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Conversion of forestland to intensively managed agricultural land occurs worldwide and can increase soil nitrous oxide (N 2 O) emissions by altering the transformation processes of nitrogen (N) cycling related microbes and environmental conditions. However, little research has been conducted to assess the relationships between nitrifying and denitrifying functional genes and enzyme activities, the altered soil environment and N 2 O emissions under forest conversion in subtropical China. Here, we investigated the long-term (two decades) effect of converting natural forests to intensively managed tea (Camellia sinensis L.) plantations on soil potential N 2 O emissions, inorganic N concentrations, functional gene abundances of nitrifying and denitrifying bacteria, as well as nitrifying and denitrifying enzyme activities in subtropical China. The conversion significantly increased soil potential N 2 O emissions, which were regulated directly by increased denitrifying enzyme activity (52 %) and nirS + nirK gene abundance (38 %) as shown by structural equation modeling, and indirectly by AOB-amoA gene abundance and inorganic N concentration. Our results indicate that converting natural forests to tea plantations directly increases soil inorganic N concentration, resulting in increases in the abundance of soil nitrifying and denitrifying microorganisms and the associated N 2 O emissions. These findings are crucial for disentangling the factors that directly and indirectly affect soil potential N 2 O emissions respond to the conversion of forest to tea plantation., 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 © 2022 Elsevier B.V. All rights reserved.)

Agroforestry systems (AFS) contribute to carbon (C) sequestration and reduction in greenhouse gas emissions from agricultural lands. However, previously understudied differences among AFS may underestimate their climate change mitigation potential. In this 3-year field study, we assessed various C stocks and greenhouse gas emissions across two common AFS (hedgerows and shelterbelts) and their component land uses: perennial vegetated areas with and without trees (woodland and grassland, respectively), newly planted saplings in grassland, and adjacent annual cropland in central Alberta, Canada. Between 2018 and 2020 (~April-October), nitrous oxide emissions were 89% lower under perennial vegetation relative to the cropland (0.02 and 0.18 g N m -2  year -1 , respectively). In 2020, heterotrophic respiration in the woodland was 53% lower in shelterbelts relative to hedgerows (279 and 600 g C m -2  year -1 , respectively). Within the woodland, deadwood C stock was particularly important in hedgerows (35 Mg C ha -1 or 7% of ecosystem C) relative to shelterbelts (2 Mg C ha -1 or <1% of ecosystem C), and likely affected C cycling differences between the woodland types by enhancing soil labile C and microbial biomass in hedgerows. Deadwood C stock was positively correlated with annual heterotrophic respiration and total (to ~100 cm depth) soil organic C, water-soluble organic C, and microbial biomass C. Total ecosystem C was 1.90-2.55 times greater within the woodland than all other land uses, with 176, 234, 237, and 449 Mg C ha -1 found in the cropland, grassland, planted saplings treatment, and woodland, respectively. Shelterbelt and hedgerow woodlands contained 2.09 and 3.03 times more C, respectively, than adjacent cropland. Our findings emphasize the importance of AFS for fostering C sequestration and reducing greenhouse gas emissions and, in particular, retaining hedgerows (legacy woodland) and their associated deadwood across temperate agroecosystems will help mitigate climate change., (© 2022 John Wiley & Sons Ltd.)

Unprecedented increases in agricultural nitrous oxide (N 2 O) emissions in recent years have caused substantial environmental pollution that leads to ozone depletion and global warming. Application of biochar and/or nitrification inhibitors (NIs) has the potential to reduce N 2 O emissions; however, it is not clear how biochar application may affect the efficacy of NI in reducing nitrification rates, soil enzyme activities, and N 2 O emissions under different soil moisture regimes. We conducted a 60-day laboratory incubation experiment to study the effects of manure biochar and nitrapyrin (as a NI) on N 2 O emissions from a urea fertilized soil with either 60 (low) or 80% (high) water-filled pore space (WFPS). Nitrification rates were significantly affected by biochar × NI × WFPS and biochar × WFPS interactions. Biochar initially increased and then decreased the rates, resulting in 45.2 and 26.6% (P < 0.001 for both) overall reductions in low and high WFPS, respectively while NI reduced the rates only in the first 10 days at 60% WFPS. Biochar decreased (P < 0.001) and NI increased (P = 0.007) β-1,4-N-acetyl glucosaminidase activities while urease activities were increased (P < 0.001) by biochar across WFPS. Biochar had significant interaction with NI in cumulative N 2 O emissions with the efficacy of NI being reduced when co-applied with biochar. Cumulative N 2 O emissions were greater at high than at low WFPS; the emissions were decreased by biochar at 60% WFPS and NI at both 60 and 80% WFPS. We conclude that biochar reduces efficacy of nitrapyrin in mitigating N 2 O emissions and their effects on net nitrification rates, enzyme activities and N 2 O emissions are dependent on soil moisture level., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

We assessed the response of soil microbial nitrogen (N) cycling and associated functional genes to elevated temperature at the global scale. A meta-analysis of 1,270 observations from 134 publications indicated that elevated temperature decreased soil microbial biomass N and increased N mineralization rates, both in the presence and absence of plants. These findings infer that elevated temperature drives microbially mediated N cycling processes from dominance by anabolic to catabolic reaction processes. Elevated temperature increased soil nitrification and denitrification rates, leading to an increase in N2 O emissions of up to 227%, whether plants were present or not. Rates of N mineralization, denitrification and N2 O emission demonstrated significant positive relationships with rates of CO2 emissions under elevated temperatures, suggesting that microbial N cycling processes were associated with enhanced microbial carbon (C) metabolism due to soil warming. The response in the abundance of relevant genes to elevated temperature was not always consistent with changes in N cycling processes. While elevated temperature increased the abundances of the nirS gene with plants and nosZ genes without plants, there was no effect on the abundances of the ammonia-oxidizing archaea amoA gene, ammonia-oxidizing bacteria amoA and nirK genes. This study provides the first global-scale assessment demonstrating that elevated temperature shifts N cycling from microbial immobilization to enhanced mineralization, nitrification and denitrification in terrestrial ecosystems. These findings infer that elevated temperatures have a profound impact on global N cycling processes with implications of a positive feedback to global climate and emphasize the close linkage between soil microbial C and N cycling.

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]

A 120-day field experiment was conducted to investigate the responses of soil N2O emissions, plant biomass N content, and N cycling-related functional genes to yak (Bos grunniens) dung pat size, including full-size dung pat (FDP), 1/4FDP, 1/8FDP, and 1/16FDP (i.e., FDP split into four, eight, and sixteen equal-sized dung pat fragments) in an alpine steppe on the Qinghai-Tibetan Plateau. The yield-scaled and cumulative N2O emissions were lower in the 1/16FDP and 1/8FDP than in the FDP and 1/4FDP treatments. In addition, the 1/16FDP treatment had the smallest N2O emission factor (0.002%), possibly due to lower denitrification as shown by the lower nisS, nirK, and nosZ gene copy numbers in the first (day 30) and second (day 72) samplings, and increased aboveground plant N concentration and content, which was 23–32% and 21–36%, respectively, greater than in the other treatments. In conclusion, splitting the yak dung pat into 1/16 fragments would be an effective strategy for managing yak dung to reduce N2O emissions and improve aboveground plant biomass N content which enhances the sustainability of alpine steppe ecosystems on the Qinghai-Tibetan Plateau. The implication from this study is that long-term field experiments should be conducted to further investigate the potential antagonistic or synergistic effects of yak dung pat fragmentation combined with other amendments (e.g., nitrogen inhibitors, lime, or biochar) on reducing N2O emissions. [ABSTRACT FROM AUTHOR]

A 28-day microcosm experiment was conducted using three paddy soils (an alluvial paddy soil, a loess-formed paddy soil, and a yellow clayey paddy soil) to investigate the impact of procyanidin on N2O emissions and associated microbial mechanisms. The efficacy of procyanidin on N2O emissions varied among the paddy soils tested, with an average inhibition rate ranging from 2.7% in the alluvial paddy soil to 57.1% in the loess-formed paddy soil. Furthermore, suppression of N2O emissions by procyanidin occurred alongside fluctuations in nitrate reductase activity and nirS- and nirK-type denitrifiers abundance. The correlation analysis indicates that nitrate reductase, clade I nirS-denitrifiers, clade I or II, and clade III nirK-denitrifiers were closely linked to N2O emissions. These findings provide evidence that procyanidin is capable of limiting N2O emissions in paddy soils by inhibiting nitrate reductase and different clades of nirS-/nirK-denitrifiers. [ABSTRACT FROM AUTHOR]

The effects of biochar application combined with different forms and rates of inorganic nitrogen (N) addition on nitrous oxide (N2O) emissions from forest soils have not been well documented. A microcosm experiment was conducted to study the effects of rice husk and its biochar in combination with the addition of N fertilizers in different forms (ammonium [NH4+] and nitrate [NO3−]) and rates (equivalent to 150 and 300 kg N ha−1 yr−1) on N2O emissions from Lei bamboo (Phyllostachys praecox) soils. The application of rice husk significantly increased cumulative N2O emissions under the addition of both NO3−-N and NH4+-N. Biochar significantly reduced cumulative N2O emissions by 15.2 and 5.8 μg N kg−1 when co-applied with the low and high rates of NO3−–N, respectively, compared with the respective NO3−-N addition rate without biochar. There was no significant difference in soil N2O emissions between the two NH4+-N addition rates, and cumulative N2O emission decreased with increasing soil NH4+-N concentration, mainly due to the toxic effect caused by the excessive NH4+-N on soil N2O production from the nitrification process. Cumulative N2O emissions recorded 18.74 and 14.04 μg N kg−1 under low and high rates of NO3−-N addition, respectively, which were higher than those produced by NH4+-N addition. Our study demonstrated that the conversion of rice husk to biochar could reduce N2O emissions under the addition of different N forms and rates. Moreover, rice husk or its biochar in combination with NH4+-N fertilizer produced less N2O in Lei bamboo soil, compared with NO3−-N fertilizer. [ABSTRACT FROM AUTHOR]

The effect of biochar and nitrapyrin (a nitrification inhibitor) applications on nitrous oxide (N2O) emissions from a cropland soil was studied in a 35-day incubation experiment. The biochars were produced using canola (Brassica napus L.) straw under two pyrolysis temperatures: 300 (BC300) and 700 °C (BC700). Biochars (20 g kg−1 soil) and nitrapyrin (80 mg kg−1 soil) were applied alone or in combination. The cumulative N2O emissions were affected by both biochar and nitrapyrin applications (p < 0.05, same below) but not by their interaction. Cumulative N2O emissions were not affected by BC700, but were increased by BC300, as compared with the CK treatment (no biochar addition). Nitrapyrin significantly decreased cumulative N2O emissions by inhibiting nitrification, whether biochar was applied or not. There were positive relationships (p < 0.05) between cumulative N2O emissions and soil microbial biomass carbon to nitrogen ratio, nitrate and dissolved organic nitrogen concentrations, and net nitrification rates. Our results show that biochars need to be appropriately selected (such as the use of BC700) that do not increase N2O emissions, while the effectiveness of nitrapyrin in reducing N2O emissions was not affected by the co-application of biochars. We conclude that the co-application of biochar and nitrapyrin may be able to both increase soil C sequestration by the addition of stable C contained in the biochar and reduce N2O emissions from agricultural production systems. [ABSTRACT FROM AUTHOR]

Acidic soils, occupying ca. 40% of the world's arable soils, often need to be managed (e.g., to raise their pH and to improve crop productivity); however, the environmental impact of raising soil pH is often difficult to assess. Increasing soil pH stimulates the reduction of N2O to N2, thus lowering N2O emissions associated with denitrification, but can also increase autotrophic nitrification rates and related N2O emission. Using a 15N tracing technique, we provide process‐based insights into the effects of two acid‐neutralizing materials (quicklime [CaO] vs. pig manure) on N2O emissions in an acidified upland soil that had experienced excessive N application. Without pH adjustments we found that N2O emissions, stimulated by supply of reactive N, were related to denitrification‐ and heterotrophic nitrification‐derived N2O emissions, whereas autotrophic nitrification‐derived N2O emissions declined with decreasing soil pH. These effects were reversed by increasing soil pH via liming. However, increasing the soil pH via application of pig manure significantly increased soil N2O emissions from both nitrification and denitrification. Our study highlights that pH‐amelioration practices may enhance N2O emissions depending on the type of material applied to the soil. Therefore, both pH remediation and greenhouse gas mitigation options need to be considered together to avoid adverse environmental effects. The effect of different acid‐neutralizing materials on soil N2O emissions should be incorporated into ecosystem models to better estimate global N2O emissions when pH amelioration is practised. Highlights: Enhanced N2O emission by N input was from denitrification and heterotrophic nitrification.Chemical N input and liming have reversible effects on N2O emission.Soil N2O emission was decreased by liming but increased by animal manure input.Careful consideration of pH raising substrates is needed to avoid adverse effects. [ABSTRACT FROM AUTHOR]

In order to better understand factors affecting greenhouse gas (GHG) emissions in Canadian agroforestry systems, we conducted a laboratory incubation study to assess N2O, CO2 and CH4 emissions from soils in response to land use (forestland vs. cropland) and agroforestry system type (hedgerow vs. shelterbelt) in central Alberta, Canada. Emissions of N2O were lower in soils from forestland than cropland, and forest soils acted as a net sink of atmospheric CH4 while cropland soils were weak sources of CH4. However, the forest soil had higher CO2 emission rates than the cropland soil within both agroforestry systems. Soil CH4 oxidation was higher in soil from hedgerow (consisted of natural forest vegetation) than from shelterbelt system (planted forest vegetation), while the former also had lower N2O emissions. Overall, soil CO2 emissions were significantly higher from hedgerow than from shelterbelt systems. Emissions of N2O were positively related with gross nitrification rates and soil pH, and negatively related with gross N immobilization rates. The CO2 emissions were positively related with water‐soluble organic C contents, while CH4 emissions were positively related with clay content, but negatively with gross N immobilization rates and soil organic C content. The global warming potential was higher in forestland soil than in cropland soil within agroforestry systems, and higher in forestland soil of the hedgerow compared to that in shelterbelts. Our results suggest that we need to select land uses or agroforestry systems that have a higher potential of mitigating GHG emissions from soils. [ABSTRACT FROM AUTHOR]

More livestock is being raised globally (increasing from 3.55 billion in 2000 to 4.24 billion in 2014 for cattle, sheep, goats and horses, based on 2017 FAO data) due to the increasing demand for livestock products, which inevitably results in increased excreta (urine and dung) deposition onto grasslands. Urine and dung patches are hotspots for emissions of the three principal greenhouse gases (GHGs): nitrous oxide (N 2 O), methane (CH 4 ) and carbon dioxide (CO 2 ) from grazed grasslands; however, the underlying mechanisms controlling GHG emissions are still not well understood and few strategies have been developed to mitigate such GHG emissions. Here, we review research on GHG emissions from excreta patches and propose possible mitigation strategies. The emission of N 2 O from excreta patches is mainly caused by increased nitrification and denitrification, in association with the increased abundance of ammonia-oxidizing bacteria (AOB) and denitrifying bacteria. Emission of N 2 O increases after urine deposition regardless of the type of urine (net increases ranged from 1.06 to 6.51 kg N ha − 1 ), while it increases (2.42 ± 1.95 kg N ha − 1 ; mean ± 95% confidence interval) only after cattle dung deposition, which also increases CH 4 (11.8 ± 5.32 kg C ha − 1 ) and CO 2 (893 ± 693 kg C ha − 1 ) emissions. The effect of urine on CH 4 emission is complex and further research is required. The application of dicyandiamide (DCD) is effective in reducing N 2 O emissions from both cattle urine (− 4.24 ± 1.10 kg N ha − 1 ) and dung (− 0.66 ± 0.61 kg N ha − 1 ) patches. In urine patches, DCD can reduce AOB population size, but does not influence the denitrifying bacteria population size. Diet manipulation and grazing management are also potential measures for mitigating GHG emissions from excreta patches. Further research is required to ascertain the overall emission of GHGs from excreta patches at the ecosystem level and to explore strategies for the sustainable development of grazed grassland ecosystems. [ABSTRACT FROM AUTHOR]

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• Biochar effects on greenhouse gas emission and SOC were studied in a 2-year vegetable–rice rotation. • Biochar decreased C emission per unit of C sequestered in the rice season. • Biochar increased net ecosystem carbon budget by increasing soil C sequestration. • Biochar increased CH 4 emission linked with increased mcrA and decreased pmoA. • Biochar decreased net global warming potential and greenhouse gas emission intensity in the rice season. The effect of biochar application on the net ecosystem carbon budget (NECB) and the mechanism controlling methane (CH 4) emission in paddy soils under vegetable–rice rotations are poorly understood. A 2-year field experiment was conducted with three treatments: control (no fertilizer or biochar application), chemical fertilizer (BC0) and biochar plus chemical fertilizer application (BC1) to analyze greenhouse gas (GHG) fluxes, soil organic carbon (SOC) content, as well as the abundance and community structure of methanogens and methanotrophs in a vegetable–rice rotation. Biochar addition (BC1) did not affect the yield, or the emission of total CH 4 or nitrous oxide (N 2 O) but significantly increased carbon dioxide (CO 2) emission as compared to BC0 in the vegetable season. Rice yield in BC1 was 14.1 % higher than in the control but was lower than in BC0 because of lower available nutrients in BC1 than in BC0. During the rice season, cumulative CH 4 emission under BC1 was increased by 2.65 times as compared with BC0 (P < 0.01), in association with an increase in methanogenic and decrease in methanotrophic gene abundances. The cumulative CO 2 emission was not different between BC0 and BC1 while cumulative and yield-scaled N 2 O emissions were significantly higher in BC1 than in BC0 in the rice season. However, BC1 increased SOC and NECB, but decreased the ratio of carbon (C) emission to C sequestration, net global warming potential (NGWP) and greenhouse gas emission intensity (NGHGI) as compared to the BC0 and control treatments (P < 0.01). The increase in GHG emissions in the biochar-amended soil was compensated by the increase in soil C storage and C uptake by rice, based on NGWP and NGHGI. The increase in NECB and SOC in the BC1 treatment indicates the benefit of biochar in restoring SOC during the rice season. This study provides insights into the effects of biochar addition on changes in bacterial abundance and community structure which increased CH 4 emission in the rice season of a vegetable–paddy rotation. [ABSTRACT FROM AUTHOR]

• Straw applied with reduced fertilizer (SFR) was studied in a vegetable-rice rotation. • SFR decreased N 2 O emissions and maintained crop yield. • SFR increased mcrA gene abundance in the rice season. • Straw retention increased CH 4 emissions, DOC and mcrA abundance in rice season. • SFR could increase agronomic efficiency in a vegetable-rice rotation. Retaining crop residues on site after harvesting can maintain soil fertility, reduce fertilizer requirements and restore soil organic carbon on intensively cultivated land. However, how crop residue retention and reduced chemical fertilizer application affect greenhouse gas emissions and crop yield in vegetable-rice rotations is poorly understood. We studied the effect of chemical fertilizer application alone (control, without straw retention), straw retention with 100 % nitrogen fertilizer application (STF) or with three levels of reduced chemical fertilizer application (SFR1, SFR2 and SFR3) in a vegetable-rice rotation in a mesocosm system. In the vegetable season, crop yield was maintained but the agronomic efficiency (AE) was higher in SFR1, SFR2 and SFR3 as compared to STF and the control. In the rice season under flooded condition, the methanogens were higher in SFR1, SFR2 and SFR3 compared to the control, but not different between STF and SFR1. The STF showed higher methane and nitrous oxide emissions, but carbon dioxide emissions and AE remained unaffected compared to the control in the vegetable-rice rotation. The SFR2 and SFR3 treatments maintained crop yields, increased AE, and decreased N 2 O emissions as compared with STF, but the CH 4 emissions were 29.8 % lower in SFR2 than SFR3 in the vegetable-rice rotation. We concluded that straw retention with reduced chemical fertilizer application can maintain crop yield in a vegetable-rice rotation but has the potential to increase CH 4 emissions in the rice cultivation season. Note: The maize straw was applied on May 5th, 2017 and the rice straw was applied on April 9th, 2018. The seedlings of chili were transplanted to the plots (21 stems per plot) on May 11th, 2017. After harvesting pakchoi, the experimental plots were left as fallow for one and a half months. The arable soil used in vegetable cultivation was then flooded to grow rice on April 4th, 2018. The seedlings of rice were transplanted to the plots (21 stems per plot) on May 2nd, 2018. [Display omitted] [ABSTRACT FROM AUTHOR]

• Atmospheric N deposition increases soil N 2 O emissions from a Moso bamboo forest. • Understory N deposition has a stronger promoting effect on N 2 O than canopy N. • Inorganic N deposition induced more N 2 O emissions than organic N deposition. • Canopy processes are important when assessing N deposition and its effect on N 2 O. Deposition of atmospheric inorganic and organic nitrogen (N) may increase soil nitrous oxide (N 2 O) emissions. To simulate and quantify such effects in forest ecosystems, understory N application, usually directly to the soil surface, has been used. However, this approach overlooks N interception by forest canopies, resulting in overestimates of actual impacts from N deposition. To test our assumptions, we monitored soil N 2 O emissions over one year in a Moso bamboo (Phyllostachys edulis) forest using different N deposition simulation approaches (canopy vs. understory application) and forms of N (inorganic vs. organic N). Our results revealed that cumulative N 2 O emissions from understory N application treatments were 20–50% higher than the corresponding canopy treatments, with greater N 2 O emissions under inorganic N than organic N application. Our study underscores the importance of considering canopy processes in future studies on N deposition and soil N 2 O emissions. [ABSTRACT FROM AUTHOR]

Adding carbon nanotubes (CNTs) and manipulating plant diversity are ways to improve the functioning of constructed wetlands (CWs), such as by maintaining the high nitrogen (N) removal efficiency and low emission of gaseous pollutants from CWs used for wastewater treatment. The conversion of biomass improved by diversity to bioenergy can further reduce greenhouse gas emissions. We established 108 microcosms to simulate CWs to explore the effects of adding CNTs to wastewater and assembling plant diversity on ammonia (NH 3), nitrous oxide (N 2 O), and methane (CH 4) emissions from CWs. The results showed that (1) plant species mixtures with CNTs lowered NH 3 emissions and NH 3 emissions per unit N removal (NH 3 /NR) to 5 and 10%, respectively, compared with monocultures without CNTs; (2) mixtures with CNTs decreased global warming potential integrating N 2 O and CH 4 emissions (GWP non-CO2) and GWP non-CO2 per unit N removal (GWP non-CO2 /NR) to 28 and 32%, respectively, compared with monocultures without CNTs; (3) CNTs decreased the biomass production in some monocultures, while the mixture with CNTs doubled the biomass production compared with monocultures without CNTs; and (4) the presence of Arundo donax (high mass species) in communities with CNTs decreased GWP non-CO2 /NR to 23% and NH 3 /NR to 9% of that under monoculture without CNTs. This study suggests that adding CNTs and increasing high species richness or assembling mixtures with high-biomass species are more effective and cleaner for maintaining high N removal and bioenergy production while reducing N 2 O, CH 4 , and NH 3 emissions in CWs. [Display omitted] • Carbon nanotube and plant diversity reduced ammonia emissions in microcosms. • Carbon nanotube and plant diversity synergically reduced global warming potential. • Carbon nanotube and biodiversity reduced ammonia emission per unit nitrogen removal. • Plant diversity mitigated inhibition of carbon nanotube on biomass of some species. • Arundo donax raised nitrogen removal and lowered ammonia, nitrous oxide emissions. [ABSTRACT FROM AUTHOR]