Abundance Of Ammonia-oxidizing Bacteria Research Articles

Response of soil microbial activities and ammonia oxidation potential to environmental factors in a typical antimony mining area

Mining, smelting and tailing deposition activities can cause metal(loid) contamination in surrounding soils, threatening ecosystems and human health. Microbial indicators are sensitive to environmental factors and have a crucial role in soil ecological risk assessment. Xikuangshan, the largest active antimony (Sb) mine in the world, was taken as the research area. The soil properties, metal(loid) contents and microbial characteristics were investigated and their internal response relationships were explored by multivariate statistical analysis. The assessment of the single pollution index and Nemerow synthetic pollution index (PN) showed that the soils were mainly polluted by Sb, followed by Cd and As, in which sampling site S1 had a slight metal(loid) pollution and the other sampling sites suffered from severe synthetic metal(loid) pollution. The microbial characteristics were dissimilar among sampling points at different locations from the mining area according to hierarchical cluster analysis. The correlation analysis indicated that fluorescein diacetate hydrolase, acid phosphatase, soil basal respiration and microbial biomass carbon were negatively correlated with PN, indicating their sensitivity to combined metal(loid) contamination; that dehydrogenase was positively correlated with pH; and that urease, potential ammonia oxidation and abundance of ammonia-oxidizing bacteria and archaea were correlated with N (nitrogen) contents. However, β-glucosidase activity had no significant correlations with physicochemical properties and metal(loid) contents. Principal components analysis suggested bioavailable Sb and pH were the dominant factors of soil environment in Xikuangshan Sb mining area. Our results can provide a theoretical basis for ecological risk assessment of contaminated soil.

Nitrous oxide and carbon dioxide emissions from two soils amended with different manure composts in aerobic incubation tests

ABSTRACT Identification of nitrous oxide (N2O) and carbon dioxide (CO2) emissions from soils amended with different types of compost is needed for appropriate use of manure in agriculture. This study aimed at investigating the interaction effects of compost type and soil properties and effects of moisture contents on N2O and CO2 emissions, with identification of relative abundances of functional ammonia-oxidizing genes. Laboratory tests were conducted using cattle manure compost (CC) or mixed compost (MC) (cattle, poultry, and swine manure) amended Kochi (from a greenhouse) or Ushimado (from a paddy field) soils (3% by weight) with controls (no compost). Initial moisture contents were adjusted to 60% water-holding capacity (WHC) for Kochi soil and 70% WHC for both soils. The samples were aerobically incubated at 25°C. Emissions of N2O and CO2 and contents of ammonium N (NH4 +-N) and nitrate N in soils were measured continuously until day 42. The abundances of ammonia-oxidizing bacteria (AOB) and archaea genes were estimated to evaluate nitrifying activities. Cumulative N2O and CO2 emissions were significantly higher (p < 0.05) in MC than those in CC treatments probably due to higher NH4 +-N content and lower C/N ratio, which facilitated faster N mineralization and C decomposition. Emissions of N2O and CO2 were higher in compost-amended Kochi soil (70% WHC) with high total C and N, mineral N, and clay contents than those in less fertile Ushimado soil. Interestingly, interactions of compost type and soil properties on N2O emissions were significant (p < 0.05) only in Kochi soil because the addition of decomposition resistant CC increased N2O emissions only from this soil with high C and N contents. Higher soil moisture contents increased N2O and CO2 emissions significantly (p < 0.05) in Kochi soil. Emissions of N2O until day 15 were mainly due to activities of AOB amoA genes (R2 = 0.91). This study suggests that N2O emissions are increased by high NH4 +-N contents and a low C/N ratio in compost and high total C and N, mineral N, and clay contents in soil. The application of compost with less decomposable C increases N2O emissions only from nutrient-rich soil.

Plastic-shed vegetable cultivation alters soil gross nitrogen transformation rates and nitrous oxide production pathways

Plastic-shed vegetable cultivation is characterized by high nitrogen (N) application rates, frequent irrigation and multiple cropping, probably leading to different soil N transformation rates compared to open-field cultivation. However, how continuous cultivation of vegetables under plastic sheds affects soil N transformation rates and associated nitrous oxide (N2O) emissions remains unclear. Here, a 15N-tracing experiment in combination with the qPCR technique was used to investigate the effects of conversion from conventional open-field cultivation to plastic-shed vegetable cultivation, as well as the age of this shift, on soil gross N transformation rates, N2O emission pathways and associated microbial abundances. Five typical fields, including a wheat–maize rotation system field and four adjacent plastic-shed vegetable fields under cultivation for 2, 5, 12 and 20 years, were selected. Soil gross N mineralization rates increased significantly after two years after conversion from a wheat–maize rotation system to a plastic-shed vegetable system, and then decreased with an increase in plantation age, which could be attributed to decreased soil total phosphorus availability. Long-term vegetable plantation under plastic-shed decreased soil gross autotrophic nitrification rates significantly by decreasing ammonia-oxidizing bacteria abundance probably due to decreasing soil pH. Such decreased rates of autotrophic nitrification further led to decreased N2O emissions under plastic-shed cultivation. Under long-term plastic-shed cultivation (>2 years), negligible gross nitrate-N (NO3−-N) immobilization rates were observed due to the preferential use of ammonium-N by soil microbes, which was probably responsible for rapid NO3−-N accumulation in soils. Overall, these results could be of help to elucidate the mechanisms of soil N2O emission and NO3−-N accumulation in plastic-shed vegetable fields.

Comparative analysis of nitrogen removals and microbial communities in air and pure oxygen aeration systems during treatment of municipal solid waste incineration (MSWI) leachate

MSWI leachate contain high concentrations of ammonium nitrogen (NH4+-N). The conventional submerged air-diffusing (CSA) system are the dominant oxygen supply in the aerobic process for NH4+-N removal from leachate. However, it carries high energy consumption. In this study, Pure oxygen (PO), which is more environmentally friendly, was used as an alternative to air for solving this problem. For comprehensive analysis the effects of PO supersede air on nitrogen removals and microbial diversities in the aerobic process during treatment of MSWI leachate, two parallel full-scale anoxic-oxic systems were set with the floating Praxair's in situ oxygenation (I-SO™) system and the CSA system, respectively. Compared to the CAS system, the removal efficiency of total nitrogen (TN) increased by 9.79% with the I-SO™ system but COD and NH4+-N removals reduced by 6.83% and 1.19%, respectively. Metagenomic studies revealed that the bacterial richness, diversity, and evenness decreased with PO aeration, while the abundances of ammonia-oxidizing bacteria (AOB) and denitrifying bacteria (DNB) increased, as well as the AOB/nitrite-oxidizing bacteria (NOB) ratios. In addition, the nitrite-denitrification functional genes (nirK and nirS) deposited from autotrophic and Heterotrophic bacteria were more predominant and accounted for the higher efficiency of TN removal in the PO aeration treatment, while complete nitrification and nitrate-denitrification were dominant in the air aeration anoxic-oxic system. Therefore, nitrogen removal from MSWI leachate by using PO aeration provided theoretical perspective for engineering applications.

Seasonal dynamics of ammonia-oxidizing bacteria but not archaea influence soil nitrogen cycling in a semi-arid agricultural soil

Nitrification, a key pathway of nitrogen (N) loss from agricultural soils, is performed by ammonia-oxidizing bacteria (AOB) and archaea (AOA). We examined the seasonal dynamics (2 years) of ammonia oxidizer gene abundances across a gradient of soil carbon (C) and N in a semi-arid soil after 8 years of tillage and crop residue treatments. AOB was more dominant than AOA in the surface soil, as AOA were undetected in 96% of samples. Seasonal variation in AOB abundance was related to substrate availability; AOB gene copy numbers increased at the end of the growing season (during summer fallow) following higher concentrations in dissolved organic matter soil water. This suggests increased co-location between AOB and substrate resources in pores still filled with water as the soils dried. AOB was however not statistically related to soil ammonium concentrations, soil water content, rainfall or temperature. Organic matter inputs enhanced AOB abundance independent of seasonal variation. AOB abundance was greatest in autumn and immediately preceding the start of the growing season, and coincided with elevated soil nitrate concentrations. The growth of the AOB population is likely to contribute to increased risk of N loss through leaching and/or denitrification at the start of the crop growing season following summer fallow.

Effects of free-air temperature increase on grain yield and greenhouse gas emissions in a double rice cropping system

The responses of grain yield and greenhouse gas (GHG) emissions to climate warming in rice paddies are serious concerns for both global food security and climate change mitigation. However, the impact of free-air temperature increase (FATI) on grain yield and methane (CH 4 ) and nitrous oxide (N 2 O) emissions remains unclear for one of the most globally significant rice production practices: the double rice cropping system. Here, we conducted a two-year field experiment to examine the effect of FATI by infrared heaters on grain yield and CH 4 and N 2 O emissions in a double rice field in subtropical China. FATI increased rice canopy temperature by 2.0 °C and soil temperature by 1.2 °C on average but had no effect on either early or late rice yield production. FATI did not affect CH 4 emissions, but significantly increased N 2 O emissions in both the early and late rice seasons. Averaged across two years, N 2 O emissions increased by 0.3 kg ha −1 and 0.7 kg ha −1 in the warmed plots for the early and late rice seasons, respectively. Consequently, FATI enhanced the global warming potential (GWP) and GHG intensity (i.e., yield scaled GWP) in the double rice cropping system. In addition, warming increased the abundance of ammonia-oxidising bacteria, ammonia-oxidising archaea, and a nitrite reductase gene ( nirS ), but decreased that of a nitrous oxide reductase gene ( nosZ ). Our results indicate that warming by FATI does not affect grain yield and CH 4 emissions but stimulates N 2 O emissions in the double rice cropping system and therefore promotes a potential positive feedback with future climate warming. • Free-air temperature increase (FATI) with infrared heater was performed in a double rice field. • Moderate warming by FATI had no significant effect on rice yield. • Moderate warming by FATI did not significantly affect CH 4 emissions. • Moderate warming by FATI stimulated N 2 O emissions.

Functional N-cycle genes in soil and N2O emissions in tropical grass-maize intercropping systems

There is evidence that forage grasses such as Megathyrsus and Urochloa can suppress nitrification, with direct or indirect consequences on soil inorganic N dynamics and nitrous oxide (N2O) emissions. However, the influence of soil chemical properties on the dynamics of functional N-genes and losses of N in maize (Zea mays L.) intercropped with forage grasses under N fertilization is poorly understood. In this study, soil samples and N2O emissions were analyzed from a field experiment in which maize (fertilized or not with ammonium-based fertilizer) was intercropped with Guinea grass (M. maximus cv. Tanzânia), palisade grass (U. brizantha cv. Marandu), and ruzigrass (U. ruziziensis cv. Comum). Soil N-cycle microorganisms [16S rRNA of bacteria and archaea, nifH (gene encoding N2-fixing bacteria), ammonia-oxidizing bacteria (AOB) and archaea (AOA), nirS (encoding nitrite reductase), and nosZ (encoding nitrous oxide reductase)] were influenced by forage grass, N fertilization, and sampling time, but no evidence of biological nitrification inhibition was found. Palisade grass was associated with a higher abundance of nifH (7.0 × 105 gene copies g−1 soil, on average) in the absence of N compared with the other grasses (4.3 × 105 gene copies g−1 soil, on average). Nitrogen fertilization increased the abundance of AOB but not AOA. Furthermore, N2O flux was influenced by AOB, water-filled pore space, and N fertilization, whereas the cumulative N2O emission and fertilizer-induced emission factor (0.36%, on average) were not affected by the grasses. In conclusion, this study reveals the strong dominance of AOB under ammonium supply, potentially stimulating N2O emissions in maize-forage grass intercropping systems.

High concentration powder carrier bio-fluidized bed process: A new perspective for domestic wastewater treatment

The nitrogen removal mechanism of the high concentration powder carrier bio-fluidized bed (HPB) process was investigated with actual domestic wastewater. The micron-size (10–70 μm) powder carriers were diatomite and Fe–C. Results showed diatomite enriched the relative abundances of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria, accordingly increasing the rate of nitrification. Even a 100% increase of genes associated with the ammonia oxidation was achieved. Fe–C enhanced the rate of substrate utilization mainly by increasing the activity of the electron transfer system. Hydrocyclone separator, as a key device of HPB, was able to recover the carriers with high efficiency (recovery efficiency of 72.66 ─ 82.50% after 75 days), thus, indirectly improving the functionality of the carriers. Furthermore, it could renew the surface of microbial aggregations, consequently improving the adsorption capacity to substrates. HPB could provide the feasibility of shortening the hydraulic retention time and expanding the capacity of wastewater treatment plants.

Performance of partial nitrification process in a zeolite biological aerated filter with the addition of sulfamethoxazole

Due to the rapid development of medical industries, wastewater treatment plants have become sinks for residual antibiotics. However, the contribution of novel partial nitrification processes to the bioremediation of antibiotics remains unclear. In this study, the removal rate of a partial nitrification process on the biotransformation of sulfamethoxazole (SMZ) was evaluated. A biological aerated filter made from zeolite successfully achieved stable partial nitrification. A nitrite accumulation percentage (NAP) greater than 85% was obtained when the influent ammonium concentration was increased to 300 mg/L with a nitrogen loading rate of 1.24 kg/(m3 d). Batch tests were performed on support collected from different heights of the up-flow reactor at the end of the pilot monitoring experiment. The maximum ammonium oxidation rate of 5.63 mg/(g VSS·L) in one hour was recorded at a height of 0.32–0.48 m in the reactor, indicating nitrifying bacteria activity link between the free ammonia (FA) and biomass concentration was found. After the addition of SMZ (2.5 mg/L), the NAP declined to approximately 70%, and the abundance of Nitrosomonas (the main ammonia oxidizing bacteria (AOB) genus in the zeolite biological aerated filter (ZBAF)) decreased 7.24–6.10%. Lower abundance and activity of AOB oxidized ineffectively the primary amine of SMZ, which led to lower than 19% of the SMZ removal efficiency.

Salinity and N input drive prokaryotic diversity in soils irrigated with treated effluents from fish-processing industry

Wastewater reuse for irrigation has become an important practice in many countries in the context of global water scarcity. However, knowledge about the potential soil impact of reusing treated fish-processing (TFP) effluents for irrigation is still limited. The aim of this study was to investigate the response of the soil prokaryotic community in general, and the nitrifying taxa in particular, to TFP-effluent irrigation. We analyzed the impacts of irrigation with two effluent dilutions (EF1 and EF2, with electrical conductivities of 2.7 and 6 mS cm−1, respectively) or water (W) as a control on soil chemical properties, dehydrogenase and nitrifying activities, amoA gene abundances of ammonia-oxidizing bacteria (AOB) and archaea (AOA), and soil prokaryotic community structure and diversity. At the end of the irrigation experiment, soil ammonium, nitrate plus nitrite, dehydrogenase and nitrifying activities, soil electrical conductivity (EC), and sodium adsorption ratio (SAR) were significantly higher in TFP-irrigated treatments than in water irrigated controls. Prokaryotic richness and diversity indices followed the pattern W > EF1 > EF2, and negatively correlated with soil EC, SAR, ammonium, nitrate plus nitrite, and total N concentrations. In particular, EF2-irrigation stimulated soil copiotrophic bacteria (e.g. Proteobacteria and Bacteroidetes) to the detriment of oligotrophic members such as Acidobacteria. TFP-effluent irrigation also influenced the relative abundance of the amoA gene of AOB but not that of AOA; and the composition of nitrifying taxa, by inducing a significant increase in OTUs whose closest cultured matches were ‘Candidatus Nitrosocosmicus franklandus’ and Nitrosospira briensis Nsp10. Overall, irrigation with the more diluted effluent (classified as slight to moderate degree of restriction by local regulations) induced a reduction of soil prokaryotic diversity, whereas the less diluted effluent (severe irrigation restriction) promoted the greatest changes in the prokaryotic community due to the increase in soil salinity and N content.

Effects of aquatic nitrogen pollution on particle-attached ammonia-oxidizing bacteria in urban freshwater mesocosms.

Ammonia-oxidizing bacteria (AOB) attached to aquatic particles are important participants in ammonia oxidation within hypereutrophic urban river systems. To explore the effects of aquatic nitrogen pollution on particle-attached AOB in urban river, we utilized laboratory mesocosms to investigate the responses of abundances and community structure of particle-attached AOB to ammonium (NH4+) and glycine (C2H5NO2) amendments. The abundance and community structure of particle-attached AOB were determined with quantitative real-time polymerase chain reaction (qRT-PCR) analysis and high-throughput sequencing based on the AOB amoA gene, respectively. Most of the bacterial amoA sequences from different treatments were affiliated with uncultured Nitrosomonadaceae bacterium, uncultured Nitrosomonadales bacterium, and uncultured Nitrosomonas sp., which are closely associated with organic pollution. The species richness and diversity of particle-attached AOB communities increased with increasing NH4+ and glycine concentrations. Treatment effects contributed significantly to the variance in particle-attached AOB communities. Although, glycine was completely transformed to ammonium within a few days and ammonium amendments would change the community structure of particle-attached AOB, the effect of glycine on the particle-attached AOB community was regulated by both the resulting ammonium concentration, as well as organic matter availability to the heterotrophic bacteria. Results suggested that high anthropogenic nitrogen loadings appeared to promote higher particle-attached AOB richness and diversity in the hypereutrophic urban river, but the effect of organic nitrogen on the particle-attached AOB community was different from the effect of inorganic nitrogen. This study informs ammonia oxidization mechanisms in the hypereutrophic urban rivers, which contributes to remediation/restoration strategies.

Impact of influent strengths on nitrous oxide emission and its molecular mechanism in constructed wetlands treating swine wastewater

Constructed wetlands (CWs) can remove nitrogen (N) through plant assimilation and microbial nitrification and denitrification, while it also releases large greenhouse gas nitrous oxide (N2O) into the atmosphere. However, N2O emissions and the underlying microbial mechanisms of CWs when treating high-strength wastewater have not been systematically surveyed. Here, the effect of three influent strengths on N2O emissions in a pilot-scale CW treatment of swine wastewater was determined and the underlying microbial mechanisms were explored. The results showed that the removal rates of ammonium (NH4+) and total nitrogen (TN) increased significantly with the increasing influent strengths, however, the ratio of N2O emission/TN removal rose by 1.5 times at the same time. Quantitation of microorganisms responsible for N-cycle in the sediment indicated that the abundance of ammonia-oxidizing bacteria (AOB) in high influent strengths (COD, 962.38 ± 3.05 mg/L; NH4+, 317.89 ± 4.24 mg/L) was 51.6-fold compared with that in low influent strengths (COD, 516.94 ± 4.18 mg/L; NH4+, 100.65 ± 2.65), and AOB gradually replaced ammonia-oxidizing archaea (AOA) to dominate ammonia oxidizers. Structural equation models demonstrated that NO2− accumulations promoted the ratio of AOB/AOA, which further led to an increase in the ratio of N2O emission/TN removal. It is worth noting both the N removal rates and N2O emissions increased with the increasing influent strength. To obtain reduced N2O emissions, pretreatment technology for strength reduction should be supplemented before high-strength wastewater enters the CWs. This study may shed new light on the sustainable operation and application of CWs.

Effects of Nitrification Inhibitors on Nitrogen Dynamics and Ammonia Oxidizers in Three Black Agricultural Soils

The application of nitrification inhibitors (NIs) based on ammonium (NH4+) is considered to be an efficient way to reduce nitrogen (N) loss by delaying the nitrification process through influencing ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). However, the inhibition mechanisms of NIs on AOA and AOB in different soils remain unclear. Hence, we explored the two commonly used NIs (3, 4-dimethylepyrazole phosphate (DMPP) and dicyandiamide (DCD) and their combination (DMPP + DCD) on the soil nitrification and abundance of ammonia oxidizers (AOA and AOB) in three black soils (HLJ, NA, and DA) with different physicochemical properties using a 120-day incubation experiment. The results demonstrated that NIs significantly increased NH4+-N concentrations and decreased NO3−-N concentrations in all three tested soils. There was no significant difference in inhibiting nitrification in HLJ among all NI treatments, while DCD was more efficient in NA, DMPP + DCD had better efficiency in DA. The potential nitrification rate (PNR) was greatly decreased by NIs addition, and PNR was significantly positively correlated with AOB (p &lt; 0.05). AOA was dominant in the acid soil. All NI treatments significantly inhibited soil nitrification through inhibiting the growth of AOB in the two soils with higher pH. The abundance of AOA and AOB was significantly correlated with different soil types (positively correlated with soil pH, and negatively correlated with organic matter). Moreover, soil pH and soil organic matter were considered to be the most important factors influencing the inhibition efficiency of NIs and the abundance of AOA and AOB. The application of the NIs combination (DMPP + DCD) was considered to be the most cost-effective way to inhibit soil nitrification in soil with higher pH and lower SOM, which provides a theoretical basis for a field experiment.

A novel stable nitritation process: Treating sludge by alternating free nitrous acid/heat shock

The feasibility of stable nitritation of sludge alternately treated by free nitrous acid (FNA) and heat shock in a sequencing batch reactor (SBR) was investigated in this study. The linear regression method was used to determine the optimal treatment conditions. Results revealed that an FNA concentration of 2.20 mg HNO2-N/L, exposure time of 24 h, and treatment ratio of 20% could inhibit nitrite oxidizing bacteria (NOB) activity to the greatest extent while maintaining the maximum ammonium oxidizing bacteria (AOB) activity; after heat shock at 60 °C for 20 min, NOB were inhibited while AOB still had certain activity. In the long-term continuous-flow experiment, the single FNA or heat shock treatments easily allowed adapt NOB to affect the stability of nitritation. The alternating FNA/heat shock treatment can achieve long-term stability of nitritation. Microbial community analysis revealed that the alternating FNA/heat shock treatment could inhibit NOB while maintaining high AOB abundance.

Enhanced soil quality after forest conversion to vegetable cropland and tea plantations has contrasting effects on soil microbial structure and functions

Land-use changes could potentially exert a strong influence on soil quality and soil microbial communities. Moreover, microbial taxa are also important drivers of soil ecological functions. However, the linkage between soil quality and soil microbial communities is in need of deeper understanding. Here, we examined the effects of soil fertility quality on microbial community structure that identified by pyrosequencing and functions that predicted by the FAPROTAX functional annotations dataset after forest conversion to vegetable cropland and tea plantations. Soil quality index was significantly increased after natural forest (0.2) conversion to vegetable cropland (0.7) and tea plantations (0.3–0.6). Soil bacterial beta diversity significantly correlated to soil quality index, but the sensitivity of individual microbial groups varied in response to changes in soil quality. Higher soil quality promoted bacterial diversity in vegetable cropland but decreased it in tea plantations, which implied soil quality was a structural factor in bacterial community composition but had contrasting effects for croplands versus plantations. Agricultural management played a negative role in maintaining microbial interactions, as identified by the network analysis, and furthermore the analysis revealed key functions of the microbial communities. After land-use change, the abundance (e.g., level, intensity) of microbial groups involved in N-cycling increased in tea plantations but decreased in vegetable cropland. The abundance of microbes involved in C-cycling featured an opposite trend. Higher level of N-fixation in tea plantations but the higher abundance of N-oxidation in vegetable cropland was demonstrated. Higher abundance of ammonia-oxidizing bacteria (8.5 × 104 vs. 0.9–2.4 × 104 copies) and ammonia-oxidizing archaea (3.0 × 105 vs. 0.5–1.0 × 105 copies) as identified by qPCR in cropland than that in plantations corroborated the FAPROTAX prediction. Therefore, the key taxa of soil microbial communities and microbial functions were largely dependent on changes in soil quality and determined responses to specific agricultural management.

Global meta-analysis of terrestrial nitrous oxide emissions and associated functional genes under nitrogen addition

Functional genes involved in nitrogen (N) cycling regulate soil nitrification, denitrification and N2O emissions. However, the general patterns and variability of N functional genes in response to N addition, and their association with N2O emission have not been synthesized for terrestrial ecosystems. We synthesized 2068 observations from 144 papers to explore the impact of N addition on the abundance and diversity of N functional genes, and their relationship to N2O emissions in croplands, grasslands and forests on a global scale. In croplands, N addition increased N2O emissions (109%), the abundance of ammonia-oxidizing archaea (AOA) (19%), ammonia-oxidizing bacteria (AOB) (95%), nirK (52%), nirS (40%) and nosZ (41%), and the diversity of AOB (15%), nirS (12%) and nosZ (11%). In grassland, N addition increased AOB abundance (130%) and decreased the abundance of nirS (−99%) and nosZ (−58%) genes, but in forests, significant effects were only found for the abundance of AOA (35%) and AOB (121%). N2O emission was negatively correlated with the abundance of nosZ, but positively correlated with the abundance of AOA and AOB. Apart from the abundance of functional AOA, AOB and nosZ genes, climate variables (precipitation and temperature), and available N concentrations were the main factors explaining the variation in N2O emission with N addition, as shown by random forest analysis. These findings indicate that impacts on N functional genes that encode enzymes involved in nitrification (AOA, AOB) and in the transformation of N2O to N2 (nosZ) are the main mechanisms behind the effect on N fertilizer-induced N2O emissions.

Investigating the conversion from nitrifying to denitrifying water-treatment efficiencies of the biofloc biofilter in a recirculating aquaculture system

In the current study, two nitrifying suspended growth bioreactor processes (denoted as R1 and R2) was investigated based on biofloc technology (BFT) in recirculating aquaculture systems (RAS). The conversion of nitrifying R1 to denitrifying biofilter via adding carbohydrates was studied. It was observed that the dominant functional microbes of nitrifying BFT biofilters were ammonia-oxidizing bacteria (AOB), denitrifying bacteria (DNB), phosphorus/glycogen accumulating organisms (PAOs/GAOs), and nitrite-oxidizing bacteria (NOB). The removal efficiencies of the total ammonium nitrogen and nitrite were prominent, while the treatment efficiencies respected to nitrate and soluble reactive phosphate (SRP) were insignificant. More than 16 h after the addition of carbohydrates to R1, the regular dynamics of dissolved oxygen (DO), dissolved organic carbon, and C/N ratio became conducive to the notable removal of nitrate and SRP. Furthermore, the relative abundances of AOB and NOB decreased, and that of PAOs, GAOs, and DNB increased. Redundancy analysis indicated that, among the environmental factors and functional microbes involved in converting to a denitrifying biofilter, DO was the most important. Also, Spearman correlation heatmap elucidated Flavobacterium sp. and Norank_Nitrosomonadaceae were the dominants bacteria affected by environmental factors. This study found a high abundance of functionally active microbes participated in nitrogen and phosphorus removal in the BFT biofilters. Thus, the water-treatment efficiency of the BFT biofilter could be flexibly and controlled by adding carbohydrates.

Elevated carbon dioxide stimulates nitrous oxide emission in agricultural soils: A global meta-analysis

Elevated carbon dioxide (CO 2 ) (eCO 2 ) has been shown to affect the nitrous oxide (N 2 O) emission from terrestrial ecosystems by altering the interaction of plants, soils, and microorganisms. However, the impact of eCO 2 on the N 2 O emission from agricultural soils remains poorly understood. This meta-analysis summarizes the effect of eCO 2 on N 2 O emission in agricultural ecosystems and soil physiochemical and biological characteristics using 50 publications selected. The eCO 2 effect values, which equal to the percentage changes of N 2 O emission under eCO 2 , were calculated based on the natural logarithm of the response ratio to eCO 2 . We found that eCO 2 significantly increased N 2 O emission (by 44%), which varied depending on experimental conditions, agricultural practices, and soil properties. In addition, eCO 2 significantly increased soil water-filled pore space (by 6%), dissolved organic carbon content (by 11%), and nitrate nitrogen content (by 13%), but significantly reduced soil pH (by 1%). Moreover, eCO 2 significantly increased soil microbial biomass carbon (by 28%) and soil microbial biomass nitrogen (by 7%) contents. Additionally, eCO 2 significantly increased the abundances of ammonia-oxidizing bacteria (AOB) amoA (by 21%), nirK (by 15%), and nirS (by 15%), but did not affect the abundances of ammonia-oxidizing archaea (AOA) amoA and nosZ . Our findings indicate that eCO 2 substantially stimulates N 2 O emission in agroecosystems and highlight that optimization of nitrogen management and agronomic options might suppress this stimulation and aid in reducing greenhouse effect.

Nitrifier community assembly and species co-existence in forest and meadow soils across four sites in a temperate to tropical region

Nitrification is a central process in terrestrial N cycling. However, the role of diversity of ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and nitrite-oxidizing bacteria (NOB) in shaping nitrifier communities remains underexplored. This study deciphered the nitrifier community assembly by analyzing amplicon sequence variants (ASVs) of amoA and nxrB genes from soil microbiomes in forest and meadow ranging from the temperate monsoon to the tropic monsoon climate areas. The abundance, α-diversity, and β-diversity of AOA, AOB, Nitrobacter, and Nitrospira were dominantly distinguished by geographical variation and less by vegetation type. The overall environmental factors, including the soil properties and climate factors, significantly correlated with the β-diversity of AOA and Nitrospira, but not with AOB and Nitrobacter community. The assembly process of AOA was dominated by heterogeneous selection, while that of AOB, Nitrobacter, and Nitrospira by dispersal limitation. We found that AOA and Nitrospira dominated the combined nitrifier network, and several phylotypes exhibited extensive segregation between different modules, suggesting niche partition was present within subgroups or lineages of AOA, AOB, and Nitrospira. Links between different functional groups might reflect functional coupling, while links between the same lineage or subgroup could result from niche overlap or unknown mechanisms. As network connectors, some AOA and Nitrospira belonged to generalists, which could be essential to keep the stability of the network. Nitrospira inopinata-like node in module 24 suggested that comammox might not be an ecologically isolated bacterium in nitrification. We hypothesized that a balance between species sorting in AOA and dispersal limitation in AOB and NOB communities determined the species co-existence in the forest and meadow soils from temperate to tropical regions. This study might enhance our understanding of contemporary co-existence in different functional groups driving nitrification.

Nitrification mainly driven by ammonia-oxidizing bacteria and nitrite-oxidizing bacteria in an anammox-inoculated wastewater treatment system

Anaerobic ammonium oxidation (anammox) process has been acknowledged as an environmentally friendly and time-saving technique capable of achieving efficient nitrogen removal. However, the community of nitrification process in anammox-inoculated wastewater treatment plants (WWTPs) has not been elucidated. In this study, ammonia oxidation (AO) and nitrite oxidation (NO) rates were analyzed with the incubation of activated sludge from Xinfeng WWTPs (Taiwan, China), and the community composition of nitrification communities were investigated by high-throughput sequencing. Results showed that both AO and NO had strong activity in the activated sludge. The average rates of AO and NO in sample A were 6.51 µmol L−1 h−1 and 6.52 µmol L−1 h−1, respectively, while the rates in sample B were 14.48 µmol L−1 h−1 and 14.59 µmol L−1 h−1, respectively. The abundance of the nitrite-oxidizing bacteria (NOB) Nitrospira was 0.89–4.95 × 1011 copies/g in both samples A and B, the abundance of ammonia-oxidizing bacteria (AOB) was 1.01–9.74 × 109 copies/g. In contrast, the abundance of ammonia-oxidizing archaea (AOA) was much lower than AOB, only with 1.28–1.53 × 105 copies/g in samples A and B. The AOA community was dominated by Nitrosotenuis, Nitrosocosmicus, and Nitrososphaera, while the AOB community mainly consisted of Nitrosomonas and Nitrosococcus. The dominant species of Nitrospira were Candidatus Nitrospira defluvii, Candidatus Nitrospira Ecomare2 and Nitrospira inopinata. In summary, the strong nitrification activity was mainly catalyzed by AOB and Nitrospira, maintaining high efficiency in nitrogen removal in the anammox-inoculated WWTPs by providing the substrates required for denitrification and anammox processes.