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Nitrous oxide (N2O) emissions are a major source of gaseous nitrogen loss, causing environmental pollution. The low organic content in the Loess Plateau region, coupled with the high fertilizer demand of maize, further exacerbates these N losses. N fertilizers play a primary role in N2O emissions by influencing soil denitrifying bacteria, however, the underlying microbial mechanisms that contribute to N2O emissions have not been fully explored. Therefore, the research aimed to gain insights into the intricate relationships between N fertilization, soil denitrification, N2O emissions, potential denitrification activity (PDA), and maize nitrogen use efficiency (NUE) in semi-arid regions. Four nitrogen (N) fertilizer rates, namely N0, N1, N2, and N3 (representing 0, 100, 200, and 300 kg ha−1 yr.−1, respectively) were applied to maize field. The cumulative N2O emissions were 32 and 33% higher under N2 and 37 and 39% higher under N3 in the 2020 and 2021, respectively, than the N0 treatment. N fertilization rates impacted the abundance, composition, and network of soil denitrifying communities (nirS and nosZ) in the bulk and rhizosphere soil. Additionally, within the nirS community, the genera Cupriavidus and Rhodanobacter were associated with N2O emissions. Conversely, in the nosZ denitrifier, the genera Azospirillum, Mesorhizobium, and Microvirga in the bulk and rhizosphere soil reduced N2O emissions. Further analysis using both random forest and structural equation model (SEM) revealed that specific soil properties (pH, NO3−-N, SOC, SWC, and DON), and the presence of nirS-harboring denitrification, were positively associated with PDA activities, respectively, and exhibited a significant association to N2O emissions and PDA activities but expressed a negative effect on maize NUE. However, nosZ-harboring denitrification showed an opposite trend, suggesting different effects on these variables. Our findings suggest that N fertilization promoted microbial growth and N2O emissions by increasing the abundance of nirS and nosZ denitrifiers and altering the composition of their communities. This study provides new insights into the relationships among soil microbiome, maize productivity, NUE, and soil N2O emissions in semi-arid regions. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) emissions are a major source of gaseous nitrogen loss, causing environmental pollution. The low organic content in the Loess Plateau region, coupled with the high fertilizer demand of maize, further exacerbates these N losses. N fertilizers play a primary role in N2O emissions by influencing soil denitrifying bacteria, however, the underlying microbial mechanisms that contribute to N2O emissions have not been fully explored. Therefore, the research aimed to gain insights into the intricate relationships between N fertilization, soil denitrification, N2O emissions, potential denitrification activity (PDA), and maize nitrogen use efficiency (NUE) in semi-arid regions. Four nitrogen (N) fertilizer rates, namely N0, N1, N2, and N3 (representing 0, 100, 200, and 300 kg ha−1 yr.−1, respectively) were applied to maize field. The cumulative N2O emissions were 32 and 33% higher under N2 and 37 and 39% higher under N3 in the 2020 and 2021, respectively, than the N0 treatment. N fertilization rates impacted the abundance, composition, and network of soil denitrifying communities (nirS and nosZ) in the bulk and rhizosphere soil. Additionally, within the nirS community, the genera Cupriavidus and Rhodanobacter were associated with N2O emissions. Conversely, in the nosZ denitrifier, the genera Azospirillum, Mesorhizobium, and Microvirga in the bulk and rhizosphere soil reduced N2O emissions. Further analysis using both random forest and structural equation model (SEM) revealed that specific soil properties (pH, NO3−-N, SOC, SWC, and DON), and the presence of nirS-harboring denitrification, were positively associated with PDA activities, respectively, and exhibited a significant association to N2O emissions and PDA activities but expressed a negative effect on maize NUE. However, nosZ-harboring denitrification showed an opposite trend, suggesting different effects on these variables. Our findings suggest that N fertilization promoted microbial growth and N2O emissions by increasing the abundance of nirS and nosZ denitrifiers and altering the composition of their communities. This study provides new insights into the relationships among soil microbiome, maize productivity, NUE, and soil N2O emissions in semi-arid regions.

Denitrifying bacteria produce and utilize nitrous oxide (N2O), a potent greenhouse gas. However, there is little information on how organic fertilization treatments affect the denitrifying communities and N2O emissions in the semi-arid Loess Plateau. Here, we evaluated how the denitrifying communities are responsible for potential denitrification activity (PDA) and N2O emissions. A field experiment was conducted with five fertilization treatments, including no fertilization (CK), mineral fertilizer (MF), mineral fertilizer plus commercial organic fertilizer (MOF), commercial organic fertilizer (OFP), and maize straw (MSP). Our result showed that soil pH, soil organic carbon (SOC), and dissolved organic nitrogen (DON) were significantly increased under MSP treatment compared to MF treatment, while nitrate nitrogen (NO3 −−N) followed the opposite trend. Organic fertilization treatments (MOF, OFP, and MSP treatments) significantly increased the abundance and diversity of nirS- and nosZ-harboring denitrifiers, and modified the community structure compared to CK treatment. The identified potential keystone taxa within the denitrifying bacterial networks belonged to the distinct genera. Denitrification potentials were significantly positively correlated with the abundance of nirSharboring denitrifiers, rather than that of nirK- and nosZ-harboring denitrifiers. Random forest modeling and structural equation modeling consistently determined that the abundance, community composition, and network module I of nirS-harboring denitrifiers may contribute significantly to PDA and N2O emissions. Collectively, our findings highlight the ecological importance of the denitrifying communities in mediating denitrification potentials and the stimulatory impact of organic fertilization treatments on nitrogen dynamics in the semi-arid Loess Plateau. [ABSTRACT FROM AUTHOR]

Denitrifying bacteria produce and utilize nitrous oxide (N2O), a potent greenhouse gas. However, there is little information on how organic fertilization treatments affect the denitrifying communities and N2O emissions in the semi-arid Loess Plateau. Here, we evaluated how the denitrifying communities are responsible for potential denitrification activity (PDA) and N2O emissions. A field experiment was conducted with five fertilization treatments, including no fertilization (CK), mineral fertilizer (MF), mineral fertilizer plus commercial organic fertilizer (MOF), commercial organic fertilizer (OFP), and maize straw (MSP). Our result showed that soil pH, soil organic carbon (SOC), and dissolved organic nitrogen (DON) were significantly increased under MSP treatment compared to MF treatment, while nitrate nitrogen (NO3−−N) followed the opposite trend. Organic fertilization treatments (MOF, OFP, and MSP treatments) significantly increased the abundance and diversity of nirS- and nosZ-harboring denitrifiers, and modified the community structure compared to CK treatment. The identified potential keystone taxa within the denitrifying bacterial networks belonged to the distinct genera. Denitrification potentials were significantly positively correlated with the abundance of nirS-harboring denitrifiers, rather than that of nirK- and nosZ-harboring denitrifiers. Random forest modeling and structural equation modeling consistently determined that the abundance, community composition, and network module I of nirS-harboring denitrifiers may contribute significantly to PDA and N2O emissions. Collectively, our findings highlight the ecological importance of the denitrifying communities in mediating denitrification potentials and the stimulatory impact of organic fertilization treatments on nitrogen dynamics in the semi-arid Loess Plateau.

Abstract Nitrous oxide (N 2 O) is a potent greenhouse gas emitted at considerable rates from agricultural soils. A few recent studies have indicated the potential to reduce N 2 O emission rates in agricultural systems through management of soil microbiota, such as mycorrhizal fungi. Our limited understanding of how mycorrhiza influences N 2 O emission rates, however, forestalls such management practices. To address the knowledge gap regarding the mechanism of mycorrhizal modification of N 2 O formation and denitrification, we disentangle the direct effects of arbuscular mycorrhizal fungi (AMF) via hyphal growth on potential denitrification activity from those resulting from indirect AMF-induced changes in soil aggregation. We manipulated AMF status in a factorial experiment through adding or not AMF inoculum in the form of Rhizophagus irregularis and soil aggregation state through either crushing soil aggregates or using agricultural soil with intact soil aggregates. We then grew Zea mays (maize) in compartmentalized mesocosms for 4 months. At harvest, we observed approximately three-fold higher AMF root colonization and hyphal densities in the treatments where we had added Rhizophagus irregularis. Potential N 2 O activity rates and the denitrification ratio were higher in the undisturbed soil and in the mesocosms with a dense AMF hyphal network (direct effect of mycorrhiza). Further, AM-hyphae promoted soil aggregation while also altering potential denitrification activity (indirect effect of mycorrhiza). Overall, we present here a comprehensive case study on how mycorrhiza alters potential denitrification activity and related N 2 O activity from agricultural soils. Highlights • We disentangled direct and indirect effects of AM on denitrification. • AM hyphae (direct) promoted N 2 O activity. • Soil aggregation (indirect) also promoted N 2 O activity. • Mycorrhiza, here, stimulated potential N 2 O activity. [ABSTRACT FROM AUTHOR]

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Nitrous oxide (N 2 O) emissions are a major source of gaseous nitrogen loss, causing environmental pollution. The low organic content in the Loess Plateau region, coupled with the high fertilizer demand of maize, further exacerbates these N losses. N fertilizers play a primary role in N 2 O emissions by influencing soil denitrifying bacteria, however, the underlying microbial mechanisms that contribute to N 2 O emissions have not been fully explored. Therefore, the research aimed to gain insights into the intricate relationships between N fertilization, soil denitrification, N 2 O emissions, potential denitrification activity (PDA), and maize nitrogen use efficiency (NUE) in semi-arid regions. Four nitrogen (N) fertilizer rates, namely N0, N1, N2, and N3 (representing 0, 100, 200, and 300 kg ha -1 yr. -1 , respectively) were applied to maize field. The cumulative N 2 O emissions were 32 and 33% higher under N2 and 37 and 39% higher under N3 in the 2020 and 2021, respectively, than the N0 treatment. N fertilization rates impacted the abundance, composition, and network of soil denitrifying communities ( nirS and nosZ ) in the bulk and rhizosphere soil. Additionally, within the nirS community, the genera Cupriavidus and Rhodanobacter were associated with N 2 O emissions. Conversely, in the nosZ denitrifier, the genera Azospirillum , Mesorhizobium , and Microvirga in the bulk and rhizosphere soil reduced N 2 O emissions. Further analysis using both random forest and structural equation model (SEM) revealed that specific soil properties (pH, NO 3 - -N, SOC, SWC, and DON), and the presence of nirS -harboring denitrification, were positively associated with PDA activities, respectively, and exhibited a significant association to N 2 O emissions and PDA activities but expressed a negative effect on maize NUE. However, nosZ -harboring denitrification showed an opposite trend, suggesting different effects on these variables. Our findings suggest that N fertilization promoted microbial growth and N 2 O emissions by increasing the abundance of nirS and nosZ denitrifiers and altering the composition of their communities. This study provides new insights into the relationships among soil microbiome, maize productivity, NUE, and soil N 2 O emissions in semi-arid regions., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Fudjoe, Li, Anwar, Shi, Xie, Wang, Xie and Yongjie.)

This research investigate the population and potentials denitrification activity from three different soils, organically farmed soil, intensive farmed soil and forest soil. Our objectives were to explore spatial gradients in denitrifier populations, examine whether populations density and its potential activity was related to soil chemical properties (C and N content), and determine the potential emission of gas N2O. Results indicated biological functional differences between these three different soil ecosystems. Forest soil had the highest population density of denitrifying bacteria and also had significant potential denitrifying activities. The highest potentials denitrifying activity in the soil affected to the lowest emission of N2O gas. The lowest population and potential denitrifying activity was measured in the intensive farmed soil. Those conditions might be promoted the potentials emission of N2O.

Denitrification is one of the most important biological process by which reactive N is removed in the biosphere, but the responses of potential denitrification activity (PDA) and associated gene abundances to long-term N fertilization are poorly understood. We compiled data from 1041 observations across 62 studies and quantified the effects of long-term N input on PDA, the denitrification N 2 O/(N 2 O+N 2) product ratio, and abundances of denitrifying communities using meta-analysis. Boosted regression tree (BRT) analysis showed that soil pH was the most important explanatory variables among which explained the change of PDA, followed by soil organic carbon (SOC) and duration of fertilization. Long-term N fertilization significantly increased potential denitrification activity by 75.9% and increased the relative abundances of nirK , nirS , and nosZ gene copies by 60.4%, 77.0%, and 25.1%, respectively. Further, long-term N loading increased the denitrification N 2 O/(N 2 O+N 2) ratio by 22.1% and nir(K+S) / nosZ ratios by 27.7%, respectively. The effect of long-term N fertilization on potential denitrification activity was positively correlated with SOC (R2 = 0.11; n = 132; P < 0.001), while long-term N loading increased the SOC by 29.0% compared to the unfertilized control. The responses of nirK , nirS , and nosZ abundances to long-term N fertilization were positively correlated with soil pH, whereas N loading decreased the soil pH by 4.6%. Thus, we postulate that long-term N fertilization might have a double effect on the activities and populations of denitrifying communities due to the increased SOC and decreased soil pH. Conceptual diagram illustrating how long-term N fertilization influences N denitrification processes and related microbial community genes. The symbols "+" and "−" in the circles associated with each arrow represent stimulatory and inhibitory effects, respectively, on the N denitrification process. [Display omitted] • Long-term N loading increased soil potential denitrification activity (PDA). • Long-term N loading increased N 2 O/(N 2 O+N 2) ratio and nir (K + S)/ nosZ ratio. • The effect of increased SOC and decreased soil pH counteracts each other on PDA. [ABSTRACT FROM AUTHOR]

Denitrification is important for nitrogen balance in agricultural ecosystems. It is well established that the abundance and structure of denitrifier are strongly influenced by environmental factors. However, knowledge of how nirS - and nirK -harboring microbial communities vary in paddy soils of different climatic regions is lacking, along with how these microbes are associated with denitrification potential. In this study, forty paddy soils from tropical, sub-tropical, warm-temperate, and mid-temperate climate zones were collected. The results showed that soils from the sub-tropical zone had the highest denitrification rates. The abundances of nirS and nirK had a strong negative association with C/N ratio and clearly varied among the four climate zones. Variation in nirS- and nirK- containing communities existed across sampling sites from each climate zone in terms of α- and β-diversity. Soil pH and climate factors significantly affected community diversity. Network analysis revealed that different climate regions had similar keystone taxa like Azospira , and Achromobacter , which were significantly related to denitrification rates. Structural equation modeling indicated that the differences in denitrifying enzyme activity among the four climate zones were mostly explained by climate factors, soil pH, and nirS biodiversity. Specifically, the biodiversity of nirS was more important than that of nirK in regulating potential denitrification activity in paddy soil, suggesting that nirS- type denitrifiers may have high activity under anaerobic conditions. Our results allow a deeper insight into the relative contribution of nirS- and nirK- containing communities to the soil denitrification activity in paddy soils across climate zones. This study highlighted the need of manipulation experiment to explain how denitrifier biodiversity affect potential denitrification activity in the future. • Soils from the sub-tropical zone have the highest denitrification rates. • nirS and nirK gene abundances show clear variations among the four climate zones. • nirS and nirK gene abundances have strong negative associations with C/N ratio. • The pH, C/N and climate factor significantly affected the community structure. • nirS gene biodiversity is important to regulate denitrification rates in paddy soil. [ABSTRACT FROM AUTHOR]

• Ecological intensification (EI) approach successfully enhanced maize yield over farmer's practice (FP). • Lower abundance of microbial communities involved in N cycling was noted in EI approach as compared to FP. • Lower N 2 O emissions and greenhouse gas (GHG) emissions were found in EI approach than FP. There is global concern about the adverse impacts of conventional agricultural practices on the environment. Recent evidence has shown that ecological intensification (EI) of agriculture can safeguard the environment from negative impacts of agricultural practices and simultaneously produce substantially higher crop productivity. Here, we employed the concept of EI and compared it with conventional agriculture or farmer's practice (FP). We explored the effects of EI and FP treatments on maize yield, N losses via potential nitrification activity (PNA), potential denitrification activity (PDA), N 2 O emissions, greenhouse gas (GHG) emissions, and nitrogen (N) cycling microbial populations associated with nitrification and denitrification in fluvo-aquic soil and black soil of North China. There were four treatments, i.e., EI N-, FP N-, EI N+, FP N + at each site, - and + indicate no N addition and N addition, respectively. The results revealed that across the two soils, N addition increased PNA and PDA; however, compared with the FP N + treatment, lower PNA and PDA were observed in the EI N + treatment. Similarly, the abundance of N cycling genes, including AOA amoA and AOB amoA, for nitrification and nirS , nirK , and nosZ for denitrification were significantly increased under N addition, and compared with the FP N + treatment, reduced abundance was noted in the EI N + treatment. N 2 O and GHG emissions were quantified, and it was observed that, in comparison to the FP treatment, reduced N 2 O and GHG emissions occurred in EI treatments in the two locations. EI with best management practices also increased crop yield relative to FP. Owing to higher N rates in FP treatments, substantial soil acidification was noted in FP plots but not in EI plots. In addition, PNA and PDA were significantly positively linked with soil nitrifying and denitrifying communities, particularly in the black soil. Moreover, the N availability pathway rather than soil acidification mainly regulated N cycling microbial communities. Our results suggest that EI could be a sustainable and environmentally friendly approach due to higher crop productivity and lower N losses via PNA, PDA, N 2 O, and GHG emissions, thus preventing the negative impact of agricultural practices, especially N fertilization, on the environment. [ABSTRACT FROM AUTHOR]

We investigated the variation of denitrifying communities in rice rhizosphere at tillering and booting stages in comparison with bulk soils with a pot experiment. The techniques of quantitative polymerase chain reaction (qPCR) and terminal restriction fragment length polymorphism (T-RFLP) were used to measure the abundance and community composition of denitrifiers (narG and nosZ), respectively. The results showed that the potential denitrification activity in the rhizosphere at tillering stage was significantly lower than bulk soils. No significant difference was detected between the rhizosphere and bulk soils at booting stage. The abundance of both narG- and nosZ-containing denitrifying bacteria was significantly higher in rhizosphere than in bulk soils at both tillering and booting stages. In comparison with narG-containing community, community composition and diversity of nosZ-containing bacteria were more sensitive to rice growth. In conclusion, the exudates of rice could induce significantly more denitrifying bacteria in rhizosphere, whose denitrifying activities were related to growth stage of rice. At the period with strong growth, the secretion of roots showed clear restriction to the functions of rhizospheric denitrifiers compared to booting stage.