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Arbuscular mycorrhizal fungi (AMF) are key soil organisms and their extensive hyphae create a unique hyphosphere associated with microbes actively involved in N cycling. However, the underlying mechanisms how AMF and hyphae-associated microbes may cooperate to influence N2O emissions from “hot spot” residue patches remain unclear. Here we explored the key microbes in the hyphosphere involved in N2O production and consumption using amplicon and shotgun metagenomic sequencing. Chemotaxis, growth and N2O emissions of isolated N2O-reducing bacteria in response to hyphal exudates were tested using in vitro cultures and inoculation experiments. Results: AMF hyphae reduced denitrification-derived N2O emission (max. 63%) in C- and N-rich residue patches. AMF consistently enhanced the abundance and expression of clade I nosZ gene, and inconsistently increased that of nirS and nirK genes. The reduction of N2O emissions in the hyphosphere was linked to N2O-reducing Pseudomonas specifically enriched by AMF, concurring with the increase in the relative abundance of the key genes involved in bacterial citrate cycle. Phenotypic characterization of the isolated complete denitrifying P. fluorescens strain JL1 (possessing clade I nosZ) indicated that the decline of net N2O emission was a result of upregulated nosZ expression in P. fluorescens following hyphal exudation (e.g. carboxylates). These findings were further validated by re-inoculating sterilized residue patches with P. fluorescens and by an 11-year-long field experiment showing significant positive correlation between hyphal length density with the abundance of clade I nosZ gene. Conclusions: The cooperation between AMF and the N2O-reducing Pseudomonas residing on hyphae significantly reduce N2O emissions in the microsites. Carboxylates exuded by hyphae act as attractants in recruiting P. fluorescens and also as stimulants triggering nosZ gene expression. Our discovery indicates that reinforcing synergies between AMF and hy

Background Arbuscular mycorrhizal fungi (AMF) are key soil organisms and their extensive hyphae create a unique hyphosphere associated with microbes actively involved in N cycling. However, the underlying mechanisms how AMF and hyphae‑associated microbes may cooperate to influence N2O emissions from “hot spot” residue patches remain unclear. Here we explored the key microbes in the hyphosphere involved in N 2O production and consumption using amplicon and shotgun metagenomic sequencing. Chemotaxis, growth and N2O emissions of isolated N2O‑reducing bacteria in response to hyphal exudates were tested using in vitro cultures and inoculation experiments. Results AMF hyphae reduced denitrification‑derived N 2O emission (max. 63%) in C‑ and N‑rich residue patches. AMF consistently enhanced the abundance and expression of clade I nosZ gene, and inconsistently increased that of nirS and nirK genes. The reduction of N2 O emissions in the hyphosphere was linked to N2O‑reducing Pseudomonas specifically enriched by AMF, concurring with the increase in the relative abundance of the key genes involved in bacterial citrate cycle. Phenotypic characterization of the isolated complete denitrifying P. fluorescens strain JL1 (possessing clade I nosZ) indicated that the decline of net N 2 O emission was a result of upregulated nosZ expression in P. fluorescens following hyphal exudation (e.g. carboxylates). These findings were further validated by re‑inoculating sterilized residue patches with P. fluorescens and by an 11‑year‑long field experiment showing significant positive correlation between hyphal length density with the abundance of clade I nosZ gene. Conclusions The cooperation between AMF and the N2O‑reducing Pseudomonas residing on hyphae significantly reduce N2O emissions in the microsites. Carboxylates exuded by hyphae act as attractants in recruiting P. fluorescens and also as stimulants triggering nosZ gene expression. Our discovery indicate

BACKGROUND: Arbuscular mycorrhizal fungi (AMF) are key soil organisms and their extensive hyphae create a unique hyphosphere associated with microbes actively involved in N cycling. However, the underlying mechanisms how AMF and hyphae-associated microbes may cooperate to influence N$_{2}$O emissions from "hot spot" residue patches remain unclear. Here we explored the key microbes in the hyphosphere involved in N$_{2}$O production and consumption using amplicon and shotgun metagenomic sequencing. Chemotaxis, growth and N$_{2}$O emissions of isolated N$_{2}$O-reducing bacteria in response to hyphal exudates were tested using in vitro cultures and inoculation experiments. RESULTS: AMF hyphae reduced denitrification-derived N$_{2}$O emission (max. 63%) in C- and N-rich residue patches. AMF consistently enhanced the abundance and expression of clade I nosZ gene, and inconsistently increased that of nirS and nirK genes. The reduction of N$_{2}$O emissions in the hyphosphere was linked to N$_{2}$O-reducing Pseudomonas specifically enriched by AMF, concurring with the increase in the relative abundance of the key genes involved in bacterial citrate cycle. Phenotypic characterization of the isolated complete denitrifying P. fluorescens strain JL1 (possessing clade I nosZ) indicated that the decline of net N$_{2}$O emission was a result of upregulated nosZ expression in P. fluorescens following hyphal exudation (e.g. carboxylates). These findings were further validated by re-inoculating sterilized residue patches with P. fluorescens and by an 11-year-long field experiment showing significant positive correlation between hyphal length density with the abundance of clade I nosZ gene. CONCLUSIONS: The cooperation between AMF and the N$_{2}$O-reducing Pseudomonas residing on hyphae significantly reduce N$_{2}$O emissions in the microsites. Carboxylates exuded by hyphae act as attractants in recruiting P. fluorescens and also as stimulants triggering nosZ gene expression. Our dis

Two virtual joint centers for nitrogen agronomy were established between the UK and China to facilitate collaborative research aimed at improving nitrogen use efficiency (NUE) in agricultural production systems and reducing losses of reactive N to the environment. Major focus areas were improving fertilizer NUE, use of livestock manures, soil health, and policy development and knowledge exchange. Improvements to fertilizer NUE included attention to application rate in the context of yield potential and economic considerations and the potential of improved practices including enhanced efficiency fertilizers, plastic film mulching and cropping design. Improved utilization of livestock manures requires knowledge of the available nutrient content, appropriate manure processing technologies and integrated nutrient management practices. Soil carbon, acidification and biodiversity were considered as important aspects of soil health. Both centers identified a range of potential actions that could be taken to improve N management, and the research conducted has highlighted the importance of developing a systems-level approach to assessing improvement in the overall efficiency of N management and avoiding unintended secondary effects from individual interventions. Within this context, the management of fertilizer emissions and livestock manure at the farm and regional scales appear to be particularly important targets for mitigation.

Nitrous oxide (N2O) emissions make up a significant part of agricultural greenhouse gas emissions. There is an urgent need to identify new approaches to the mitigation of these emissions with emerging technology. In this short review four approaches to precision managements of agricultural systems are described based on examples of work being undertaken in the UK and New Zealand. They offer the opportunity for N2O mitigation without any reduction in productivity. These approaches depend upon new sensor technology, modeling and spatial information with which to make management decisions and interventions that can both improve agricultural productivity and environmental protection.

Human interference with the nitrogen cycle has doubled reactive nitrogen inputs to the global biosphere over the past century, leading to changes across multiple environmental issues that require urgent action. Nitrogen fertilizers and biological nitrogen fixation have allowed benefits of increased crop harvest and livestock production, while in some areas there is insufficient nitrogen to fertilize crops. Whether in excess or deficit, nitrogen losses from its inefficient use are causing a combination of freshwater and marine pollution, air pollution, alteration of climate balance, stratospheric ozone loss, biodiversity loss and reduction of soil quality. The resulting nitrogen pollution affects human health, well-being and livelihoods. Scientific efforts have begun to bring these issues together. However, there is still a high degree of fragmentation between research on the different benefits and threats of reactive nitrogen and between the respective policy frameworks, especially at the global scale. We argue that a more joined-up approach to managing the global nitrogen cycle is needed to develop the ‘gravity of common cause’ between nitrogen issues and to avoid policy trade-offs. We describe how a coherent system for science evidence provision is being developed to support policy development through the ‘International Nitrogen Management System’ (INMS). There is now a matching challenge to bring together the multiple policy agreements relevant for nitrogen as a foundation to address synergies/trade-offs and to set priorities. Based on review of existing frameworks, we outline the concept for an Interconvention nitrogen coordination mechanism. This could make a major contribution to multiple Sustainable Development Goals by stimulating the next generation of international nitrogen strategies: maximizing the benefits of efficient nitrogen use, while minimizing its many environmental threats.

Nitrous oxide (N2O) emissions make up a significant part of agricultural greenhouse gas emissions. There is an urgent need to identify new approaches to the mitigation of these emissions with emerging technology. In this short review four approaches to precision managements of agricultural systems are described based on examples of work being undertaken in the UK and New Zealand. They offer the opportunity for N2O mitigation without any reduction in productivity. These approaches depend upon new sensor technology, modeling and spatial information with which to make management decisions and interventions that can both improve agricultural productivity and environmental protection.

Nitrous acid (HONO) is a precursor of the hydroxyl radical (OH), a key oxidant in the degradation of most air pollutants. Field measurements indicate a large unknown source of HONO during the day time. Release of nitrous acid (HONO) from soil has been suggested as a major source of atmospheric HONO. We hypothesize that nitrite produced by biological nitrate reduction in oxygen-limited microzones in wet soils is a source of such HONO. Indeed, we found that various contrasting soil samples emitted HONO at high water-holding capacity (75–140%), demonstrating this to be a widespread phenomenon. Supplemental nitrate stimulated HONO emissions, whereas ethanol (70% v/v) treatment to minimize microbial activities reduced HONO emissions by 80%, suggesting that nitrate-dependent biotic processes are the sources of HONO. High-throughput Illumina sequencing of 16S rRNA as well as functional gene transcripts associated with nitrate and nitrite reduction indicated that HONO emissions from soil samples were associated with nitrate reduction activities of diverse Proteobacteria. Incubation of pure cultures of bacterial nitrate reducers and gene-expression analyses, as well as the analyses of mutant strains deficient in nitrite reductases, showed positive correlations of HONO emissions with the capability of microbes to reduce nitrate to nitrite. Thus, we suggest biological nitrate reduction in oxygen-limited microzones as a hitherto unknown source of atmospheric HONO, affecting biogeochemical nitrogen cycling, atmospheric chemistry, and global modeling.

The nitrogen cycle has been radically changed by human activities(1). China consumes nearly one third of the world's nitrogen fertilizers. The excessive application of fertilizers(2,3) and increased nitrogen discharge from livestock, domestic and industrial sources have resulted in pervasive water pollution. Quantifying a nitrogen 'boundary'(4) in heterogeneous environments is important for the effective management of local water quality. Here we use a combination of water-quality observations and simulated nitrogen discharge from agricultural and other sources to estimate spatial patterns of nitrogen discharge into water bodies across China from 1955 to 2014. We find that the critical surface-water quality standard (1.0 milligrams of nitrogen per litre) was being exceeded in most provinces by the mid-1980s, and that current rates of anthropogenic nitrogen discharge (14.5 +/- 3.1 megatonnes of nitrogen per year) to fresh water are about 2.7 times the estimated 'safe' nitrogen discharge threshold (5.2 +/- 0.7 megatonnes of nitrogen per year). Current efforts to reduce pollution through wastewater treatment and by improving cropland nitrogen management can partially remedy this situation. Domestic wastewater treatment has helped to reduce net discharge by 0.7 +/- 0.1 megatonnes in 2014, but at high monetary and energy costs. Improved cropland nitrogen management could remove another 2.3 +/- 0.3 megatonnes of nitrogen per year-about 25 per cent of the excess discharge to fresh water. Successfully restoring a clean water environment in China will further require transformational changes to boost the national nutrient recycling rate from its current average of 36 per cent to about 87 per cent, which is a level typical of traditional Chinese agriculture. Although ambitious, such a high level of nitrogen recycling is technologically achievable at an estimated capital cost of approximately 100 billion US dollars and operating costs of 18-29 billion US dollars per year, and, QC 20190423

Nitrous acid (HONO) is a precursor of the hydroxyl radical (OH), a key oxidant in the degradation of most air pollutants. Field measurements indicate a large unknown source of HONO during the day time. Release of nitrous acid (HONO) from soil has been suggested as a major source of atmospheric HONO. We hypothesize that nitrite produced by biological nitrate reduction in oxygen-limited microzones in wet soils is a source of such HONO. Indeed, we found that various contrasting soil samples emitted HONO at high water-holding capacity (75–140%), demonstrating this to be a widespread phenomenon. Supplemental nitrate stimulated HONO emissions, whereas ethanol (70% v/v) treatment to minimize microbial activities reduced HONO emissions by 80%, suggesting that nitrate-dependent biotic processes are the sources of HONO. High-throughput Illumina sequencing of 16S rRNA as well as functional gene transcripts associated with nitrate and nitrite reduction indicated that HONO emissions from soil samples were associated with nitrate reduction activities of diverse Proteobacteria. Incubation of pure cultures of bacterial nitrate reducers and gene-expression analyses, as well as the analyses of mutant strains deficient in nitrite reductases, showed positive correlations of HONO emissions with the capability of microbes to reduce nitrate to nitrite. Thus, we suggest biological nitrate reduction in oxygen-limited microzones as a hitherto unknown source of atmospheric HONO, affecting biogeochemical nitrogen cycling, atmospheric chemistry, and global modeling., Accepted version

Managing reactive nitrogen (Nr) to achieve a sustainable balance between production of food, feed and fiber, and environmental protection is a grand challenge in the context of an increasingly affluent society. Here, we propose a novel framework for national nitrogen (N) assessments enabling a more consistent comparison of the uses, losses and impacts of Nr between countries, and improvement of Nr management for sustainable development at national and regional scales. This framework includes four key components: national scale N budgets, validation of N fluxes, cost-benefit analysis and Nr management strategies. We identify four critical factors for Nr management to achieve the sustainable development goals: N use efficiency (NUE), Nr recycling ratio (e.g., ratio of livestock excretion applied to cropland), human dietary patterns and food waste ratio. This framework was partly adopted from the European Nitrogen Assessment and now is successfully applied to China, where it contributed to trigger policy interventions toward improvements for future sustainable use of Nr. We demonstrate how other countries can also benefit from the application our framework, in order to include sustainable Nr management under future challenges of growing population, hence contributing to the achievement of some key sustainable development goals (SDGs).

Nitrous acid (HONO) is a precursor of the hydroxyl radical (OH), a key oxidant in the degradation of most air pollutants. Field measurements indicate a large unknown source of HONO during the day time. Release of nitrous acid (HONO) from soil has been suggested as a major source of atmospheric HONO. We hypothesize that nitrite produced by biological nitrate reduction in oxygen-limited microzones in wet soils is a source of such HONO. Indeed, we found that various contrasting soil samples emitted HONO at high water-holding capacity (75–140%), demonstrating this to be a widespread phenomenon. Supplemental nitrate stimulated HONO emissions, whereas ethanol (70% v/v) treatment to minimize microbial activities reduced HONO emissions by 80%, suggesting that nitrate-dependent biotic processes are the sources of HONO. High-throughput Illumina sequencing of 16S rRNA as well as functional gene transcripts associated with nitrate and nitrite reduction indicated that HONO emissions from soil samples were associated with nitrate reduction activities of diverse Proteobacteria. Incubation of pure cultures of bacterial nitrate reducers and gene-expression analyses, as well as the analyses of mutant strains deficient in nitrite reductases, showed positive correlations of HONO emissions with the capability of microbes to reduce nitrate to nitrite. Thus, we suggest biological nitrate reduction in oxygen-limited microzones as a hitherto unknown source of atmospheric HONO, affecting biogeochemical nitrogen cycling, atmospheric chemistry, and global modeling., Accepted version

Managing reactive nitrogen (Nr) to achieve a sustainable balance between production of food, feed and fiber, and environmental protection is a grand challenge in the context of an increasingly affluent society. Here, we propose a novel framework for national nitrogen (N) assessments enabling a more consistent comparison of the uses, losses and impacts of Nr between countries, and improvement of Nr management for sustainable development at national and regional scales. This framework includes four key components: national scale N budgets, validation of N fluxes, cost-benefit analysis and Nr management strategies. We identify four critical factors for Nr management to achieve the sustainable development goals: N use efficiency (NUE), Nr recycling ratio (e.g., ratio of livestock excretion applied to cropland), human dietary patterns and food waste ratio. This framework was partly adopted from the European Nitrogen Assessment and now is successfully applied to China, where it contributed to trigger policy interventions toward improvements for future sustainable use of Nr. We demonstrate how other countries can also benefit from the application our framework, in order to include sustainable Nr management under future challenges of growing population, hence contributing to the achievement of some key sustainable development goals (SDGs).

Biosphere carbon sinks are crucial for reducing atmospheric carbon dioxide (CO2) concentration to mitigate global warming, but are substantially affected by the input of reactive nitrogen (Nr). Although the effects of anthropogenic CO2 emission and nitrogen deposition (indicated by Nr emission to atmosphere) on carbon sink have been studied, it is unclear how their ratio (C/N) changes with economic development and how such change alters biosphere carbon sinks. Here, by compiling datasets for 132 countries we find that the C/N ratio continued to increase despite anthropogenic CO2 and Nr emissions to atmosphere both showing an asymmetric para-curve with economic growth. The inflection points of CO2 and Nr emissions are found at around $15,000 gross domestic product per capita worldwide. Economic growth promotes the use of Nr and energy, while at the same time increases their use efficiencies, together resulting in occurrences of inflection points of CO2 and Nr emissions. Nr emissions increase slower but decrease faster than that of CO2 emissions before and after the inflection point, respectively. It implies that there will be relatively more anthropogenic CO2 emission but less N deposition with economic growth. This may limit biosphere carbon sink because of relative shortage of Nr. This finding should be integrated/included in global climate change modelling. Efforts, such as matching N deposition with carbon sequestration on regional scale, to manage CO2 and Nr emissions comprehensively to maintain a balance are critical.

Biosphere carbon sinks are crucial for reducing atmospheric carbon dioxide (CO2) concentration to mitigate global warming, but are substantially affected by the input of reactive nitrogen (Nr). Although the effects of anthropogenic CO2 emission and nitrogen deposition (indicated by Nr emission to atmosphere) on carbon sink have been studied, it is unclear how their ratio (C/N) changes with economic development and how such change alters biosphere carbon sinks. Here, by compiling datasets for 132 countries we find that the C/N ratio continued to increase despite anthropogenic CO2 and Nr emissions to atmosphere both showing an asymmetric para-curve with economic growth. The inflection points of CO2 and Nr emissions are found at around $15,000 gross domestic product per capita worldwide. Economic growth promotes the use of Nr and energy, while at the same time increases their use efficiencies, together resulting in occurrences of inflection points of CO2 and Nr emissions. Nr emissions increase slower but decrease faster than that of CO2 emissions before and after the inflection point, respectively. It implies that there will be relatively more anthropogenic CO2 emission but less N deposition with economic growth. This may limit biosphere carbon sink because of relative shortage of Nr. This finding should be integrated/included in global climate change modelling. Efforts, such as matching N deposition with carbon sequestration on regional scale, to manage CO2 and Nr emissions comprehensively to maintain a balance are critical.

The global food system is a main source of nitrous oxide (N2O), estimated at 4.1–4.4 Tg N2O-N for 2010. Here, we review this source and assess its mitigation potential. Five mitigation strategies were explored and compared to a ‘business as usual’ (BAU) scenario: firstly, improved crop production; secondly, improved animal production; thirdly, improved manure management; fourthly improved food utilization; and finally, less animal-derived protein in diets. In the BAU scenario, emissions increased to 6.4 Tg for 2030 and 7.5 Tg for 2050. Emission reduction strategies could potentially reduce emissions to 4.1 Tg in 2030 and to 3.3 Tg in 2050, but there is considerable uncertainty in these estimates. In conclusion, packages of coherent strategies may offset the projected increases in N2O emissions from the global food system.

The global food system is a main source of nitrous oxide (N2O), estimated at 4.1–4.4 Tg N2O-N for 2010. Here, we review this source and assess its mitigation potential. Five mitigation strategies were explored and compared to a ‘business as usual’ (BAU) scenario: firstly, improved crop production; secondly, improved animal production; thirdly, improved manure management; fourthly improved food utilization; and finally, less animal-derived protein in diets. In the BAU scenario, emissions increased to 6.4 Tg for 2030 and 7.5 Tg for 2050. Emission reduction strategies could potentially reduce emissions to 4.1 Tg in 2030 and to 3.3 Tg in 2050, but there is considerable uncertainty in these estimates. In conclusion, packages of coherent strategies may offset the projected increases in N2O emissions from the global food system.

Nitrous oxide is a potent pollutant that has both ozone layer-damaging properties and the ability to contribute to climate change. This dual characteristic makes nitrous oxide a gas that needs to be targeted for emissions reduction. This is especially the case, since its emission has been increasing since the preindustrial era. However, it could be argued that not enough attention has been given to reducing nitrous oxide emissions. UNEP has therefore developed this report with the aim of informing policymakers and stakeholders about the impacts of nitrous oxide emissions on climate and ozone layer and to present available opportunities for reducing emissions. The report also articulates how efforts associated with reducing nitrous oxide emissions are closely linked to the concept of an inclusive “green economy”.

Nitrous oxide is a potent pollutant that has both ozone layer-damaging properties and the ability to contribute to climate change. This dual characteristic makes nitrous oxide a gas that needs to be targeted for emissions reduction. This is especially the case, since its emission has been increasing since the preindustrial era. However, it could be argued that not enough attention has been given to reducing nitrous oxide emissions. UNEP has therefore developed this report with the aim of informing policymakers and stakeholders about the impacts of nitrous oxide emissions on climate and ozone layer and to present available opportunities for reducing emissions. The report also articulates how efforts associated with reducing nitrous oxide emissions are closely linked to the concept of an inclusive “green economy”.

Excessive amounts of nitrate have accumulated in many soils on the North China Plain due to the large amounts of chemical N fertilizer used combined with low carbon inputs. The present study investigated the promotion of soil nitrate transformation to soil organic N by different carbon amendments. A laboratory incubation experiment using 15N tracer (K15NO3) was employed to elucidate the proportion of soil organic N derived from accumulated soil nitrate following amendment with glucose (G) or maize straw (S) at controlled soil temperature and moisture content. During the 56-d incubation period we determined the dynamics and isotopic abundance of mineral N (NO3- and NH4+) and soil organic N and greenhouse gas (N2O and CO2) emissions. Carbon amendment markedly stimulated transformation of nitrate to soil organic N. Mineralization of native soil organic N was also enhanced because soil organic N at the end of the incubation period was not significantly different from that in the control without added C. Glucose had a greater effect on nitrate-N immobilization (25.0 mg kg-1) than maize straw (9.4 mg kg-1) and glucose addition also led to highest greenhouse gas emissions. With glucose and straw amendment total N2O-N emissions were 1.01 and 0.03 mg kg-1, respectively. Similarly, glucose amendment lowered the concentration and abundance of NO3--N and increased that of NH4+-N more than maize straw. In agricultural practice straw amendment may be an effective strategy to deplete the excess NO3--N pool and restrict leaching, to promote nitrate-N immobilization and to decrease greenhouse gas emissions.

Excessive amounts of nitrate have accumulated in many soils on the North China Plain due to the large amounts of chemical N fertilizer used combined with low carbon inputs. The present study investigated the promotion of soil nitrate transformation to soil organic N by different carbon amendments. A laboratory incubation experiment using 15N tracer (K15NO3) was employed to elucidate the proportion of soil organic N derived from accumulated soil nitrate following amendment with glucose (G) or maize straw (S) at controlled soil temperature and moisture content. During the 56-d incubation period we determined the dynamics and isotopic abundance of mineral N (NO3- and NH4+) and soil organic N and greenhouse gas (N2O and CO2) emissions. Carbon amendment markedly stimulated transformation of nitrate to soil organic N. Mineralization of native soil organic N was also enhanced because soil organic N at the end of the incubation period was not significantly different from that in the control without added C. Glucose had a greater effect on nitrate-N immobilization (25.0 mg kg-1) than maize straw (9.4 mg kg-1) and glucose addition also led to highest greenhouse gas emissions. With glucose and straw amendment total N2O-N emissions were 1.01 and 0.03 mg kg-1, respectively. Similarly, glucose amendment lowered the concentration and abundance of NO3--N and increased that of NH4+-N more than maize straw. In agricultural practice straw amendment may be an effective strategy to deplete the excess NO3--N pool and restrict leaching, to promote nitrate-N immobilization and to decrease greenhouse gas emissions.