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Both nitrous oxide (N 2 O) and nitric oxide (NO) emissions are typically high in greenhouse-based high N input vegetable soils. Biochar amendment has been widely recommended for mitigating soil N 2 O emissions in agriculture. However, knowledge of the regulatory mechanisms of fresh and aged biochar for both N 2 O and NO production during ammonia oxidation is lacking. Two vegetable soils with different pH values were used in aerobic incubation experiments with 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO), 1-octyne and acetylene. The relative importance of ammonia-oxidizing archaea (AOA) and bacteria (AOB) to N 2 O and NO production was investigated as influenced by fresh and aged biochar amendments. The results showed that AOA dominated N 2 O production in acidic soil, while AOB dominated N 2 O production in alkaline soil. Aged biochar stimulated both AOA- and AOB-derived N 2 O and NO production by 84.8 and 340%, respectively, in acidic soil but only increased AOA-derived N 2 O and NO production in alkaline soil. Fresh biochar amendment increased AOA- and AOB-derived NO in acidic soil and AOA-derived NO in alkaline soil but had negligible effects on AOA- and AOB-derived N 2 O in both soils. Fresh biochar decreased AOA- amoA but increased AOB- amoA gene abundances in acidic soil, whereas aged biochar increased AOA- and AOB- amoA gene abundances in both soils. These findings improved our understanding of N 2 O and NO production mechanisms under different biochar amendments in alkaline and acidic vegetable soils. Unlabelled Image • N 2 O and NO production in acid and alkaline vegetable soils were assessed by inhibitors. • AOB and AOA dominated in alkaline and acidic soils, respectively. • Aged biochar stimulated AOA and AOB in acidic and AOA-derived N 2 O and NO in alkaline soil. • Fresh biochar produced negligible effects on AOA- and AOB-derived N 2 O in both soils. [ABSTRACT FROM AUTHOR]

The influence of temperature on soil ammonia (NH 3) and nitrite (NO 2 −) oxidation and related NO 2 − accumulation in soils remain unclear. The soil potential NH 3 oxidation (PAO) and NO 2 − oxidation (PNO) rates were evaluated over a temperature gradient of 5–45 °C in six greenhouse vegetable soils using inhibitors. The values of temperature sensitivity traits such as temperature minimum (T min), temperature optimum (T opt), and maximum absolute temperature sensitivity (T m_sens) were also fitted to the square root growth (SQRT) and macromolecular rate theory (MMRT) models. The ammonia-oxidizing archaea (AOA) and bacteria (AOB) were determined by quantifying amoA , and nitrite-oxidizing bacteria (NOB) were determined by quantifying the nxrA and nxrB. Both models identified that T opt for PAO (34.0 °C) was significantly greater than that for PNO (26.0 °C). The T m_sens (23.4 ± 2.1 °C) and T min (1.0 ± 2.0 °C) for PAO were higher than those for PNO (16.8 ± 3.2 °C and − 11.7 ± 6.7 °C). PAO was positively correlated with AOB- amoA at 20–30 °C and with AOA- amoA at 30–35 °C, while PNO was positively correlated with nxrB at 5–30 °C. Additionally, NO 2 − and N 2 O were positively correlated with the (AOA + AOB amoA) to (nxrA + nxrB) ratio, and the concentration of N 2 O was positively correlated with NO 2 − accumulation. These results highlight that elevated temperatures resulted in the uncoupling of NH 3 oxidation and NO 2 − oxidation, leading to NO 2 − accumulation, which could stimulate N 2 O emissions. Unlabelled Image • Ammonia- and nitrite-oxidation become decoupled with increasing temperature. • Potential ammonia-oxidation had a >8 °C higher T opt than the nitrite-oxidation rate. • NO 2 − and N 2 O increased with gene ratio (AOA + AOB amoA):(nxrA + nxrB) in nitrification. [ABSTRACT FROM AUTHOR]

Organic material (OM) applied to cropland not only enhances soil fertility but also profoundly affects soil nitrogen cycling. However, little is known about the relative contributions of soil ammonia-oxidizing archaea (AOA) and bacteria (AOB) to nitrous oxide (N 2 O) production during ammonia oxidation in response to the additions of diverse types of OMs in the tropical soil for vegetable production. Herein, the soils were sampled from a tropical vegetable field subjected to 4-year consecutive amendments of straw or manure. All the soils were amended with ammonium sulfate ((NH 4 ) 2 SO 4 , applied at a dose of 150 mg N kg -1 ) and incubated aerobically for four weeks under 50% water holding capacity. 1-octyne or acetylene inhibition technique was used to differentiate the relative contributions of AOA and AOB to N 2 O production. Results showed that AOA dominated N 2 O production in soil managements of unfertilized control (CK), chemical fertilization (NPK), and NPK with straw (NPKS), whereas AOB contributed more in soil under NPK with manure (NPKM). Straw addition stimulated AOA-dependent N 2 O production by 94.8% despite the decreased AOA-amoA abundance. Moreover, manure incorporation triggered both AOA- and AOB-dependent N 2 O production by 147.2% and 233.7%, respectively, accompanied with increased AOA and AOB abundances. Those stimulating effects were stronger for AOB, owing to its sensitivity to the alleviated soil acidification and decreased soil C/N ratio. Our findings highlight the stimulated N 2 O emissions during ammonia oxidation by historical OM amendments in tropical vegetable soil, with the magnitude of those priming effects dependent on the types of OM, and appropriate measures need to be taken to counter this challenge in tropical agriculture ecosystems., Competing Interests: Declaration of competing interest The author 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. Published by Elsevier B.V.)

Biochar amendment has been recommended as a potential strategy to mitigate nitrous oxide (N 2 O) and nitric oxide (NO) emissions for wheat production, but its mechanism and effective duration are not well understood. The 1-octyne and 2-pheny l-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO) in combination with potassium chlorate were used to evaluate the relative contribution of ammonia-oxidizing bacteria (AOB) and archaea (AOA) to potential ammonia oxidation (PAO) and N 2 O and NO production as affected by biochar. Acidic and alkaline soils were collected during wheat-growing season, and four treatments were installed in each soil type: CK, urea alone; BE, biochar-enriched soil for 2-6 years; FB, fresh biochar added to CK; and AB, aged biochar added to CK. The results showed that octyne and PTIO efficiently assessed AOB and AOA activities in soil incubation. The AOB-driven PAO in acidic soil was largely enhanced by increased soil pH in BE and FB treatments, whereas AOA-driven PAO was not. And the contribution of AOB to PAO exceeded 80% in alkaline soil. The N 2 O and NO production were positively correlated with PAO in both soils. BE treatment decreased the direct N 2 O and NO production in alkaline soil, while both BE and FB treatments decreased the N 2 O and NO yields in acidic soil, indicating that biochar mitigated soil N 2 O and NO emissions for wheat production. The lack of differences between AB and CK treatments indicated that aged biochar lost its initial effects on PAO, while the biochar-enriched soil amended with biochar years earlier still functioned similarly as fresh biochar., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Evidence suggests that biochar is among ideal strategies for climate change mitigation and sustainable agriculture. However, the effects of soil aging on the physicochemical characteristics of biochar and nitrous oxide (N 2 O) production remain elusive. We set up a microcosm experiment with two greenhouse vegetable production (GVP) (alkaline and acid) soils by using the 15 N tracing technique and quantitative polymerase chain reaction (qPCR) to investigate the mechanisms of N 2 O production as affected by fresh (FB) and aged biochar (AB) amendment. The results showed that AB increased the specific surface area, organic C, ammonium sorption capacity and cation exchange capacity, whereas decreased the pore size and pH relative to the FB. Results also demonstrated that FB effectively decreased N 2 O emissions from both soils while it enhanced the abundance of nirK and nosZI genes in alkaline soil and reduced the abundance of ammonia-oxidizing bacteria (AOB) amoA and increased nirK and nosZII genes in acid soil. In contrast, AB significantly stimulated nitrification and denitrification in both soils and thus significantly increased the N 2 O emissions by 43-78%. Furthermore, AB induced increases in ammonia-oxidizing archaeal (AOA) amoA and nirK gene abundances in alkaline soil and fungal nirK gene abundances in acid soil. These results suggest that AB may not be suitable for the mitigation of soil N 2 O emissions in GVP soils thus improving our understanding of the potential mechanism of biochar in N 2 O emissions., (Copyright © 2018. Published by Elsevier B.V.)