulation as important source areas for nitrogen trace gas emissions. Because humans continue to alter these ecosystems extensively for agricultural uses, our results suggest that more study is needed in seasonally dry ecosystems of the tropics in order to understand the global impacts of land use change on soil sources for N2O and NO.

NO2 and N2O emission from soil

Article

Dec 1992

Emission Of NOx (principally NO) and N2O from soils is reviewed with particular emphasis placed on the atmospheric and ecological implications of this source. The photochemistry of these species in the atmosphere is summarized as well as the methods available for the determination of fluxes. Processes which produce and consume both NO and N2O in soils are principally microbiological in nature and are linked directly and indirectly with the chemical and physical factors that control gaseous transport through the soil medium. Linkages among these processes occur over many different temporal and spatial scales which makes interpretation of the available data difficult. A summary of results from laboratory and field studies shows that considerable spatial and temporal variability exists in the emissions. This variability can be related to factors such as temperature, water content, soil composition, nutrient availability, vegetation, disturbances (e.g., burning, agricultural practices), and others. Because NOx and N2O play central roles in many important environmental problems, there is a need for accurate estimates of the magnitude of the soil source, but the large degree of variability in the existing data makes extrapolation highly uncertain. To overcome this uncertainty, models are required which can simulate the processes responsible for production, consumption, and transport of these species at all relevant temporal and spatial scales. Integrated field studies will also be required to validate the model results.

Generalized model for N2 and N2O production from nitrification and denitrification

Article

Sep 1996

We describe a model of N2 and N2O gas fluxes from nitrification and denitrification. The model was developed using laboratory denitrification gas flux data and field-observed N2O gas fluxes from different sites. Controls over nitrification N2O gas fluxes are soil texture, soil NH4, soil water-filled pore space, soil N turnover rate, soil pH, and soil temperature. Observed data suggest that nitrification N2O gas fluxes are proportional to soil N turnover and that soil NH4 levels only impact N2O gas fluxes with high levels of soil NH4 (>3 μg N g−1). Total denitrification (N2 plus N2O) gas fluxes are a function of soil heterotrophic respiration rates, soil NO3, soil water content, and soil texture. N2:N2O ratio is a function of soil water content, soil NO3, and soil heterotrophic respiration rates. The denitrification model was developed using laboratory data [Weier et al, 1993] where soil water content, soil NO3, and soil C availability were varied using a full factorial design. The Weier's model simulated observed N2 and N2O gas fluxes for different soils quite well with r2 equal to 0.62 and 0.75, respectively. Comparison of simulated model results with field N2O data for several validation sites shows that the model results compare well with the observed data (r2 = 0.62). Winter denitrification events were poorly simulated by the model. This problem could have been caused by spatial and temporal variations in the observed soil water data and N2O fluxes. The model results and observed data suggest that approximately 14% of the N2O fluxes for a shortgrass steppe are a result of denitrification and that this percentage ranged from 0% to 59% for different sites.

Modeling Oxygen Diffusion in Aggregated Soils: II. Anaerobiosis in Topsoil Layers

Article

Jul 1994

Denitrification may appear in soil anaerobic regions. In order to estimate the anaerobic fraction of a soil, a finite element method was used to simulate 02 diffusion and consumption in topsoil layers. The soil is considered as a set of aggregates of various shapes and dimensions. Their external transport areas are reduced by contacts between the aggregates and by areas covered with water in the intercrumb pore space. In some simulations, the role of water from the intercrumb pore space in partially occluding the aggregate surface area has not been taken into account. In this case, anaerobiosis only becomes significant near saturation and is due to the reduction of the intercrumb O2 diffusion. When water of the intercrumb pore space is considered, anaerobiosis appears at lower water contents and is due primarily to the reduction of the aggregate external transport area. In this case, O2 concentration in the intercrumb pore space is high at all depths, except near soil saturation. The results of this study were compared with some published relationships between the water saturation level and denitrification, obtained from experimental data. There is a good agreement between our calculations and these functions. In addition, our simulations show that the relationship between the soil anaerobic fraction and the water content is highly dependent on soil structure, soil temperature, and microbial activity. Thus, multiplicative functions are inadequate to describe the effects of water and temperature on soil anaerobiosis or denitrification.

Denitrification response to soil wetting in aggregated and unaggregated soil

Article

Dec 1988
SOIL BIOL BIOCHEM

On etudie les causes de l'augmentation des taux de denitrification observes peu apres l'humidification du sol. Pour un sol bien structure, la discontinuite spatiale du carbone, des nitrates et des bacteries denitrifiantes limite la denetrification. L'augmentation de l'humidite accroit le volume anaerobie et redistribue le carbone et les nitrates solubles. Ceci est valable aussi pour le sol sableux. Dans ce dernier, l'inhibition de l'oxygene est le facteur limitant plutot que la disponibilite du substrat

Studies on NO and N2O fluxes from a wheat field

Article

Jul 1995
ATMOS ENVIRON

The importance of soil parameters and the other environmental conditions that affect emission rates of NO and N20 were studied over a fertilised wheat field. Open-chamber and closed-chamber techniques were used for the flux measurement of NO and N20, respectively. Both gases showed variation in the emission rates which followed the seasonal variation in the available NH4+ and N03− and the moisture content of the soil. Whilst N20 emission rates increased with the moisture content of the soil,NO emissions decreased with increasing soil moisture and rainfall. The results suggested that most soil variables and atmospheric parameters had similar effects on both NO and N2O emission rates but that the overriding influence upon the NOJN2O emission ratio is the soil moisture content. The NO flux showed a clear diurnal variation which followed the surface soil temperature with an activation energy of 108 kJ mol− . The annual NO flux estimated from this study (0.79 kg N ha-−) was approximately half the corresponding N20 (1.42 kg N ha−1).

Soil Microsites as a Source of Denitrification Variability1

Article

Sep 1987

Timothy B. Parkin

The spatial variability exhibited by soil denitriflcation rates is high. As is typical for natural denitriflcation rate measurements, the individual rates of most samples of a given data set are low; however, a few samples often exhibit extremely high rates. Such data are characterized by highly skewed sample frequency distributions. This study was initiated to investigate the underlying mechanisms re-sponsible for these observations. It was found that "hot-spots" of high specific denitriflcation activity were associated with particulate organic C material in the soil. The high specific activities of these hot-spots (incubated under aerobic conditions with no amendments) were similar to the denitrification activity of the bulk soil measured under conditions of anaerobiosis with added glucose and NO 3 . This observation served as the basis of a computer model that evaluates the influence of the density and dispersion pattern of these high activity sites on the measured rates of denitrification. Histograms generated from computer simulations are very similar to histograms obtained for real data, supporting the concept that the patchy dis-persion of particulate organic material in soil is a major factor in-fluencing the variability of natural denitrification rates.

Metabolism of nitric oxide in soil and denitrifying bacteria

Article

Feb 1991
FEMS MICROBIOL ECOL

Production and consumption of NO was measured under anaerobic conditions in a slightly alkaline and an acidic soil as well as in pure cultures of denitrifying Pseudomonas aeruginosa, P. stutzeri, P. fluorescens, Paracoccus denitrificans, Azospirillum brasilense, and A. lipoferum. Growing bacterial cultures reduced nitrate and intermediately accumulated nitrite, NO, N2O, but not NO2. Addition of formaldehyde inhibited NO production and NO consumption. In the presence of acetylene NO was reduced to N2O. Net NO release rates in denitrifying bacterial suspensions and in soil samples decreased hyperbolically with increasing NO up to mixing ratios of about 5 ppmv NO. This behaviour could be modelled by assuming a constant rate of NO production simultaneously with a NO consumption activity that increased with NO until Vmax was reached. The data allowed calculation of the gross rates (P) of NO production, of the rate constants (k), Vmax and Km of NO consumption, and of the NO compensation mixing ratio (mc). In soil, P was larger than Vmax resulting in net NO release even at high NO mixing ratios unless P was selectively inhibited by chlorate + chlorite or by aerobic incubation conditions. In bacteria, Vmax was somewhat larger than P resulting in net NO uptake at high NO mixing ratios. Both P and Vmax were dependent on the supply of electron donor (e.g. glucose). Both in soil (aerobic or anaerobic) and in pure culture, the Km values of NO consumption were in a similar low range of about 0.5–6.0 nM. Anaerobic soil and denitrifying bacteria exhibited mc values of 1.6–2.1 ppmv NO and 0.2–4.0 ppmv NO, respectively.

Soil Properties Affecting Formation of Nitric Oxide by Chemical Reactions of Nitrite1

Article

Sep 1986

Gas chromatography was used to determine the amounts of nitric oxide (NO) in the headspaces above samples of 28 soils that had been autoclaved, treated with nitrite, and sealed in all‐glass flasks with He atmospheres for 18 h. When nitrite was added at a rate of 100 mg N kg ⁻¹ soil, the amounts of NO‐N found ranged from less than 1 to 35 mg kg ⁻¹ soil, and statistical analyses indicated that 95% of the variability in the amounts of NO found among the soils could be explained by a model that considered only soil organic C content, pH, and an interaction of these factors. The formation of CO 2 and the ratios of NO to NO ‐ 3 observed indicate that production of NO cannot be explained solely by self‐decomposition of nitrous acid. When various amounts of soil were added to identical samples of nitrite solution, the amounts of NO‐N found increased with amounts of soil added. These findings indicate that NO is formed by reactions of nitrite with the organic fraction of soils as well as by self‐decomposition of nitrous acid.

Relationships between denitrification, CO2 production and air-filled porosity in soils of different texture and drainage

Article

Dec 1991
SOIL BIOL BIOCHEM

Specifying land surface characteristics in general circulation models: Soil profile data set and derived water-holding capacities

Article

Mar 1993

A standardized global data set of soil horizon thicknesses and textures (particle size distributions) has been compiled from the Food and Agriculture Organization of the United Nations/United Nations Educational, Scientific, and Cultural Organization (FAO/UNESCO) Soil Map of the World, Vols. 2–10 [1971–1981]. This data set was developed for use by the improved land-surface hydrology parameterization designed by Abramopoulos et al. [1988] for the Goddard Institute for Space Studies General Circulation Model II (GISS GCM). The data set specifies the top and bottom depths and the percent abundance of sand, silt, and clay of individual soil horizons in each of the 106 soil types cataloged for nine continental divisions. When combined with the World Soil Data File [Zobler, 1986], the result is a l°×l° global data set of variations in physical properties throughout the soil profile. These properties are important in the determination of water storage in individual soil horizons and exchange of water with the lower atmosphere within global climate models. We have used these data sets, in conjunction with the Matthews [1983] global vegetation data set and texture-based estimates of available soil moisture, to calculate the global distributions of soil profile thickness, potential storage of water in the soil profile, potential storage of water in the root zone, and potential storage of water derived from soil texture. Comparisons with the water-holding capacities used in the GISS Model II show that our derived values for potential storage of water are consistently larger than those previously used in the GISS GCM. Preliminary analyses suggest that incorporation of this data set into the GISS GCM has improved the model's performance by including more realistic variability in land surface properties.

The Role of NO and NO2 in the Chemistry of the Troposphere and Stratosphere

Article

Nov 2003

Paul Jozef Crutzen

Oxides of nitrogen play an important role in the radical chemistry of the atmosphere and in the production and destruction of tropospheric and stratospheric ozone. Ozone is a principal agent in forming the OH radical which attacks inert gases in the troposphere; the acidity of precipitation is in part the result of HNO3 and H2SO4 formed by reactions involving the OH radical. Fast removal processes for oxides of nitrogen in the lower troposphere are described. Long-distance transport of oxides of nitrogen in peroxy-acetyl nitrate also receives attention. In the stratosphere, the participation of NO and NO2 in reactions that influence the equilibrium of photochemical systems may render the total ozone abundance insensitive to additions of oxides of nitrogen.

Influence of oxygen on production and consumption of nitric oxide in soil

Article

Apr 1991

NO and N2O release rates were measured in an acidic forest soil (pH 4.0) and a slightly alkaline agricultural soil (pH 7.8), which were incubated at different O2 concentrations (2) and at different NO concentrations (40 – 1000 ppbv NO). The system allowed the determination of simultaneously operating NO production rates and NO uptake rate constants, and the calculation of a NO compensation concentration. Both NO production and NO consumption decreased with increasing O2. NO consumption decreased to a smaller extent than NO production, so that the NO compensation concentrations also decreased. However, the NO compensation concentrations were not low enough for the soils to become a net sink for atmospheric NO. The release of N2O increased relative to NO release when the gases were allowed to accumulate instead of being flushed out. The forest soil contained only denitrifying, but not nitrifying bacteria, whereas the agricultural soil contained both. Nevertheless, NO release rates were less sensitive to O2 in the forest soil compared to the agricultural soil.

Recovery of nitrification and production of NO and N2O after exposure of soil to acetylene

Article

Jan 1997

Incubation of soil under low partial pressures of acetylene (10 Pa) is a widely used method to specifically inhibit nitrification due to the suicide inhibition of ammonium monooxygenase (AMO), the first enzyme in NH4 + oxidation by nitrifying bacteria. Although the inhibition of AMO is irreversible, recovery of activity is possible if new enzyme is synthesized. In experiments with three different soils, NH4 + concentrations decreased and NO3 – concentrations increased soon after acetylene was removed from the atmosphere. Recovery of NO production started immediately after the removal of acetylene. The release rates of NO and N2O were higher in soil samples which were only preincubated with 10 Pa acetylene than in those which were kept in the presence of 10 Pa acetylene. In the permanent presence of 10 Pa acetylene, NH4 + and NO3 – concentrations stayed constant, and the release rates of NO and N2O were low. These low release rates were apparently due to processes other than nitrification. Our experiments showed that the blockage of nitrification by low (10 Pa) acetylene partial pressures is only reliable when the soil is kept in permanent contact with acetylene.

Production of nitric oxide in Nitrosomonas europaea by reduction of nitrite

Article

Jul 1990

Nitrosomonas europaea and Nitrosovibrio sp. produced NO and N2O during nitrification of ammonium. Less then 15% of the produced NO was due to chemical decomposition of nitrite. Production of NO and especially of N2O increased when the bacteria were incubated under anaerobic conditions at decreasing flow rates of air, or at increasing cell densities. Low concentrations of chlorite (10 M) inhibited the production of NO and N2, but not of nitrite indicating that NO and N2O were not produced during the oxidative conversion of ammonium to nitrite. NO and N2O were produced during reduction of nitrite with hydrazine as electron donor in almost stoichiometric quantities indicating that reduction of nitrite was the main source of NO and N2O.

A method of selective inhibition to distinguish between nitrification and denitrification as sources of nitrous oxide in soil

Article

Jan 1988

Nitrapyrin and C2H2 were evaluated as nitrification inhibitors in soil to determine the relative contributions of denitrification and nitrification to total N2O production. In laboratory experiments nitrapyrin, or its solvent xylene, stimulated denitrification directly or indirectly and was therefore considered unsuitable. Low partial pressures of C2H2 (2.5–5.0 Pa) inhibited nitrification and had only a small effect on denitrification, which made it possible to estimate the contribution of denitrification. The contribution of nitrification was estimated by subtracting the denitrification value from total N2O production (samples without C2H2). The critical C2H2 concentrations needed to achieve inhibition of nitrification, without affecting the N2O reductase in denitrifiers, must be individually determined for each set of experimental conditions.

Acetylene blockage technique leads to underestimation of denitrificat1on rates in oxic soils due to scavenging of intermediate nitric oxide

Article

Jul 1997
SOIL BIOL BIOCHEM

We used the acetylene inhibition technique to measure the denitrification rates, the rates of gross production or net release of NO by denitrification (NOD), and the rates of net release of N2O by denitrification (N2OD) in 29 different soils. The denitrification rates were measured by accumulation of N2O in the presence of 10 kPa acetylene. The rates of NOD and N2OD were measured in the presence of only 10Pa acetylene, which inhibits nitrification, but not denitrification. We assumed that the residual rates of NO and N2O production were due to denitrification. Most of the soils (24 out of 29) showed NOD rates that were higher than denitrification rates themselves. Only five soils with very low NOD rates had denitrification rates that were higher than the NOD rates. The discrepancy between the NOD and the denitrification rates increased with increasing NOD rates. The discrepancy was highest at a soil moisture content of 70% of the water holding capacity and decreased at higher soil moisture. We have shown that the oxidation of NO to NO2 was enhanced by the presence of acetylene at concentrations >0.1% (>0.1 kPa). The resulting NO2 was taken up by soil. We therefore interpret the observed discrepancies between NOD rates and denitrification rates as an artifact created by the acetylene (10 kPa) used in the denitrification assay. The acetylene probably resulted in scavenging of part of the NO that was produced as intermediate in the denitrification sequence and thus could not be further reduced to N2O. Consequently, the denitrification rates were underestimated.

Metabolism of nitric oxide and nitrous oxide during nitrification and denitrification in soil at different incubation conditions

Article

Jul 1992
FEMS MICROBIOL LETT

NO production and consumption rates as well as N2O accumulation rates were measured in a loamy cambisol which was incubated under different conditions (i.e. soil moisture content, addition of nitrogen fertilizer and/or glucose, aerobic or anaerobic gas phase). Inhibition of nitrification with acetylene allowed us to distinguish between nitrification and denitrification as sources of NO and N2O. Under aerobic conditions untreated soil showed very low release of NO and N2O but high consumption of NO. Fertilization with NH4+ or urea stimulated both NO and N2O production by nitrification. Addition of glucose at high soil moisture contents led to increased N2 and N2O production by denitrification, but not to increased NO production rates. Anaerobic conditions, however, stimulated both NO and N2O production by denitrification. The production of NO and N2O was further stimulated at low moisture contents and after addition of glucose or NO3−. Anaerobic consumption of NO by denitrification followed Michaelis-Menten kinetics and was stimulated by addition of glucose and NO3−. Aerobic consumption of NO followed first-order kinetics up to mixing ratios of at least 14 ppmv NO, was inhibited by autoclaving but not by acetylene, and decreased with increasing soil moisture content. The high NO-consumption activity and the effects of soil moisture on the apparent rates of anaerobic and aerobic production and consumption of NO suggest that diffusional constraints have an important influence on the release of NO, and may be a reason for the different behaviour of NO release vs N2O release.

Soil water controls on aerobic soil emission of gaseous nitrogen oxides

Article

Jan 1993
SOIL BIOL BIOCHEM

Soil water content has multiple effects on the emission of gaseous N oxides. To separate and characterize these effects, we monitored rates of CO2, NO2 and N2O evolution and changes in inorganic N concentrations of soil under a factorial combination of three N treatments and three water treatments during a 10-day laboratory incubation study. Because the emission of NO from control and NH4NO3-amended soil varied with the rate of chemoautotrophic NH4+ oxidation and was virtually eliminated by a specific inhibitor of that process [nitrapyrin (2-chloro-6-(trichloromethyl)-pyridine)], we concluded that nitrification was the principal NO source over the entire tested range of soil water potentials (−10 to less than − 1000 kPa). Denitrifikation made no significant contribution to N oxide emissions from even the wettest soil, so nitrifiers were probably also responsible for the much smaller emission of N2O under all treatments. Slower gas diffusion in soil with highest, compared to lowest, water content caused a 3-fold reduction in the mean NO:NO3− product ratio of nitrification, suggesting that the NO produced by NH4+ -oxidizers is further oxidized unless conditions permit its rapid escape to the atmosphere. Nitrapyrin also eliminated the brief burst of N oxide emissions that typically follows wetting of dry soil, indicating that chemoautotrophic NH4+ oxidation is also involved in this phenomenon despite the poor correlation of the burst's magnitude with soil NH4+ or NO2− concentrations. A second burst of N oxide emissions from control or NH4NO3 -amended soil with no inhibitor occurred only where desiccation reduced both NO and CO2 evolution to near zero prior to rewetting the soil after a 7-day drying cycle.

Denitrification coupleD to nitrification in the rhizosphere of rice

Article

Apr 1998
SOIL BIOL BIOCHEM

The N2 flux method, which has only been used for marine sediments, was adapted to a vegetated submerged soil. Denitrification was measured by the emission of N2 from the rice rhizosphere and the bulk soil in flux chambers with a He+O2 (79/21%) atmosphere. Without addition of N-fertilizer, no N2 emission was detected. However, after the addition of urea a high rate of N2 emission was observed. Mean rate was 34.3±3.8 nmol N h−1 cm−2 (±SE). By the application of the nitrification inhibitor methyl fluoride (1%), the N2 emission decreased by nearly 80%, indicating that nitrification of urea-N to nitrate or nitrite was necessary for denitrification. For the localization of this coupled nitrification–denitrification process rice plants were clipped below the water surface. Clipping resulted in a considerable decrease of N2 emission (3.6±0.3 nmol N h−1 cm−2). Measurements of N2O emission gave similar results (0.350±0.035 nmol N h−1 cm−2 for microcosms with intact plants and 0.034±0.3 nmol N h−1 cm−2 for microcosms with clipped plants). These experiments showed that the aerenchymateous rice plants are important for the transport of O2 and N2 into and from the rhizosphere. The rhizosphere is the major site of coupled nitrification–denitrification in planted rice soil.

Nitrification and denitrification as sources of nitric oxide and nitrous oxide in a sandy loam soil

Article

Nov 1993
SOIL BIOL BIOCHEM

Emissions of nitric oxide (NO) and nitrous oxide (N2O) from a freely drained sandy loam, fertilized with (NH4)2SO4 or KNO3 (100 kg N ha−1) with or without the addition of the nitrification inhibitor dicyandiamide (DCD), were measured. The addition of N fertilizers increased emissions of NO and N2O. For plots fertilized with (NH4)2SO4, NO emissions increased from 2.4 to 46.9 ng NO-N m−2 s−1 (2.1–40.5 g NO-N ha−1 day−1), in the first 7 days after fertilizer application. Nitrous oxide emission rates were considerably lower, ranging from 0.95 to 7.4 ng N2O-Nm−2s−1 (0.82–6.4 g N2O-Nha−1 day−1).Nitrification rather than denitrification was the source of the NO emitted from the soil; additions of DCD inhibited the emissions by at least 92%. Nitrous oxide, on the other hand, was a product of both nitrification and denitrification. When soils were dry, N2O was produced predominantly by nitrification and DCD reduced emissions by at least 40%. In contrast, in wet conditions denitrification was the main source of N2O and emissions were not inhibited by DCD.Nitric oxide emissions correlated significantly with soil temperature (30 mm depth), the air temperature inside the chamber, soil available NH4+, and were significantly reduced by watering the soil. Apparent activation energies, calculated from the temperature response in the NO emission rates, ranged from 30 to 71 kJmol−1. It was concluded from the close links between air temperature in the chamber and the NO emission rates that the NO was produced very close to the soil surface.During nitrification the rate of depletion of NH4+-N emitted as NO-N was 5.5 × 10−5s−1. It was estimated that for cultivated fields 0.15–0.75% of the applied NH4+ fertilizer is released as NO.

Microbial production and consumption of greenhouse gases : methane, nitrogen oxides, and halomethanes / [editors by] John E. Willian B. Whitman

Article

Willian Barnaby Whitman

Incluye bibliografía e índice

Effect of Water-Filled Pore Space on Carbon Dioxide and Nitrous Oxide Production in Tilled and Nontilled Soils1

Article

Nov 1984

The percentage of soil pore space filled with water (percent water-filled pores, % WFP), as determined by water content and total porosity, appears to be closely related to soil microbial activity under different tillage regimes. Soil incubated in the laboratory at 60% WFP supported maximum aerobic microbial activity as determined by CO2 production and O2 uptake. In the field, % WFP of surface no-tillage soils (0-75 mm) at four U.S. locations averaged 62% at time of sampling, whereas that for plowed soils was 44%. This difference in % WFP was reflected in 3.4 and 9.4 times greater CO2 and N2O production, respectively, from surface no-tillage soils over a 24-h period as compared to plowed soils. At a depth of 75 to 150 mm, % WFP values increased in both no-tillage and plowed soils, averaging approximately 70% for no tillage compared with 50 to 60% for plowed soils. Production of CO2 in the plowed soils was enhanced by the increased % WFP, resulting in little or no difference in CO2 production between tillage treatments. Nitrous oxide production, however, remained greater under no-tillage conditions. Substantially greater amounts of N2O were produced from the N-fertilized soils, regardless of tillage practice. Production of CO2 and N2O was primarily related to the % WFP of tillage treatments although, in several instances, soil-water-soluble C and NO-3 levels were important as well. Calculations of relative aerobic microbial activity between no-tillage and plowed soils, based on differences in % WFP relative to maximum activity at 60%, indicated linear relationships for CO2 and N2O production between WFP values of 30 to 70%. Below 60% WFP, water limits microbial activity, but above 60%, aerobic microbial activity decreases - - -apparently the result of reduced aeration.

Dickinson RE, Cicerone RJ.. Future global warming from atmospheric trace gases. Nature 319: 109-115

Article

Jan 1986

Human activity this century has increased the concentrations of atmospheric trace gases, which in turn has elevated global surface temperatures by blocking the escape of thermal infrared radiation. Natural climate variations are masking this temperature increase, but further additions of trace gases during the next 65 years could double or even quadruple the present effects, causing the global average temperature to rise by at least 1 °C and possibly by more than 5 °C. If the rise continues into the twenty-second century, the global average temperature may reach higher values than have occurred in the past 10 million years.

Climate-chemical interactions and effects of changing atmospheric trace gases

Article

Sep 1987

The paper considers trace gas-climate effects including the greenhouse effect of polyatomic trace gases, the nature of the radiative-chemical interactions, and radiative-dynamical interactions in the stratosphere, and the role of these effects in governing stratospheric climate change. Special consideration is given to recent developments in the investigations of the role of oceans in governing the transient climate responses, and a time-dependent estimate of the potential trace gas warming from the preindustrial era to the early 21st century. The importance of interacting modeling and observational efforts is emphasized. One of the problems remaining on the observational front is the lack of certainty in current estimates of the rate of growth of CO, O3, and NOx; the primary challenge is the design of a strategy that will minimize the sampling errors.

Simultaneous field measurements of biogenic emissions of nitric oxide and nitrous oxide

Article

Feb 1987

Seasonal and diurnal emissions of NO and N2O from agricultural sites in Jamestown, Virginia and Boulder, Colorado are estimated in terms of soil temperature; percent moisture; and exchangeable nitrate, nitrite, and ammonium concentrations. The techniques and procedures used to analyze the soil parameters are described. The spatial and temporal variability of the NO and N2O emissions is studied. A correlation between NO fluxes in the Virginia sample and nitrate concentration, temperature, and percent moisture is detected, and NO fluxes for the Colorado site correspond with temperature and moisture. It is observed that the N2O emissions are only present when percent moisture approaches or exceeds the field capacity of the soil. The data suggest that NO is produced primarily by nitrification in aerobic soils, and N2O is formed by denitrification in anaerobic soils.

Production of NO and N2O by Soil Nitrifying Bacteria

Article

Jan 1982

The composition of the atmosphere is influenced both directly and indirectly by biological activity. Evidence is presented here to suggest that nitrification in soil is a potentially significant source of both NO and N2O. Between 0.3 and 10% of the ammonium oxidized by cultures of the soil bacterium Nitrosomonas europaea is converted to these gases. The global source for NO associated with nitrification could be as large as 15,000,000 tonnes N/yr, with a source for N2O of 5,000,000-10,000,000 tonnes N/yr. Nitric oxide has a key role in tropospheric chemistry, participating in a complex set of reactions regulating OH and O3. Nitrous oxide is a dominant source of stratospheric NO and has a significant influence on climate.

Identification of the sources of nitrous oxide produced by oxidative and reductive processes in Nitrosomonas europaea

Article

Apr 1972

1. Cells of Nitrosomonas europaea produced N(2)O during the oxidation of ammonia and hydroxylamine. 2. The end-product of ammonia oxidation, nitrite, was the predominant source of N(2)O in cells. 3. Cells also produced N(2)O, but not N(2) gas, by the reduction of nitrite under anaerobic conditions. 4. Hydroxylamine was oxidized by cell-free extracts to yield nitrite and N(2)O aerobically, but to yield N(2)O and NO anaerobically. 5. Cell extracts reduced nitrite both aerobically and anaerobically to NO and N(2)O with hydroxylamine as an electron donor. 6. The relative amounts of NO and N(2)O produced during hydroxylamine oxidation and/or nitrite reduction are dependent on the type of artificial electron acceptor utilized. 7. Partially purified hydroxylamine oxidase retained nitrite reductase activity but cytochrome oxidase was absent. 8. There is a close association of hydroxylamine oxidase and nitrite reductase activities in purified preparations.

The biological role of nitric oxide in bacteria. Arch. Microbiol.160(4), 253-264

Article

Feb 1993

Walter G. Zumft

Quantification and Removal of Some Contaminating Gases from Acetylene Used to Study Gas-Utilizing Enzymes and Microorganisms

Article

Mar 1987

Acetylene generated from various grades of calcium carbide and obtained from commercial- and purified-grade acetylene cylinders was shown to contain high concentrations of various contaminants. Dependent on the source of acetylene, these included, at maximal values, H(2) (0.023%), O(2) (0.779%), N(2) (3.78%), PH(3) (0.06%), CH(4) (0.073%), and acetone (1 to 10%). The concentration of the contaminants in cylinder acetylene was highly dependent on the extent of cylinder discharge. Several conventional methods used to partially purify cylinder acetylene were compared. A small-scale method for extensively purifying acetylene is described. An effect of acetylene quality on acetylene reduction assays conducted with purified nitrogenase from Azotobacter vinelandii was demonstrated.

Dinitrogen Production from Nitrite by a Nitrosomonas Isolate

Article

Nov 1986

Mark Poth

A chemolithotrophic ammonium-oxidizing bacterium that was able to reduce NO(2) to N(2) (m/z 30) while oxidizing ammonium under conditions of oxygen stress was isolated from stream sediments. Energy was derived from ammonium oxidation, as evidence by growth, with CO(2) serving as the sole C source. The organism was a gram-negative, motile, short rod that failed to grow either aerobically or anaerobically in heterotroph media. The organism was identified as a Nitrosomonas sp.

15N Kinetic Analysis of N2O Production by Nitrosomonas europaea: an Examination of Nitrifier Denitrification

Article

Jun 1985

A series of N isotope tracer experiments showed that Nitrosomonas europaea produces nitrous oxide only under oxygen-limiting conditions and that the labeled N from nitrite, but not nitrate, is incorporated into nitrous oxide, indicating the presence of the "denitrifying enzyme" nitrite reductase. A kinetic analysis of the m/z 44, 45, and 46 nitrous oxide produced by washed cell suspensions of N. europaea when incubated with 4 mM ammonium (99% N) and 0.4 mM nitrite (99% N) was performed. No labeled nitrite was reduced to ammonium. All labeled material added was accounted for as either nitrite or nitrous oxide. The hypothesis that nitrous oxide is produced directly from nitrification was rejected since (i) it does not allow for the large amounts of double-labeled (m/z 46) nitrous oxide observed; (ii) the observed patterns of m/z 44, 45, and 46 nitrous oxide were completely consistent with a kinetic analysis based on denitrification as the sole mechanism of nitrous oxide production but not with a kinetic analysis based on both mechanisms; (iii) the asymptotic ratio of m/z 45 to m/z 46 nitrous oxide was consistent with denitrification kinetics but inconsistent with nitrification kinetics, which predicted no limit to m/z 45 production. It is concluded that N. europaea is a denitrifier which, under conditions of oxygen stress, uses nitrite as a terminal electron acceptor and produces nitrous oxide.

Influence of O2 availability on NO and N2O release by nitrification and denitrification in soils

Abstract

No full-text available

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