Mitigate N2O Emissions Research Articles

Large nitrous oxide emissions from arable soils after crop harvests prior to sowing

Abstract Global agriculture is the largest anthropogenic source for nitrous oxide (N2O) emissions. During crop rotations, periods with arable soils without crops, thereafter called “bare soils” are often impossible to avoid after the crop is harvested, prior to sowing of the next crop. However, such periods are underrepresented in studies focussing on N2O emissions. Here, we present continuous, high-temporal-resolution N2O fluxes during bare soil periods after four major crops, using the eddy-covariance technique at two sites in Switzerland. Overall, periods with bare soil were net sources for N2O as well as for carbon dioxide (CO2) and methane (CH4). Daily average sums of N2O emissions varied between 10 ± 2 and 38 ± 5 g N2O-N ha−1 d−1 after the respective rapeseed, winter wheat, pea, and maize harvests. While CO2 emissions contributed 86–96% to the total GHG budgets, N2O fluxes accounted for 2% after pea, but for 10–12% after rapeseed, winter wheat, and maize. In contrast, CH4 fluxes were negligible (< 2%). N2O fluxes during bare soil periods increased for all cropland sites with increasing water-filled pore space, particularly at high soil temperatures. Thus, our study emphasizes the significance of avoiding bare soil periods to mitigate N2O emissions from croplands.

Membrane-covered aerobic composting mitigated nitrous oxide emission through improved micro-aerobic state and enhanced carbon source utilization.

In this study, the variables related to nitrous oxide (N2O) emissions and their interactions during membrane-covered aerobic composting (MCAC) and conventional aerobic composting were characterized at multiple scales. For the first time, it was quantified that the MCAC-created micro-positive pressure (50-500Pa) significantly increased compost particles aerobic layer thickness by 24%-27% (P<0.001). Pile-scale results demonstrated that MCAC decreased the abundance of key functional genes (nirS, nirK, cnorB, and nosZ) and microbes (norank_f__A4b, Halomonas, norank_f__norank_o__SBR1031, and norank_f__Xanthomonadaceae) associated with N2O emissions (P<0.001); MCAC significantly enhanced the microbial metabolic potential for carbohydrate-based, carboxylic acid-based, amino acid-based, lipid-based, organic phosphate-based, and amine-based carbon sources (P<0.05). Interaction analysis suggested that the improved micro-aerobic state inhibited the N2O generation pathway, while the increased microbial utilization of carbon facilitated the N2O reduction pathway. Consequently, MCAC decreased N2O emissions by 20%-27%. These findings offer valuable insights for optimizing MCAC strategies to mitigate N2O emissions.

Mechanism of nitrous oxide emission reduction in constructed wetlands based on plant harvesting management.

The impact of plant harvesting on nitrous oxide (N2O) emission reduction in constructed wetlands (CWs) remains uncertain. This study focused on the Myriophyllum aquaticum wetland treating swine wastewater, with three different plant harvesting frequencies implemented: high harvesting (HF), low harvesting (LF), and no harvesting (CK). Results showed that compared to CK, cumulative N2O emissions decreased by 7.4 % (HF) and 18.5 % (LF), with only LF showing a significant reduction. The primary reductions in N2O emissions occurred during winter and summer, accounting for 26.2 %∼39.7 % and 14.0 %∼49.2 % of the total reductions, respectively. Crucial contributors to mitigating N2O emissions included water redox potential, sediment dissolved organic carbon, and ammonia nitrogen levels. Additionally, increased denitrification gene abundance in harvesting treatments reduced N2O emissions. These findings suggest that low-frequency plant harvesting, particularly in winter and summer, can significantly reduce N2O emissions from CWs.

Freshwater Salinization Mitigated N2O Emissions in Submerged Plant-Covered Systems: Insights from Attached Biofilms.

Submerged plants (SMPs) play a critical role in improving water quality and reducing N2O greenhouse gas emissions. However, freshwater salinization represents a major environmental challenge in aquatic systems. To investigate the impact of salinization on N2O emissions, this study conducted indoor mesocosm experiments simulating SMP and nonsubmerged plant (Non_SMP) areas in freshwater lakes. The objective was to explore the effects and microbial mechanisms of the attached biofilm on N2O emission in freshwater salinization. Salinization systems (700-1500 μS cm-1) reduced N2O flux by 37.0 and 40.5% compared to freshwater systems (<700 μS cm-1) of SMPs and Non_SMPs, respectively. Kinetic experiments showed that the reduction in N2O emissions was mainly attributed to the attached biofilm rather than the sediment or water. The N2O net emission rates of the attached biofilm decreased by 47.1 and 71.8% in salinization systems of SMPs and Non_SMPs, respectively, compared with freshwater systems. Additionally, biofilms in salinization systems exhibited lower denitrification rates. Furthermore, salinization reduced the N2O production potential ((nirS + nirK)/(nosZI + nosZII)), thereby further decreasing N2O emissions. This study provides valuable insights into the role and mechanisms of biofilms in mitigating N2O emissions in salinized freshwater lakes.

Efficiency of 3,4-Dimethylpyrazole Phosphate in Mitigating N2O Emission Varied with Irrigation Regime in Drip-Irrigated Wheat Field

Agricultural soils are major anthropogenic sources of N2O emissions. The application of nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) has been proved to be an effective management measure to mitigate N2O emissions. However, the influence mechanism of DMPP on the mitigation of soil N2O emissions under different irrigation regimes remains unclear. Therefore, a lysimeter experiment was conducted to study the effects of irrigation level (lower irrigation limits of 75%, 65%, and 55% of field capacity (FC), signed as WH, WM, and WL) and DMPP addition (0% and 1% of N application, signed as D0 and D1) on N2O emissions, soil environmental factors such as ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3−-N), water-filled pore space (WFPS), soil temperature, and the abundances of N2O-related genes (AOA amoA, AOB amoA, nirS, and nirK). The results showed that soil N2O emissions increased with the increasing of irrigation level. The efficiency of DMPP mitigating N2O emissions varies depending on irrigation regime. Compared to D0, D1 strongly decreased cumulative N2O emissions by 11.27%, 18.96%, and 15.05% in the WL, WM, and WH conditions, respectively. Meanwhile, D1 caused an obvious reduction in the AOB amoA gene by 29.73%, 47.02%, and 22.41%, respectively, but there was no significant effect on the AOA amoA gene. D1 was effective in decreasing nirS and nirK genes except in the WL condition; the percentages of reduction were 48.45%, 40.84% and 37.18%, 44.97% in the WM and WH conditions, respectively. In addition, D1 caused an increase in NH4+-N content and a decrease in NO3−-N content, WFPS, and soil temperature in all irrigation regimes. A higher significant correlation was observed between N2O emissions and NH4+-N and AOB amoA in the WL and WM conditions, while a significant correlation was observed between N2O emissions and NO3−-N, nirK, and nirS in the WH condition. It was revealed that with the increase in irrigation level, the main source of N2O emissions might change from nitrification to denitrification. Overall, our study indicated that in the WL and WM conditions, the mitigation of N2O emissions by DMPP was primarily attributable to the inhibition of the AOB amoA gene, whereas the inhibition of nirS and nirK genes was likely the dominant mechanism in the WH condition. The findings of this study will provide a theoretical basis for the application of a nitrification inhibitor for drip-irrigated winter wheat fields in the North China Plain.

Urease Inhibitors Weaken the Efficiency of Nitrification Inhibitors in Mitigating N2O Emissions from Soils Irrigated with Alternative Water Resources

Urease Inhibitors Weaken the Efficiency of Nitrification Inhibitors in Mitigating N2O Emissions from Soils Irrigated with Alternative Water Resources

Distribution and key influential factors of comammox in drained and waterlogged soils of zoige plateau peatland

Peatlands are important carbon and nitrogen reservoirs, playing crucial roles in nitrogen cycling. During microbially-driven nitrogen cycling, nitrous oxide (N2O, 298 times global warming potential of CO2) can be emitted, exacerbating global warming. Complete ammonia-oxidizing bacteria (comammox), a newly discovered group of prokaryotes, can independently oxidize ammonia directly to nitrate, bypassing the nitrite stage, and thereby reducing N2O production associated with the traditional two-step nitrification process. However, information on comammox distribution and its key influential factors in plateau peatlands remains scarce. Thus, this study chose Zoige plateau peatland in China to collect soil samples from different soil types (drained and waterlogged), across different seasons (non-growing and growing), and at various depth (0–100 cm) to assess comammox abundance and community composition. Additionally, soil properties were analyzed and correlated with comammox abundance and community composition to identify the key factors affecting comammox distribution. Comammox abundance varied significantly across soil types, depth, and sampling seasons. Waterlogged soils demonstrated higher comammox abundance than drained soils. In waterlogged soils, comammox abundance showed higher during growing season than non-growing season, while the opposite trend was observed in drained soils. Regardless of soil types, comammox abundance decreased with increasing soil depth. In soils of Zoige plateau peatland, comammox clades A.1, A.2, A.3 and B.1 were identified, with clade B.1 dominating the comammox community. Both Nitrospira sp. CG24A (clade B.1) and Candidatus Nitrospira nitrificans (clade A.1) showed great seasonal variations. Soil properties, including moisture, pH, carbon, and nutrients, collectively influenced comammox abundance and diversity. Among these factors, NH4+-N was the main factor affecting comammox abundance, while moisture primarily drove community distribution. These findings provide valuable insights into comammox distribution, enhancing our understanding of its potential role in mitigating N2O emissions and thus nitrogen cycling in plateau peatland soils.

Soil properties drive nitrous oxide accumulation patterns by shaping denitrifying bacteriomes

In agroecosystems, nitrous oxide (N₂O) emissions are influenced by both microbiome composition and soil properties, yet the relative importance of these factors in determining differential N₂O emissions remains unclear. This study investigates the impacts of these factors on N₂O emissions using two primary agricultural soils from northern China: fluvo-aquic soil (FS) from the North China Plain and black soil (BS) from Northeast China, which exhibit significant differences in physicochemical properties. In non-sterilized controls (NSC), we observed distinct denitrifying bacterial phenotypes between FS and BS, with BS exhibiting significantly higher N₂O emissions. Cross-inoculation experiments were conducted by introducing extracted microbiomes into sterile recipient soils of both types to disentangle the relative contributions of soil properties and microbiomes on N₂O emission potential. The results showed recipient-soil-dependent gas kinetics, with significantly higher N₂O/(N₂O + N₂) ratios in BS compared to FS, regardless of the inoculum type. Metagenomic analysis further revealed significant shifts in denitrification genes and microbial diversity of the inoculated bacteriomes influenced by the recipient soil. The higher ratios of nirS/nosZ in FS and nirK/nosZ in BS indicated that the recipient soil dictates the formation of different denitrifying guilds. Specifically, the BS environment fosters nirK-based denitrifiers like Rhodanobacter, contributing to higher N₂O accumulation, while FS supports a diverse array of denitrifiers, including Pseudomonas and Stutzerimonas, associated with complete denitrification and lower N₂O emissions. This study underscores the critical role of soil properties in shaping microbial community dynamics and greenhouse gas emissions. These findings highlight the importance of considering soil physicochemical properties in managing agricultural practices to mitigate N₂O emissions.

Arbuscular mycorrhizal fungi mediate soil N dynamics, mitigating N2O emissions and N-leaching while promoting crop N uptake in green manure systems

Arbuscular mycorrhizal fungi (AMF), as symbionts of the plant root system, play a pivotal ecological role in soil nutrient dynamics. However, the mechanisms by which AMF mediates nitrogen (N) transformation at the soil-crop interface, particularly under green manure management, remain insufficiently understood. This study investigates these mechanisms through a long-term field experiment, employing four green manure management practices during the flowering stage of common vetch: tillage with total green manure incorporation (TG), no-tillage with total green manure mulching (NTG), aboveground biomass removal with root incorporation (T), and aboveground biomass removal with no-tillage (NT), alongside a conventional tillage control without green manure (CT). Results indicate that NTG notably enhanced AMF abundance and dominant species, attributed largely to increases in soil available N, microbial biomass carbon (MBC), and soil pH. AMF colonization rates in maize roots peaked at 69.7 % under NTG. Additionally, soil mineral N was 17.7 % higher under NTG than TG, with aggregate N concentration increasing by 72.4 %. A strong positive correlation emerged between aggregate N and AMF colonization rates. NTG also significantly elevated nos Z gene abundance and nitrous oxide (N2O) reductase activity while lowering the (nir K +nir S) / nos Z ratio. Optimized root architecture under NTG was similarly correlated with AMF colonization, supporting N retention and uptake. Structural equation modeling further confirmed that aggregate N and root structure were primary contributors to reduced N leaching, while root architecture enhanced maize N uptake and N2O reductase activity. The increase in nos Z and N2O reductase reductase significantly reduced N2O emissions. In summary, no-tillage with green manure mulching effectively mitigated N loss and improved crop N uptake by enhancing AMF abundance and colonization.

Improved nitrogen fertilizer management reduces nitrous oxide emissions in a northern Prairie cropland

Arable croplands are a significant source of nitrous oxide (N2O) emissions, largely due to nitrogen (N) fertilizer applications to support crop production. Nevertheless, there is limited research on the N2O dynamics from canola-wheat rotations in the semi-arid northern Prairies, an important agricultural region. Here, we present micrometeorological N2O fluxes measured from January 2021 to April 2024 in Saskatchewan, Canada, to evaluate the impact of N fertilizer management on the year-round N2O emissions from a canola-wheat rotation. A combination of two 4R (Right Source, Right Rate, Right Time, Right Place) N management practices – a reduced N rate and an enhanced efficiency N fertilizer source – was compared to common fertilizer management practices for the region. Two periods at high risk for N2O flux events were identified, after N fertilizer applications and the following spring thaw, with the magnitude of emissions varying over the multi-year period. As for cumulative emissions, the growing season (GS) N2O emissions were 50 % of annual emissions, presenting an opportunity to mitigate N2O emissions through improved N fertilizer management. Indeed, the improved 4R N management reduced N2O emissions by 57 % over the entire study period without impacting yields. The reduction in GS N2O emissions resulted from the 4R N management lowering mean N2O flux at times of high WFPS (>50 %). The non-growing season (NGS) N2O accounted for 11–67 % of annual emissions. Fall soil nitrate levels were a strong explanatory variable of NGS emissions (r2 = 0.69, r2 = 0.39), but the rate of change and magnitude of NGS emissions depended on thawing conditions – lower for drier thaws, higher for wetter thaws. Ultimately, better N fertilizer management reduces cumulative N2O emissions from cropping systems when practiced for several years.

Modifying functional groups of straw-based hydrogel provide soil N2O mitigation potential by complete denitrification

Farmed soil is considered to contribute more than 60% anthropogenic N2O emission which plays critical role in global warming potential. Straw-based hydrogels with abundant functional groups are commonly used in environmental and agronomic applications primarily as adsorbents. Those functional groups could mediate electron transfer in the process of adsorbates and might also regulate N2O emission. However, it was still unclear whether and how these functional groups affect the process. To address this knowledge gap, we employed spectral analysis and a robotized incubation system to determine mechanisms of different functional groups in influencing soil N2O. The results indicated that the straw-based hydrogel was capable of significantly reducing the emission of N2O in denitrification, and the electrochemical properties of the hydrogel had promoting effect of the microbial genetic potential for N2O reduction. Specifically, carboxymethyl (R-COO) and primary amine groups (R-NH2) promoted complete denitrification through electron supply. Furthermore, R-NH2 had a significant negative correlation with N2O emissions. To further verify the role of specific structures and functional groups in denitrification, we conducted an experiment using pure lignin as a template. This experiment resulted in an increase in R-NH2 content to 13.2% and a decrease in N2O emissions by 49.1% compared with straw hydrogel. These results prove the feasibility of straw-based hydrogel as a redox system to accelerate complete denitrification, and the electron-donating functional groups were significantly related to the reduction rate of N2O. Finally, based on these mechanisms, functional group targeted grafting technology was proposed to improve its ability to mitigate N2O emission reduction.

Labile organic matter favors a low N2O yield during nitrogen removal in estuarine sediments

Estuary harbors the active sediment denitrification and nitrous oxide (N2O) emission, while the knowledge of environmental controls on the denitrification-derived N2O yield remains underexplored. Here, we quantitatively assess the potential and in situ rates of N2O production during sediment denitrification in the Pearl River Estuary (PRE), China. Organic matter determines the product stoichiometry and capacity of nitrogen removal. In particular, labile organic matter (LOM) reduces N2O yield via enhancing the complete coupled nitrification-denitrification. Our results reveal that the chain processes, primary production-LOM settling-sedimentary respiration-coupled nitrification-denitrification, control the sediment denitrification and N2O production, linking the carbon and nitrogen biogeochemical cycles in the atmosphere-water column-sediment continuum. The PRE sediments serve as nitrogen removal hotspots but with low efficiency (~25 % of riverine input) and strong N2O release (~66 % of daily sea-air N2O efflux). These findings contribute to policy makers to develop knowledge-based management actions for achieving sustainable coastal environments and mitigating N2O emission.

Complex factors combinations driving tea growers to adopt ecological agricultural practices in tea gardens

IntroductionThe implementation of ecological agriculture practices in Chinese tea gardens plays a vital role in mitigating N2O emissions and addressing environmental degradation. Nevertheless, a dearth of discourse exists regarding the intricacies surrounding farmers' adoption of tea garden ecological agriculture practices (TGEAP), particularly the complex interplay between adoption factors and outcomes.MethodsUsing data of 310 farmers, this study employed complexity theories and Stimulus-Organism-Response theories, and integrated Partial Least Squares Structural Equation Modeling and fuzzy-set Qualitative Comparative Analysis to explore the complex relationships between farmer characteristics, internal and external factors, and adoption of farmer.ResultsThe results show three influential paths in the Stimulus-Organism-Response model, and environmental protection attitude (EPA) and production expectation (PE) act as intermediaries. Notably, EPA exhibits a masking effect in one pathway. These paths linked closely to three farmer characteristics. Beyond the Stimulus-Organism-Response model, nine combinations lead to farmers' adoption, and four to non-adoption.DiscussionWe discover scenarios where opposing environmental states or age lead to adoption, explaining the masking effect. These combinations highlight how a favorable environment influences both adoption and non-adoption. We also discuss other combinations that lead to adoption or non-adoption. The study suggests that governments employ targeted incentives to facilitate tea farmers' transition in agriculture.

Application of straw-derived biochar: a sustainable approach to improve soil quality and crop yield and reduce N2O emissions in paddy soil.

The burning of agricultural straw is a pressing environmental issue, and identifying effective strategies for the rational utilization of straw resources is decisive for achieving sustainable development. Owing to its high carbon content and exceptional stability, straw biochar produced via pyrolysis has emerged as a key focus in multidisciplinary research. However, the efficacy of biochar in mitigating nitrous oxide (N2O) emissions from paddy soils is not consistent. A 2-year field experiment was conducted and investigated the impact of biochar derived from two feedstocks (rice straw and wheat straw, pyrolyzed at 450°C) on N2O emissions, global warming potential (GWP), greenhouse gas intensity (GHGI), nitrogen use efficiency (NUE), crop yield, and soil quality. The static chamber technique was used for collecting N2O gas samples, and concentrations were analyzed through gas chromatography methods. The treatment combinations included BR0 (control), BR1 (NPK at the recommended dose, 120:60:40kgha-1), BR2 (wheat straw biochar, 5 t ha-1), and BR3 (rice straw biochar, 5 t ha-1). The results exhibited that cumulative N2O emissions from BR2 and BR3 treatments decreased by 10.55% and 13.75% respectively, compared to BR1. Lower GWP and GHGI were observed under both biochar treatments compared with BR1. The highest rice grain yield (3.48Mgha-1) and NUE (76.72%) were recorded from BR3, which also exhibitedthe lowest yield-scaled N2O emission. We observed positive correlations between soil nitrate, ammonia and water-filled pore spaces, while NUE showed negative correlations with N2O emissions. Significant (p < 0.05) improvements in soil quality were also detected in both the biochar treated plots, indicated by increased soil pH, water holding capacity, porosity, and nutrient contents. Overall, the results suggest that applying biochar at a rate of 5 t ha-1 in paddy soil is a viable nutrient management strategy with the potential to reduce reliance on inorganic fertilizers, mitigate N2O emissions, and contribute to sustainable food production.

Strip clear-cutting transformations increase soil N2O emissions in abandoned Moso bamboo forests

Forest transformation can markedly impact soil greenhouse gas emissions and soil environmental factors. Due to increasing labor costs and declining bamboo prices, the abandonment of Moso bamboo forests is sharply escalating in recent years, which weakens the carbon sequestration capacity and decreases the ecological function of forests. To improve the ecological quality of abandoned Moso bamboo forests, transformations of abandoned bamboo forests have occurred. However, the impact of such transformations on N2O emissions remains elusive. To bridge the knowledge gap, we conducted a 23-month field experiment to compare the effects of various forest management practices on soil N2O emissions and soil environmental factors in abandoned Moso bamboo forests in subtropical China. These practices included uncut abandonment as a control, intensive management, three intensities (light, moderate, and heavy) of strip clear-cutting with replanting local tree species, and clear-cutting with replanting transformation. During the experimental period, the mean soil N2O flux in abandoned Moso bamboo forests was 13.2 ± 0.1 μg m−2 h−1, representing a 44% reduction compared to intensive management forests. In comparison to the uncut control, light, moderate, and heavy strip clear-cutting and clear-cutting transformations increased soil N2O emission rates by 20%, 43%, 64%, and 94%, respectively. Soil temperature (69–71%), labile C (2–6%) and N (3–8%) were the main factors that explain N2O emissions following the transformation of abandoned Moso bamboo forests. Additionally, replanting could decrease soil N2O emissions by increasing the contribution of soil moisture. Overall, the light strip clear-cutting transformation is suggested to convert abandoned Moso bamboo forests to mitigate N2O emissions.

Organic fertilizer significantly mitigates N2O emissions while increase contributed of comammox Nitrospira in paddy soils

Nitrification is the dominant process for nitrous oxide (N2O) production under aerobic conditions, but the relative contribution of the autotrophic nitrifiers (the ammonia-oxidising archaea (AOA), the ammonia-oxidising bacteria (AOB) and the comammox) to this process is still unclear in some soil types. This is particularly the case in paddy soils under different fertilization regimes. We investigated active nitrifiers and their contribution to nitrification and N2O production in a range of unfertilized and fertilized paddy soils, using 13CO2-DNA based stable isotope probing (SIP) technique combined with a series of specific nitrification inhibitors, including acetylene (C2H2), 3, 4-dimethylpyrazole phosphate (DMPP) and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO). The soils had a long-term history of fertilizer application, including chemical fertilizer only, a mixture of chemical fertilizers (70 %) and chicken manure (30 %) or a mixture of rice straw and chemical fertilizers. 13CO2-DNA-SIP and Illumina MiSeq sequencing demonstrated that comammox clades A.1 and B were active nitrifiers in all fertilized paddy soils. Inhibitor experiment showed that AOB largely contributed to nitrification activity and N2O emission in all paddy soils, while comammox contribution was more significant than AOA. Fertilization considerably altered nitrifiers' relative contribution to nitrification activity and N2O emissions. Applying organic fertilizers significantly decreased the N2O emissions but increased the contribution of comammox to the process. These findings expand the functional ecological niche of comammox, revealing their nitrification role and N2O production in other ecosystems than oligotrophic habitats.

Meta-analysis of GHG emissions stimulated by crop residue return in paddy fields: Strategies for mitigation

The stimulating impact of crop residue return on greenhouse gas (GHG) emissions from paddy fields have been widely accepted, while the influence of site environmental and human factors on the simulating degree remains unclear. Here, we performed a meta-analysis to assess the GHG emissions affected by residue return, and its mitigation potential combined with key factors in paddy fields. Drawing upon 1047 observation sets of CH4 and N2O emissions from 155 peer-reviewed publications we found that residue return to paddy fields caused an average increase of 73% CH4 emissions and 14% in N2O emissions. Utilizing meta-analytical models, we identified pH as the most significant driver modulating GHG emissions, followed by soil organic matter (SOC) and total nitrogen. In alkaline soils, combining straw return with intermittent irrigation (285.2%) or mid-season drainage (118.9%) significantly reduced CH4 emissions compared to continuous flooding (1201.9%). Additionally, pairing straw return with higher nitrogen inputs (above 150 kg N ha−1) improved soil N2O uptake by −11.5%. In acid and neutral soils, straw carbonization achieved soil CH4 negative emissions (from −2.9% to −39.3%), but the long-term effects remained unclear. Reduced drainage frequency mitigates N2O emissions but may increase CH4 emissions. To efficiently mitigate GHG emissions, we proposed low-carbon schemes for acid or neutral soils based on specific SOC content: For soils with SOC content <10 g kg−1, prioritize nitrogen input control with rates not exceeding 174 kg N ha−1. For soils with SOC content >10 g kg−1, prioritize adjusting the type of straw. Our study underscores the significance of site-specific factors in modulating GHG emissions. Efficient GHG mitigation can be achieved by combining residue return with other agronomic measures tailored to different soil conditions.

Diversity and Activity of Soil N2O-Reducing Bacteria Shaped by Urbanization.

Nitrous oxide (N2O) is a potent greenhouse gas with various production pathways. N2O reductase (N2OR) is the primary N2O sink, but the distribution of its gene clades, typically nosZI and atypically nosZII, along urbanization gradients remains poorly understood. Here we sampled soils from forests, parks, and farmland across eight provinces in eastern China, using high-throughput sequencing to distinguish between two N2O-reducing bacteria clades. A deterministic process mainly determined assemblies of the nosZI communities. Homogeneous selection drove nosZI deterministic processes, and both homogeneous and heterogeneous selection influenced nosZII. This suggests nosZII is more sensitive to environmental changes than nosZI, with significant changes in community structure over time or space. Ecosystems with stronger anthropogenic disturbance, such as urban areas, provide diverse ecological niches for N2O-reducing bacteria (especially nosZII) to adapt to environmental fluctuations. Structural equation modeling (SEM) and correlation analyses revealed that pH significantly influences the community composition of both N2O-reducing bacteria clades. This study underscores urbanization's impact on N2O-reducing bacteria in urban soils, highlighting the importance of nosZII and survival strategies. It offers novel insights into the role of atypical denitrifiers among N2O-reducing bacteria, underscoring their potential ecological importance in mitigating N2O emissions from urban soils.

Variability in N2O emission controls among different ponds within a hilly watershed

While it is well established that small water bodies like ponds play a disproportionately large role in contributing to N2O emissions, few studies have focused on lowland ponds in hilly watersheds. Here, we explored the characteristics of N2O concentrations and emissions from various typical ponds (village, tea, forested, and aquaculture ponds) in a hilly watershed and examined the specific controls influencing N2O production. Our findings revealed that tea ponds exhibited the highest N2O flux (8.42 ± 8.23 μmol m-2 d-1), which was 2.8 to 3.3 times greater than other types of ponds. Remarkable seasonal variations were observed in tea and forested ponds due to the seasonality of nutrient-enriched runoff, whereas such variations were less pronounced in village and aquaculture ponds. Key factors such as nitrogen levels, temperature, and dissolved oxygen (DO) emerged as the primary controls of N2O concentrations in ponds, heavily influenced by land use and human activities in their drainage areas. Specifically, N2O production in tea and aquaculture ponds was driven by N inputs from fertilization and feed, respectively, while DO levels governed the process in village and forested ponds, influenced by abundant algae and forest vegetation. This study emphasizes that environmental factors predominantly drive N2O production in ponds within hilly watersheds, but land use in the pond drainages acts as an indirect yet crucial influence. This highlights the need for future research to develop targeted emission reduction strategies based on land use to effectively mitigate N2O emissions, promising a path toward more sustainable and climate-friendly watershed management.

Investigating drivers of N2 loss and N2O reducers in paddy soils across China

Denitrification plays a pivotal role in nitrogen (N) cycling in rice paddies, significantly impacting N loss and greenhouse gas emissions. Accurate quantification of net N2 emissions from paddy fields is therefore essential for improving fertilizer N use efficiency. However, challenges in directly measuring gaseous N2 hinder our understanding of microbially-mediated N loss in paddy soils at large scales. In this study, we investigated net N2 loss and its influencing factors in 45 paddy soils across China using membrane inlet mass spectrometry and N2/Ar technique, complemented by microbial community analysis via metagenomics. Potential N2 loss rates varied from 0.41 to 3.58 nmol N g−1 h−1, with no significant regional differences. However, soils from rice-upland rotation (1.72 ± 0.64 nmol N g−1 h−1) and mono-rice cropping systems (1.41 ± 0.53 nmol N g−1 h−1) exhibited higher N2 loss rates compared to double-rice cropping soils (1.13 ± 0.62 nmol N g−1 h−1). Our results revealed a unimodal relationship between soil N2 loss rates and soil pH, with N2O reducers and soil properties primarily regulating regional variations in N2 loss. Significant ecological differentiation was observed within both nosZ Clade I and Clade II, with soil pH emerging as the key factor shaping their community composition. Specifically, in rice-upland rotations, soil moisture and pH significantly influenced nosZ Clade I, while in double-rice cropping systems, soil texture and pH were the main factors affecting nosZ Clade II, thereby driving N2 loss. These findings enhance our understanding of N2 loss dynamics in paddy soil ecosystems, underscoring the critical role of N2O reducers on microbial-derived N2 loss and highlighting the importance of developing strategies to mitigate N2O emissions by balancing N2 loss through the manipulation of N2O-reducing and N2O-producing microbes.