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Nitrous oxide (N 2 O) is a significant contributor to global warming and possesses an ozone-depleting impact nearly 298 times that of CO 2 . To reduce N 2 O emissions, the newly-discovered nod gene which can directly convert NO into N 2 and O 2 was successfully cloned from the anaerobic denitrification sludge. The recombinant plasmid containing the nod gene was built, and the expression of nod gene in Escherichia coli was determined, leading to the construction of recombinant engineering bacteria. Results showed that the recombinant engineering bacteria E. coli BL21 (DE3)-pET28a-nod could autonomously degrade NO, with a degradation rate of 72 % within 48 h, and could produce 2479.72 ppm of N 2 and 75.12 mL of O 2 . The cumulative O 2 production of the sludge sample and recombinant E. coli within 8 h was 1.75 mL and 8.45 mL, respectively. The cumulative O 2 production of recombinant E. coli was at least 4.82 times higher than that of the sludge sample. The investigation proposed a new biodegradation pathway for nitrogen pollution., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Elucidating the responses of soil microbial functional groups to changes in stand density is crucial for understanding the sustainability of forest development. In this study, we obtained soil samples from Robinia pseudoacacia plantations of three different stand densities (low, middle, and high densities of 750, 1125, and 1550 trees ha -1 , respectively) in the hilly and gully region of the Loess Plateau, China. We sought to determine the effects of stand density on the structure of soil microbial functional groups. Stand density had no significant effects on species diversity indices of fungal trophic modes or bacterial functional groups involved in carbon (C) cycling and nitrogen (N) cycling. However, differences in stand density substantially altered the composition of fungal functional groups. In low-density plantations, saprophytic fungi were the main trophic mode, with a high relative abundance of ∼62 %, whereas the fungal communities associated with middle- and high-density plantations were dominated by other fungi with a combined trophic mode, which accounted for ∼43 % and ∼41 % of the fungal trophic modes, respectively. Furthermore, we detected increases in the relative abundance of plant pathogens, nitrifiers, and nitrous oxide-denitrifying bacteria with increasing stand density. Results of the Monte Carlo test showed that soil pH influenced the composition of soil fungal (but not bacterial) groups. These findings suggested that a high density of trees might inhibit the decomposition of recalcitrant organic material and stimulate nitrous oxide emission, consequently decreasing soil nutrient availability and stimulating soil N loss. Moreover, high-density stands might increase the potential risk for plant disease. Overall, the present study suggested that reducing stand density to coverage between 750 and 1125 trees ha -1 would increase soil nutrient availability and prevent N loss from the soil. To verify these suppositions, further research is needed to determine the links between microbial functional groups composition and soil biogeochemistry., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

NO 2 − plays a crucial role in regulating N 2 O formation from the soil, while how it affects the production of soil N 2 O is still not well understood. In this study, N 2 O and NO emissions from an agricultural field of the North China Plain (NCP) were comparatively investigated under five different fertilizer treatments (NH 4 +, NO 3 −, NO 2 −, NH 4 + + NO 2 − and NO 3 − + NO 2 −). Additionally, soil NH 4 +, NO 2 − and NO 3 − concentrations and the abundance of functional genes associated with nitrogen cycling were also analyzed in the incubation experiment. The results showed that the N 2 O average fluxes from the complex treatments of NO 2 − + NO 3 - were 1.4–2.4 times the sum of those from the separate treatments of NO 2 - and NO 3 - whereas from the complex treatments of NO 2 - + NH 4 + were a factor of 1-1.4 larger than those from the separate treatments of NO 2 − and NH 4 +, indicating the coupling interaction of NO 2 − with NH 4 + or NO 3 − makes a remarkable contribution to N 2 O emission from the soil. Significant reduction of the activity of N 2 O reductase was found in the soil with the addition of NO 2 −, which favored the accumulation of N 2 O formed through nitrification of NH 4 + and denitrification of NO 2 −, resulting in relatively high N 2 O emissions from the complex treatments. As the intermediate product of nitrification and denitrification, NO 2 − produced is also expected to interact with NH 4 + or NO 3 - to promote N 2 O emission from the soil, especially during fertilization events when NO 2 − is easily accumulated due to the acceleration of the nitrification and denitrification processes. Unlabelled Image • Coupling interaction of NO 2 − with NH 4 + or NO 3 − is a great source of N 2 O emission. • The addition of NO 2 − could significantly promote the N 2 O emission. • The activity of N 2 O reductase decreased after the introduce of NO 2 −. [ABSTRACT FROM AUTHOR]

This study intended to evaluate the combined effects of both biochar and organic fertilizer on nitrous oxide (N 2 O) fluxes and composition of nitrifier and denitrifier of saline-alkali soil. Therefore, four different treatments such as CK (only chemical fertilizer), B (only biochar), M (only organic fertilizer), BM (B:M = 1:1) were used in this experiment. The results showed that N 2 O emissions were decreased in B and BM treatments compare to the control. In contrast, N 2 O emissions were highest before day 12 but lowest after day 19 in M treatment compare to the control. Application of biochar, organic fertilizer and biochar plus organic fertilizer decreased the nirS and nirK genes copies and enhanced the nosZ gene copies which resulting in the lower N 2 O fluxes. The ammonia-oxidizing bacteria (AOB) amoA and nirK genes copies were significantly increased by organic fertilizer before day 12, leading to high N 2 O emissions. The genera Nitrosospira (AOB) and Nitrososphaera (ammonia-oxidizing archaea, AOA) assumed absolute superiority. Additionally, Nitrosospira (AOB) was also appeared in nirK -type denitrifiers, illustrating denitrification was carried out by nitrifiers. The genera Azospirillum (nirS), Burkholderia (nosZ) and Polymorphum (nosZ) were dominant in CK. There was only one dominant genus, Mesorhizobium (nosZ) in the B treatment. The genera Mesorhizobium (nirK), Azoarcus (nirS), Kocuria (nirS) and Pseudomonas (nosZ) occupied the main status in the M treatment. The relative abundance of Rhodanobacter (nirS) and Azospirillum (nosZ) were higher in the BM treatment compared with other treatments. Soil water content (SWC), pH, NH 4 +-N and NO 3 −-N were the main factors affecting AOB and denitrifiers, which influencing N 2 O emissions. Overall, combined application of biochar and organic fertilizer can reduce the N 2 O emission where AOB and nirK -type denitrifier were the main contributors to the N 2 O emission. Unlabelled Image • Combined application of biochar and organic fertilizer decreased the N 2 O emission. • Biochar plus organic fertilizer decreased the nirS and enhanced the nosZ abundances. • The genus Nitrosospira was the main contributor for N 2 O emission. • SWC, pH, NH 4 +-N and NO 3 −-N were the main factors affecting AOB and denitrifiers, and then influencing N 2 O emissions. [ABSTRACT FROM AUTHOR]

The global climate change is related with greenhouse gas emission from cultivated soils – carbon dioxide, methane and nitrous oxide. The emissions of N 2 O also have negative influence on ozone layer of our planet. The major source of the nitrous oxide is denitrification process in soil, which controlled by specific soil microbe society. The pot experiment with flooding to accelerate the denitrification process and the application of the monosilicic acid as a source of soluble form of Si was carried out with barley. Several forms of nitrous oxide emission (unlimited carbon denitrification and potential denitrification with or without ethylene application) were measured. The obtained data showed that the application of monosilicic acid to brown soil when growing barley under conditions of soil flooding has a significant effect on nitrogen emission and can change the N 2 O:N 2 ratio. The application of the monosilicic acid reduced the uC-D N 2 O emission, while increased the PD N emission. Generally the application of the water soluble Si decreased the N 2 O:N 2 ratio. We suggested that the presence of monosilicic acid in the system provides a more complete denitrification process with the formation of N 2 in the NO 3 − → NO 2 − → NO→N 2 O → N 2 reaction sequence, while the deficiency of bioactive Si mainly provides the formation and emission of N 2 O. Considering that N 2 is not a greenhouse gas, we can conclude that application of monosilicic acid to the soil can reduce greenhouse gas emissions and reduce the impact of global climate change on agricultural activity. Unlabelled Image • The application of monosilicic acid increases barley resistance under hypoxia. • High concentration of the monosilicic acid in flooded soil provides N 2 emission increasing and reduction N 2 O emission. • Increasing of the monosilicic acid in the soil provides more complete denitrification process in soil. [ABSTRACT FROM AUTHOR]

Concentrations and emissions of greenhouse gases CO 2 , CH 4 , and N 2 O commonly are examined individually in aquatic environments in which each is expected to be relatively important; however, their co-occurrence and dynamic interactions in fluvial settings could provide important information about their controlling biogeochemical processes and potential contributions to global climate change. Spatial and temporal variability of CH 4 , N 2 O, and CO 2 concentrations were measured from June 1999 to September 2003 in two nitrate-rich (40–1200 μM) streams draining agricultural land in the midwestern USA that differed ~13-fold in flow. Seasonal (biweekly), diel (hourly), and transport-oriented (reach-scale) sampling approaches were compared. Dissolved gas concentrations exceeded atmospheric equilibrium values up to 700- and 16-fold, for CH 4 and N 2 O, respectively. Mean concentrations were higher in the larger stream than in the smaller stream. In both streams, CH 4 emissions were generally higher in summer-fall and negatively correlated with flow and NO 3 − concentration while N 2 O emissions were generally higher in winter/spring and positively correlated with flow and NO 3 −. In the small stream, diel variations in the concentrations, emissions, and isotopic compositions of CH 4 , N 2 O, and NO 2 − resulted from diel variations in sources, sinks, and air-water gas exchange velocities. Seasonal mean total (CH 4 + N 2 O) area-normalized emission rates, expressed as CO 2 warming potential equivalents, were similar for the two streams, but the total reach-scale emission rate for the larger stream, including CO 2 , was about 2.9 times that of the smaller stream (131.6 vs 46.0 kg CO 2 equivalents km−1 day−1, respectively). The CH 4 contribution to this flux was 9–28%, despite the relatively high NO 3 − and O 2 concentrations in the streams, indicating contributions from upwelling groundwater or reactions in streambed sediment. Unlabelled Image • CH 4 concentrations were higher than N 2 O concentration in nitrate-rich streams. • CH 4 and N 2 O concentrations exhibited seasonal, synoptic and diel variations. • CH 4 and N 2 O concentrations were inversely correlated seasonally. • Combined CH 4 and N 2 O emissions resulted in seasonally constant global warming potentials. [ABSTRACT FROM AUTHOR]

This study argues that several metrics are necessary to build up a picture of yield gain and nitrogen losses for ryegrass sheep pastures. Metrics of resource use efficiency, nitrous oxide emission factor, leached and emitted nitrogen per unit product are used to encompass yield gain and losses relating to nitrogen. These metrics are calculated from field system simulations using the DAYCENT model, validated from field sensor measurements and observations relating to crop yield, fertilizer applied, ammonium in soil and nitrate in soil and water, nitrous oxide and soil moisture. Three ryegrass pastures with traditional management for sheep grazing and silage are studied. As expected, the metrics between long-term ryegrass swards in this study are not very dissimilar. Slight differences between simulations of different field systems likely result from varying soil bulk density, as revealed by a sensitivity analysis applied to DAYCENT. The field with the highest resource use efficiency was also the field with the lowest leached inorganic nitrogen per unit product, and vice versa. Field system simulation using climate projections indicates an increase in nitrogen loss to water and air, with a corresponding increase in biomass. If we simulate both nitrogen loss by leaching and by gaseous emission, we obtain a fuller picture. Under climate projections, the field with the lowest determined nitrous oxide emissions factor, had a relatively high leached nitrogen per product amongst the three fields. When management differences were investigated, the amount of nitrous oxide per unit biomass was found to be significantly higher for an annual management of grazing only, than a silage harvest plus grazing, likely relating to the increased period of livestock on pasture. This work emphasizes how several metrics validated by auto-sampled data provide a measure of nitrogen loss, efficiency and best management practise. Unlabelled Image • Provides yield-nitrogen metrics for ryegrass sheep pastures • Combination of climate, sensor and sampling data applied to agri-system modelling • Highest resource use efficiency coincides with lowest leaching per unit product. • N 2 O per unit biomass significantly lower for silage & grazing than grazing only. • Several related metrics reveal info about the system, hidden by using one metric. [ABSTRACT FROM AUTHOR]