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•Biochar added at the beginning of composting reduced 55% of total N2O emission.•N2O emission showed significant relationships with most environmental factors.•Biochar mitigated N2O ...mainly by regulating the physicochemical properties of compost.•Genes and enzymes influenced the overall effect of environmental factors to N2O.
The effects and mitigation mechanisms of biochar added at different composting stages on N2O emission were investigated. Four treatments were set as follows: CK: control, BB10%: +10 % biochar at beginning of composting, BB5%&T5%: +5% biochar at beginning and + 5 % biochar after thermophilic stage of composting, BT10%: +10 % after thermophilic stage of composting. Results showed that treatment BB10%, BB5%&T5%, and BT10% reduced total N2O emissions by 55 %, 37 %, and 36 %, respectively. N2O emission was closely related to most physicochemical properties, while it was only related to amoA gene and hydroxylamine oxidoreductase. Different addition strategies of biochar changed the contributions of physicochemical properties, functional genes and enzymes to N2O emission. Organic matter and C/N contributed 23.7 % and 27.6 % of variations in functional gene abundances (P < 0.05), respectively. pH and C/N (P < 0.05) contributed 37.3 % and 17.3 % of variations in functional enzyme activities. These findings provided valuable insights into mitigating N2O emissions during composting.
The microbial reduction of N2O serves as a “gatekeeper” for N2O emissions, determining the flux of N2O release into the atmosphere. Estuaries are active regions for N2O emissions, but the microbial ...functions of N2O-reducing bacteria in estuarine ecosystems are not well understood. In this study, the 15N isotope tracer method, qPCR, and high-throughput sequencing were used to analyze N2O production, reduction, and emission processes in surface sediments of the Pearl River Estuary. The 15N isotope tracer experiment showed that the N2O production rates declined and the N2O reduction potential (Rr, the ratio of N2O reduction rates to N2O production rates) increased from upstream to downstream of the Pearl River Estuary, leading to a corresponding decrease of the N2O emission rates from upstream to downstream. The gene abundance ratio of nosZ/nir gradually increased from upstream to downstream and was negatively correlated with the water N2O saturation. The gene abundance of nosZ II was significantly higher than that of nosZ I in the estuary, and the nosZ II/nosZ I abundance ratio was positively correlated with N2O reduction potential. Furthermore, the community composition of NosZ-I- and NosZ–II–type N2O-reducing bacteria shifted from upstream to downstream. NosZ–II–type N2O-reducing bacteria, especially Myxococcales, Thiotrichales, and Gemmatimonadetes species, contributed to the high N2O reduction potential in the downstream. Our results suggest that NosZ–II–type N2O-reducing bacteria play a dominant role in determining the release potential of N2O from sediments in the Pearl River Estuary. This study provides a new insight into the function of microbial N2O reduction in estuarine ecosystems.
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•The N2O reduction potential increased from upstream to downstream in the PRE.•nosZ II/nosZ I ratio positively correlated with N2O reduction potential.•The community of N2O-reducing bacteria shifted from the upstream to downstream.•NosZ–II–type N2O-reducing bacteria determined the N2O release potential in the PRE.
As aquatic-terrestrial ecotones, riparian zones are hotspots not only for denitrification but also for nitrous oxide (N2O) emission. Due to the potential role of nosZ II in N2O mitigation, emerging ...studies in terrestrial ecosystems have taken this newly reported N2O-reducer into account. However, our knowledge about the interactions between denitrification activities and both N2O-producers and reducers (especially for nosZ II) in aquatic ecosystems remains limited. In this study, we investigated spatiotemporal distributions of in situ N2O flux, potential N2O production rate, and potential denitrification rate, as well as of the related genes in a riparian zone of Baiyangdian Lake. Real-time quantitative PCR (qPCR) and high-throughput sequencing targeted functional genes were used to analyze the denitrifier communities. Results showed that great differences in microbial activities and abundances were observed between sites and seasons. Waterward sediments (constantly flooded area) had the lowest N2O production potential in both seasons. Not only the environmental factors (moisture content, NH4+ content and TOM) but also the community structure of N2O-producers and N2O-reducers (nirK/nirS and nosZ II/nosZ I ratios) could affect the potential N2O production rate. The abundance of the four functional genes in the winter was higher than in the summer, and the values all peaked at the occasionally flooded area in the winter. The dissimilarity in community composition was mainly driven by moisture content. Altogether, we propose that the N2O production potential was largely regulated by the community structure of N2O-producers and N2O-reducers in riparian zones. Increasing the constantly flooded area and reducing the occasionally flooded area of lake ecosystems may help reduce the level of denitrifier-produced N2O.
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•The constantly flooded area had lower N2O production potential than other areas.•Denitrifying community structure determined the N2O production potential.•Moisture content was the main driver for dissimilarity in community composition.•nosZ II had a higher diversity in the riparian zone than in other environments.
Soils, a sink for N₂O? A review CHAPUIS-LARDY, LYDIE; WRAGE, NICOLE; METAY, AURÉLIE ...
Global change biology,
January 2007, Letnik:
13, Številka:
1
Journal Article
Recenzirano
Soils are the main sources of the greenhouse gas nitrous oxide (N₂O). The N₂O emission at the soil surface is the result of production and consumption processes. So far, research has concentrated on ...net N₂O production. However, in the literature, there are numerous reports of net negative fluxes of N₂O, (i.e. fluxes from the atmosphere to the soil). Such fluxes are frequent and substantial and cannot simply be dismissed as experimental noise. Net N₂O consumption has been measured under various conditions from the tropics to temperate areas, in natural and agricultural systems. Low mineral N and large moisture contents have sometimes been found to favour N₂O consumption. This fits in with denitrification as the responsible process, reducing N₂O to N₂. However, it has also been reported that nitrifiers consume N₂O in nitrifier denitrification. A contribution of various processes could explain the wide range of conditions found to allow N₂O consumption, ranging from low to high temperatures, wet to dry soils, and fertilized to unfertilized plots. Generally, conditions interfering with N₂O diffusion in the soil seem to enhance N₂O consumption. However, the factors regulating N₂O consumption are not yet well understood and merit further study. Frequent literature reports of net N₂O consumption suggest that a soil sink could help account for the current imbalance in estimated global budgets of N₂O. Therefore, a systematic investigation into N₂O consumption is necessary. This should concentrate on the organisms, reactions, and environmental factors involved.
In the automobile sector, the removal of pollutants (NOx) generated by diesel engines remains a fascinating scientific and technological issue. The emissions of the vehicle are in compliance with BS ...III standards. The Indian government came up with the Bharat Stage Emission Standards in order to place limitations on the amount of air pollution that can be released into the atmosphere by machinery that uses an internal combustion engine, such as automobiles. The central pollution control board, which is an agency under the ministry of environment and forests, is in charge of defining the requirements and the timetable for their implementation. The brake-specific fuel consumption decreased by 4.5% and 8%, while brake thermal efficiency rose by 5.5% and 14.6%. However, with CO additions of 1000 and 2000 ppm, respectively, nanoparticles increased the chemical processes and decreased the ignition delay time by 3.03% and 5.45%. The amounts of CO, HC, and NOx emissions decreased by 14.6%, 20.8%, 6.2%, and 13.4%, respectively. The catalytic oxidation of carbon monoxide is an important reaction in both commercial and academic settings. For the past years, hoplite, which is composed of copper-manganese oxides, has served as a low-cost and widely available carbon monoxide abatement catalyst.
Yield-scaled nitrous oxide (N2O) emission (YSNE) has been recognized as a means for developing appropriate nitrogen (N) management strategies to balance food security and mitigating N2O emissions. To ...better understand and use the concept of YSNE, it is essential to be assessed under various field conditions. The main objectives of this study were to assess the relationship between N inputs and YSNE with published results and identify response patterns of YSNE to N inputs. We assessed the relationship between N inputs and YSNE using published results encompassing 1800 observations (published from 1980 to 2020) from maize, rice, and wheat crops worldwide. Background yield-scaled N2O emission (BYSNE; a YSNE in the condition of zero N input) was significantly different by crop type. Rice (90.8 ± 12.9 g N2O−N Mg−1) had lower BYSNE compared to maize (174.2 ± 30.1 g N2O−N Mg−1) and wheat (325.4 ± 41.8 g N2O−N Mg−1). BYSNE was positively correlated with annual mean temperature in maize, rice, and wheat fields. BYSNE was negatively correlated with soil total nitrogen contents in rice fields. Over 60% data set showed a positive relationship between N inputs and YSNE in all three crops studied. A small proportion of the dataset had an optimum N rate that minimized YSNE. The results suggest that in general, lower N input rates result in lower YSNE in crop production. YSNE can be reduced in three ways: increasing yields (Type 1), reducing N2O emissions (Type 2), and both increasing yields and reducing N2O emissions (Type 3). To identify appropriate measures, we suggest a N2O emission-yield curve combining responses of yields and N2O emissions to N inputs. In type 1, 2, and 3 measures, an N2O emission-yield curve is shifted to the right, down, and both right and down, respectively. Through identifying direction and magnitude of the shifting, the effects of applied measures on yields and N2O emission in N input levels can be easily compared and recognized. This study provided insights into the nature of YSNE and how YSNE responds to N inputs. It also suggested an N2O emission-yield curve, which can be useful to identify how certain measures affect both N2O emissions and crop yields. The information can be useful for scientific community and policymakers developing appropriate N management strategies to balance food security and the mitigation of N2O emissions.
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•Background yield-scaled N2O emission (BYSNE) varied by crop type.•BYSNE was positively correlated with annual mean temperature.•Over 60% data sets showed consistently lower yield-scaled N2O emission as N input decreased.•N2O emissionyield curve showed the effects of mitigation measures on both yields and N2O emission.
The last step of denitrification, i.e. the reduction of N2O to N2, has been intensively studied in the laboratory to understand the denitrification process, predict nitrogen fertiliser losses, and to ...establish mitigation strategies for N2O. However, assessing N2 production via denitrification at large spatial scales is still not possible due to lack of reliable quantitative approaches. Here, we present a novel numerical “mapping approach” model using the δ15Nsp/δ18O slope that has been proposed to potentially be used to indirectly quantify N2O reduction to N2 at field or larger spatial scales. We evaluate the model using data obtained from seven independent soil incubation studies conducted under a He–O2 atmosphere. Furthermore, we analyse the contribution of different parameters to the uncertainty of the model. The model performance strongly differed between studies and incubation conditions. Re-evaluation of the previous data set demonstrated that using soils-specific instead of default endmember values could largely improve model performance. Since the uncertainty of modelled N2O reduction was relatively high, further improvements to estimate model parameters to obtain more precise estimations remain an on-going matter, e.g. by determination of soil-specific isotope fractionation factors and isotopocule endmember values of N2O production processes using controlled laboratory incubations. The applicability of the mapping approach model is promising with an increasing availability of real-time and field based analysis of N2O isotope signatures.
•An isotope based model to quantify N2O reduction to N2 at field scales are presented.•Model evaluation were conducted based on seven independent studies.•The model performance strongly differed between studies and incubation conditions.•Using soils-specific instead endmember values largely improve model performance.
Agricultural management practices can induce changes in soil aggregation structure that alter the microbial nitrous oxide (N2O) production and reduction processes occurring at the microscale, leading ...to large-scale consequences for N2O emissions. However, the mechanistic understanding of how organic fertilization affects these context-dependent small-scale N2O emissions and associated key nitrogen (N) cycling microbial communities is lacking. Here, denitrification gas (N2O, N2) and potential denitrification capacity N2O/(N2O + N2) were assessed by automated gas chromatography in different soil aggregates (>2 mm, 2–0.25 and <0.25 mm), while associated microbial communities were assessed by sequencing and qPCR of N2O-producing (nirK and nirS) and reducing (nosZ clade I and II) genes. The results indicated that organic fertilization reduced N2O emissions by enhancing the conversion of N2O to N2 in all aggregate sizes. Moreover, potential N2O production and reduction hotspots occurred in smaller soil aggregates, with the degree depending on organic fertilizer type and application rate. Further, significantly higher abundance and diversity of nosZ clades relative to nirK and nirS revealed complete denitrification promoted through selection of denitrifying communities at microscales favouring N2O reduction. Communities associated with high and low emission treatments form modules with specific sequence types which may be diagnostic of emission levels. Taken together, these findings suggest that organic fertilizers reduced N2O emissions through influencing soil factors and patterns of niche partitioning between N2O-producing and reducing communities within soil aggregates, and selection for communities that overall are more likely to consume than emit N2O. These findings are helpful in strengthening the ability to predict N2O emissions from agricultural soils under organic fertilization as well as contributing to the development of net-zero carbon strategies for sustainable agriculture.
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•N2O production and reduction hotspots occurred in smaller soil aggregates.•Organic fertilization reduced N2O emissions by promoting complete denitrification.•Reduction is linked to a dynamic community with reduced NO3− to N2O-reducer ratios.•Emission is linked to interaction between soil condition and denitrifies selection.
Biochar is an efficacious amendment for mitigating nitrous oxide (N2O) emissions in soils. Nevertheless, the underlying mechanisms responsible for reduced N2O emissions by biochar in paddy soils ...remain inadequately elucidated. Here, using two typical paddy soils with contrasting pH values (5.40 and 7.56), the N2 and N2O fluxes and the associated functional genes were investigated in soil amended with varying amounts of biochar (0%, 0.5%, and 5%, weight/weight) via soil slurry incubation integrated with the N2/Ar technique and qPCR analysis. The results showed that N2O fluxes were significantly (p < 0.05) reduced by 0.65–3.64 times following biochar amendment, concomitant with a significant (p < 0.05) increase in N2 fluxes (5.47–46.14%) in both acidic and alkaline paddy soils. As a result, the N2O/(N2O + N2) ratios were significantly (p < 0.05) reduced by 1.53–4.65 fold in both soil types. In acidic paddy soils, the enhanced denitrification rates and the decreased N2O/(N2O + N2) ratios exhibited a strong correlation with increased pH values. In alkaline paddy soil, these changes were ascribed to the enhanced nosZ Clade I gene abundance and nosZ/(nirS + nirK) ratio. Our findings reveal that biochar primarily mitigates N2O emissions in paddy soils by promoting its reduction to N2.
Biochar promotes denitrification in acidic paddy soil by increasing soil pH and enhances the same process in alkaline paddy soil by increasing nosZ gene abundance, resulting in reduced N2O emissions.
Bacteria and archaea colonizing on biochar have been reported to possess nitrogen-metabolizing abilities. A larger specific surface area of biochar may enhance the activities of nitrous oxide ...(N2O)-reducing microbes, thereby mitigating N2O emission; however, the underlying mechanisms remain unclear. A 56-day incubation assay was performed with five treatments: no addition, urea only, and addition of three types of biochars (with different specific surface areas: 1193, 2023, and 2773 m2 g−1) combined with urea. N2O emission increased with the specific surface area of biochar up to 2023 m2 g−1 and decreased thereafter by 37% as compared with the urea only addition. By increasing soil pH, C/N ratio, nitrogen availability, and cation exchange capacity, the biochar with the largest specific surface area decreased soil N2O emission by affecting the diversity, abundance, and composition of total bacteria and N2O-producing microbial communities. A larger specific surface area of biochar correlated with a higher abundance of nitrogen-fixing (nifH), -nitrifying (amoA), and -denitrifying (nirK, nirS, and nosZ) genes. An increased abundance of ammonia-oxidizing bacteria and archaea, in the biochar with a smaller specific surface area, resulted in higher N2O emission. As the abundance of nosZ increased, the addition of the biochar with the largest specific surface area resulted in a higher ratio of nosZ/(amoA + nirS + nirK), leading to decreased N2O emission. Furthermore, the abundance of nifH, amoA, nirK, and nosZ on biochar (extraction from soil after 56-day incubation) was positively correlated with that in soil. Thus, the relative specific surface area of biochar should be taken into consideration when using it in agriculture, as our results show that biochars with larger specific surface areas decrease N2O emission by recruiting N2O-reducing microbes and upregulating the abundance of nitrogen-fixing, -nitrifying, and -denitrifying genes.
•A larger biochar surface area decreases soil N2O emission.•Bacteria stimulated by biochar possesses nitrogen-metabolizing activity.•N2O reducing microbes on biochar and in the soil are positively related.•nosZ, a functional marker gene, localization on biochar decreases soil N2O emission.
