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To gain insight into the microbial mechanisms associated with the replacement of chemical fertilizers with organic or bio-organic fertilizers to mitigate soil nitrous oxide (N 2 O) emissions, we measured N 2 O emissions from greenhouse vegetable soils through field observations and pot experiments. Results showed that organic substitution suppressed N 2 O emissions by reducing soil mineral N content and stimulating the abundance of the nosZII gene. The trade-off effect of bio-organic substitution on N 2 O emissions may be due to the stimulated activity of the AOA-amoA gene, resulting in unfavorable conditions for N 2 O production and thus reduced N 2 O loss. We also linked the inhibitory effect of organic and bio-organic substitution on N 2 O emissions to the increased abundance of key species in bacterial co-occurrence networks represented by Patescibacteria as they were significantly and negatively correlated with N 2 O emissions. However, the mitigation effect of bio-organic substitution on N 2 O emissions was conteracted by an increase in Bacillus abundance due to the direct negative effect of Bacillus on the nosZII gene abundance. These findings suggest that conventional or bio-organic substitution is a promising strategy for alleviating the environmental costs of crop production., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Inland waters (rivers, reservoirs, lakes, ponds, streams) and estuaries are significant emitters of methane (CH 4 ) and nitrous oxide (N 2 O) to the atmosphere, while global estimates of these emissions have been hampered due to the lack of a worldwide comprehensive data set of CH 4 and N 2 O flux components. Here, we synthesize 2997 in-situ flux or concentration measurements of CH 4 and N 2 O from 277 peer-reviewed publications to estimate global CH 4 and N 2 O emissions from inland waters and estuaries. Inland waters including rivers, reservoirs, lakes, and streams together release 95.18 Tg CH 4  year -1 (ebullition plus diffusion) and 1.48 Tg N 2 O year -1 (diffusion) to the atmosphere, yielding an overall CO 2 -equivalent emission total of 3.06 Pg CO 2  year -1 . The estimate of CH 4 and N 2 O emissions represents roughly 60% of CO 2 emissions (5.13 Pg CO 2  year -1 ) from these four inland aquatic systems, among which lakes act as the largest emitter for both CH 4 and N 2 O. Ebullition showed as a dominant flux component of CH 4 , contributing up to 62%-84% of total CH 4 fluxes across all inland waters. Chamber-derived CH 4 emission rates are significantly greater than those determined by diffusion model-based methods for commonly capturing of both diffusive and ebullitive fluxes. Water dissolved oxygen (DO) showed as a dominant factor among all variables to influence both CH 4 (diffusive and ebullitive) and N 2 O fluxes from inland waters. Our study reveals a major oversight in regional and global CH 4 budgets from inland waters, caused by neglecting the dominant role of ebullition pathways in those emissions. The estimated indirect N 2 O EF 5 values suggest that a downward refinement is required in current IPCC default EF 5 values for inland waters and estuaries. Our findings further indicate that a comprehensive understanding of the magnitude and patterns of CH 4 and N 2 O emissions from inland waters and estuaries is essential in defining the way of how these aquatic systems will shape our climate., (© 2022 John Wiley & Sons Ltd.)

Aquaculture ponds are of increasing worldwide concerns as critical sources of atmospheric methane (CH 4 ) and nitrous oxide (N 2 O), but little is known about these gases emissions as affected by aquaculture species, stocking and water management in aquaculture ponds. Here, a two-year study was carried out to quantify CH 4 and N 2 O emissions from freshwater crab and fish aquaculture ponds in subtropical China. We further explored how the microbial functional genes [CH 4 : mcrA and pmoA; N 2 O: archaeal and bacterial amoA (AOA + AOB), nirS, nirK, nosZ] may drive CH 4 and N 2 O release in the crab aquaculture pond typically undergoing flooding-to-drainage alteration. Over the two-year period, annual CH 4 and N 2 O fluxes averaged 0.95 mg m -2  h -1 and 20.94 μg m -2  h -1 in the fish aquaculture, and 0.78 mg m -2  h -1 and 28.48 μg m -2  h -1 in the crab aquaculture, respectively. The direct N 2 O emission factors were estimated to be 0.77% and 0.36% of the total N input by feed or 1.59 g N 2 O-N kg -1 and 1.06 g N 2 O-N kg -1 aquaculture yield in the crab and fish ponds, respectively. Among three functional stocking areas, CH 4 and N 2 O emissions were consistently the highest at the feeding area (FA) in the both aquaculture ponds, followed by at the undisturbed area (UA) and aerated area (AA). The shift in sediment soil moisture from waterlogging to drainage conditions significantly increased the abundance of AOB relative to AOA and pmoA, decreased those of denitrifying functional genes (nirS, nirK, nosZ) and mcrA, while did not alter the functional group ratio of nirS + nirK relative to nosZ. Our results highlight that a better understanding of CH 4 and N 2 O emissions from aquaculture ponds requires taking into consideration of data sourced from more diverse aquaculture systems with different management patterns. In addition, a deep analysis of the microbial processes that drive CH 4 and N 2 O production and consumption from aquaculture ponds remains to be addressed in future studies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Agricultural nitrate leaching and runoff incurs high nitrogen loads in agricultural irrigation watersheds, constituting one of important sources of atmospheric nitrous oxide (N 2 O). Two independent sampling campaigns of N 2 O flux measurement over diel cycles and N 2 O flux measurements once a week over annual cycles were carried out in an agricultural irrigation watershed in southeast China using floating chamber (chamber-based) and gas transfer equation (model-based) methods. The diel and seasonal patterns of N 2 O fluxes did not differ between the two measurement methods. The diel variation in N 2 O fluxes was characterized by the pattern that N 2 O fluxes were greater during nighttime than daytime periods with a single flux peak at midnight. The diel variation in N 2 O fluxes was closely associated with water environment and chemistry. The time interval of 9:00-11:00 a.m. was identified to be the sampling time best representing daily N 2 O flux measurements in agricultural irrigation watersheds. Seasonal N 2 O fluxes showed large variation, with some flux peaks corresponding to agricultural irrigation and drainage episodes and heavy rainfall during the crop-growing period of May to November. On average, N 2 O fluxes calculated by model-based methods were 27% lower than those determined by the chamber-based techniques over diel or annual cycles. Overall, more measurement campaigns are highly needed to assess regional agricultural N 2 O budget with low uncertainties.

Soils are among the important sources of atmospheric nitric oxide (NO) and nitrous oxide (N 2 O), acting as a critical role in atmospheric chemistry. Updated data derived from 114 peer-reviewed publications with 520 field measurements were synthesized using meta-analysis procedure to examine the N fertilizer-induced soil NO and the combined NO+N 2 O emissions across global soils. Besides factors identified in earlier reviews, additional factors responsible for NO fluxes were fertilizer type, soil C/N ratio, crop residue incorporation, tillage, atmospheric carbon dioxide concentration, drought and biomass burning. When averaged across all measurements, soil NO-N fluxes were estimated to be 4.06 kg ha -1  yr -1 , with the greatest (9.75 kg ha -1  yr -1 ) in vegetable croplands and the lowest (0.11 kg ha -1  yr -1 ) in rice paddies. Soil NO emissions were more enhanced by synthetic N fertilizer (+38%), relative to organic (+20%) or mixed N (+18%) sources. Compared with synthetic N fertilizer alone, synthetic N fertilizer combined with nitrification inhibitors substantially reduced soil NO emissions by 81%. The global mean direct emission factors of N fertilizer for NO (EF NO ) and combined NO+N 2 O (EF c ) were estimated to be 1.16% and 2.58%, with 95% confidence intervals of 0.71-1.61% and 1.81-3.35%, respectively. Forests had the greatest EF NO (2.39%). Within the croplands, the EF NO (1.71%) and EF c (4.13%) were the greatest in vegetable cropping fields. Among different chemical N fertilizer varieties, ammonium nitrate had the greatest EF NO (2.93%) and EF c (5.97%). Some options such as organic instead of synthetic N fertilizer, decreasing N fertilizer input rate, nitrification inhibitor and low irrigation frequency could be adopted to mitigate soil NO emissions. More field measurements over multiyears are highly needed to minimize the estimate uncertainties and mitigate soil NO emissions, particularly in forests and vegetable croplands., (© 2016 John Wiley & Sons Ltd.)

It is of great concern worldwide that active nitrogenous gases in the global nitrogen cycle contribute to regional and global-scale environmental issues. Nitrous oxide (N2O) and nitric oxide (NO) are generally interrelated in soil nitrogen biogeochemical cycles, while few studies have simultaneously examined these two gases emission from typical croplands. Field experiments were conducted to measure N2O and NO fluxes in response to chemical N fertilizer application in annual greenhouse vegetable cropping systems in southeast China. Annual N2O and NO fluxes averaged 52.05 and 14.87 μg N m(-2) h(-1) for the controls without N fertilizer inputs, respectively. Both N2O and NO emissions linearly increased with N fertilizer application. The emission factors of N fertilizer for N2O and NO were estimated to be 1.43% and 1.15%, with an annual background emission of 5.07 kg N2O-N ha(-1) and 1.58 kg NO-N ha(-1), respectively. The NO-N/N2O-N ratio was significantly affected by cropping type and fertilizer application, and NO would exceed N2O emissions when soil moisture is below 54% WFPS. Overall, local conventional input rate of chemical N fertilizer could be partially reduced to attain high yield of vegetable and low N2O and NO emissions in greenhouse vegetable cropping systems in China.

Aquaculture is an important source of atmospheric methane (CH4) and nitrous oxide (N2O), while few direct flux measurements are available for their regional and global source strength estimates. A parallel field experiment was performed to measure annual CH4 and N2O fluxes from rice paddies and rice paddy-converted inland crab-fish aquaculture wetlands in southeast China. Besides N2O fluxes dependent on water/sediment mineral N and CH4 fluxes related to water chemical oxygen demand, both CH4 and N2O fluxes from aquaculture were related to water/sediment temperature, sediment dissolved organic carbon, and water dissolved oxygen concentration. Annual CH4 and N2O fluxes from inland aquaculture averaged 0.37 mg m(-2) h(-1) and 48.1 μg m(-2) h(-1), yielding 32.57 kg ha(-1) and 2.69 kg N2O-N ha(-1), respectively. The conversion of rice paddies to aquaculture significantly reduced CH4 and N2O emissions by 48% and 56%, respectively. The emission factor for N2O was estimated to be 0.66% of total N input in the feed or 1.64 g N2O-N kg(-1) aquaculture production in aquaculture. The conversion of rice paddies to inland aquaculture would benefit for reconciling greenhouse gas mitigation and agricultural income increase as far as global warming potentials and net ecosystem economic profits are of concomitant concern. Some agricultural practices such as better aeration and feeding, and fallow season dredging would help to lower CH4 and N2O emissions from inland aquaculture. More field measurements from inland aquaculture are highly needed to gain an insight into national and global accounting of CH4 and N2O emissions.

Measurements of methane (CH(4)) and nitrous oxide (N(2)O) fluxes have been extensively taken following rice seedlings transplanted into paddy fields, while little is known about CH(4) and N(2)O fluxes from rice seedling nurseries. Fluxes of CH(4) and N(2)O were simultaneously measured in rice seedling nurseries under the water regimes of continuous flooding and moist irrigation without waterlogging in Southeast China in 2010. Fluxes of CH(4) and N(2)O from continuously flooded nurseries averaged 10.33-14.84 mg m(-2) h(-1) and 28.64-34.35 μg N(2)O-Nm(-2) h(-1) for the different fertilizer applied plots, respectively. Relative to continuous flooding, moist irrigation decreased total CH(4) by 14-50% but increased N(2)O by 72-186%, dependent on the fertilizer types. Compared with inorganic N fertilizer, organic manure application increased CH(4) by 44% and 148% in the continuously flooded and moist irrigation nurseries, respectively. Rice seedling growth parameters were the greatest in moist irrigation nurseries with inorganic N fertilizer application. Moist irrigation instead of continuous waterlogging and shifts from organic manure to combined organic/inorganic N fertilizer inputs have been increasingly experienced in Chinese rice seedling nurseries, which would benefit for mitigating the combined global warming potentials of CH(4) and N(2)O from rice seedling nurseries in China., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Existing studies suggest that biochar application can reduce soil nitrous oxide (N2O) emissions, mainly based on short‐term results. However, it remains unclear what the effects (i.e., legacy effects) and underlying mechanisms are on N2O emissions after many years of a single application of biochar. Here, we collected intact soil columns from plots without and with biochar application in a subtropical tea plantation 7 years ago for an incubation experiment. We used the N2O isotopocule analysis combined with ammonia oxidizer‐specific inhibitors and molecular biology approaches to investigate how the legacy effect of biochar affected soil N2O emissions. Results showed that the soil in the presence of biochar had lower N2O emissions than the control albeit statistically insignificant. The legacy effect of biochar in decreasing N2O emissions may be attributed to the reduced effectiveness of the soil substrate, nitrification and denitrification activities, and the promotion of the further reduction of N2O. The legacy effect of biochar reduced the relative contribution of nitrifier denitrification/bacterial denitrification, nitrification‐related N2O production, and the relative abundance of several microorganisms involved in the nitrogen cycle. Our global meta‐analysis also showed that the reduction of N2O by biochar increased with increasing application rate but diminished and possibly even reversed with increasing experimental time. In conclusion, our findings suggest that the abatement capacity of biochar on soil N2O emissions may weaken over time after biochar application, but this remains under further investigation. [ABSTRACT FROM AUTHOR]

Soils are among the important sources of atmospheric nitric oxide ( NO) and nitrous oxide (N2O), acting as a critical role in atmospheric chemistry. Updated data derived from 114 peer-reviewed publications with 520 field measurements were synthesized using meta-analysis procedure to examine the N fertilizer-induced soil NO and the combined NO+N2O emissions across global soils. Besides factors identified in earlier reviews, additional factors responsible for NO fluxes were fertilizer type, soil C/N ratio, crop residue incorporation, tillage, atmospheric carbon dioxide concentration, drought and biomass burning. When averaged across all measurements, soil NO-N fluxes were estimated to be 4.06 kg ha−1 yr−1, with the greatest (9.75 kg ha−1 yr−1) in vegetable croplands and the lowest (0.11 kg ha−1 yr−1) in rice paddies. Soil NO emissions were more enhanced by synthetic N fertilizer (+38%), relative to organic (+20%) or mixed N (+18%) sources. Compared with synthetic N fertilizer alone, synthetic N fertilizer combined with nitrification inhibitors substantially reduced soil NO emissions by 81%. The global mean direct emission factors of N fertilizer for NO ( EFNO) and combined NO+N2O ( EFc) were estimated to be 1.16% and 2.58%, with 95% confidence intervals of 0.71-1.61% and 1.81-3.35%, respectively. Forests had the greatest EFNO (2.39%). Within the croplands, the EFNO (1.71%) and EFc (4.13%) were the greatest in vegetable cropping fields. Among different chemical N fertilizer varieties, ammonium nitrate had the greatest EFNO (2.93%) and EFc (5.97%). Some options such as organic instead of synthetic N fertilizer, decreasing N fertilizer input rate, nitrification inhibitor and low irrigation frequency could be adopted to mitigate soil NO emissions. More field measurements over multiyears are highly needed to minimize the estimate uncertainties and mitigate soil NO emissions, particularly in forests and vegetable croplands. [ABSTRACT FROM AUTHOR]

A full accounting of net greenhouse gas balance ( NGHGB) and greenhouse gas intensity ( GHGI) was examined in an annual coastal reclaimed saline Jerusalem artichoke-fallow cropping system under various soil practices including soil tillage, soil ameliorant, and crop residue amendments. Seasonal fluxes of soil carbon dioxide ( CO2), methane ( CH4), and nitrous oxide (N2O) were measured using static chamber method, and the net ecosystem exchange of CO2 ( NEE) was determined by the difference between soil heterotrophic respiration ( RH) and net primary production ( NPP). Relative to no-tillage, rotary tillage significantly decreased the NPP of Jerusalem artichoke while it had no significant effects on the annual RH. Rotary tillage increased CH4 emissions, while seasonal or annual soil N2O emissions did not statistically differ between the two tillage treatments. Compared with the control plots, soil ameliorant or straw amendment enhanced RH, soil CH4, and N2O emissions under the both tillage regimes. Annual NGHGB was negative for all the field treatments, as a consequence of net ecosystem CO2 sequestration exceeding the CO2-equivalents released as CH4 and N2O emissions, which indicates that Jerusalem artichoke-fallow cropping system served as a net sink of GHGs. The annual net NGHGB and GHGI were estimated to be 11-21% and 4-8% lower in the NT than in RT cropping systems, respectively. Soil ameliorant and straw amendments greatly increased NPP and thus significantly decreased the negative annual net NGHGB. Overall, higher NPP but lower climatic impacts of coastal saline bioenergy production would be simultaneously achieved by Jerusalem artichoke cultivation under no-tillage with improved saline soil conditions in southeast China. [ABSTRACT FROM AUTHOR]

Background and aims: The rice production is experiencing a shift from conventionally seedling-transplanted (TPR) to direct-seeded (DSR) cropping systems in Southeast Asia. Besides the difference in rice crop establishment, water regime is typically characterized as water-saving moist irrigation for DSR and flooding-midseason drainage-reflooding and moist irrigation for TPR fields, respectively. A field experiment was conducted to quantify methane (CH) and nitrous oxide (NO) emissions from the DSR and TPR rice paddies in southeast China. Methods: Seasonal measurements of CH and NO fluxes from the DSR and TPR plots were simultaneously taken by static chamber-GC technique. Results: Seasonal fluxes of CH averaged 1.58 mg m h and 1.02 mg m h across treatments in TPR and DSR rice paddies, respectively. Compared with TPR cropping systems, seasonal NO emissions from DSR cropping systems were increased by 49 % and 46 % for the plots with or without N application, respectively. The emission factors of NO were estimated to be 0.45 % and 0.69 % of N application, with a background emission of 0.65 and 0.95 kg NO-N ha under the TPR and DSR cropping regimes, respectively. Rice biomass and grain yield were significantly greater in the DSR than in the TPR cropping systems. The net global warming potential (GWP) of CH and NO emissions were comparable between the two cropping systems, while the greenhouse gas intensity (GHGI) was significantly lower in the DSR than in the TPR cropping systems. Conclusions: Higher grain yield, comparable GWP, and lower GHGI suggest that the DSR instead of conventional TPR rice cropping regime would weaken the radiative forcing of rice production in terms of per unit of rice grain yield in China, and DSR rice cropping regime could be a promising rice development alternative in mainland China. [ABSTRACT FROM AUTHOR]

A complete accounting of net greenhouse gas balance (NGHGB) and greenhouse gas intensity (GHGI) affected by Fe(III) fertilizer application was examined in typical annual paddy rice-winter wheat rotation cropping systems in southeast China. Annual fluxes of soil carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) were measured using static chamber method, and the net ecosystem exchange of CO2 (NEE) was determined by the difference between soil CO2 emissions (R H) and net primary production (NPP). Fe(III) fertilizer application significantly decreased R H without adverse effects on NPP of rice and winter wheat. Fe(III) fertilizer application decreased seasonal CH4 by 27–44%, but increased annual N2O by 65–100%. Overall, Fe(III) fertilizer application decreased the annual NGHGB and GHGI by 35–47% and 30–36%, respectively. High grain yield and low greenhouse gas intensity can be reconciled by Fe(III) fertilizer applied at the local recommendation rate in rice-based cropping systems. [Copyright &y& Elsevier]

Abstract: Annual paddy rice–winter wheat rotation constitutes one of the typical cropping systems in southeast China, in which various water regimes are currently practiced during the rice-growing season, including continuous flooding (F), flooding-midseason drainage-reflooding (F-D-F), and flooding-midseason drainage-reflooding and moisture but without waterlogging (F-D-F-M). We conducted a field experiment in a rice–winter wheat rotation system to gain an insight into the water regime-specific emission factors and background emissions of nitrous oxide (N2O) over the whole annual cycle. While flooding led to an unpronounced N2O emission during the rice-growing season, it incurred substantial N2O emission during the following non-rice season. During the non-rice season, N2O fluxes were, on average, 2.61 and 2.48mg N2O–Nm− 2 day−1 for the 250kg N ha−1 applied plots preceded by the F and F-D-F water regimes, which are 56% and 49% higher than those by the F-D-F-M water regime, respectively. For the annual rotation system experienced by continuous flooding during the rice-growing season, the relationship between N2O emission and nitrogen input predicted the emission factor and background emission of N2O to be 0.87% and 1.77kg N2O–Nha−1, respectively. For the plots experienced by the water regimes of F-D-F and F-D-F-M, the emission factors of N2O averaged 0.97% and 0.85%, with background N2O emissions of 2.00kg N2O–Nha−1 and 1.61kg N2O–Nha−1 for the annual rotation system, respectively. Annual direct N2O–N emission was estimated to be 98.1Gg yr−1 in Chinese rice-based cropping systems in the 1990s, consisting of 32.3Gg during the rice-growing season and 65.8Gg during the non-rice season, which accounts for 25–35% of the annual total emission from croplands in China. [Copyright &y& Elsevier]

Greenhouse gas emissions from rice paddies under sewage irrigation deserve much attention since domestic sewage effluents are increasingly used for agriculture in developing countries. A field experiment was conducted to simultaneously measure methane (CH4) and nitrous oxide (N2O) emissions from rice (Oryza sativa L.) paddies under sewage and unpolluted river water irrigation in southeast China. The rice paddies were under a local typical water regime, which was characterized by flooding–midseason drainage–reflooding–moist intermittent irrigation but without water logging. Relative to unpolluted river water irrigation, sewage irrigation significantly increased CH4 and N2O emissions from rice paddies. Seasonal fluxes of CH4 averaged 1.51mgm−2 h−1 for the plots irrigated by river water and 1.92mgm−2 h−1 for the plots irrigated by sewage. In contrast with river water irrigation, sewage irrigation increased CH4 by 27% and 33% for paddy plots with and without chemical N addition, respectively. Under sewage irrigation, seasonal fluxes of N2O-N averaged 26.79μgm−2 h−1 for the plots without N application and 74.07μgm−2 h−1 for the plots applied at the rate of 200kgNha−1. Relative to river water irrigation, sewage irrigation increased N2O by 68% and 170% for the plots with and without N application, respectively. The direct emission factor of fertilizer N for N2O was estimated to be 0.71% for the rice paddies under sewage irrigation and 0.52% for the plots irrigated by river water. Besides direct N2O emissions, N input by sewage irrigation induced substantial indirect N2O emission from rice paddies. The results of the net GWPs from CH4 and N2O indicate that sewage irrigation would intensify the radiative forcing of rice paddies with midseason drainage and moist irrigation... [Copyright &y& Elsevier]

Nitrogen fertilizer-induced direct nitrous oxide (N2O) emissions depend on water regimes in paddy fields, such as seasonal continuous flooding (F), flooding–midseason drainage–reflooding (F-D-F), and flooding–midseason drainage–reflooding–moist intermittent irrigation but without water logging (F-D-F-M). In order to estimate the changes in direct N2O emission from paddy fields during the rice-growing season in Mainland of China between the 1950s and the 1990s, the country-specific emission factors of N2O-N under different water regimes combined with rice production data were adopted in the present study. Census statistics on rice production showed that water management and nitrogen input regimes have changed in rice paddies since the 1950s. During the 1950s–1970s, about 20–25% of the rice paddy was continuously waterlogged, and 75–80% under the water regime of F-D-F. Since the 1980s, about 12–16%, 77%, and 7–12% of paddy fields were under the water regimes of F, F-D-F, and F-D-F-M, respectively. Total nitrogen input during the rice-growing season has increased from 87.5 kg N ha−1 in the 1950s to 224.6 kg N ha−1 in the 1990s. The emission factors of N2O-N were estimated to be 0.02%, 0.42%, and 0.73% for rice paddies under the F, F-D-F, and F-D-F-M water regimes, respectively. Seasonal N2O emissions have increased from 9.6 Gg N2O-N each year in the 1950s to 32.3 Gg N2O-N in the 1990s, which is accompanied by the increase in rice yield over the period 1950s–1990s. The uncertainties in N2O estimate were estimated to be 59.8% in the 1950s and 37.5% in the 1990s. In the 1990s, N2O emissions during the rice-growing season accounted for 8–11% of the reported annual total of N2O emissions from croplands in China, suggesting that paddy rice development could have contributed to mitigating agricultural N2O emissions in the past decades. However, seasonal N2O emissions would be increased, given that saving-water irrigation and nitrogen inputs are increasingly adopted in rice paddies in China. [ABSTRACT FROM AUTHOR]

Livestock manure contributes to global warming due to greenhouse gas (GHG) emissions, especially nitrous oxide (N 2 O) and methane (CH 4). In the arid and semi-arid lands of Sub-Saharan Africa (SSA), extensive pastoral grazing systems are common, with cattle grazing in the savanna during the day and kept in enclosures (called bomas in Kenya) during the night. Manure is usually not removed from bomas but left to accumulate, leading to excessive local nitrogen loads, making these bomas an overlooked N 2 O emission hotspot in SSA that is currently not accounted for in national and regional GHG budgets. Here, we present the first in-situ isotope measurements of N 2 O fluxes from 37 cattle bomas along an age gradient ranging from 0 to 5 years after boma abandonment in Kenya along with functional gene analysis of soil and manure samples. The isotopic composition of the emitted N 2 O from bomas suggests that on average 91 ± 8% N 2 O was produced via bacterial denitrification and/or nitrifier denitrification, with little variation across boma age class. We also found high levels of N 2 O reduction to N 2 across all sample sites (81 ± 9%), indicating high levels of N 2 O consumption. The abundances of denitrification-related genes (nirK and narG) were significantly higher than those of nitrification-related genes (amoA : AOA and AOB) in the cattle manure samples taken from the bomas, corroborating N 2 O emissions largely being attributed to denitrification. Significant abundance of the reduction-related gene (nosZ) also corroborated the high potential for microbial N 2 O reduction in bomas. Thus, by combining dual-isotope and functional gene analysis, we were able to identify source processes that govern N 2 O emissions from these systems. More generally, making use of the manure by spreading it in the vicinity of the bomas or on dedicated forage plots could provide a win-win by enhancing savanna productivity while simultaneously mitigating GHG emissions. • Natural abundance dual-isotope measurements were combined with functional gene analyses to explore processes of N 2 O formation in cattle bomas. • Denitrification dominated N 2 O emissions in cattle bomas. • Higher abundance of denitrification-related genes (nirK and narG) than nitrification-related genes (amoA) were observed in cattle bomas. • A high reduction (81% ± 9%) of N 2 O to N 2 was observed in cattle bomas. [ABSTRACT FROM AUTHOR]

Highlights • Biochar amendment reduced annual emission factor of N fertilizer for N 2 O + NO. • The ratio of NO-N/N 2 O-N was negatively correlated with soil water content. • Biochar enhanced the negative response of NO-N/N 2 O-N ratio to soil moisture. • Biochar rate of 20 t ha−1 gained the lowest N 2 O and NO emissions. Abstract Biochar impact on soil nitrous oxide (N 2 O) and nitric oxide (NO) emissions from intensive greenhouse vegetable cropping systems is not well established. Annual soil N 2 O and NO emissions were simultaneously measured from a typical greenhouse vegetable field treated with different biochar application rates in southeast China. Both N 2 O and NO emissions differed greatly across the individual vegetable cropping seasons, of which being higher in green soybean and tomato growing seasons, respectively. Over the annual vegetable cropping rotation, biochar amendment decreased soil N 2 O and NO emissions by 10–23% and 18–19% relative to N fertilization alone, respectively. Biochar rate of 20 t ha−1 gained the lowest N 2 O and NO emissions over the annual cycle. The ratio of NO/N 2 O was negatively correlated with soil moisture and depends on biochar addition or not. On average, annual emission factor (EF) of N 2 O and NO combined was accounted for 2.13% with biochar amendment, which was decreased by 22% compared with N fertilization alone (EF = 2.74%). Vegetable yield was significantly enhanced under the biochar combined with N fertilizer plots relative to control, while there is no difference among the N fertilization treatments with or without biochar amendment. Therefore, biochar could be used as an effective management mitigating soil N 2 O and NO emissions while maintaining crop yield in greenhouse vegetable cropping systems in southeast China. [ABSTRACT FROM AUTHOR]

Inland aquaculture ponds have been documented as important sources of atmospheric methane (CH 4 ) and nitrous oxide (N 2 O), while their regional or global source strength remains unclear due to lack of direct flux measurements by covering more typical habitat-specific aquaculture environments. In this study, we compared the CH 4 and N 2 O fluxes from rice paddies and nearby inland fish aquaculture wetlands that were converted from rice paddies in southeast China. Both CH 4 and N 2 O fluxes were positively related to water temperature and sediment dissolved organic carbon, but negatively related to water dissolved oxygen concentration. More robust response of N 2 O fluxes to water mineral N was observed than to sediment mineral N. Annual CH 4 and N 2 O fluxes from inland fish aquaculture averaged 0.51 mg m −2 h −1 and 54.78 μg m −2 h −1 , amounting to 42.31 kg CH 4 ha −1 and 2.99 kg N 2 O-N ha −1 , respectively. The conversion of rice paddies to conventional fish aquaculture significantly reduced CH 4 and N 2 O emissions by 23% and 66%, respectively. The emission factor for N 2 O was estimated to be 0.46% of total N input in the feed or 1.23 g N 2 O-N kg −1 aquaculture production. The estimate of sustained-flux global warming potential of annual CH 4 and N 2 O emissions and the net economic profit suggested that such conversion of rice paddies to inland fish aquaculture would help to reconcile the dilemma for simultaneously achieving both low climatic impacts and high economic benefits in China. More solid direct field measurements from inland aquaculture are in urgent need to direct the overall budget of national or global CH 4 and N 2 O fluxes. [ABSTRACT FROM AUTHOR]

• CH 4 and N 2 O emissions from rice-aquaculture systems remain poorly constrained. • Rice-crayfish co-culture production is beneficial to reduce CH 4 and N 2 O emissions. • Ditched culture areas release more CH 4 but less N 2 O relative to rice planted areas. • Lower emission factors of N 2 O in rice-crayfish co-culture than monoculture systems. Rice paddies and rice-aquaculture co-culture systems are important sources of methane (CH 4) and nitrous oxide (N 2 O) to the atmosphere. Due to the growing human demand of aquaculture protein and the rapid development of green agriculture, rice-aquaculture co-culture systems have been increasingly developed from rice paddies in southeast China. However, the strength of CH 4 and N 2 O emissions from rice-aquaculture co-culture systems remains poorly quantified, in particular the contribution of these emissions from different functional cultivation areas. Here, a two-year parallel field experiment was conducted to examine the changes in CH 4 and N 2 O fluxes following the conversion from rice paddies to rice-crayfish co-culture systems in southeast China. Over the two-year period, annual CH 4 and N 2 O fluxes from rice-crayfish co-culture systems averaged 4.59 mg m-2 h-1 and 39.50 μg m -2 h -1, amounting to 391.9 kg ha−1 and 3.46 kg ha−1, respectively. The conversion from rice paddies to rice-crayfish co-culture systems significantly reduced CH 4 and N 2 O emissions by 14% and 31%, respectively. The emission factors of N 2 O were estimated to be 1.25–1.61% in the rice-crayfish co-culture system. Relative to rice planted areas, CH 4 and N 2 O fluxes from crayfish ditched culture areas were three times higher and 50% lower, which contributed 26% and 5% to the total CH 4 and N 2 O emissions from rice-crayfish co-culture systems, respectively. Our results highlight that the conversion of paddy rice monoculture to rice-crayfish co-culture systems can benefit low greenhouse gas emissions and high ecosystem economic profits as a potential option to sustain agricultural development and achieve carbon neutrality. [Display omitted] [ABSTRACT FROM AUTHOR]

The potential of biochar for mitigating climatic impacts of coastal saline bioenergy production is not well established. A full accounting of net greenhouse gas balance (NGHGB) and greenhouse gas intensity (GHGI) affected by biochar amendment combined with or without nitrogen (N) fertilizer application was examined in an annual coastal reclaimed Jerusalem artichoke bioenergy cropping system. The net ecosystem exchange of CO 2 (NEE) was determined by the difference between soil heterotrophic respiration ( R H ) and net primary production (NPP) using static chamber method. Biochar amendment raised the seasonal R H but without suppressing the NPP during the Jerusalem artichoke cropping season. Soil CH 4 emissions were 72% and 80% lower in the biochar amended than unamended plots when combined with N fertilizer application during the Jerusalem artichoke cropping and non-cropping seasons, respectively. The biochar-induced soil N 2 O mitigation efficiency was weakened by N fertilizer input over the annual cycle. Annual NGHGB and GHGI were negative for all the field treatments and were significantly lower in biochar amended than in unamended soils, suggesting that Jerusalem artichoke cropping system served as a net sink of GHGs due to net ecosystem CO 2 and biochar-induced C sequestration exceeding CO 2 -equivalents released as CH 4 and N 2 O emissions. On average, biochar amendment significantly enhanced GHGs sink capacity by resulting in almost 4–5 folds decrease in annual NGHGB or GHGI when combined with N fertilizer application or not. Therefore, higher biomass gain as potential alternative source of biofuels but lower climatic impacts of bioenergy production would be reconciled by biochar use in southeast coastal China. [ABSTRACT FROM AUTHOR]

Efforts to advance our knowledge on the potential of bioenergy instead of fossil fuels in terms of mitigating climatic impact are in urgent need. No data is currently available on the use of urease and nitrification inhibitors in costal saline bioenergy cropping systems. An overall accounting of net greenhouse gas balance (NGHGB) and greenhouse gas intensity (GHGI) affected by combined effects of urease inhibitor hydroquinone (HQ) and nitrification inhibitor dicyandiamide (DCD) amendment was examined in a coastal saline Jerusalem artichoke bioenergy cropping system. The net ecosystem exchange of CO 2 (NEE) was determined by the difference between soil heterotrophic respiration ( R H ) and net primary production (NPP) using static chamber method. Urease and nitrification inhibitors amendment increased the NPP but exerted a suppression effect on soil R H over the Jerusalem artichoke cropping system. A trade-off relationship was observed by decreasing soil N 2 O but stimulating soil CH 4 emissions following HQ+DCD amendment. The plots combined urea with HQ+DCD application increased soil CH 4 by 167% while decreased N 2 O by 16% as compared to with urea only in the bioenergy cropping system. On average, the fertilizer N-induced emission factor of N 2 O was estimated to be 0.25% across the fertilized plots. Compared with urea, the plots with urea and HQ+DCD resulted in a further decrease by 37% and 15% in estimated NGHGB and GHGI over the Jerusalem artichoke cropping system, respectively. Overall, Jerusalem artichoke production would achieve higher biomass as source of biofuels but lower climatic impacts, particularly when together with urease and nitrification inhibitors amendment in coastal saline soils. [ABSTRACT FROM AUTHOR]

Biochar amendment has been shown to reduce nitrous oxide (N 2 O) emissions from acidic soils in tea plantations. Given that both soil bacterial and fungal denitrifications can produce N 2 O, their relative contributions to the decrease in N 2 O emissions following biochar amendment remain unclear. Here, we examined soils sampled from a subtropical tea plantation that had received 2 years of biochar amendment. Measurements of the relative contributions of fungi and bacteria to N 2 O production were taken by the substrate-induced respiration method implemented with the addition of selective inhibitors. The abundances of total fungi, bacteria, and key N 2 O-related bacterial genes were quantified by q-PCR, and the composition of the fungal community was analyzed by 18S rRNA amplicon sequencing. The results showed that the contribution of fungi to N 2 O production (52%) was greater than that of bacteria (18%) for the N-applied acidic soils. Biochar amendment significantly decreased the fungal abundances and the fungal contribution to N 2 O production (by 28%). In contrast, biochar amendment significantly increased the abundances of N 2 O-related bacteria (e.g., ammonia-oxidizing bacteria (AOB), nirS , nosZ). Structural equation models (SEMs) revealed that biochar decreased the fungal contribution to N 2 O production through enhancing the soil pH and shifting the fungal community composition. Our results highlight that the decreased N 2 O emissions could be ascribed to the stimulated N 2 O consumption process (driven by N 2 O-consuming bacteria encoded by the nosZ gene) and suppressed fungal dominance in acidic soils from tea plantations. This study presents relatively comprehensive insights into the regulatory roles of biochar on soil microbe-mediated N 2 O production processes. • Fungi played a more important role than bacteria in N 2 O production from acidic soils. • Biochar shifted the fungal community on genus level from acidic soils. • Biochar decreased the fungal contribution to N 2 O production. [ABSTRACT FROM AUTHOR]

• IndirectN2Oemissions from rivers draining agricultural watersheds are of increasing concerns. • Seasonal dissolved N2O concentrationsand N2O fluxes showed a similar variation pattern. • Annual mean model-based N2O fluxes werecomparable with chamber-based N2O fluxes. • The indirect riverine EFof N2O dependedlargely on surface water NO3–N concentrations. • Annual mean riverine indirect EF of N2O was significant lower than the IPCC default value. Indirect nitrous oxide (N 2 O) emissions from rivers draining agricultural watersheds are of increasing concerns due to riverine abundant sources of nitrogen loaded through leaching and runoff. However, the seasonal variation of N 2 O emissions from agricultural drainage rivers is poorly explored, especially the uncertainty in quantifying indirect N 2 O emission factors (EFs) from these aquatic environments. Here, a two-year study (2014-2016) was conducted to quantify indirect N 2 O emissions from a river draining a rice paddy watershed in subtropical China. Indirect N 2 O fluxes were simultaneously determined using the floating chamber method (chamber-based) and the gas exchange modeling approach (model-based) based on the measurement of dissolved N 2 O concentration. Results showed that seasonal dissolved N 2 O concentration and N 2 O fluxes had a similar variation pattern, with the highest and the lowest levels in summer and winter, respectively. The annual mean of model-based N 2 O fluxes (20.24 ± 3.34 μmol m−2 d−1) was generally in agreement with chamber-based N 2 O fluxes (18.70 ± 3.56 μmol m−2 d−1). The indirect emission factor of N 2 O was highly dependent on the surface water NO 3 −-N concentration. Annual mean indirect EF of N 2 O from the drainage river was estimated to be 0.00051, which was significantly lower than the default EF 5r value (0.0025) proposed by the Intergovernmental Panel on Climate Change (IPCC). These results suggest that the use of IPCC default value might have overestimated indirect N 2 O emissions from agricultural impacted riverine systems. Our study also highlights that more extensive in-situ measurements are required for monitoring indirect N 2 O emissions from agricultural impacted waters with different drainage characteristics, which would benefit for refining the IPCC EF 5r default value to further constrain global N 2 O budget. [ABSTRACT FROM AUTHOR]

[Display omitted] • Soil N-oxide fluxes showed high spatiotemporal variability in tea plantations. • N-oxide emissions from soils between rows were higher than those under the canopy. • Factors regulating N-oxide emissions were different between tea plantations. • Acidic tea plantations are hotspots of N-oxide emissions in subtropical regions. Subtropical agricultural soils are hotspots of nitrogen(N)-oxide emissions, whereas the spatiotemporal variability and driving factors of their emissions in different cultivation systems are poorly understood. Here, to assess the magnitude and pattern of soil N-oxide emissions, we conducted measurements of nitrous oxide (N 2 O) and nitric oxide (NO) fluxes from the soil between rows and under the canopy of tea plants in two subtropical tea plantations over a one-year period. Results showed that N 2 O and NO emissions from the soil between rows were 32.6 and 9.1 kg N ha−1 for the Yixing (YX) site and 33.9 and 9.9 kg N ha−1 for the Jurong (JR) site, respectively. Across both sites, N 2 O and NO emissions from the soil between rows were 2.8–5.2 and 1.4–4.0 times, respectively, larger than those from the soil under the canopy. We attributed greater N-oxide emissions from the soil between rows mainly to increased soil mineral N and water contents as compared to the soil under the canopy. On average, N 2 O and NO emissions from the soil under the canopy accounted for 36% and 44% of the total losses from the entire field, respectively. For the entire tea field, N 2 O emissions were 12.6 and 15.7 kg N ha−1 for the YX and JR sites, respectively, but the difference was not statistically different. In contrast, NO emissions from the YX and JR sites were 3.8 and 5.7 kg N ha−1 and differed significantly between the two sites, which was due to higher NO emissions from the soil under the canopy in the JR site. The greatest N-oxide fluxes occurred in the spring and summer seasons after topdressing when soil conditions were conducive to microbial N-oxide production. The structural equation modeling analyses suggested that the variables explaining the variances of soil N-oxide emissions were different between the two tea plantations. Our results indicated that microbial nitrification and abiotic chemodenitrification processes were likely the major pathways leading to N-oxide emissions in the soil under the canopy. Our findings highlight the importance of N-oxide fluxes simultaneously taken from the soil between rows and under the canopy and implementing mitigation practices in subtropical tea plantations. [ABSTRACT FROM AUTHOR]

The optimization of fertilization management has the potential to improve crop yield, reduce greenhouse gas (GHG) emissions and enhance nitrogen agronomy efficiency (NAE). However, less is known about whether these benefits can be simultaneously achieved by optimizing fertilization regimes in Chinese croplands. We carried out a year-round field experiment to measure methane (CH 4) and nitrous oxide (N 2 O) fluxes, crop yield and NAE under different fertilization regimes in a subtropical double-rice cropping system. Relative to the conventional chemical N fertilizer application (F), alternative fertilization strategies significantly decreased N 2 O emissions by 26–78% when averaged across the options of chemical N fertilizer application with reduced rates (RF, 30% off), chemical N fertilizer fully replaced by organic N fertilizer with reduced rates (OF, 30% off) and chemical N fertilizer fully replaced by controlled-release N fertilizer with reduced rates (CF, 30% off), with the largest mitigation potential occurring in OF-treated plots, but comparable extents between the early- and late-rice seasons. Soil CH 4 emissions had no consistent response to alternative fertilization regimes, showing contrasting seasonal patterns between in the early- and late-rice seasons. Alternative fertilization options consistently increased NAE by 7–36% and 30–38% in the early- and late-rice seasons, respectively, and this benefit was maximized in OF-treated plots. Direct emission factors of N fertilizer for N 2 O and the combined greenhouse gas intensity (GHGI) of N 2 O and CH 4 were negatively related to NAE while rice yield was positively related to NAE. Our findings suggest that optimized fertilization strategies especially through the option of chemical N fertilizer fully substituted by organic N fertilizer can reconcile low climatic impact and high NAE, but without compromising yield in double-rice cropping systems. • Soil GHG emissions were linked to NAE in double-rice under different fertilization regimes. • Soil N 2 O emissions showed a significant decrease by 26–78% across optimized fertilization regimes. • Optimized fertilization alternatives consistently increased NAE in double-rice cropping seasons. • Direct EFs of N 2 O and annual combined GHGI of CH 4 and N 2 O were negatively related to NAE. • Organic N substitution stood out to reconcile low SGWP and high NAE of double-rice production. [ABSTRACT FROM AUTHOR]

• Biochar amendment decreased N 2 O and NO emissions from acidic soils. • Biochar amendment stimulated both nitrification and denitrification processes. • Soil N 2 O was produced mainly through denitrification in acidic soils. • Soil DOC and pH were key factors to N 2 O and NO emissions from acidic soils. • Soil N 2 O emissions were negatively related to nosZ gene abundances. Acidic soils are hotspots of nitrous oxide (N 2 O) and nitric oxide (NO) and biochar is documented to have the potential for mitigating N 2 O and NO. The N 2 O and NO emissions associated with soil functional genes and physicochemical properties under biochar amendment remains unclear in acidic soils. Here, we carried out a two-year field study to examine the responses of soil N 2 O and NO emissions to biochar amendment in a subtropical tea plantation in China. Measurements of N 2 O and NO fluxes were taken from inter-row soils using the static chamber method. We also measured the seasonal changes in soil key nitrogen (N)-cycling functional genes and physicochemical properties. Annual N 2 O and NO emissions averaged 27.31 kg N 2 O-N ha−1 yr−1 and 8.75 kg NO-N ha−1 yr−1 for the N fertilizer applied plots, which were decreased by 24% and 16% due to biochar application, respectively. In addition, both potential nitrification (PNR) and denitrification (PDR) rates were stimulated by biochar amendment, which significantly increased the abundances of bacterial amoA (AOB), nirK and nosZ genes. Changes in the composition of the N 2 O-related microbial functional community were closely associated with soil PNR, pH, DOC, and NO 3 −-N contents. The ratios of NO/N 2 O were mainly lower than 1, suggesting that N 2 O was produced mostly through denitrification rather than nitrification. There were negative correlations between soil N 2 O and NO emissions and soil PDR and pH, and soil N 2 O emissions were negatively correlated with nosZ gene abundances. Together, the decrease in N 2 O and NO emissions following biochar application could be largely attributed to the enhanced denitrification process, in which biochar enriched the nirK and nosZ genes abundance, resulting from the enhancement of soil DOC and pH in acidic soils. [ABSTRACT FROM AUTHOR]

Biochar amendment has been proposed as a potential strategy to reduce soil nitrous oxide (N 2 O) emissions, although experimental studies have generated inconsistent results on N 2 O emissions following biochar amendment. Differential responses of soil N 2 O to biochar amendment may depend on soil microbial functional genes abundance and abiotic properties. Here we sampled three types of soil from fields under long-term cultivation of green tea (TG), film greenhouse vegetable cabbage (GV) and Jerusalem artichoke (JA), respectively. We conducted a microcosm experiment to examine N 2 O emissions from the different soils following biochar amendment. Results showed that biochar amendment increased N 2 O emissions from the GV soil while decreasing N 2 O emissions from the TG and JA soils in the presence of nitrogen fertilizer. Biochar amendment increased soil pH and C/N ratio across the three soils. Quantitative PCR (qPCR) analysis showed that biochar amendment also consistently increased the abundances of AOB and nosZ genes but decreased the AOA abundances for all the soils, while the effects of biochar on the abundances of nirK and nirS genes differed between the soils. Our results suggest that biochar amendment can affect the processes of both ammonia oxidation and reduction of N 2 O to N 2 for all the soils and the net effect of biochar on N 2 O emissions depended on the predominant process in a specific soil. Biochar-induced increase in N 2 O emissions in the GV soil was largely attributed to the stimulated nitrification rate, which was primarily driven by AOB. Biochar-induced decreases in N 2 O emissions in the TG and JA soils were linked to the increased nosZ gene abundances. Overall, the effectiveness of biochar for mitigating N 2 O emissions is linked to its dominant N 2 O production pathway in soils. • Biochar increased the abundances of AOB and nosZ gene across all the soils. • Effects of biochar on N 2 O emissions differed with N addition and soil type. • Biochar increased soil N 2 O emissions produced by AOB-dominated pathways. • Biochar decreased soil N 2 O emissions produced by denitrification-mediated pathways. [ABSTRACT FROM AUTHOR]