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Four new tirucallane-type triterpenoids, polystanins H–K (1–4), were obtained from the stems and leaves of Aphanamixis polystachya. Their structures were elucidated by analysis of the spectroscopic data and comparison with literature data. Compounds 1 and 2 showed week inhibitory effects against NO production in LPS-stimulated RAW264.7 cells. All the isolates were investigated for their antifungal activities against drug-resistant Candida albicans. [ABSTRACT FROM AUTHOR]

The abuse of nitrous oxide (N2O) poses a substantial public health challenge. In many countries, including China, regulations governing the utilization and accessibility to N2O remain ambiguous, particularly within the food industry. Here, we report a case of a 21-year-old female who presented with symptoms of subacute combined degeneration (SCD) of the spinal cord due to N2O abuse. The patient exhibited bilateral lower limb numbness and weakness, low serum vitamin B12 levels with elevated homocysteine levels, and lumbar spine magnetic resonance imaging (MRI) revealed abnormal signals of the spinal cord. Following cessation of N2O and comprehensive therapy including methylcobalamin and nerve growth factor, the symptoms significantly improved. A follow-up examination 3 months later showed good progress in gait stability. At a 5-year follow-up, the patient’s previous clinical symptoms had completely disappeared, and her quality of life had returned to normal. This case underscores the urgency of raising awareness and prevention of N2O abuse, emphasizing the importance of timely diagnosis and comprehensive treatment for patient recovery. Clear formulation and enforcement of relevant regulatory measures are equally crucial in reducing instances of abuse. [ABSTRACT FROM AUTHOR]

[Display omitted] • The deviation of N 2 O emission factor (EF) from short-term monitoring can reach 20%. • The N 2 O EF for sludge incineration in China may be smaller than the default value. • The N 2 O EF decreases as the temperature in the furnace increases. • The N 2 O EF of the sludge incinerators with smaller heat loads fluctuates more. • The fluctuation range of the N 2 O EF narrows with the increase of temperature. The N 2 O emissions resulting from sludge incineration are estimated using the default values published by the Intergovernmental Panel on Climate Change (IPCC), which may differ significantly from the actual emissions. In this investigation, N 2 O emissions from four sludge incineration lines in two plants were monitored for varying durations. The variation in N 2 O emission factors (EFs) between incineration lines of the same plant was much smaller than the difference between different plants. Data on N 2 O EFs obtained from brief monitoring may contain variabilities of up to 30%. N 2 O EFs were more sensitive to temperature changes at low temperatures, necessitating extended monitoring periods to improve the reliability of N 2 O monitoring outcomes in cases of low furnace temperatures. Excessive use of the SNCR system to reduce NOx emissions resulted in concentrations of N 2 O and NH 3 in the exhaust gases exceeding NOx levels. In the case of furnace temperature control and advanced reburning technology, it is advisable to utilize actual monitoring data or the smaller default values provided by the IPCC in China. Otherwise, the estimated N 2 O emissions may exceed the actual emissions. [ABSTRACT FROM AUTHOR]

Constructing a highly resolved comprehensive emission dataset for China is challenging due to limited availability of refined information for parameters in a unified bottom-up framework. Here, by developing an integrated modeling framework, we harmonized multi-source heterogeneous data, including several up-to-date emission inventories at national and regional scales and for key species and sources in China to generate a 0.1° resolution inventory for 2017. By source mapping, species mapping, temporal disaggregation, spatial allocation, and spatial–temporal coupling, different emission inventories are normalized in terms of source categories, chemical species, and spatiotemporal resolutions. This achieves the coupling of multi-scale, high-resolution emission inventories with the Multi-resolution Emission Inventory for China (MEIC), forming the high-resolution INTegrated emission inventory of Air pollutants for China (INTAC). We find that INTAC provides more accurate representations for emission magnitudes and spatiotemporal patterns. In 2017, China's emissions of sulfur dioxide (SO2), nitrous oxides (NOx), carbon monoxide (CO), non-methane volatile organic compounds (NMVOCs), ammonia (NH3), PM10 and PM2.5 (particulate matter), black carbon (BC), and organic carbon (OC) were 12.3, 24.5, 141.0, 27.9, 9.2, 11.1, 8.4, 1.3, and 2.2 Tg , respectively. The proportion of point source emissions for SO2 , PM10 , NOx , and PM2.5 increases from 7 %–19 % in MEIC to 48 %–66 % in INTAC, resulting in improved spatial accuracy, especially mitigating overestimations in densely populated areas. Compared with MEIC, INTAC reduces mean biases in simulated concentrations of major air pollutants by 2–14 µgm-3 across 74 cities, compared against ground observations. The enhanced model performance by INTAC is particularly evident at finer-grid resolutions. Our new dataset is accessible at http://meicmodel.org.cn/intac (last access: 15 April 2024) and 10.5281/zenodo.10459198 (Wu et al., 2024), and it will provide a solid data foundation for fine-scale atmospheric research and air-quality improvement. [ABSTRACT FROM AUTHOR]

The use of oilseed rape (OS, Brassica napus L.) as a winter green manure is crucial for enhancing soil fertility and reducing chemical N application in paddy fields. However, the impacts of replacing varying amounts of chemical N with OS on CH4 and N2O emissions in paddy soils have not been well evaluated. In this study, GHG emissions, soil properties and OS decomposition in a rice-ratooning system with different OS-urea N replacement rates (0%, 25%, 50%, 75% and 100%) were investigated. Our results indicate that 84.7–90.7% of the initial C and 97.5–98.4% of the N were released during the 192-day decomposition process, and that the mineralization patterns of net C and net N in the OS residue were consistent with a single exponential decay model. The lowest CH4 emissions (9.97 g m−2) were observed at 0% OS, while the highest N2O emissions (0.40 g m−2) were observed at this level of substitution. Conversely, the highest CH4 emissions (20.71 g m−2) and lowest N2O emissions (0.07 g m−2) were observed at 100% OS. Compared to 0% substitution, 25% substitution significantly decreased GWP and GHGI without reducing rice grain yield. Environmental parameters such as soil redox, NH4+-N and residual N and C were shown to be significantly associated with CH4 emissions, whereas soil redox, NH4+-N and residual C were the main drivers of N2O emissions. In conclusion, 25% substitution of OS was the most cost-effective measure for balancing greenhouse gas emission and rice yield. [ABSTRACT FROM AUTHOR]

Vegetable production in Subtropical China is distinguished by excessive nitrogen (N) fertilization, frequent irrigation, and multiple crop rotations in a single year. The aforementioned variables are closely related to soil nitrous oxide (N2O) and methane (CH4) emissions. Hence, we conducted a field trial to measure N2O and CH4 emissions using static chamber–gas chromatograph. Four treatments were used: control (CK) with no fertilizer, 100% chemical N fertilization (CN), the conventional 30% chicken manure N plus 70%CN (CMN + CN), and 30% chicken manure biochar N plus 70%CN (CMBN + CN). The annual cumulative N2O emissions reached 12.4, 63.5, 111.8, and 44.1 kg N2O-N ha−1 for the CK, CN, CMN + CN, and CMBN + CN treatments, respectively. Compared to the CN and CMN + CN treatments, the CMBN + CN treatment reduced N2O emissions by 35.9%–65.7%, while it simultaneously increased the total vegetable yield by 16.1% compared to the CN treatment. Seven seasons mean N2O emission factors are 1.3% for CN, 3.8% for CMN + CN, and 0.9% for CMBN + CN. The CH4 emission was negligible, ranging from 0.07 kg CH4-C ha−1 for the CK treatment to 0.8 kg CH4-C ha−1 for the CN treatment. N2O emissions peaked under the conditions of an interior chamber temperature of around 31.9 °C and the water-filled pore space (WFPS) of the soil being approximately 60%. Future climate change will intensify, triggering higher N2O emissions from subtropical vegetable fields. CMB can be one of the best substitutes for direct chicken manure application as a soil supplement because it has a beneficial effect on improving vegetable yield and reducing N2O emissions in Subtropical China. [ABSTRACT FROM AUTHOR]

The emission factor method (Tier 1) recommended by the Intergovernmental Panel on Climate Change (IPCC) is commonly used to estimate greenhouse gas (GHG) emissions from livestock and poultry farms. However, the estimation accuracy may vary due to practical differences in manure management across China. The objectives of this study were to estimate the direct and indirect nitrous oxide (N2O) emissions from dairy manure management between 1990 and 2021 in China and characterize its spatial and temporal variations following IPCC guideline Tier 2. The N2O emission factor (EF) of dairy cow manure management systems was determined at the national level and regional level as well. The results showed that the national cumulative N2O emission of manure management from 1990 to 2021 was 113.1million tons of CO2 equivalent, ranging from 90.3 to 135.9 million tons with an uncertainty of ±20.2%. The annual EF was 0.021 kg N2O-N (kg N)−1 for total emissions, while it was 0.014 kg N2O-N (kg N)−1 for direct emissions. The proportions of N2O emissions in North China, Northeast China, East China, Central and Southern China, Southwest China and Northwest China were 32.3%, 18.6%, 11.4%, 5.8%, 6.1% and 25.8%, respectively. In addition, N2O emissions varied among farms in different scales. The respective proportions of total N2O emissions from small-scale and large-scale farms were 64.8% and 35.2% in the past three decades. With the improvement in farm management and milk production efficiency, the N2O emissions per unit mass of milk decreased from 0.77 × 10−3 kg to 0.48 × 10−3 kg in 1990–2021. This study may provide important insights into compiling a GHG emission inventory and developing GHG emission reduction strategies for the dairy farming system in China. [ABSTRACT FROM AUTHOR]

• The nosZ gene of N 2 O reductase determined by paddy soil tillage state. • The clade Ⅱ and Ⅰ nosZ gene was dominated in the tillage and fallow period, respectively. • Heavy-metal pollution inhibited the N 2 O emission while not affecting the genes' switch. • The genus Bradyhizobium most significantly regulated the N 2 O flux. Paddy soils are an important source of atmospheric nitrous oxide (N 2 O). However, numerous studies have focused on N 2 O production during the soil tillage period, neglecting the N 2 O production during the dry fallow period. In this study, we conducted an incubation experiment using the acetylene inhibition technique to investigate N 2 O emission and reduction rates of paddy soil profiles (0-1 m) from Guangdong Province and Jinlin Province in China, with different heavy-metal pollution levels. The abundance and community structures of denitrifying bacteria were determined via quantitative -PCR and Illumina MiSeq sequencing of nosZ, nirK , and nirS genes. Our results showed that the potential N 2 O emission rate, N 2 O production rate, and denitrification rate have decreased with increasing soil vertical depth and heavy-metal pollution. More importantly, we found that the functional gene type of N 2 O reductase switched with the tillage state of paddy soils, which clade Ⅱ nosZ genes were the dominant gene during the tillage period, while clade Ⅰ nosZ genes were the dominant gene during the dry fallow period. The heavy-metal pollution has less effect on the niche differentiation of the nosZ gene. The N 2 O emission rate was significantly regulated by the genus Bradyhizobium , which contains both N 2 O reductase and nitrite reductase genes. Our findings suggests that the nosZ gene of N 2 O reductase can significantly impact the N 2 O emission from paddy soils. [Display omitted] [ABSTRACT FROM AUTHOR]

China is among the top nitrous oxide (N2O)-emitting countries, but existing national inventories do not provide full-scale emissions including both natural and anthropogenic sources. We conducted a four-decade (1980 – 2020) of comprehensive quantification of Chinese N2O inventory using empirical emission factor method for anthropogenic sources and two up-to-date process-based models for natural sources. Total N2O emissions peaked at 2287.4 (1774.8 – 2799.9) Gg N2O yr−1 in 2018, and agriculture-developed regions, like the East, Northeast, and Central, were the top N2O-emitting regions. Agricultural N2O emissions have started to decrease after 2016 due to the decline of nitrogen fertilization applications, while, industrial and energetic sources have been dramatically increasing after 2005. N2O emissions from agriculture, industry, energy, and waste represented 49.3%, 26.4%, 17.5%, and 6.7% of the anthropogenic emissions in 2020, respectively, which revealed that it is imperative to prioritize N2O emission mitigation in agriculture, industry, and energy. Natural N2O sources, dominated by forests, have been steadily growing from 317.3 (290.3 – 344.1) Gg N2O yr−1 in 1980 to 376.2 (335.5 – 407.2) Gg N2O yr−1 in 2020. Our study produces a Full-scale Annual N2O dataset in China (FAN2020), providing emergent counting to refine the current national N2O inventories. [ABSTRACT FROM AUTHOR]

A multiple cropping system is beneficial for utilizing natural resources, while increasing the grain production and economic outputs. However, its impact on greenhouse gas emissions is unclear. The objective of this study was to evaluate the influence of rice-based cropping systems on methane (CH4) and nitrous oxide (N2O) emissions, the carbon footprint (CF), grain yields, and net economic returns in eastern China. Four treatments were applied: rice–fallow (as a control), rice–milk vetch, rice–wheat, and rice–rapeseed. Methane and N2O emissions were measured every 7 days via static chamber and gas chromatography methods from the 2019 rice season to the 2021 non-rice season. The CF was calculated based on the life cycle assessment. The results showed that multiple cropping systems significantly increased the annual grain yield by 1.2–6.4 t ha−1 and the annual CH4 and N2O emissions by 38–101 kg CH4-C ha−1 and 0.58–1.06 kg N2O-N ha−1, respectively. The average annual net returns for rice–wheat and rice–rapeseed were 131–150% greater than those for rice–milk vetch and rice–fallow. The annual CFs increased in the following order: rice–wheat (19.2 t CO2-eq ha−1) > rice–rapeseed (16.6 t CO2-eq ha−1) > rice–milk vetch (13.9 t CO2-eq ha−1) > rice–fallow (11.5 t CO2-eq ha−1). The CH4 emissions contributed to the largest share of the CF (60.4–68.8%), followed by agricultural inputs (27.2–33.7%) and N2O emissions (2.9–5.9%). Moreover, nitrogen fertilizer accounted for 65.6–72.4% of the indirect greenhouse gas emissions from agricultural inputs. No significant difference in the CF per unit grain yield was observed between the four rice-based cropping systems. The CF per net return of rice–wheat and rice–rapeseed significantly decreased by 37–50% relative to that of rice–fallow and rice–milk vetch. These findings suggest the potential to optimize rice-based cropping systems for environmental sustainability and grain security. [ABSTRACT FROM AUTHOR]

Denitrification plays a critical role in soil nitrogen (N) cycling, affecting N availability in agroecosystems. However, the challenges in direct measurement of denitrification products (NO, N2O, and N2) hinder our understanding of denitrification N losses patterns across the spatial scale. To address this gap, we constructed a data‐model fusion method to map the county‐scale denitrification N losses from China's rice fields over the past decade. The estimated denitrification N losses as a percentage of N application from 2009 to 2018 were 11.8 ± 4.0% for single rice, 12.4 ± 3.7% for early rice, and 11.6 ± 3.1% for late rice. The model results showed that the spatial heterogeneity of denitrification N losses is primarily driven by edaphic and climatic factors rather than by management practices. In particular, diffusion and production rates emerged as key contributors to the variation of denitrification N losses. These findings humanize a 38.9 ± 4.8 kg N ha−1 N loss by denitrification and challenge the common hypothesis that substrate availability drives the pattern of N losses by denitrification in rice fields. [ABSTRACT FROM AUTHOR]

Flooded paddy soils after rewetting dry soils accompanied by extensive nitrogen fertilizer input are important anthropogenic N2O emitters due to the denitrification process. Owing to multiple complex denitrifying N2O sources, however, the extent to which biotic (fungal or bacterial) and abiotic (chemical) denitrification contribute to total N2O emissions remains largely unquantified. Here we sampled across eight provinces where most of the flooded paddy soils were in China to explore microbial and abiotic denitrification potentials and decipher N2O dynamics. N2O isotopocules and site preference (δ15NSP) analyses found that in most of the sampled paddy soils, fungi‐mediated denitrification was the largest N2O contributor (51%–63%); while bacterial and chemical denitrifications contributed 12%–31% and 12%–28% of N2O emissions, respectively. Further, using 15N labeling, a significant spatial heterogeneity of denitrification performance was observed among these flooded paddy soils. As indicated by variance partitioning and regression analyses, this heterogeneity was mainly determined by soil properties (especially soil organic carbon and total nitrogen) rather than by denitrifying communities. Our findings provide insights into the establishment of predictive models of future N2O emission from global paddy soils considering both the biotic and abiotic contributions. [ABSTRACT FROM AUTHOR]

Cropland ecosystems are significant emission sources of N2O, but a limited number of studies have focused on the impact of extreme weather events on N2O fluxes from cropland. This present study integrated field observations and model simulations to explore the responses of N2O fluxes to extreme weather events in typical rice and wheat rotation croplands in the middle and lower reaches of the Yangtze River (MLRYR) in China. The findings revealed that the studied rice-wheat rotation cropland exhibited a net source of N2O over the three-year monitoring period, with annual cumulative N2O emissions ranging from 190.4 to 261.8 mg N m−2. N2O emissions during the rice and wheat growing seasons accounted for 29% and 71% of the total yearly emissions, respectively. Extreme heat events led to a 23% to 32% increase in observed N2O emissions from cropland. Observed N2O emissions from irrigated rice fields during extreme precipitation events were 45% lower than those during extreme drought events. In contrast, extreme precipitation events raised observed N2O emissions from rain-fed wheat fields by 36% compared to the multi-year average, while extreme drought events reduced N2O emissions from wheat fields by 20%. Regional simulations indicated that annual cumulative N2O emissions from croplands in the MLRYR are projected to increase from 207.8 mg N m−2 under current climate to 303.4 mg N m−2 in the future. Given the episodic nature and uncertainties associated with N2O emissions from cropland, further validation is necessary for utilizing the model to explore the effects of extreme weather events on N2O in cropland ecosystems. [ABSTRACT FROM AUTHOR]

Anthropogenic greenhouse gas (GHG) emissions from croplands are primarily attributed to nitrogen (N) fertilization in agricultural production. However, the interactive effects of various agricultural management practices, climatic conditions, soil properties, and fertilization on non-CO2 GHG emissions (specifically methane (CH4) and nitrous oxide (N2O)) and gross global warming potential (GGWP) have been scarcely discussed. In this study, we conducted a meta-analysis of 326 agricultural treatments in China from 76 literature sources to elucidate the relationship between the response ratio (RR) of GGWP (GGWP RR), CH4 (CH4 RR), and N2O emissions (N2O RR) and various explanatory variables using redundancy analysis. Generally, nitrogen fertilizer application increased the N2O and CH4 emissions and GGWP by 120.0%, 32.5%, and 107.9%, respectively. We found that the GGWP RR was closely related to the rate of organic fertilizer application and initial bulk density, while it showed a negative association with the initial total soil nitrogen content. We found that CH4-RR was positively associated with the rate of synthetic fertilizer application, and N2O-RR exhibited a positive association with initial soil organic carbon and annual mean precipitation. Notably, the total fertilizer application rate had the most significant impact on both the GGWP RR and the N2O RR, while mean annual precipitation contributed the most to CH4-RR. Furthermore, a sensitivity analysis using a machine learning model suggested that the GGWP RR was more sensitive to synthetic fertilizer than to straw application, and reducing synthetic fertilizer by 30% from the current condition is likely to be the most effective way to alleviate the effect of fertilization on GGWP. [ABSTRACT FROM AUTHOR]

In the pursuit of establishing a more environmentally sustainable and low-carbon hog farming system, the accurate quantification of emissions of greenhouse gas emanating from these systems, especially within the context of China, becomes imperative. Here, drawing insights from a life cycle approach, exhaustive field surveys, and context-specific analyses, we establish an emission measurement index system tailored to hog farming enterprises in China's Shaanxi Province. Using this methodology, we probed the emission profiles and characteristics of three emblematic hog farming enterprises in the region. Our key findings are as follows: (1) The carbon dioxide emissions per kilogram of pork, factoring in feed cultivation, processing, and transportation, for Pucheng Xinliu Science and Technology, Baoji Zhengneng Farming, and Baoji Zhenghui Farming were quantified as 0.80298 kg, 1.52438 kg, and 0.81366 kg, respectively. (2) Presently, the methane emission coefficient due to enteric fermentation in large-scale hog farms in Shaanxi surpasses the default value set by the Intergovernmental Panel on Climate Change (IPCC). There appears to be a consistent underestimation of enteric methane emissions from live pigs in the province, as gauged against the IPCC metrics. Notably, the emission factor for fattening pigs averaged 2.61823 kgCH4/head/year, while that for breeding pigs stood at 2.96752 kgCH4/head/year. (3) When examining methane and nitrous oxide outputs from manure across various production stages, we observed that emissions from lactating pigs significantly outweigh those from other stages. Interestingly, nitrous oxide emissions from breeding pigs during fattening, finishing, and gestation remained nearly the same, regardless of the manure treatment method. (4) Under the management protocols followed by Pucheng and Baoji, the total carbon emissions from an individual fattening pig amounted to 328.5283 kg and 539.2060 kg, respectively, whereas for breeding pigs, these values were 539.2060 kg and 551.6733 kg, respectively. Further calculations showed that the average carbon footprint CF of large-scale pig farms in China was 3.6281 kgCO2/kg pork. In conclusion, optimizing feed cultivation and transportation logistics, promoting integrated breeding and rearing practices, refining feed formulation, and advancing manure management practices can collaboratively attenuate greenhouse gas emissions. Such synergistic approaches hold promise for steering the hog industry towards a greener, low-carbon, and sustainable trajectory. [ABSTRACT FROM AUTHOR]

The increasing atmospheric nitrous oxide (N2O) concentration stems from the development of agriculture. However, N2O emissions from global rice‐based ecosystems have not been explicitly and systematically quantified. Therefore, this study aims to estimate the spatiotemporal magnitudes of the N2O emissions from global rice‐based ecosystems and determine different contribution factors by improving a process‐based biogeochemical model, TRIPLEX‐GHG v2.0. Model validation suggested that the modeled N2O agreed well with field observations under varying management practices at daily, seasonal, and annual steps. Simulated N2O emissions from global rice‐based ecosystems exhibited significant increasing trends from 0.026 ± 0.0013 to 0.18 ± 0.003 TgN yr−1 from 1910 to 2020, with ∼69.5% emissions attributed to the rice‐growing seasons. Irrigated rice ecosystems accounted for a majority of global rice N2O emissions (∼76.9%) because of their higher N2O emission rates than rainfed systems. Regarding spatial analysis, Southern China, Northeast India, and Southeast Asia are hotspots for rice‐based N2O emissions. Experimental scenarios revealed that N fertilizer is the largest global rice‐N2O source, especially since the 1960s (0.047 ± 0.010 TgN yr−1, 35.24%), while the impact of expanded irrigation plays a minor role. Overall, this study provides a better understanding of the rice‐based ecosystem in the global agricultural N2O budget; further, it quantitively demonstrated the central role of N fertilizer in rice‐based N2O emissions by including rice crop calendars, covering non‐rice growing seasons, and differentiating the effects of various water regimes and input N forms. Our findings emphasize the significance of co‐management of N fertilizer and water regimes in reducing the net climate impact of global rice cultivation. Plain Language Summary: Nitrous oxide (N2O) is a greenhouse gas with ∼300 times greater effect on climate warming than carbon dioxide. Global croplands represent the largest source of anthropogenic N2O emissions. However, the contribution of global rice‐based cropping ecosystems to the N2O budget remains largely uncertain because of inconsistent observed results. Inspired by the increasing availability of reliable global data sets, we improved and applied a process‐based biogeochemical model by describing the dynamics of various microbial activities to simulate N2O emissions from rice‐based ecosystems on a global scale. Model simulations showed that 0.18 million tons of N2O‐N were emitted from global rice‐based N2O emissions in the 2010s, which was five times larger than that in the 1910s. In the context of regional contribution, southern China, northern India, and Southeast Asia are responsible for more than 80% of the total emissions during 1910–2020. Results suggest that N fertilizer is the most important rice‐N2O source quantitively and that increasing irrigation exerts a buffering effect. This study confirmed the potential mitigating effect of co‐managing N fertilizer and irrigation on mitigating rice‐based N2O emissions globally. Key Points: N2O emissions from global rice‐based ecosystem increased from 0.026 to 0.18 TgN yr−1 between 1910 and 2020Irrigated rice‐based ecosystems showed larger N2O fluxes than rainfed rice globally due to higher N fertilizer use and frequent aerationsN fertilizer represents the largest N2O source, and co‐management of N fertilizer and flooding regimes is important for mitigation [ABSTRACT FROM AUTHOR]

To evaluate the effects of application of biochar and straw return for consecutive years on N2O emissions and crop yields in North China, a three-year field experiment of applying biochar and straw following a ten-year application was conducted in a wheat–maize rotation system. Four treatments were set up, including F (NPK fertilizer only); FB (NPK fertilizer + 9.0 t·ha−1 biochar); FS (NPK fertilizer + straw); and FSB ((NPK fertilizer + 9.0 t·ha−1 biochar combined with straw). The results showed that compared with the F treatment, the FB treatment significantly reduced soil N2O emissions by 20.2%, while the FS and FSB treatments increased it by 23.7% and 41.4%, respectively. The FB treatment reduced soil N2O emissions by 15.1% in the wheat season and 23.2% in the maize season, respectively. The FS and FSB treatments increased the N2O emissions by 20.7% and 36.7% in the wheat season, respectively, and by 25.5% and 44.2% in the maize season, respectively. In the wheat season, the soil water content (SWC), NO3−-N content and pH were the main influencing factors of the soil N2O emissions. In the maize season, SWC and NO3−-N content were the main influencing factors. In addition, the FB, FS and FSB treatments increased the crop yield by 4.99%, 8.40% and 10.25% compared with the F treatment, respectively. In conclusion, consecutive application of biochar can significantly reduce N2O emissions and improve crop yield. Although FS and FSB treatments can also improve the crop yield, they are not beneficial to suppressing N2O emissions. Therefore, the successive application of biochar is an effective measure to reduce N2O emissions and maintain crop yield. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) is a long-lived potent greenhouse gas and stratospheric ozone-depleting substance, which has been accumulating in the atmosphere since the pre-industrial period. The mole fraction of atmospheric N2O has increased by nearly 25% from 270 parts per billion (ppb) in 1750 to 336 ppb in 2022, with the fastest annual growth rate since 1980 of more than 1.3 ppb yr-1 in both 2020 and 2021. As a core component of our global greenhouse gas assessments coordinated by the Global Carbon Project (GCP), we present a global N2O budget that incorporates both natural and anthropogenic sources and sinks, and accounts for the interactions between nitrogen additions and the biochemical processes that control N2O emissions. We use Bottom-Up (BU: inventory, statistical extrapolation of flux measurements, process-based land and ocean modelling) and Top-Down (TD: atmospheric measurement-based inversion) approaches. We provide a comprehensive quantification of global N2O sources and sinks in 21 natural and anthropogenic categories in 18 regions between 1980 and 2020. We estimate that total annual anthropogenic N2O emissions increased 40% (or 1.9 Tg N yr-1) in the past four decades (1980-2020). Direct agricultural emissions in 2020, 3.9 Tg N yr-1 (best estimate) represent the large majority of anthropogenic emissions, followed by other direct anthropogenic sources (including 'Fossil fuel and industry', 'Waste and wastewater', and 'Biomass burning' 2.1 Tg N yr-1), and indirect anthropogenic sources (1.3 Tg N yr-1). For the year 2020, our best estimate of total BU emissions for natural and anthropogenic sources was 18.3 (lower-upper bounds: 10.5-27.0) Tg N yr-1, close to our TD estimate of 17.0 16.6-17.4) Tg N yr-1. For the period 2010-2019, the annual BU decadal-average emissions for natural plus anthropogenic sources were 18.1 (10.4-25.9) Tg N yr-1 and TD emissions were 17.4 (15.8-19.20 Tg N yr-1. The once top emitter Europe has reduced its emissions since the 1980s by 31% while those of emerging economies have grown, making China the top emitter since the 2010s. The observed atmospheric N2O concentrations in recent years have exceeded projected levels under all scenarios in the Coupled Model Intercomparison Project Phase 6 (CMIP6), underscoring the urgency to reduce anthropogenic N2O emissions. To evaluate mitigation efforts and contribute to the Global Stocktake of the United Nations Framework Convention on Climate Change, we propose establishing a global network for monitoring and modeling N2O from the surface through the stratosphere. The data presented in this work can be downloaded from https://doi.org/10.18160/RQ8P-2Z4R (Tian et al. 2023). [ABSTRACT FROM AUTHOR]

The article presents the discussion on neuropathy being severe coming on rapidly, mimicking Guillain-Barré syndrome (GBS). Topics include electrodiagnostic studies typically showing a predominantly sensorimotor axonal neuropathy, mostly involving the legs, with decreased motor and sensory amplitudes; and resulting in gait ataxia, paresthesiae, autonomic dysfunction, and cognitive impairment.

Biochar has been widely recommended as an effective soil amendment for reducing nitrous oxide (N2O) emissions and nitrogen (N) leaching. However, the effects of biochar application to Lei bamboo plantations on soil N2O emissions and N leaching remain unclear. These effects on soil N2O emissions and N leaching were investigated in the present study using five treatments applied with the same amount of N: rice husk at 10 t ha−1 (10H) and 30 t ha−1 (30H), biochar at 10 t ha−1 (10B) and 30 t ha−1 (30B), and no additions (control, CK). Both the 10H and 30H treatments significantly increased cumulative N2O emissions compared to the CK treatment, with an increment of 0.78 and 2.20 kg N ha−1, respectively. The 30B treatment significantly reduced cumulative N2O emissions by 0.90 kg N ha−1, whereas the 10B treatment had no significant effect. The reduction in N2O emissions following the high-rate biochar addition was probably due to the increased pH and the total abundance of nosZ I and nosZ II genes. The 30H treatment significantly increased nitrate N (NO3−–N) and dissolved organic N (DON) leaching by 38% and 170% respectively compared to the CK treatment, and had the largest N loss via N2O emissions and N leaching, while the 30B treatment had the lowest N loss. Partial least squares path modeling revealed that soil chemical properties [ammonium nitrogen (NH4+–N), NO3−–N, DON, dissolved organic C (DOC), total N (TN), soil organic C (SOC), and pH] dominantly affected soil N2O emissions, while the total abundance of denitrifying genes (nirS, nirK, nosZ I, and nosZ II) were the key factors involved in reducing NO3−–N leaching. There was a strong positive correlation between cumulative N2O emissions and N leaching loss, which may be related to excessive N surplus in the soil. Our results suggest that the replacement of rice husk by its biochar at a high-rate would reduce the risk of N2O emissions and N leaching loss effectively from Lei bamboo forests in subtropical China. [ABSTRACT FROM AUTHOR]

Anthropogenic activity has caused rivers and reservoirs to become sources of nitrous oxide (N2O), which is thought to play an important role in global climate change. There are thermal and DO stratification in deep-water reservoirs with long hydraulic retention time, which change N2O production mechanism compared with shallow-water reservoirs. To promote our understanding of the relationship of N2O production in reservoirs at different depths, spatiotemporal variations in water environmental factors and N2O from cascade reservoirs of Chaishitan (CST), Longtan (LT), Yantan (YT) and Dahua (DH) reservoirs in the Zhujiang River were detected, and the LT and YT reservoirs were compared as representatives of deep-water and shallow-water reservoirs in April and July 2019. The average N2O concentrations in the LT and YT reservoirs were 22.82 ± 2.21 and 21.55 ± 1.65 nmol L−1, respectively. During spring and summer, the WT (water temperature) and DO (dissolved oxygen) concentrations in the YT reservoir were well mixed. In contrast, the LT reservoir, as a deep-water reservoir, had thermal and DO stratifications in both the shallow and middle water, especially in the summer when the solar radiation intensity was high. During summer stratification, the DO concentration in the LT reservoir showed obvious spatial variation, ranging from 1.23 to 9.84 mg L−1, while the DO concentration in the YT reservoir showed very little variation, ranging from 6.45 to 7.09 mg L−1. Structural equation modeling results showed that NH4+ was the main determinant of the N2O concentration in the YT reservoir, and DO was the most influential factor of the N2O concentration in the LT reservoir. These results suggest significant variations in the factors influencing N2O concentration among reservoirs. Additionally, the mechanisms of N2O production differ between deep-water and shallow-water reservoirs. This study highlights the spatio-temporal variations and influential factors contributing to N2O concentration. Furthermore, it discusses the production mechanisms of N2O in different types of reservoirs. These findings contribute to our understanding of N2O distribution in hydropower systems and provide valuable data for the management of hydropower facilities and research on greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

In the light of China's carbon-neutral goal, this study examines how food production, forest cover, trade openness, and rural population contribute to the quest of addressing China's agricultural nitrous oxide emissions. Time series data ranging from 1971 to 2018 was used for analysis in this study. The autoregressive distributed lag (ARDL) technique was employed to evaluate potential cointegration as well as to ascertain the long and short-run effects of food production, forest cover, income, trade openness, and rural population on agricultural nitrous oxide emission. The Toda-Yamomoto causality analysis was also used to identify the causal relations between covariates (food production, forest cover, income, trade openness, and rural population) and the outcome variable (agricultural nitrous oxide emission). The long-run evidence is that rural population in itself tends to increase agricultural nitrous oxide emissions likewise food production. There is also validation of the existence of environmental Kuznets curve for agricultural nitrous oxide emissions. Moreover, income interacts with rural population to reduce agricultural nitrous oxide emissions in the long-run. Causality analysis indicated rural population affects the level of forest cover; forest cover is found to cause agricultural nitrous oxide emissions but the converse is not established, and income as well as the interaction between income and rural population determines agricultural nitrous oxide emissions. The short-run dynamics results establish an oscillatory equilibrium convergence for agricultural nitrous oxide emissions in event of structural disturbances. From the findings, the EKC hypothesis is relevant by offering avenue to reduce emission. Thus, income growth remains helpful in addressing nitrous oxide emission from the agricultural sector. However, research is needed to unravel why nitrous oxide tends to increase in many forest areas. Since food production cannot be halted, policy makers need to enhance the uptake of efficient food production technologies including developing and using more renewable energy for food production. It is important for authorities to attend to rural development in order to mitigate agricultural nitrous oxide emissions in China. [ABSTRACT FROM AUTHOR]

It is widely acknowledged that greenhouse gases (GHG) like carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) play a key role in the development of global climate change. 17% of China's GHG came from the agricultural industry. For China's future development, it is essential to investigate low-carbon emission paths in planting fields, as one of the key components of agriculture. In this study, the IPCC method was used to estimate the total carbon emission from cultivation in Eastern China. The Tapio decoupling model was used to study the relationship between economic growth and carbon emission. An extended STIRPAT stimulus model was established to predict the carbon emission of the planting industry in East China with three development paths. The results show that carbon emission in East China has shown a fluctuating downward trend with a peak in 1999, which has strong decoupling characteristics with economic growth. Adjusting agricultural structure and raising the mechanization rate can remarkably reduce agricultural carbon emission. Compared to 2020, carbon emission in 2035 will decrease by 12.50%, 13.68%, and 14.32% with Baseline, Low-carbon, and Enhanced Low-carbon scenarios, respectively. Effective measures such as optimizing planting structure by adjusting rice area, promoting intensive mechanization, and improving fertilizer use efficiency can reduce carbon emission actively. [ABSTRACT FROM AUTHOR]

Purpose: We sought to identify the effects of elevationally (1560−2160 m) driven climate (mean annual air temperatures of + 4.0 to + 10 oC and mean annual precipitation of 900–1200 mm), forest type and soil property variations on soil greenhouse gas (GHG) fluxes in the Qinling Mountains, China. Methods: Soil GHGs were monitored at five temperate forest sites using static chambers for two full years. The related edaphoclimatic parameters were also monitored. Results: The cumulative soil CO2 and N2O emissions and the CH4 uptake from the five sites ranged between 3.82 to 7.48 t CO2-C ha−1 yr−1, 1.19 to 2.25 kg N2O-N ha−1 yr−1, and 0.89 to 5.67 kg CH4-C ha−1 year−1, respectively. Average soil CO2 emissions decreased with increasing site elevation, whereas CH4 and N2O fluxes showed no clear relationship with site elevation. All sites were net CH4 sinks. Occasionally, soils switched to net sources of CH4 during summer or autumn rainfall events at all sites. All sites were net N2O sources although short periods of soil N2O uptake were observed during freeze–thaw cycles and during summer rainfall. The source strength of N2O and CH4 differed during summer and winter and snowfall which had direct effects on soil water content. Conclusions: Site elevation could be used as a predictive variable for constructing regional soil CO2 emissions budgets, whereas soil CH4 and N2O fluxes are driven by a more complex interplay of climatic and soil biochemical variables, which are more difficult to integrate on a regional scale. [ABSTRACT FROM AUTHOR]

Hydroxylamine (NH2OH) is an important intermediate of nitrification and can contribute to nitrous oxide (N2O) production through abiotic and biotic pathways. NH2OH concentrations and associated biogeochemical controls in estuarine water and sediments remain poorly understood. Here, we investigated spatial and seasonal variability of NH2OH concentrations in water and sediments and determined the correlation between NH2OH and N2O in the Min River Estuary off southeast China. NH2OH concentrations in water and sediments ranged from 0.22 to 140 nmol N L−1 and from 0.17 to 9.22 μmol N kg−1, respectively. High differences in NH2OH concentrations between sediments and water could drive diffusion of NH2OH from sediments to water. NH2OH concentrations were significantly higher in warm than in cold seasons, suggesting that NH2OH production is highly dependent on temperature. Upper estuary (urban section) showed higher NH2OH concentrations in water and sediments, followed by lower and middle estuary. Temperature, dissolved oxygen, and pH were the major factors driving spatial and seasonal variability in NH2OH concentrations. Water dissolved N2O concentrations and air‐water N2O fluxes varied between 1.52 and 55.9 nmol N L−1 and between −57.7 and 78.7 nmol N m−2 h−1, respectively, with switches from net sinks in spring to net sources of N2O emissions in other seasons. Although N2O concentrations and fluxes were linearly correlated with water NH2OH concentrations, the contribution of NH2OH to N2O production could not be addressed. Therefore, the dynamics of NH2OH concentrations are a useful tool to assess potential production and consumption pathways of N2O in estuarine and coastal ecosystems. Plain Language Summary: Hydroxylamine (NH2OH) can produce nitrous oxide (N2O) through abiotic and biological processes in estuarine and coastal environments. This study investigated seasonal and spatial variability of NH2OH concentrations in water and sediments and determined the correlation between N2O and NH2OH concentrations in the Min River Estuary off southeast China. NH2OH concentrations in water and sediments varied significantly across the seasons and along this estuary, with higher concentrations in warm seasons and in upper estuary. High temperature could cause low dissolved oxygen and low pH that stimulate nitrification to produce more NH2OH and NO2−, which increased NH2OH oxidation and nitrifier‐denitrification to yield more N2O. N2O concentrations and fluxes were significantly related to NH2OH concentrations, suggesting that NH2OH could be a relevant source of N2O emissions. This study shows the effect of NH2OH production in the emissions of N2O, providing insights which can be used to better constrain the projections on future emissions of this gas in estuarine environments. Key Points: Hydroxylamine concentrations in water and sediments were significantly higher in warm than in cold seasonsAmmonium and temperature were the major drivers of spatiotemporal variability in hydroxylamine concentrationsHydroxylamine and nitrous oxide concentrations in water and sediments were strongly correlated [ABSTRACT FROM AUTHOR]

Greenhouse gas (GHG) and ammonia (NH3) emissions from wheat fields have been a serious challenge to agriculture and the environment. The integration of the use of inorganic N fertilizer, organic fertilizer, and crop residues and their environmental effects is needed under conventional tillage. In situ field experiments were established to evaluate the impact of different fertilization practices on soil greenhouse gas and ammonia emissions from a winter wheat field. A fertilizer experiment was performed from 24th October 2019 to 11th June 2020 in a winter wheat (Triticum aestivum L.) field in China with six fertilization treatments: (1) unfertilized control (UC); (2) recommended mineral fertilizer application of 200 kg ha−1 N (RF); (3) RF plus 15 t ha−1 of organic fertilizer (RFLO); (4) RF plus 30 t ha−1 of organic fertilizer (RFMO); (5) RF plus 45 t ha−1 of organic fertilizer (RFHO); and (6) traditional mineral fertilizer application of 300 kg ha−1 N (TF). The results showed that the RF plus organic fertilizer treatments increased the soil organic total carbon (TC) and nitrogen (TN) levels. Under long-term fertilization, the CO2 emissions from the RFLO, RFMO, and RFHO treatments were 18.3, 19.9, and 20.0 t ha-1, respectively, compared with those from the RF and TF treatments (13.2 and 16.0 t ha-1, respectively). In addition, the N2O emissions from the organic-inorganic fertilizer treatment were 7.6 kg ha-1 for the RFLO treatment, 12.4 kg ha-1 for the RFMO treatment, and 8.1 kg ha-1 for the RFHO treatment, which were higher than those from the RF and TF treatments (3.1 and 5.6 kg ha-1, respectively). The NH3 emissions from the RFLO, RFMO, and RFHO treatments (17.3, 26.2, and 22.4 kg ha-1, respectively) were lower than those from the RF (31.2 kg ha-1) and TF (49.7 kg ha-1) treatments under long-term fertilization. The methane emission potential of organic-inorganic fertilizer applications was 27.0% to 98.5% higher than a single application of inorganic fertilizer. [ABSTRACT FROM AUTHOR]

Open vegetable fields in China are a major anthropogenic source of nitrous oxide (N2O) emissions due to excessive nitrogen (N) fertilization. A 4 yr lettuce experiment was conducted to determine the impacts of controlled-release fertilizers (CRFs) and nitrification inhibitors (NIs) on lettuce yield, N2O emissions and net economic benefits. Five treatments included (i) no N fertilizer (CK), (ii) conventional urea at 255 kg N ha–1 based on farmers' practice (FP), (iii) conventional urea at 204 kg N ha–1 (OPT), (iv) CRF at 204 kg N ha–1 (CU) and (v) CRF (204 kg N ha–1) added with NI (CUNI). No significant differences were found in the lettuce yields among different N fertilization treatments. Compared with FP, the cumulative N2O emissions were significantly decreased by 8.1%, 38.0% and 42.6% under OPT, CU and CUNI, respectively. Meanwhile, the net benefits of OPT, CU and CUNI were improved by USD 281, USD 871 and USD 1024 ha–1 compared to CN, respectively. This study recommends the combined application of CRF and NI at a reduced N rate as the optimal N fertilizer management for the sustainable production of vegetables in China with the lowest environmental risks and the greatest economic benefits. [ABSTRACT FROM AUTHOR]

It is well recognized that straw return (SR) can improve soil fertility and soil organic carbon (SOC) storage. Increasing planting density and reducing nitrogen fertilizer application is considered an effective cultivation technique for japonica rice in central and northern China. However, few are known about the mechanisms of differences between wheat SR with rice planting densification and N reduction (SRD) and wheat SR on greenhouse gas emissions and soil bacteria communities in central China. A 2-year experiment was conducted to evaluate the effects of SR and SRD compared with straw removal (NS) on methane (CH4) and nitrous oxide (N2O) emission, rice yield, and soil properties in Henan Province, China, in 2019 and 2020. We found that SRD increased SOC, available phosphorous (AP), and available potassium (AK) compared to SR and NS in 2019 and 2020. The mean CH4 flux was positively correlated with SOC, and the cumulative CH4 emissions of SR and SRD plots were significantly higher than those of NS plots. No significant difference in cumulative CH4 emissions was detected between the SR and SRD treatments. N2O emissions were significantly lower under SRD than SR. SRD significantly affected soil bacteria diversity and composition at a depth of 0–15 cm. The relative abundance of Bacteroidota in SRD soil was 1.37- and 3.73-fold higher than that in NS and SR soils, respectively. The relative abundance of nitrate reduction–related operational taxonomic units enriched under SRD was significantly lower than that under SR, indicating that lower nitrate reduction of N2O production was induced by soil bacteria under SRD. N partial factor productivity was 21.4% and 28.5% higher under SRD than SR in 2019 and 2020, respectively. Our results suggest that SRD decreased soil bacteria N2O emissions; increased SOC, AP, and AK; and improved N fertilizer use efficiency, thereby improving rice yield in central China. [ABSTRACT FROM AUTHOR]

Streams and rivers are important sources of nitrous oxide (N2O), a powerful greenhouse gas. Estimating global riverine N2O emissions is critical for the assessment of anthropogenic N2O emission inventories. The indirect N2O emission factor (EF5r) model, one of the bottom‐up approaches, adopts a fixed EF5r value to estimate riverine N2O emissions based on IPCC methodology. However, the estimates have considerable uncertainty due to the large spatiotemporal variations in EF5r values. Factors regulating EF5r are poorly understood at the global scale. Here, we combine 4‐year in situ observations across rivers of different land use types in China, with a global meta‐analysis over six continents, to explore the spatiotemporal variations and controls on EF5r values. Our results show that the EF5r values in China and other regions with high N loads are lower than those for regions with lower N loads. Although the global mean EF5r value is comparable to the IPCC default value, the global EF5r values are highly skewed with large variations, indicating that adopting region‐specific EF5r values rather than revising the fixed default value is more appropriate for the estimation of regional and global riverine N2O emissions. The ratio of dissolved organic carbon to nitrate (DOC/NO3−) and NO3− concentration are identified as the dominant predictors of region‐specific EF5r values at both regional and global scales because stoichiometry and nutrients strictly regulate denitrification and N2O production efficiency in rivers. A multiple linear regression model using DOC/NO3− and NO3− is proposed to predict region‐specific EF5r values. The good fit of the model associated with easily obtained water quality variables allows its widespread application. This study fills a key knowledge gap in predicting region‐specific EF5r values at the global scale and provides a pathway to estimate global riverine N2O emissions more accurately based on IPCC methodology. [ABSTRACT FROM AUTHOR]

Aquatic environments are hot spots of nitrogen (N) cycling and nitrous oxide (N2O) emission. Understanding key N biogeochemical processes and N2O dynamics is critical for uncovering the responses of aquatic environments to human activities. In this study, we summarized the development of techniques and approaches for determination of N cycling processes and N2O sources in aquatic environments of China. We also reviewed the main N transformation processes and associated biogeochemical controls in aquatic environments of China (e.g., constructed wetlands, paddy fields, lakes, rivers, aquaculture ponds, and estuaries and coasts). In addition, we further synthesized N2O dynamics in these aquatic environments. The results suggested that N cycling processes have been greatly concerned in various aquatic environments of China, whereas more comprehensive analyses of N cycling processes are still sparse for projecting N fates and dynamics in response to changing environments, largely limiting the implementation of N management strategy of China. Aquatic environments of China may be the important sources of atmospheric N2O, but the production and consumption processes of N2O need to be further studied for effective greenhouse gas mitigation. We also argued that it is urgently necessary to incorporate microbial traits into biogeochemical ecosystem modeling to improve the estimation reliability of N cycling and N2O dynamics. This review highlights the importance of N cycling and N2O dynamics, as well as associated environmental implications, and presents the directions of future research on N cycling in aquatic environments of China. [ABSTRACT FROM AUTHOR]

As one of the important greenhouse gas, nitrous oxide (N2O) has attracted much attention globally under climate change context. Agricultural practices are the main sources of greenhouse gas emissions. Nevertheless, scarcity of literature is available on the effects of different tillage measures on soil N2O emission under spring wheat (Triticum aestivum L.) ecosystem in the semi-arid area of the Loess Plateau. The main objective of the experimental study was to explore the influence of conservation tillage techniques on soil physicochemical properties, nitrous oxide emission and yield in the Northern semi-arid Dingxi region of China. Four treatments viz., conventional tillage (CT), no tillage (NT), straw mulch with conventional tillage (TS) and stubble-return with no-till (NTS) were evaluated under randomized complete block design with three replications. Our results depicted that compared with conventional tillage, bulk density and water content of topsoil was increased and soil pH value was reduced under conservation tillage techniques. Conservation tillage NT, TS and NTS increased organic carbon, TN, MBN and NH4+-N and reduced the accumulation of NO3–N. Additionally, although the N2O emission under NT, TS and NTS was 8.95, 41.90 and 21.05% respectively higher than under T treatment, the corresponding wheat yield was 15.40, 31.97 and 63.21% higher than T treatment. Moreover, correlation analysis showed that soil moisture and temperature were the most significant factors affecting soil N2O emission. The NTS treatment pointedly increased crop yield without significantly increasing soil N2O emission. Consequently, based on economic and environmental benefits and considering N2O emission and crop yield, we suggest that NTS technique is the best conservation tillage strategy in the semi-arid environmental zone of the Loess Plateau of Dingxi China. [ABSTRACT FROM AUTHOR]

A systematic understanding of nitrous oxide (N2O) emission and grain yield in winter wheat–summer maize rotation, one of the most important cereal cropping systems in China, is still lacking. The primary aim of this study was to quantify the N2O emissions and grain yield, as well as responses to mitigation strategies, in this intensively managed agroecosystem. We conducted a pairwise meta-analysis by compiling a comprehensive dataset of annual N2O emissions (n = 530) and grain yields (n = 352) from peer−reviewed publications. The N2O emissions increased with nitrogen (N) fertilizer input rates following a linear model (r2 = 0.295, p < 0.001), giving a specific emission coefficient and background emission of 0.71% and 0.5 kg N ha−1 yr−1, respectively. The grain yields responded to the N input rates following a linear-plateau model (r2 = 0.478, p < 0.001), giving an optimal N input rate and maximum grain yield of 405 kg N ha−1 yr−1 and 15.5 t ha−1 yr−1, respectively. The meta-analyses revealed that reducing N fertilizers (approximately 50% of the full N input), water-saving irrigation, reduced or no tillage, and applying enhanced efficiency fertilizers significantly decreased N2O emissions (range: −45% to −9%) and increased or did not impact grain yields (range: −1% to 3%). We recommend that reducing agricultural inputs (i.e., N fertilizers, irrigation, and tillage) is a feasible N2O mitigation strategy in the intensively managed winter wheat–summer maize rotation that can be employed without additional environmental risks. [ABSTRACT FROM AUTHOR]

Background: Continuous nitrogen (N) deposition interferes with soil N cycling in forests, which highly impacts soil nitrous oxide (N2O) emissions and accelerates global warming. Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) is one of the most widely planted species in southern China, and is usually located in areas with high N deposition rates. However, the impact of N deposition on soil N2O emissions in subtropical Chinese fir plantations and the potential risk of increasing N input remain elusive. Methods: Here, we conducted an in situ study in a subtropical Chinese fir plantation at Fengyang Mountain Nature Reserve, China, from 2019 to 2020 with four N addition rates: control (CK: ambient N deposition), low-N (LN: 50 kg N ha−1 yr−1), medium-N (MN: 100 kg N ha−1 yr−1), and high-N (HN: 200 kg N ha−1 yr−1). Results: We found that soil N2O emission rates increased with N addition rates by 71%, 176%, and 241% under LN, MN, and HN treatment compared to CK, respectively, and reached a significant level only under HN. Soil moisture was significantly reduced together with increased leaf N concentrations under N addition. Meanwhile, the microbial biomass in the middle of the growing season was significantly lower than at the end of the growing season. These results may suggest that N deposition stimulated plants to take up more N and water, which intensified plant-microbe competition and therefore alleviated further increases in N2O emissions under N deposition, especially under low N inputs. N deposition enhanced the abundance of ammonia oxidizing archaea and bacteria and the accumulation of NO3−-N in the soil but did not affect the abundance of nitrate-reducing bacteria (nirS and nirK). The results likely support that nitrification processes act as the major source of enhanced N2O emissions under N fertilization. Conclusions: Our study advances our understanding of the impacts of N deposition on the soil N2O emissions in the Chinese fir plantations and highlights that plant N acquisition needs to be incorporated as an important explanatory variable when predicting N2O fluxes under global increases in N deposition. [ABSTRACT FROM AUTHOR]

Marginal seas play a critical role in the earth's systems as hotspots of microbially-mediated nitrogen (N) cycling. Meanwhile, human activities and global changes strongly impact this land-ocean boundary. Understanding the key N cycling processes and their climatic feedback is crucial for predicting the status of earth in the future and developing global N-driven physical-biogeochemical models. Although N cycling processes in China marginal seas have received great attention, a systematic analysis over a large geographical scale from estuaries to the deep ocean is still missing. This gap hinders us from concretely determining the sources and fate of N and predicting their responses to changing environments. This review compiles and re-analyzes historical data of source terms, encompassing N fluxes from riverine inputs and atmospheric deposition, as well as N 2 fixation. We also examine sinks related to sedimentary N loss processes (denitrification and anammox), internal N cycling processes (uptake and nitrification), short-lived N intermediates, and nitrous oxide, by considering rates, spatiotemporal variability, and environmental factors. Finally, we outline future research directions pertaining to marine N cycling in China marginal seas. [ABSTRACT FROM AUTHOR]

Large-scale planting of Chinese fir (Cunninghamia lanceolata) can bring considerable economic benefits but also seriously alters soil properties, disrupting soil microbial survival patterns and giving rise to distinct microbial communities. Nitrous oxide (N 2 O) reduction is the sole recognized biological sink for N 2 O, thereby playing a critical role in forest nitrogen cycling. However, the distribution of N 2 O reducers in Chinese fir plantation soils and the underlying factors at a regional scale remain unclear. Here, we assessed the abundance, diversity, and community structure of nosZ I-type N 2 O reducers in soil samples collected from nine state-owned forest farms in Fujian Province, China. The abundance of nosZ I-type reducers exhibited significant variation across sites, with altitude exerting the greatest influence, positively influencing their abundance. Soil organic carbon (SOC) and dissolved organic carbon (DOC) were the strongest predictors of alpha-diversity. Interestingly, SOC and DOC exhibited a negative association with nosZ I-type reducer alpha-diversity. Additionally, DOC played a significant role in influencing community structure. All nosZ I sequences were associated with Alphaprotebacteria and Betaproteobacteria, with Alphaproteobacteria dominating nosZ I-type reducer communities in all soils, accounting for over 90 % of the total sequences. Moreover, the modified stochasticity ratio values exceeded 0.5 at all sampling sites except for one, characterized by the lowest pH and relatively lower nutrient content, indicating the predominance of stochastic processes in community assembly. Taken together, our results provide novel evidence that the augmentation of organic carbon content could potentially reduce diversity and alter the structure of nosZ I-type reducer communities, with potential implications for N 2 O emissions in Chinese fir plantations. • Soil N 2 O reduction rates were positively associated with nosZ I gene abundance. • SOC and DOC were negatively associated with nosZ I-type reducer alpha-diversity. • DOC was a critical factor influencing nosZ I-type reducer community structure. • Alphaproteobacteria accounting for >90 % of nosZ I-type reducer sequences. • Stochastic processes dominated the community assembly of nosZ I-type reducer. [ABSTRACT FROM AUTHOR]

Nitrogen (N) fertilisation is critical for sugarcane crop production. Consequently, overuse of N fertiliser in sugarcane is widespread and it is most prevalent in China. Yet, a comprehensive analysis of sugarcane N balance accounting for different reactive N (Nr) loss pathways, crop N use and soil N retention using 15N labelled fertilisers under commercial high-input cropping conditions is lacking. A two-year field experiment with 5 N levels (0–560 kg N ha−1; N0, N210, N300, N390, N560) was conducted to quantify the effect of N rate on sugarcane yield, Nr loss through different loss pathways, crop N use and soil N retention, and to identify an optimal N rate that sustain high yield whilst reducing Nr loss in Southern China. The results showed that optimal N rate (N300) had similar yield compared with farmer practice (N560) for the plant crop and the ratoon crop. Nitrogen leaching and ammonia loss were increased significantly with increase in N rate, with farmer practice recording the highest Nr loss. Compared with farmer practice, under optimal N application, N leaching was reduced from 211 kg ha−1 to 107 kg ha−1 and from 244 kg ha−1 to 165 kg ha−1 for the plant and ratoon crops, respectively. The ammonia volatilization from the plant crop and the ratoon crop in the optimal N treatment was 24.8 kg ha−1 and 27.0 kg ha−1, respectively, which are considerably less compared with the emission from the farmer practice. There was no significant difference in nitrous oxide emission between optimal N rate and farmer practice. 15N labelling studies showed that crop N recovery, soil N residue and fertiliser N lost at the optimal N rate were 20.9%, 24.9% and 54.2%, respectively, as opposed to 12.5%, 14.8% and 72.7%. respectively, under farmer practice. To the best of our knowledge, this study forms the first comprehensive evaluation of sugarcane N balance accounting Nr loss, N use and native N soil stock covering a wide range of N supply simultaneously in the plant and ratoon crops under commercial crop production condition. This study thus provides very valuable new knowledge not only for crop N supply optimisation in high-input sugarcane production systems as in China but also for sugarcane greenhouse gas accounting studies particularly from climate change mitigation and bioenergy production context. [Display omitted] • First detailed sugarcane crop N balance (Nr loss, N use, soil N stock) estimated. • Current average sugarcane crop N input in China (560 kg N ha−1) very excessive. • Large reduction in N input and Nr loss without yield loss in multi-year field trials. • Leaching, the single largest N loss pathway in sugarcane crop. • Large crop N recovery, fertiliser N loss reduction with optimal N use (300 kg N ha−1). [ABSTRACT FROM AUTHOR]

Aquaculture systems are expected to act as potential hotspots for nitrous oxide (N 2 O) emissions, largely attributed to substantial nutrient loading from aquafeed applications. However, the specific patterns and contributions of N 2 O fluxes from these systems to the global emissions inventory are not well characterized due to limited data. This study investigates the patterns of N 2 O flux across 127 freshwater systems in China to elucidate the role of aquaculture ponds and lakes/reservoirs in landscape N 2 O emission. Our findings show that the average N 2 O flux from aquaculture ponds was 3.63 times higher (28.73 μg N 2 O m−2 h−1) than that from non-aquaculture ponds. Additionally, the average N 2 O flux from aquaculture lakes/reservoirs (15.65 μg N 2 O m−2 h−1) increased 3.05 times compared to non-aquaculture lakes/reservoirs. The transition from non-aquaculture to aquaculture practices has resulted in a net annual increase of 7589 ± 2409 Mg N 2 O emissions in China's freshwater systems from 2003 to 2022, equivalent to 20% of total N 2 O emissions from China's inland water. Particularly, the robust negative regression relationship between N 2 O emission intensity and water area suggests that small ponds are hotspots of N 2 O emissions, a result of both elevated nutrient concentrations and more vigorous biogeochemical cycles. This indicates that N 2 O emissions from smaller aquaculture ponds are larger per unit area compared to equivalent larger water bodies. Our findings highlight that N 2 O emissions from aquaculture systems can not be proxied by those from natural water bodies, especially small water bodies exhibiting significant but largely unquantified N 2 O emissions. In the context of the rapid global expansion of aquaculture, this underscores the critical need to integrate aquaculture into global assessments of inland water N 2 O emissions to advance towards a low-carbon future. [Display omitted] • N 2 O fluxes from aquaculture systems markedly increase compared to non-aquaculture systems. • The transition to aquaculture increases China's freshwater N 2 O emissions by 7589 Mg yr−1. • The net N 2 O flux from aquaculture equals 20% of China's total inland water N 2 O emissions. • Small water bodies are the hotspots for N 2 O emissions but are largely unquantified. [ABSTRACT FROM AUTHOR]

No information is available for the newly found complete ammonia-oxidizing bacteria (COX) under globally intensified agriculture. In addition to the canonical ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA), few studies have evaluated the structure and ecological niche of the community of COX. No information is available on their relative contributions to the ammonia oxidation process and related nitrous oxide (N 2 O) emissions in intensively managed vegetable fields. Therefore, in this study, fourteen soil samples were collected from vegetable fields across mainland China covering four climatic zones with distinct soil pH conditions. Two sets of microcosm incubations were combined to determine the rate of ammonia oxidation and N 2 O emissions distinguishing AOA, AOB and COX. The results indicated that COX coexisted with canonical ammonia-oxidizing microorganisms and its abundance was 1–4 orders of magnitude higher than those of AOA and AOB. COX abundance was highest in the subtropics and lowest in the tropics, whereas the ratio of COX to total ammonia-oxidizing microorganisms was highest in the tropics. The average contribution of COX to ammonia oxidation rate and N 2 O emission was 17.0% and 19.5%, respectively, while AOA contributed 47.1% to ammonia oxidation and AOB contributed 43.2% to N 2 O emissions. Interestingly, the contribution of COX to N 2 O emissions exceeded that of AOB in tropic acidic and AOA in subtropic alkaline soils. Based on high-throughput sequencing, the dominant genera of AOA, AOB, and COX were Nitrosopumilus , Nitrosospira , and Nitrospira , respectively. Reyranella and Rudaea were detected as a novel genus from COX. Furthermore, the N 2 O emissions were significantly positively correlated with Ktedonobacter in AOB, and negatively correlated with Nitrosomonas in AOB and Nitrospira in COX. In summary, COX coexisted with AOA and AOB while showed limited direct influence, but competed with AOA and AOB through ecological niche, which altered nitrification and N 2 O emissions in intensified vegetable fields. [Display omitted] • COX had greater gene abundance and coexisted with AOA & AOB at the regional scale. • COX contributed 17.0% of ammonia oxidation and 19.5% of N 2 O emission from 14 soils. • COX outdid AOB at subtropic ammonia oxidation and tropic N 2 O flux in acidic soils. • The dominant COX genus is Nitrospira which negatively correlated with N 2 O emission. [ABSTRACT FROM AUTHOR]

Anthropogenic input of excess nutrients stimulates massive nitrous oxide (N 2 O) production in estuaries with distinct seasonal variations. Here, nitrogen isotopic and isotopomeric signatures were utilized to investigate the seasonal dynamics of N 2 O production and nitrification at the middle reach of the eutrophic Pearl River Estuary in the south of China. Elevated N 2 O production primarily via ammonia oxidation (> 1 nM-N d−1) occurred from April to November, along with increased temperature and decreased dissolved oxygen concentration. This consistently oxygenated water column showed active denitrification, contributing 20–40 % to N 2 O production. The water column microbial N 2 O production generally constituted a minor fraction (10–15 %) of the estuarine water-air interface efflux, suggesting that upstream transport and tidal dilution regulated the dissolved N 2 O inventory in the middle reach of the estuary. Nitrification (up to 3000 nM-N d−1) played a critical role in bioavailable nitrogen conversion and N 2 O production, albeit with N 2 O yields below 0.05 %. • Seasonal N 2 O production peaked from April to November, primarily due to ammonia oxidation, with a significant contribution from denitrification. • Seasonal variations in temperature and dissolved oxygen were key regulators of N 2 O production. • In-situ microbial production accounted for a fraction (10-15%) of N 2 O emission at the water-air interface. [ABSTRACT FROM AUTHOR]

Comprehensive, spatially explicit understanding of N loss from N input in China's maize (Zea mays L.) belt is needed to improve N management and develop N loss mitigation measures for specific locations. However, accurate estimation of N loss remains uncertain mainly because of spatial heterogeneity of emission factors (EFs) and activity data. Here, we built random‐forest models to predict EFs for each N loss pathway (dinitrogen, nitric oxide, nitrous oxide and ammonia emissions, nitrate leaching, and N runoff) considering soil and climate factors. We then used location‐ and crop‐specific activity data to understand N loss and surplus on a 1‐ × 1‐km grid. Results showed that the N surplus and total N loss averaged 135.4 (95% confidence interval [CI], 36.6–261.5) and 87.6 (95% CI, 32.9–162.5) kg N ha–1, respectively, and nitrate leaching and ammonia emissions were primary loss pathways. There was a significant correlation between N surplus and total N loss in spatial distribution, and regions with high N surplus and total N loss were mainly in the northern China Plain and Sichuan Basin, while regions with low surplus and loss could be found in Heilongjiang and Jilin provinces. Our results are beneficial to understand specific crop N budget and develop location‐specific N management strategies. Core Ideas: A spatially explicit assessment of N loss from N input was mapped in China's maize belt.The N surplus and total N loss averaged 135.4 and 87.6 kg N ha‐1, respectively.High N surplus and total N loss was recorded in the northern China Plain and Sichuan Basin. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N 2 O) is an important ozone-depleting greenhouse gas produced and consumed by microbially mediated nitrification and denitrification pathways. Estuaries are intensive N 2 O emission regions in marine ecosystems. However, the potential contributions of nitrifiers and denitrifiers to N 2 O sources and sinks in China's estuarine and coastal areas are poorly understood. The abundance and transcription of six key microbial functional genes involved in nitrification and denitrification, as well as the clade II-type nosZ gene-bearing community composition of N 2 O reducers, were investigated in four estuaries spanning the Chinese coastline. The results showed that the ammonia-oxidizing archaeal amoA genes and transcripts were more dominant in the northern Bohai Sea (BS) and Yangtze River estuaries, which had low nitrogen concentrations, while the denitrifier nirS genes and transcripts were more dominant in the southern Jiulong River (JRE) and Pearl River estuaries, which had high levels of terrestrial nitrogen input. Notably, the nosZ clade II gene was more abundant than the clade I-type throughout the estuaries except for in the JRE and a few sites of the BS, while the opposite transcript distribution pattern was observed in these two estuaries. The gene and transcript distributions were significantly constrained by nitrogen and oxygen concentrations as well as by salinity, temperature, and pH. The nosZ clade II gene-bearing community composition along China's coastline had a high level of diversity and was distinctly different from that in the soil and in marine oxygen-minimum-zone waters. By comparing the gene distribution patterns across the estuaries with the distribution patterns of the N 2 O concentration and flux, we found that denitrification may principally control the N 2 O emissions pattern. [ABSTRACT FROM AUTHOR]

Greenhouse vegetable production in China not only increases farmers' income, but also increases the risk of nitrogen losses due to excessive water and fertilizer input. Nitrogen losses, including the potent greenhouse gas nitrous oxide (N2O), are driven by water content, soil temperature and pH; regulated by available organic carbon and inorganic nitrogen (N); and affected by management. Therefore, a process-based model was applied to explain the complex interaction of the factors affecting N losses in the form of N2O, NH3 and NO3− from a greenhouse vegetable production system in a northeast suburb of Beijing, China. We designed four treatments: two equal N input treatments with one flooding (FP) and the other drip irrigation (FPD) and two equal water input treatments (drip irrigation) with one 100% chemical N input (FPD) and the other 50% N input (OPTD). The last one was CK treatment (flooding without chemical N). We calibrated the WHCNS-veg model using year-round measurements of soil temperature, N2O emission, NH3volatilization, NO3− distribution and yields for greenhouse cucumber–tomato cultivation under farmers' practice (flooding + 100% chemical N, FP). Then, we validated the model using the data sets under drip irrigation (70% of flooding amount + 100% chemical N, FPD), reduced chemical N by 50% (drip + 50% chemical N, OPTD) and CK treatment. The WHCNS-veg model was able to capture the above processes under different treatments. Annual N2O emissions were 5.47 and 3.76kg N ha−1 for the cucumber and tomato seasons under FP, respectively. Compared to FP, drip irrigation (FPD) decreased N2O emissions by 19.0% and 45.5% in the two seasons, respectively. Compared to FPD, applying a lower rate of N (OPTD) further reduced N2O emissions by 13.7% and 40.5%, respectively. According to the model simulation, N2O emission was mainly controlled by nitrification/denitrification in the cucumber/tomato seasons, respectively. Compared to FP, drip irrigation (FPD) increased NH3 volatilization by 54.2% in the cucumber season, while in the tomato season, there were no significant differences inNH3 volatilization under the three fertilizer treatments. The nitrate leaching levels were 48.5 and 81.0 kg N ha−1 for the two seasons under FP treatment. Drip irrigation (FPD) decreased NO3− leaching by 20.6% in the cucumber season. Drip irrigation (FPD) and/or reducing chemical N (OPTD) did not compromise vegetable yields. In all, WHCNS-veg performed well in simulating N2O, NH3 and NO3− dynamics from the greenhouse vegetable field, which means that the model can be used to manage water and nitrogen precisely in greenhouse vegetable production systems by scenario analysis, and drip irrigation and/or lower N input can be applied in this area to secure yield and reduce N losses. [ABSTRACT FROM AUTHOR]

Mole fractions of atmospheric carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and sulfur hexafluoride (SF6) have been continuously measured since September 2009 at the Akedala Station (47°06′N, 87°58′E, 563.3 masl) in China. The station is located in the Central Asia and northwest of China, and it is the only station in that region with background conditions for long-term greenhouse gas observations. Characteristics of the mole fractions, growth rates, and influence of long-distance transport were studied considering data from September 2009 to December 2019. The greenhouse gases concentrations at Akedala Station show a trend of year-on-year growth, with CO2 concentrations ranging from 389.80 × 10−6 to 408.79 × 10−6 (molar fraction of substances, same below), CH4 concentrations ranging from 1890.07 × 10−9 to 1976.32 × 10−9, N2O concentrations ranging from 321.26 × 10−9 to 332.03 × 10−9, and SF6 concentrations ranging from 7.04 × 10−12 to 10.07 × 10−12, the growth rate of which is similar to the decadal average growth rate in the Northern Hemisphere. There exist obvious seasonal variations, with CO2 concentrations showing high in winter and low in summer and CH4 showing a distinct "W"-shaped trend while N2O and SF6 showing little difference between the four seasons. A relatively strong correlation and homology exist among the four greenhouse gases except in summer, and the analysis based on backward trajectories model shows that the Akedala Station is influenced by the airflow from northwest or southwest throughout the year. The Akedala Station is an important atmospheric background station in Central Asia, and its greenhouse gas concentration levels and variation characteristics are significantly different from those of the background stations in the monsoon region. Its degree changes are closely related to local source emissions, monsoon transport, and atmospheric photochemical processes. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) is an influential greenhouse gas (GHG) and an unregulated ozone‐depleting substance. The extent to which N2O emissions from natural forest soils have been enhanced by high atmospheric nitrogen (N) deposition in China during past decades is unclear; however, assessing land‐related N2O emissions for 2060 national "carbon neutrality" goal is urgent. In this study, we proposed a "gray box" conceptual model and deduced a linear relationship between soil N2O emissions and N deposition on a large scale. On this basis, we created a "process‐augmented data‐driven" approach using which we combined experimental N addition data from 38 Chinese forests with N deposition observation data to estimate regional soil N2O emissions. We found that the N2O emission budget of eastern China forest soils averaged 0.24 ± 0.07 TgN yr−1 from 1996 to 2015; of this, ∼36% (0.087 TgN yr−1) was directly induced by N deposition. Soil N2O emission rates (RN2O) fluctuated slightly after 2006, and the RN2Os of different ecoregions were significantly different (p < 0.001). Soil factors and N‐deposition‐related factors dominated the spatial variation of RN2O. Our findings provide country‐specific and ecoregion‐specific emission factors for national GHG inventories in China. Our approach bridges the gap between site‐level experiments and demand for regional N2O emissions, and is applicable for estimating N2O emissions in other countries/regions. Meanwhile, more N addition experiments are needed to comprehensively understand N cycling processes and extend the predictive capability of the approach. Plain Language Summary: Nitrous oxide (N2O) is a greenhouse gas that is around 300 times more powerful than carbon dioxide. As many countries and regions are aiming to achieve zero net carbon emission ("carbon neutrality") by the mid‐21st century, we need to evaluate the emissions of nitrous oxide to build an accurate picture of the current situation. However, it is difficult to estimate the emission of N2O from natural soils because the spatial variation is high. Inspired by the linkage between elemental nitrogen (N) that enters an ecosystem and N that leaves the ecosystem, we proposed a conceptual model and deduced a linear relationship between N deposition and soil N2O emissions. On the basis, we used experimental N addition data from various sites to quantify the linear relationship. Then, the N2O emission and its variation was estimated with dynamic N deposition data. In eastern China forests where the N deposition rate is exceptionally high, around 0.24 million tons of N2O‐N was emitted annually from 1996 to 2015, around 36% of which was directly induced by N deposition. From another perspective, soil N2O emissions in this region are expected to decline owing to pollution control practices and decreasing N deposition. Key Points: Eastern China forest soils emitted 0.24 TgN2O‐N yr−1 from 1996 to 2015N deposition directly induced ∼36% of emitted N2O from eastern China forest soilsDirect contribution of N deposition to soil N2O emissions increased from tropical to boreal forests [ABSTRACT FROM AUTHOR]

Hot moments of soil nitrous oxide (N2O) emission contribute to large fractions of total annual emissions. Magnitudes of N2O emission during hot moments to increasing water and nitrogen (N) availabilities in different steppe types were not well understood. Based on soil monoliths collected from three steppes (meadow, typical, and desert steppes) in northern China, we found that the typical steppe held the lowest N2O emission among the three steppes. Water and N co‐addition could increase soil N2O emission by up to 245‐fold. Water addition significantly enhanced soil N2O emission in all the three steppes, but the sensitivity of soil N2O emission to water addition decreased from desert steppe (r2 = 0.83) to typical (r2 = 0.73) and meadow (r2 = 0.66) steppes. Nitrogen addition significantly promoted soil N2O emission only in the meadow steppe where soil C:N was relatively higher than the other two steppes. Water and N addition displayed strong positive interaction on soil N2O emission in the meadow steppe while negative interaction in the typical steppe. Different responses of plants, microorganisms and soil NO3− concentration drove the variation in magnitude of soil N2O emission between the two steppes. Our results illustrate different interactions of water and N addition on hot moments of soil N2O emission in the three steppes. We suggest that the pulsed feature of N2O emission should be taken into account in prediction of greenhouse gas emission in the global arid and semiarid grasslands. Plain Language Summary: Nitrous oxide (N2O) is the third most important greenhouse gas in the atmosphere. The emission of soil N2O is characterized by transient hot moments. These short periods of high N2O emissions contribute to great fractions of total annual emissions. Different magnitudes of soil N2O emissions and the underlying mechanisms during large rainfall events and nitrogen (N) addition in different steppe types (meadow, typical, and desert steppes) were not well understood. To examine differences in soil N2O emission among these steppes and to identify potential drivers, we measured soil N2O emission under water and N management in intact soil monoliths from the three steppes. We found that the typical steppe held the lowest N2O emission among the three steppes. The water effect on soil N2O emission was the strongest in desert steppe, while the N effect was significant in meadow steppe where the soil C:N was relatively higher than the other two steppes. Opposite interactive effects of water and N addition on soil N2O emission between meadow and typical steppes were due to different responses of microbial biomass carbon and plant aboveground biomass. These findings provided new knowledge for reducing soil N2O emission via management of hot moments in steppe ecosystems. Key Points: Hot moments of nitrous oxide (N2O)‐nitrogen (N) accounted for 0.84% of added N within 45 days under water and N addition in meadow steppeWater addition markedly enhanced soil N2O emission in the three steppes, synergistic effect of water and N was observed in meadow steppeSoil moisture dominantly controlled soil N2O emission in the three steppes, site differences were regulated by plants and microorganisms [ABSTRACT FROM AUTHOR]

Acid forest soils in South China experience a chronically elevated input of atmospheric nitrogen (N), turning them into hot spots for gaseous N emissions. Soil moisture is known to be a major controller for the partitioning of gaseous N loss to nitric (NO) and nitrous oxide (N2O), which may be of particular relevance in the monsoonal climate of South China. To study this partitioning in more detail, we determined gas phase kinetics of NO and N2O release during laboratory dry-out of acidic surface soils from the headwater catchment TieShanPing (TSP), situated close to Chongqing, SW China. Soils were sampled from two hydrologically distinct environments, a well-drained hill slope (HS), and a periodically flooded groundwater discharge zone (GDZ). Production and consumption of NO were studied in an automated flow-through system purged with NO-free or NO-spiked air. Production rates peaked at 21% and 18% water filled pore space (WFPS) in HS and GDZ soils, respectively, suggesting nitrification as the dominant process of NO formation in both landscape units. In HS soils, maximum production and consumption occurred at the same WFPS, whereas GDZ soils displayed maximum NO consumption at higher WFPS than maximum production, suggesting that denitrification is an important NO sink in GDZ soils. Net N2O release was largest at 100% WFPS and declined steadily during drying. Integrated over the entire range of soil moisture, potential NO-N loss outweighed potential N2O-N loss, suggesting that N-saturated, acid forest soil is an important NO source. [ABSTRACT FROM AUTHOR]

Small waters, like ponds, are the most abundant freshwater environments, and are increasingly recognized for their function in ecosystem service delivery. In agricultural watershed, artificial ponds play an essential role in reducing nitrogen pollution. However, until now artificial ponds remain the least investigated part of water environments. The importance of microbial activities has seldom been discussed, which makes the microbial pathways and processes rates in nitrogen removal poorly understood. To illustrate the role of artificial ponds in microbial nitrogen removal in agricultural watersheds, 21 pond sediments and 11 soils are collected in an agricultural watershed of China. Results show that surface sediments in ponds carry significantly higher dissolved inorganic nitrogen (9.1–21.9 mg/kg) and total organic matter (64.8–113.0 g/kg) compared to the surrounding agricultural soils. High rates of microbial nitrogen removal in ponds (12.4–25.5 nmol N g−1 h−1) are observed, which are 2–9 times higher than those in dryland soils. In pond sediments, denitrification dominates (> 90% N-loss) the microbial nitrogen removal process with only a minor contribution of anaerobic ammonium oxidation. A high potential of N2O production (up to 9.4 nmol N g−1 h−1) occurs in ponds along with the rapid nitrogen removal. For denitrifier genes, nir gene are always more abundant than nosZ gene. Additionally, the nirS gene is more abundant under flooded conditions, while nirK gene prefers higher dissolved oxygen and NO3− in drylands. These findings highlight the ecosystem function of ponds in agricultural watersheds, and provide new ideas on pollution control and global nitrogen cycling. [ABSTRACT FROM AUTHOR]

Environmental changes significantly alter the structure, diversity and activity of soil microbial communities during spring freezing-thawing period, leading to changes in the soil microbial nitrogen cycle. Changes in N2O fluxes after land use conversion from primary forest to secondary forest, Korean pine plantation and cropland in northeast China have not been quantified. Field experiments were conducted to measure soil N2O fluxes in a primary forest, two secondary forests, a Korean pine plantation, and one maize field in a temperate region in northeast China from 2017-03-06 to 2017-05-28. During the experimental period, the soil was exclusively a nitrogen source for all land uses. We found that N2O emissions ranged from 15.63 to 68.74 µg m−2 h−1, and cumulative N2O emissions ranged from 0.33 to 2.10 kg ha−1 during the period. Cumulative N2O emissions from the maize field were significantly higher than that from primary forest, Korean pine plantation, hardwood forest, and Betula platyphylla forest by 262.1% to 536.4%. Compared with other ecosystems in similar studies, the N2O emission rates of all ecosystem types in this study were low during the spring thaw period. Stepwise multiple linear regression indicated that there were significant correlations between N2O emissions and environmental factors (air temperature and soil temperature, soil water content, soil pH, NH4+-N, NO3−-N, and soil organic carbon). The results showed that conversion of land use from primary forest to hardwood forest, Korean pine plantation or maize field greatly increased soil N2O emissions during spring freezing-thawing period, and N2O emissions from primary forest were almost the same as those from Betula platyphylla forest. [ABSTRACT FROM AUTHOR]

Rivers are important sites for nitrogen (N) cycling processes. N removal is thought to occur predominantly in the benthic zone and the role of the water column is frequently neglected. Here, we find that the water‐air and sediment‐water fluxes of N2 and N2O decreased, while the water column production increased with stream order through 4‐year observations across six river networks in China. The water column contribution increased with stream order and accounted for more than 50% in rivers above fifth order. The increase in the contact area of suspended sediment (SPS)‐water caused by higher SPS concentrations and river depths resulted in the shift as river size increased. N removal and N2O emissions would be underestimated approximately by 50% if neglecting water column processes for the six river networks. This study highlights the necessity and provides a pathway to incorporate water column processes into models to balance the global N budget. Plain Language Summary: The entire global N budget remains out of balance, with total N inputs exceeding N losses. Streams and rivers serve as substantial recipients and processors of reactive N transported from terrestrial landscapes. The benthic zone is traditionally identified as a hotspot for N processing in fluvial systems. However, the role of the water column is poorly understood. Here, we found that the water column area‐basis production rates of N2 and N2O increased with stream order although volumetric‐basis production rates did not change significantly with stream order through 4‐year observations across six river networks in China. The water column contribution increased with stream order and became dominant in large rivers. The increase in the contact area of SPS‐water caused by higher SPS concentrations and water volume accounted for the shift as river size increased. The current estimates would underestimate riverine N removal and N2O emissions by approximately 50% if neglecting water column processes based on the upscaling results for the six large river networks ranging from first to eighth order. Thus, our findings provide insight into the understanding of riverine N dynamics and highlight the important role of water column processes in N upscaling for closing regional and global N budgets. Key Points: Water column contribution in N removal and N2O emissions increased with stream order and it played a dominant role in large riversThe increase in the contact area of suspended sediment‐water accounted for the increasing water column contribution with river sizeRiverine N removal and N2O emissions would be underestimated approximately by 50% if neglecting water column processes [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) is an important ozone-depleting greenhouse gas produced and consumed by microbially mediated nitrification and denitrification pathways. Estuaries are intensive N2O emission regions in marine ecosystems. However, the potential contributions of nitrifiers and denitrifiers to N2O sources and sinks in China's estuarine and coastal areas are poorly understood. The abundance and transcription of six key microbial functional genes involved in nitrification and denitrification, as well as the clade II-type nosZ gene-bearing community composition of N2O reducers, were investigated in four estuaries spanning the Chinese coastline. The results showed that the ammonia-oxidizing archaeal amoA genes and transcripts were more dominant in the northern Bohai Sea (BS) and Yangtze River estuaries, which had low nitrogen concentrations, while the denitrifier nirS genes and transcripts were more dominant in the southern Jiulong River (JRE) and Pearl River estuaries, which had high levels of terrestrial nitrogen input. Notably, the nosZ clade II gene was more abundant than the clade I-type throughout the estuaries except for in the JRE and a few sites of the BS, while the opposite transcript distribution pattern was observed in these two estuaries. The gene and transcript distributions were significantly constrained by nitrogen and oxygen concentrations, as well as salinity, temperature, and pH. The nosZ clade II gene-bearing community composition along China's coastline had a high diversity and was distinctly different from that in the soil and marine oxygen-minimum-zone waters. By comparing the gene distribution patterns across the estuaries with the distribution patterns of the N2O concentration and flux, we found that denitrification may principally control the N2O emissions pattern. [ABSTRACT FROM AUTHOR]