Search

Abstract 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. Graphical abstract Unlabelled Image Highlights • Soil pH induced by N gradients controlled the abundance/contribution of AOA and AOB. • AOA-derived N 2 O were greater than AOB in the control and overdose fertilized soils. • AOB-derived N 2 O dominated in conventionally fertilized vegetable soils. [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]

In acidic paddy soils where crops with an ammonium (NH 4 +) preference are grown, ammonia (NH 3) is largely transformed to NH 4 +, and organic nitrogen (N) is often too low to support organic nitrification, heterotrophic nitrifiers may have a preference for NH 4 +. If so, acidic paddy soils are likely a hotspot of heterotrophic NH 4 + oxidation (O HNH4). To reveal if O HNH4 is active in acidic paddy soils, we investigated the existence of acetylene (C 2 H 2)-resistant NH 4 + oxidation at pH 5.4, 5.3, and 5.0 in paddy soils with 60% water holding capacity (WHC), using 15N tracing and nitrification inhibition techniques (1.0% C 2 H 2). As expected, C 2 H 2 -resistant NH 4 + oxidation (0.0088 ± 0.0012 mg N kg−1 soil d−1) was detected in soils with a pH of 5.0. In the presence of 1.0% C 2 H 2 , increased 15N in the NO 3 − pool under 15NH 4 NO 3 labelling suggested the existence of C 2 H 2 -resistant NH 4 + oxidizers. Through a concentration gradient experiment of C 2 H 2 (0, 0.01%, 0.1%, and 1.0%) on the pH 5.0 soil, 0.01% C 2 H 2 was found to be sufficient for complete inhibition of autotrophic nitrification, suggesting that NH 4 + oxidation in samples receiving 0.1% or 1.0% C 2 H 2 is unlikely driven by autotrophs. The trend toward higher rates when C 2 H 2 increased from 0.01% to 0.1% suggested that, C 2 H 2 -resistant NH 4 + oxidizers in paddy soils are likely carbon (C)-limited. The trend toward lower rates when C 2 H 2 increased from 0.1% to 1.0% implied an inhibition in the high concentration. At 0.1% C 2 H 2 , the trend toward lower rates when soil moisture increased from 60%WHC to 100%WHC indicated that C 2 H 2 -resistant NH 4 +/NH 3 oxidizers prefer drier conditions, and O HNH4 will be less active at flooded conditions. Since there is evidence of organic and inorganic N oxidation by heterotrophs are mutually exclusive, we thus used a 15N tracing model to separate organic nitrification from inorganic nitrification to clarify that low O HNH4 in samples was irrelevant to heterotrophic nitrification of organic N (O HORG). In summary, isotopic evidence has been provided to suggest that O HNH4 , although with a low rate, has the potential to proceed in acidic paddy soils. In which, low O HNH4 is unrelated to O HORG , and an exogenous C source is needed to activate heterotrophic NH 4 +/NH 3 oxidizers. [Display omitted] • C 2 H 2 -resistant NH 4 + oxidation was detected in acidic paddy soils. • Mechanisms leading to C 2 H 2 -resistant NH 4 + oxidation are summarized. • C 2 H 2 -resistant NH 4 + oxidizers may prefer drier conditions. • Heterotrophic NH 4 + oxidation was not active in acidic paddy soils. • Low rates of NH 4 + oxidation by heterotrophs was unrelated to organic nitrification. [ABSTRACT FROM AUTHOR]

Comammox Nitrospira , nitrifiers capable of performing complete nitrification on their own, are widely distributed in terrestrial ecosystems. However, their environmental preferences and factors that predict their biogeographic distribution have not been elucidated. Because most nitrifiers share the same basic life strategies and requirements, the best predictor of large-scale comammox bacterial abundance may be the abundance of other nitrifying guilds. To validate this hypothesis, we assembled data from 60 studies conducted in cropland, grassland, and forest ecosystems to identify abiotic and biotic parameters with the potential to predict comammox bacterial abundance and compare their predictive powers using random forest modelling. As expected, ammonia-oxidizing archaea (AOA) and bacteria (AOB) are the top two factors predicting comammox bacterial abundance, followed by soil pH and nitrate and ammonium (NH 4 +). Consistent evidence is present from cropland, grassland, and forest landscapes to show that comammox Nitrospira co-vary positively with AOA. On large spatial scales, soil pH and NH 4 + are the dominant influence on the abundance of clades A and B, respectively. A negative correlation with rainfall and acidity implies that clade A prefers dry, non-acidic environments, whereas a negative correlation with NH 4 + and rainfall indicates that clade B prefers dry, oligotrophic environments. These findings reveal that predictors at the aggregate and clade scales do not overlap, and the predictors of any single genetic clade may not be predictive of total abundance. Comammox Nitrospira prefer to co-metabolize with AOA with the same ecological preferences, hence the strongly positive population co-variation. However, the predictive power of incomplete nitrifiers as predictors may decline when modelling the abundance of a single genetic clade. At the clade level, comammox bacterial abundance is highly modulated by abiotic factors such as pH and NH 4 +. Niche differentiation between clade A and clade B is influenced more by pH and N status than by water status. [Display omitted] • Comammox Nitrospira clades A and B co-vary negatively with rainfall. • Comammox bacteria co-vary positively with AOA. • Biotic predictors have a stronger predictive power than abiotic predictors. • Comammox Nitrospira Clade A prefers dry, non-acidic environments. • Comammox Nitrospira Clade B prefers dry, oligotrophic environments. [ABSTRACT FROM AUTHOR]

[Display omitted] • PBAT addition increased the soil POM-C content, followed by DOM-C and MAOM-C. • Soil C accumulation was associated with N consumption in DOM and MAOM pools. • SOM pools were affected by PBAT debris directly but microbial metabolism indirectly. • N-activated and PBAT-degrading bacteria largely contributed to C accumulation. • Oligotrophic taxa associated with aggregate were key predictor for N accumulation. Microplastics (MPs) pollution is becoming an emerging global stressor for soil ecosystems. However, studies on the impacts of biodegradable MPs on soil C sequestration have been mainly based on bulk C quantity, without considering the storage form of C, its persistency and N demand. To address this issue, the common poly (butylene adipate-co-terephthalate) (PBAT) was used as the model, and its effects on soil functional organic pools, including mineral-associated (MAOM), particulate (POM) and dissolved organic matter (DOM), were investigated from the novel coupled perspective of C and N stocks. After adding PBAT-MPs, the contents of soil POM-C, DOM-C, and MAOM-C were increased by 546.9 %–697.8 %, 54.2 %–90.3 %, and 13.7 %–18.9 %, respectively. Accordingly, the total C increased by 116.0 %–191.1 %. Structural equation modeling showed that soil C pools were regulated by PBAT input and microbial metabolism associated with C and N enzymes. Specifically, PBAT debris could be disguised as soil C to promote POM formation, which was the main pathway for C accumulation. Inversely, the MAOM-C and DOM-C formation was attributed to the PBAT microbial product and the selective consumption in DOM-N. Random forest model confirmed that N-activated (e.g., Nitrospirae) and PBAT-degrading bacteria (e.g., Gemmatinadetes) were important taxa for soil C accumulation, and the key enzymes were rhizopus oryzae lipas, invertase, and ammonia monooxygenase. The soil N accumulation was mainly related to the oligotrophic taxa (e.g., Chloroflexi and Ascomycota) associated with aggregate formation, decreasing the DOM-N by 46.9 %–84.3 %, but did not significantly change the total N storage and other N pools. Collectively, the findings highlight the urgency to control the nutrient imbalance risk of labile N loss and recalcitrant C enrichment in POM to avoid the depressed turnover rate of organic matter in MPs-polluted soil. [ABSTRACT FROM AUTHOR]

Partially substituting inorganic fertilizer with organic fertilizer is widely adopted to improve intensive vegetable production as well as potentially reduce carbon (C) and reactive nitrogen (Nr) footprints, but the associated comprehensive evaluations with life-cycle assessment (LCA) from environmental and economic perspectives have rarely been executed. Covering one-year consecutive vegetable crops rotation, five fertilization strategies were established at an equal N level (SN: single inorganic fertilization; SM: single organic fertilization; mixing organic and inorganic N fertilizer at the ratio of 1:2 (M1N2), 1:1 (M1N1) and 2:1 (M2N1)) and a CK as control. Compared with the SN strategy, the M1N2, M1N1 and M2N1 strategies significantly decreased N 2 O emission (32.2–50.0%), NO emission (41.8–52.5%), NH 3 volatilization (17.8–22.2%), N runoff (29.7–35.3%) and N leaching (34.2–44.8%) as well as significantly increased vegetable yield (4.3–7.4%) and annual SOC sequestration (244.5–463.1 kg C ha−1 yr−1). Consequently, the three organic-substitute strategies significantly reduced C footprint (17.0–21.8%) and the field interface Nr footprint (34.1–43.0%). The production of both organic and inorganic N fertilizer (31.1–51.5%) and N 2 O emissions (19.9–35.1%) were the hotspots of GHG emissions. The production of organic fertilizer dominated their foreground interface Nr footprint (86.6–97.9%) and environmental damage costs (EDC, 48.6–71.0%), while N leaching dominated the field interface Nr footprint (45.1–50.0%). Therefore, the substitute strategies improved the net ecosystem economic benefits (NEEB, which integrated net economic benefit and EDC) by CNY 2,799−12,151 ha−1 yr−1 and the M2N1and M1N1 strategies produced better NEEB, highlighting that appropriate substitute fertilization strategies are recommended for simultaneously environmental and economic benefits in intensive vegetable production in China. Image 1 • Organic-substitute strategies reduced C footprint & field interface Nr footprint. • Organic fertilizer produced high foreground Nr losses during composting. • Field interface Nr footprint had significant linear relationship with C footprint. • Organic-substitute strategies gained higher NEEB than individual applications. [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]

Combined application of organic fertilizer (OF) and chemical nitrogen (N) fertilizer (CF) is a common fertilization practice, providing better N supply pattern for crop growth. However, few studies focused on the effect of granulation method of these two fertilizers on N supply to soil. To validate this effect, we mixed the CF (15N–(NH 4) 2 SO 4) into cow manure powders with maize straw powder at rate of 2% or 8% (dry weight), respectively, in two forms, homogeneous granulation (HG) and spatial heterogeneous granulation (SG), and applied them to soil to investigate their difference in N transformations during an 80–day incubation. Results showed that there were more NH 4 +, NO 3 − and microbial biomass N (MBN) in the SG granules and the surrounding soil, while more dissolved organic N (DON) in the HG granules and the corresponding soil after day 30. At day 80, compared to HG, SG released less CF–N into the surrounding soil, but primed more organic N into mineral N. Structural equation model (SEM) revealed that DON was the main form of N transported from fertilizer granules to the surrounding soil, and then drove the changes of soil microbial activity, which determined the amount and dynamic of mineral N in the surrounding soil. These results indicated that, in heterogeneous granulation, the spatial separation between OF and CF slow down, but more importantly enhanced up, the microbial transformation of CF in the granules. This demonstrated that the spatial heterogeneous granulation of OF and CF could change the pattern of N release from fertilizer to soil and offer a potential way to optimize N fertilizer management strategies in the future. Unlabelled Image • In SG granules stored more CF-N and mineralized more N from manure. • Mineral N in SG treated soil was twice as much as HG fertilizer did on day 80. • SG granules could prolong N supply and improve N supply ability of manure. [ABSTRACT FROM AUTHOR]