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Heterotrophic nitrification is regarded as an eternal mystery in the nitrogen (N) cycle, although it was first reported more than 100 years ago. In this review, we discuss microbial mechanisms driving heterotrophic nitrification of organic N (OHORG) in soil and their modulations by pH, and carbon (C) and N contents. In acidic and oligotrophic soils, OHORG may occur as endogenous respiration or during oxidation of recalcitrant organics and cell lysis. Likely in soils with a low C:N ratio and a high pH, C limitation of N immobilization creates conditions for the transformation of dissolved organic N to nitrate (NO3−). Fungi with a deficiency in ammonia mono-oxygenase can drive OHORG. Heterotrophic nitrifiers include not only acid-tolerant, nitrophobic species, but also acid-sensitive, nitrotolerant species. There is concern about OHORG in soil because of its contribution to NO3− production and nitrous oxide (N2O) emissions. Therefore, reliable measurements of soil heterotrophic nitrifying activity are needed. We propose more biochemical surveys to understand the pathway for OHORG in ecologically relevant species, considering the challenges we are facing in managing heterotrophically derived nitrification to prevent N losses from cropland, forest, and grassland soils. [ABSTRACT FROM AUTHOR]

Understanding the dynamics and availability of soil nitrogen (N) affected by the conversion of cropping patterns is critical for environmental sustainability, especially in tropical soils with low fertility and high N loss. In this study, the 15N tracing technology combined with the 15N tracer model was used to explore the dynamic change of soil N transformation in long‐estabished areca nut (Areca catechu) plantations. Areca nut plantations with different ages (2, 5, 10, 14, and 17 years) and paddy fields in the tropical region of China were studied. The results demonstrated that the gross N mineralization rate (M) of areca nut plantation soil was much lower than that of paddy soil. The NH4+ immobilization (INH4) rate was also significantly reduced in areca nut plantations. Besides, the ONH4 (autotrophic nitrification) in long‐term areca nut planted soil decreased significantly with decreasing ammonia‐oxidizing archaea (AOA) and ammonia‐oxidizing bacteria (AOB) abundance. Inorganic N supply (INS) capacity of areca nut planted soil was much lower than the paddy soil, indicating declined N supply in long‐term areca nut plantations soil. The decline in soil gross N transformations rate and INS capacity of areca nut plantations soil was significantly correlated to reduced levels of TN and soil pH. Thus, agricultural practices that increase the soil pH (e.g., biochar or lime application) and the soil organic matter content (e.g., organic fertilizers) could improve soil INS capacity. [ABSTRACT FROM AUTHOR]

[Display omitted] • BMs crippled nitrification but stimulated heterotrophic denitrification. • Denitrification was responsible for the dose-dependent increase in N 2 O emission. • The addition of BMs did not proportionally increase microbial biomass nitrogen. • Bacterial diversity and community composition were altered by BMs. Biodegradable plastic mulching films are regarded as promising substitutes for their non-degradable counterparts to ameliorate serious plastic pollution in agriculture. Inevitably, biodegradable microplastics (BMs) can be formed and profoundly affect the function of soil ecosystems. However, little is known about the effects of BMs loading on soil nitrogen (N) dynamics and loss in tropical agricultural soils. Hereby, a 120-day soil incubation trial was performed to evaluate the effects of polybutylene adipate co-terephthalate (PBAT) microplastics on nitrous oxide (N 2 O) emissions, N transformation, and bacterial community structure in latosols. The results showed that PBAT addition raised soil ammonium nitrogen (NH 4 +–N) and dissolved organic carbon (DOC) contents, but lowered nitrate nitrogen (NO 3 ––N) contents, accompanied with a smaller potential nitrification rate and a greater potential denitrification rate. The microbial biomass nitrogen and nrfA gene abundance were increased by PBAT, suggesting the processes of microbial N immobilization and dissimilatory nitrate reduction to ammonia were largely promoted. Positive correlations existed between N 2 O emissions and denitrification-related enzymatic activities and functional gene abundances (narG , nirK/S and Fungal nirK). PBAT amendment stimulated N 2 O emissions by 54.8 − 317.3 %, accompanied with increased values of those denitrification-related parameters, suggesting that stimulated denitrification was responsible for the exacerbated N 2 O emissions. Moreover, PBAT addition changed bacterial alpha diversity and bacterial community composition, where the relative abundances of Proteobacteria increased while those of Nitrospirae and Acidobacteria decreased. These findings are beneficial to understanding the fate of N in microplastics-polluted soil, which will provide a new insight into the impact of BMs on soil functions and environmental risks. [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]