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Little is known about the effects of nitrogen (N) fertilization rates on ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) and their differential contribution to nitrous oxide (N 2 O) production, particularly in greenhouse based high N input vegetable soils. Six N treatments (N1, N2, N3, N4, N5 and N6 representing 0, 293, 587, 880, 1173 and 1760 kg N ha -1  yr -1 , respectively) were continuously managed for three years in a typically intensified vegetable field in China. The aerobic incubation experiment involving these field-treated soils was designed to evaluate the relative contributions of AOA and AOB to N 2 O production by using acetylene or 1-octyne as inhibitors. The results showed that the soil pH and net nitrification rate gradually declined with increasing the fertilizer N application rates. The AOA were responsible for 44-71% of the N 2 O production with negligible N 2 O from AOB in urea unamended control soils. With urea amendment, the AOA were responsible for 48-53% of the N 2 O production in the excessively fertilized soils, namely the N5-N6 soils, while the AOB were responsible for 42-55% in the conventionally fertilized soils, namely the N1-N4 soils. Results indicated that overdose fertilization induced higher AOA-dependent N 2 O production than AOB, whereas urea supply led to higher AOB-dependent N 2 O production than AOA in conventionally fertilized soils. Additionally, a positive relationship existed between N 2 O production and NO 2 - accumulation during the incubation. Further mechanisms for NO 2 - -dependent N 2 O production in intensive vegetable soils therefore deserve urgent attention., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Vegetable fields in tropical regions characterized by intensive cultivation have the potential to be significant sources of gaseous nitrogen (N) emissions. This is primarily due to human-induced input of N fertilizer and the naturally abundant water and heat resources in these areas. While biochar and nitrification inhibitors are recognized as effective measures for mitigating soil nitrous oxide (N 2 O) and nitric oxide (NO) emissions, there is limited research on their combined effectiveness in intensively managed tropical croplands. In a 2-year field experiment conducted in a tropical vegetable ecosystem, we investigated the impact of single and combined applications of peanut biochar and nitrapyrin (a nitrification inhibitor) on N 2 O and NO emissions, N-cycling associated gene abundances, and bacterial community structure. Under conventional fertilization, cumulative N 2 O and NO emissions were 1.96 kg N ha−1 yr−1 and 1.76 kg N ha−1 yr−1, with emission factors of N fertilizer for N 2 O (EF N2O) and NO (EF NO) at 0.29% and 0.30%, respectively. The random forest model indicated that soil organic carbon (SOC) was key in regulating N 2 O+NO emissions. Biochar alone decreased cumulative N 2 O and NO emissions by 6.1 % and 13.0 %, respectively. When biochar was co-applied with nitrapyrin, the mitigation of N 2 O and NO reached up to 23.4 % and 18.6 %, respectively. This enhanced effect was attributed to the strong inhibitory impact of nitrapyrin on nitrifiers (AOA and AOB) and denitrifiers (nirK / S) in biochar-amended soils. Additionally, biochar co-application increased SOC levels in nitrapyrin-applied soils. Analysis of bacterial community structure revealed that nitrapyrin decreased the relative abundance of Nitrospirae , while biochar increased the relative abundance of Acidobacteria , Chloroflexi , Gemmatimonadetes and Nitrospirae to varying extents. Considering the carbon sequestration ability of biochar and the effective mitigation potential of nitrapyrin, the combined application of biochar with a nitrification inhibitor emerges as a promising strategy for dual objectives - reducing gaseous N emissions and enhancing soil carbon storage - in intensive vegetable ecosystems in the tropical region of China. [Display omitted] • Annual N 2 O and NO emissions factors were 0.29% and 0.30%, respectively. • Soil organic carbon regulated N 2 O+NO emissions in the tropical vegetable field. • Biochar (Bc) exhibited lower efficacy for N 2 O or NO mitigation than nitrapyrin (NI). • NI further mitigated N 2 O and NO under Bc by slowing nitrification-denitrification. [ABSTRACT FROM AUTHOR]

Nitrification inhibitors, a promising tool for reducing nitrous oxide (N 2 O) losses and promoting nitrogen use efficiency by slowing nitrification, have gained extensive attention worldwide. However, there have been few attempts to explore the broad responses of multiple reactive gaseous nitrogen emissions of N 2 O, nitric oxide (NO) and ammonia (NH 3 ) and vegetable yield to nitrification inhibitor applications across intensive vegetable soils in China. A greenhouse pot experiment with five consecutive vegetable crops was performed to assess the efficacies of two nitrification inhibitors, namely, nitrapyrin and dicyandiamide on reactive gaseous nitrogen emissions, vegetable yield and reactive gaseous nitrogen intensity in four typical vegetable soils representing the intensive vegetable cropping systems across mainland China: an Acrisol from Hunan Province, an Anthrosol from Shanxi Province, a Cambisol from Shandong Province and a Phaeozem from Heilongjiang Province. The results showed soil type had significant influences on reactive gaseous nitrogen intensity, with reactive gaseous nitrogen emissions and yield mainly driven by soil factors: pH, nitrate, C:N ratio, cation exchange capacity and microbial biomass carbon. The highest reactive gaseous nitrogen emissions and reactive gaseous nitrogen intensity were in Acrisol while the highest vegetable yield occurred in Phaeozem. Nitrification inhibitor applications decreased N 2 O and NO emissions by 1.8–61.0% and 0.8–79.5%, respectively, but promoted NH 3 volatilization by 3.2–44.6% across all soils. Furthermore, significant positive correlations were observed between inhibited N 2 O + NO and stimulated NH 3 emissions with nitrification inhibitor additions across all soils, indicating that reduced nitrification posed the threat of NH 3 losses. Additionally, reactive gaseous nitrogen intensity was significantly reduced in the Anthrosol and Cambisol due to the reduced reactive gaseous nitrogen emissions and increased yield, respectively. Our findings highlight the benefits of nitrification inhibitors for integrating environment and agronomy in intensive vegetable ecosystems in China. [ABSTRACT FROM AUTHOR]

Greenhouse vegetable soils are characterized by high N 2 O emissions, but the functional importance of potential ammonia (NH 3 ) oxidation (PAO) and nitrite (NO 2 − ) consumption (PNC) by ammonia-oxidizing archaea (AOA) and bacteria (AOB) is poorly understood. Inhibitors of 1-octyne and 2-pheny l-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO) in combination with potassium chlorate were used to examine the importance of AOA and AOB in NO 2 − production and consumption, to evaluate the soil-specific effects on N 2 O production under six long-term fertilization greenhouse vegetable soils across mainland China, and to predict their thermodynamic responses in a temperature gradient of 5–45 °C using the square root growth (SQRT) and macromolecular rate theory (MMRT) models. The ammonia oxidizers-driven PAO and PNC exhibited a strong response to temperature with maximum rates attained at 35 °C or 40 °C by AOA compared to 30 °C or 35 °C by AOB. Concomitantly, compared with ammonium amendment, NO 2 − addition stimulated N 2 O production by approximately 2–4-fold for AOA and 2–9-fold for AOB at 20–40 °C in four of six soils. AOA exhibited a broader range of temperatures (−33.2–56.8 °C vs −16.1–52.3 °C) and lower relative temperature sensitivity (Q 10 ) than AOB ( p  < 0.05). The heat capacity (ΔC P ‡ ) of AOA and AOB in PAO and PNC increased in relation to the optimum temperature (T opt ) and exhibited a greater negative value by AOB than AOA, indicating that specialized ammonia-oxidizer populations of PAO and PNC adapted to in situ soil environmental changes. Structural equation modeling revealed that potential AOA-driven N 2 O production was influenced by ΔC P ‡ and Q 10 and C/N, while AOB-driven N 2 O production by ΔC P ‡ and Q 10 and soil nitrate (NO 3 − ) content, all of which is influenced directly and indirectly by in situ climate parameters. Findings suggest the important roles of specific in situ climate and soil properties and provide new insights into the NO 2 − consumption in soil N 2 O production by ammonia-oxidizers. [ABSTRACT FROM AUTHOR]