Display omitted
•An efficient HSND-MBBR was established successfully by inoculating HNAD bacteria.•The HNAD via shortcut process dominated in HSND-MBBR and enhanced at low C/N.•HNADs (S. ...maltophilia), DPAOs and GAOs were the main function genus.•HSND-MBBR could regulate nitrogen metabolic pathways to adapt various C/N ratios.
Traditional simultaneous nitrification and denitrification process was restricted by the stringent operation conditions and the inhibition of heterotrophic bacteria to ammonia oxidizing bacteria. To address these problems, a long-term simultaneous nitrification and denitrification-moving bed biofilm reactor (SND-MBBR) was successfully started by inoculating heterotrophic nitrification and aerobic denitrification (HNAD) bacterium Stenotrophomonas maltophilia DQ01 and investigated at different C/N ratios. Remarkable SND efficiency (94.21%) and total nitrogen removal (94.43%) were achieved at C/N of 7.5, and declined with C/N decreasing due to the reduction of electron donation and consumption. The combined stoichiometry and kinetics analyses confirmed that the HNAD via short-cut process dominated in feast phase and spiraled upwards with decreasing C/N, as evidenced by extremely low NXR activity and Nitrospira abundance (below 0.1%), suggesting that the inadequate electron donation was favorable for partial nitrification and denitrification. Furthermore, endogenous nitrification and denitrification occurred without COD consumption in famine stage, and decelerated at lower C/N due to the less stored internal carbon. High throughput sequencing revealed that HNADs (represented by Stenotrophomonas maltophilia), denitrifying phosphorus accumulating organisms and denitrification glycogen accumulating organisms dominated during the community succession and nitrogen removal process. Moreover, Candidatus Competibacter and Dechloromonas were negatively correlated with nitrite, leading to the accumulation of nitrite in famine phase. COG analysis showed the accumulated nitrite might affect the defense system and signal transduction. This study provided a new strategy for nitrogen removal and gave a new insight into the SND mechanism under different C/N conditions.
Nitrogen deposition in the northeastern US changed N availability in the latter part of the twentieth century, with potential legacy effects. However, long-term N cycle measurements are scarce. N ...isotopes in tree rings have been used as an indicator of N availability through time, but there is little verification of whether species differ in the strength of this signal. Using long-term records at the Fernow Experimental Forest in West Virginia, we examined the relationship between soil conditions, including net nitrification rates, and wood delta.sup.15N in 2014, and tested the strength of correlation between tree ring delta.sup.15N of four species and stream water NO.sub.3.sup.- loss from 1971 to 2000. Higher soil NO.sub.3.sup.- was weakly associated with higher wood delta.sup.15N across species, and higher soil net nitrification rates were associated with higher delta.sup.15N for Quercus rubra only. The delta.sup.15N of Liriodendron tulipifera and Q. rubra, but neither Fagus grandifolia nor Prunus serotina, was correlated with stream water NO.sub.3.sup.-. L. tulipifera tree ring delta.sup.15N had a stronger association with stream water NO.sub.3.sup.- than Q. rubra. Overall, we found only limited evidence of a relationship between soil N cycling and tree ring delta.sup.15N, with a strong correlation between the wood delta.sup.15N and NO.sub.3.sup.- leaching loss through time for one of four species. Tree species differ in their ability to preserve legacies of N cycling in tree ring delta.sup.15N, and given the weak relationships between contemporary wood delta.sup.15N and soil N cycle measurements, caution is warranted when using wood delta.sup.15N to infer changes in the N cycle.
► Heterotrophic nitrification–aerobic denitrification of Bacillus methylotrophicus. ► Transform NH3 to N2O and NO2- to N2 for G+ bacteria were never described. ► Nitrite other than nitrate was ...employed as denitrification substrate. ► GC–MS and GC–IRMS revealed a different gaseous nitrogen compound emitting pattern.
Bacillus methylotrophicus strain L7, exhibited efficient heterotrophic nitrification–aerobic denitrification ability, with maximum NH4+-N and NO2--N removal rate of 51.58mg/L/d and 5.81mg/L/d, respectively. Strain L7 showed different gaseous emitting patterns from those strains ever described. When 15NH4Cl, or Na15NO2, or K15NO3 was used, results of GC–MS indicated that N2O was emitted as the intermediate of heterotrophic nitrification or aerobic denitrification, while GC–IRMS results showed that N2 was produced as end product when nitrite was used. Single factor experiments suggested that the optimal conditions for heterotrophic nitrification were sodium succinate as carbon source, C/N 6, pH 7–8, 0g/L NaCl, 37°C and a wide range of NH4+-N from 80 to 1000mg/L. Orthogonal tests showed that the optimal conditions for aerobic denitrification were C/N 20, pH 7–8, 10g/L NaCl and DO 4.82mg/L (shaking speed 50r/min) when nitrite was served as substrate.
Nitrification in soil converts relatively immobile ammonium-nitrogen (N) to highly mobile nitrate-N (via nitrite), and this has implications for N-use efficiency by agricultural systems as well as ...for environmental quality, especially in situations where the potential for loss of soil or added N is high following nitrate formation. The literature on various physical, environmental, and chemical factors and their interactions on nitrification in soil is reviewed and discussed with examples from natural and agro-ecosystems. Among the various factors, soil matrix, water status, aeration, temperature, and pH have strong influence on nitrification. The information on factors that influence nitrification is useful when developing strategies for regulating nitrification in soils by employing chemical or biological nitrification inhibitors.
As a key process contributing to N2O emissions, nitrification is regulated by soil microbes and mainly affected by soil pH, NH3 availability, temperature and O2 availability. Current knowledge gaps ...include how nitrification-related N2O is associated with soil microbes in different pH soils. In the current study, a microcosm incubation experiment was conducted with two contrasting soils of different pH (5.08, 8.30) under controlled conditions. The soils were amended with ammonium sulphate ((NH4)2SO4, 50 mg N kg−1) combined with or without nitrification inhibitors and incubated under 20 °C, 65% water hold capacity (WHC) for three weeks. N2O fluxes, mineral nitrogen (N) concentrations and ammonia oxidizers populations were measured during the incubation to investigate the correlations of nitrification-related N2O with ammonia oxidizers. The nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) was used to inhibit nitrification albeit to various inhibition effects with different soils. Acetylene (0.1% v/v C2H2), an inhibitor of AOA and AOB ammonia monooxygenase (AMO), was used to distinguish N2O emissions by nitrifiers and denitrifiers. 1-octyne (5 μM aqueous), a selective specific AOB inhibitor, was used to assess the relative contributions of AOA and AOB to N2O emissions. The results showed that N2O yield for AOA and AOB varied with soil pH. AOB was the key microbial player in alkaline soil, contributing about 85% of nitrification-related N2O. Conversely, about 78% of nitrification-related N2O was contributed by AOA in acidic soil. Furthermore, there was a significant and positive relationship between mineral N (NO2−, NO3−), AOA and AOB populations and nitrification-related N2O in alkaline soil. However, in acidic soil, NO3− concentration and AOA had significantly positive relationships with nitrification-related N2O. To conclude, soil pH was a key factor affecting the contribution of ammonia oxidizers to nitrification-related N2O emissions. AOA-related N2O production dominated at low pH (5.08), while AOB-related N2O was favored in alkaline soil (pH 8.3).
Display omitted
•Soil pH had a significant role in regulating AOA or AOB-related N2O.•AOA dominated in acidic soil contributing 78% of nitrification-related N2O.•AOB dominated in alkaline soil contributing 85% of nitrification-related N2O.•NO2− played an important role in nitrification-related N2O in studied alkaline soil.
The recent discovery of complete ammonia oxidation (comammox) process in a single organism challenged the division of labor between two functional groups in the classical two-step nitrification ...model. However, the distribution and activity of comammox bacteria in various environments remain largely unknown. This study presented a large-scale investigation of the geographical distribution, phylogenetic diversity, and activity of comammox Nitrospira in typical agricultural soils. Among the 23 samples harvested across China, comammox Nitrospira clade A was ubiquitously detected at 4.14 × 104–1.65 × 107amoA gene copies/g dry soil, with 90% belonging to the subclade A2. The abundance of comammox Nitrospira clade B was two orders of magnitude lower than clade A. In all samples, comammox Nitrospira were 1–2 orders of magnitude less abundant than canonical nitrifiers, and soils with slightly high pH and C/N tended to enrich more comammox Nitrospira. Unlike canonical nitrifiers, comammox Nitrospira had sustained amoA gene transcription regardless of external ammonia supply, indicating their competitive advantage over other nitrifiers under low-ammonia conditions. When fed with 1 mM ammonium for 15 days, comammox Nitrospira in tested soils were enriched 2.36 times higher than those enriched by the same amount of nitrite, indicating their preference to utilizing ammonia as the substrate. DNA-SIP further confirmed the in situ nitrification activity of comammox Nitrospira. This study provided new insights into the broad distribution and diversity of comammox Nitrospira in agricultural soils, which could potentially play an important role in the microbial nitrogen cycle in soils.
Display omitted
•Comammox Nitrospira are ubiquitous in soils but less abundant than canonical nitrifiers.•Most comammox Nitrospira in agricultural soils belong to clade A2.•Comammox Nitrospira favor growth in slightly alkaline soils with relatively high C/N.•Comammox Nitrospira prefer to use ammonia as the substrate rather than nitrite.•Comammox Nitrospira are important nitrifiers under low ammonia conditions.
The discovery of complete ammonia oxidizers (comammox) has dramatically altered our perception of nitrogen (N) biogeochemistry. However, their functional importance vs. the canonical ammonia ...oxidizers (i.e., ammonia oxidizing-archaea (AOA) and bacteria (AOB)) in agroecosystems is still poorly understood. Accordingly, a new assay, which involves the combined use of acetylene, 3,4-dimethylpyrazole phosphate (DMPP), and 1-octyne, was adopted to assess the ammonia (NH3) oxidation and nitrous oxide (N2O) production activity of these functional guilds in a subtropical Inceptisol subjected to long-term different fertilization regimes, namely CK (no fertilizer control), synthetic fertilizer only (NPK), organic manure only (M) and organic manure plus synthetic fertilizer (MNPK). AOA dominated the NH3 oxidation in M treatment, whereas AOB dominated all the NH3 oxidation and N2O production processes in all but M treatment, and comammox played a minor role in both NH3 oxidation and N2O production in all treatments. Both M and MNPK treatments significantly increased the activity and growth of comammox. Compared to NPK, comammox exhibited increases of 270 % and 326 % in the NH3 oxidation rates, and increases of 1472 % and 563 % in the N2O production rates in M and MNPK, respectively. Random forest model revealed that copper (Cu), comammox abundance, and dissolved organic nitrogen (DON) were the most important predictors for the NH3 oxidation rates of comammox. Redundancy analyses (RDA) showed that fertilizer treatments significantly altered the community composition of NH3 oxidizers, and pH was the overarching parameter underpinning the community shift of the NH3 oxidizers. Overall, this paper provides evidence that comammox play a minor yet unneglectable role in the nitrification of agroecosystems, and the long-term addition of organic manure stimulates the growth and activity of comammox in a subtropical Inceptisol.
Display omitted
•Long-term addition of organic manure stimulates the growth and activity of comammox.•Comammox played a minor role in both NH3 oxidation and N2O production in all fertilizer treatments.•Long-term fertilizer treatments significantly altered the community composition of NH3 oxidizers.•pH was the overarching parameter underpinning the community shift of the NH3 oxidizers.
BackgroundAgriculture is the single largest geo-engineering initiative that humans have initiated on planet Earth, largely through the introduction of unprecedented amounts of reactive nitrogen (N) ...into ecosystems. A major portion of this reactive N applied as fertilizer leaks into the environment in massive amounts, with cascading negative effects on ecosystem health and function. Natural ecosystems utilize many of the multiple pathways in the N cycle to regulate N flow. In contrast, the massive amounts of N currently applied to agricultural systems cycle primarily through the nitrification pathway, a single inefficient route that channels much of this reactive N into the environment. This is largely due to the rapid nitrifying soil environment of present-day agricultural systems.ScopeIn this Viewpoint paper, the importance of regulating nitrification as a strategy to minimize N leakage and to improve N-use efficiency (NUE) in agricultural systems is highlighted. The ability to suppress soil nitrification by the release of nitrification inhibitors from plant roots is termed ‘biological nitrification inhibition’ (BNI), an active plant-mediated natural function that can limit the amount of N cycling via the nitrification pathway. The development of a bioassay using luminescent Nitrosomonas to quantify nitrification inhibitory activity from roots has facilitated the characterization of BNI function. Release of BNIs from roots is a tightly regulated physiological process, with extensive genetic variability found in selected crops and pasture grasses. Here, the current status of understanding of the BNI function is reviewed using Brachiaria forage grasses, wheat and sorghum to illustrate how BNI function can be utilized for achieving low-nitrifying agricultural systems. A fundamental shift towards ammonium (NH4+)-dominated agricultural systems could be achieved by using crops and pastures with high BNI capacities. When viewed from an agricultural and environmental perspective, the BNI function in plants could potentially have a large influence on biogeochemical cycling and closure of the N loop in crop–livestock systems.
•Full nitritation and partial nitrification processes were successfully achieved.•Settling property of the sludge was improved by the strategy of reducing settling time.•AOB was the dominant ...nitrifying bacteria according to FISH analysis.•FA and FNA were the potential compounds for inhibiting the activity of NOB.
The objective of this study was to evaluate the conversion of full nitritation to partial nitrification processes by altering the influent ammonium concentration in a sequencing batch reactor at ambient temperature. After 150days’ operation, full nitritation and partial nitrification processes were successfully achieved when the influent NH4+–N concentrations up to 400 and 720mg/L, respectively. Meanwhile, sludge volumetric index (SVI) gradually decreased from 127.4 to 63.4mL/g, while the average size of sludge improved from 29.5 to 195.6μm by the strategy of reducing settling time. Ammonium-oxidizing bacteria (AOB) were the dominant nitrifying bacteria according to the fluorescence in situ hybridization (FISH) analysis. Free ammonia (FA) and free nitrous acid (FNA) were the potential compounds for inhibiting the activity of nitrite-oxidizing bacteria (NOB). The obtained results may help to promote the development of new biological nitrogen removal processes in engineering, especially in relation to nitrogen-rich wastewaters.
PDF
![Assessing tree ring [delta]...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0029-8549/small "Assessing tree ring [delta].sup.15N of four temperate deciduous species as an indicator of N availability using independent long-term records at the Fernow Experimental Forest, WV")
