Abundance Of Ammonia-oxidizing Bacteria Research Articles

The Effects of Predominantly Chemoautotrophic Versus Heterotrophic Biofloc Systems on Nitrifying Bacteria, Planktonic Microorganisms, and Growth of Penaeus vannamei, and Oreochromis niloticus in an Integrated Multitrophic Culture

The aim of this study was to evaluate the effect of predominantly chemoautotrophic and heterotrophic biofloc systems on ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), and planktonic microorganisms in an integrated Penaeus vannamei and Oreochromis niloticus integrated multitrophic culture. Shrimp and tilapia were stocked at a density of 400 shrimp m−2 and 45 fish m−3, respectively. The trial consisted of two biofloc treatments, with three replicates each: chemoautotrophic and heterotrophic. The identification and quantification of the planktonic microorganisms (ciliates, flagellates, microalgae, and total bacteria) and nitrifying bacteria were carried out through direct counting and fluorescence in situ hybridization, respectively. At the end of the trial, heterotrophic treatment had resulted in higher total abundance of bacteria. The relative abundance of AOB and NOB in relation to the total abundance was less than 0.1% for both treatments. The system was dominated by flagellates in both treatment groups. The abundance of microalgae and ciliates was higher with chemoautotrophic treatment. After 43 days, the shrimp weights were higher in the chemoautotrophic group, while the final weights of the tilapia were not significantly different between the two treatments. The type of biofloc system (Chemoautotrophic vs. Heterotrophic) did not significantly alter the establishment of AOB and NOB in a Penaeus vannamei and Oreochromis niloticus integrated multitrophic culture. The two treatments proved to be equally efficient for maintaining good water quality, but the chemoautotrophic treatment resulted in better shrimp growth. Thus, our study demonstrated that chemoautotrophic biofloc is a promising approach in integrated multitrophic aquaculture.

Sludge enrichment and intermittent gradient aeration: Modulating microbial communities for start-up of partial nitrification in a sequencing batch reactor (SBR)

A novel approach has been proposed integrating sludge enrichment with intermittent gradient aeration to achieve partial nitrification (PN). Results indicated that this method suppressed nitrite-oxidizing bacteria (NOB) activity while maintained ammonia-oxidizing bacteria (AOB) activity, achieving an 82.87 % nitrite accumulation rate (NAR) during startup. During stable operation, specific ammonia oxidation rate and specific nitrite oxidation rate reached 18.44 and 2.67 mg N/g MLVSS/h, respectively. Shortening anoxic time from 30 to 20 min enhanced ammonia removal efficiency by 12.5 %, increasing NAR to 89.55 %. Further reduction to 5 min yielded 38.46 % and 91.88 %, respectively. AOB abundance enriched from 0.62 % to 22.28 %, with the AOB-to-NOB ratio jumping from 0.22 to 59.58. This research presented a rapid and effective strategy for achieving PN.

Selecting an optimal sorghum cultivar can improve nitrogen availability and wheat yield in crop rotation.

Sorghum (Sorghum bicolor L. Moench) is a cereal crop known for its biological nitrification inhibition (BNI) capacity, a plant-mediated activity limiting nitrification pathway. The use of BNI-producing plants represents an environmentally friendly and cost-effective approach to reduce nitrogen (N) losses, such as nitrate (NO3 -) leaching and nitrous oxide (N2O) gas emissions. The present study aimed to test the effectiveness of different S. bicolor cultivars in rotation to retain ammonium (NH4 +) in soils and promote N availability for the subsequent wheat crop. A two-year field rotation was established with four sorghum cultivars followed by winter wheat (Triticum aestivum L.). Urea alone or combined with the urease inhibitor N-(n-butyl) thiophosphoric triamide was applied to promote a NH4 +-based fertilization regimes. AddingN-(n-butyl) thiophosphoric triamide maintained higher soil NH4 + content and reduced ammonia-oxidizing bacteria population during sorghum cultivation. However, the benefits of the inhibitor on sorghum growth were cultivar-dependent. Notably, the further reduction in ammonia-oxidizing bacteria abundance for sorghum Voyenn and the increased soil NH4 + content for Vilomene suggested a BNI potential for these cultivars. Importantly, the Vilomene precedent enhanced wheat yield for both fertilization regimes. Overall, the present study confirms that sorghum is a suitable catch crop and emphasizes the importance of selecting the proper sorghum cultivar to maximize the yield of the target wheat crop, at the same time as minimizing N losses. Furthermore, developing combined strategies with selected sorghum cultivars and the application of urease inhibitors enables to enhance sorghum productivity as forage, achieving added value to the rotation. © 2024 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Effects of Vegetable Planting Ages on Community Structure of Ammonia-oxidizing Archaea and Ammonia-oxidizing Bacteria in Greenhouse Vegetable Fields

The ammonia oxidation process driven by microorganisms is a dominant source for nitrous oxide （N2O） emissions. Here, we examined the influence of greenhouse vegetable planting ages on soil ammonia-oxidizing archaea （AOA） and ammonia-oxidizing bacteria （AOB）, which is of great significance for assessing the soil quality status and greenhouse gas transformations. A field study was conducted at different times （1, 5, 10, and 20 a） in greenhouse vegetable soils of Gaoyi, Hebei Province. Chemical analysis and Illumina NovaSeq high-throughput sequencing were used to analyze the soil physicochemical properties and community structures and diversity of AOA and AOB. The variation in AOA and AOB communities and the driving factors in greenhouse soils at different ages were also investigated. The results showed that the contents of total nitrogen, organic matter, alkali-hydrolyzable nitrogen, available phosphorus, and available potassium first increased and then decreased with the prolongation of growth. The contents of nitrate nitrogen, ammonium nitrogen, and electrical conductivity first decreased and then increased with the prolongation of growth. The pH value of soils decreased with the prolongation of growth. The abundance and diversity index of AOA and AOB first decreased and then increased with the prolongation of growth. Nitrososphaeria, unclassified Thaumarchaeota, and Candidatus Nitrosocaldus were the dominant species of AOA, while Betaproteobacteria and Nitrosospira were the dominant species of AOB. The composition of the soil AOA community varied greatly compared to that of AOB with the prolongation of growth. Correlation analysis showed that the changes in soil nutrient factors had a significant correlation with AOA and AOB communities. Redundancy analysis indicated that ammonium nitrogen, alkali-hydrolyzable nitrogen, and nitrate nitrogen were key factors of AOA communities, while electrical conductivity, available potassium, and nitrate nitrogen were key factors for AOB. In summary, long-term planting of greenhouse vegetables significantly affected the abundance and composition of soil AOA and AOB communities. Our results provide a theoretical basis for further studies on the greenhouse gas transformation and microbial mechanisms of the nitrogen cycle in greenhouse soils.

Maize–peanut intercropping and N fertilization changed the potential nitrification rate by regulating the ratio of AOB to AOA in soils

Maize–peanut intercropping could potentially mitigate nitrogen (N) loss from the soil, a process primarily governed by the net nitrification rate. However, the impact of maize–peanut intercropping on the potential nitrification rate (PNR) and its relationships with key players, such as ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), are not well understood. Herein, we conducted a field experiment involving two management systems and two crops, namely, maize (MPm) and peanut (MPp) intercropping, maize monoculture (MM), and peanut monoculture (PM), under three N fertilization rates (no N fertilization, 150 ​kg ​N ​ha−1, and 300 ​kg ​N ​ha−1). Under intercropping (MPm and MPp), the abundance of AOA amoA gene increased by 64.8 ​% and 60.3 ​% and the abundance of AOB amoA gene increased by 63.2 ​% and 68.2 ​% compared to the MM and PM monoculture systems, respectively. Furthermore, the abundances of AOA and AOB decreased in MPp and MM, while AOB increased in MPm and PM across the N fertilization gradient. The PNR increased corresponding to the N fertilization rates, with intercropping enhancing the PNR in peanut-planted soil but reducing the PNR in maize-planted soil compared to monocropping. Notably, no significant positive relationship between the abundances of AOA or AOB and the PNR. Random forest analysis indicated that the AOB/AOA ratio was an important predictor of the PNR. N fertilization and intercropping regulated the AOB/AOA ratio mainly through controlling the ammonia content and the soil C/N, respectively. These findings highlight the substantial impacts of N fertilization and intercropping on PNR, with the AOB/AOA ratio emerging as a valuable predictive indicator for the PNR.

Impact of Dolomite Liming on Ammonia-Oxidizing Microbial Populations and Soil Biochemistry in Acidic Rice Paddy Soils

Background and Aims: Over the last few decades, rampant nitrogen fertilization has exacerbated soil acidification in agricultural ecosystems. To counteract this, liming has become an essential technique for rehabilitating fertility in acid-degraded agricultural soils. Our research aimed to shed light on the response of ammonia oxidizers to liming in acidic soils within a controlled rice paddy experiment. We conducted a pot experiment with rice, featuring three different treatments: a control with only soil, a low dolomite dose (LD), and a high dolomite dose (HD). Various soil properties were investigated throughout the study. Under flooding, soil pH values rose across the treatments, from 5.4 in the control to 6.8 in HD. Ammonium and nitrate levels peaked in the HD treatment, reaching 30 and 22 mg kg−1, respectively. Similarly, dissolved organic carbon and microbial biomass carbon surged at mid-season aeration, hitting highs of 101 and 30 mg kg−1, respectively, in the HD treatment. Ammonia-oxidizing bacteria (AOB) and archaea (AOA) were responsive to dolomite-lime application, with distinct reactions; AOB abundance and potential nitrification rates were positively affected by higher lime doses, whereas AOA numbers decreased over time and with dolomite application. Additionally, soil enzymes such as urease, catalase, invertase, phenol oxidase, and phosphatase also increased progressively, mirroring the rise in soil pH. This study identified increased soil pH as the critical factor influencing various soil parameters, especially the balance between AOA and AOB populations. Both AOB and AOA were sensitive to liming; AOA decreased while liming stimulated AOB abundance.

Ammonia oxidizing bacteria (AOB) denitrification and bacterial denitrification as the main culprit of high N2O emission in SBR with low C/N ratio wastewater

A large amount of greenhouse gas nitrous oxide (N2O) will be produced during the biological nitrogen removal process for organic wastewater of low C/N ratio. One of the effective methods to solve this problem is to incorporate inexpensive carbon source. In this study, raw wastewater (RW) from pig farm, that was not anaerobically digested, was utilized as exogenous carbon in both A/O and SBR aerobic reactor to treat liquid digestate with high ammonia nitrogen and low C/N ratio. The results showed that N2O emission in SBR was higher than that of A/O process under the same nitrogen load. The N2O conversion in the biological nitrogen removal process was investigated by the strategy of integrating stable isotope method and metagenomics. The δO18-N2O, δN15-N2O, and SP values of the SBR were closer to the denitrification values of Ammonia-Oxidizing Bacteria (AOB) than those of A/O. The abundance of AOB in the SBR reactor was higher than that in the A/O reactor, while the abundance of denitrifying bacteria was lower. The amoA/B/C gene abundance in the SBR was greater than that in the A/O, and the NOS gene abundance was the opposite. The results indicated that both AOB denitrification and bacterial denitrification led to the increase of N2O emissions of the SBR.

Chromolaena odorata affects soil nitrogen transformations and competition in tropical coral islands by altering soil ammonia oxidizing microbes

Invasive plants can change the community structure of soil ammonia-oxidizing microbes, affect the process of soil nitrogen (N) transformation, and gain a competitive advantage. However, the current researches on competition mechanism of Chromolaena odorata have not involved soil nitrogen transformation. In this study, we compared the microbially mediated soil transformations of invasive C. odorata and natives (Pisonia grandis and Scaevola taccada) of tropical coral islands. We assessed how differences in plant biomass and tissue N contents, soil nutrients, N transformation rates, microbial biomass and activity, and diversity and abundance of ammonia oxidizing microbes associated with these species impact their competitiveness. The results showed that C. odorata outcompeted both native species by allocating more proportionally biomass to aboveground parts in response to interspecific competition (12.92 % and 22.72 % more than P. grandis and S. taccada, respectively). Additionally, when C. odorata was planted with native plants, the available N and net mineralization rates in C. odorata rhizosphere soil were higher than in native plants rhizosphere soils. Higher abundance of ammonia-oxidizing bacteria in C. odorata rhizosphere soil confirmed this, being positively correlated with soil N mineralization rates and available N. Our findings help to understand the soil N acquisition and competition strategies of C. odorata, and contribute to improving evaluations and predictions of invasive plant dynamics and their ecological effects in tropical coral islands.

Root Exudates Promoted Microbial Diversity in the Sugar Beet Rhizosphere for Organic Nitrogen Mineralization

Rhizosphere environments play a vital role in the nutrient cycling of crops and soil organic nitrogen mineralization. Sugar beet is a highly nitrogen (N)-demanding crop, and it is necessary to explore the relationship between the sugar beet root exudates, the microbial community, and nitrogen utilization. In this study, a special separation method was employed to create rhizosphere (H3) and non-rhizosphere (H2 and H1) environments for sugar beet. After 50 d of cultivation in nearly inorganic-free soil, the microbial diversity and its correlation with root metabolites and N were examined. The results showed that in H3, the inorganic N content was over 23 times higher than in H1 and H2, with a 13.1% higher relative abundance of ammonia-oxidizing bacteria compared to H2 and a 32% higher abundance than H1. The relative abundance of nitrite-oxidizing bacteria was also 18.8% higher than in H1. Additionally, a significant positive correlation was observed between inorganic nitrogen content and serine (Ser) and isoleucine (Ile). The organic nitrogen content exhibited positive correlations with glycine (Gly), alanine (Ala), and tyrosine (Tyr) but displayed negative correlations with certain amino acids, organic acids, and glucose. The co-linearity network indicated that the microbial composition in H3 also exhibited higher node connectivity. It can be inferred that under the influence of sugar beet root exudates, the changes in the rhizosphere’s microbial diversity were more intricate, thereby benefiting soil nitrogen cycling and inorganic N accumulation. These findings provide profound insight into sugar beet soil organic nitrogen mineralization and contribute to the sustainable and environmentally friendly development of modern agriculture.

The cooperative interaction of AOB and comammox clade A drives nitrification and N2O emissions in a long-term organic fertilized paddy soil

The newly discovered complete ammonia oxidizer (comammox Nitrospira) is able to single-step nitrification capability, and increased our understanding of soil nitrogen cycling. However, the response of comammox and ammonia-oxidizing bacteria (AOB) and archaea (AOA) to long-term fertilization and rhizosphere effects in paddy soils and their relative contribution to the nitrification-derived N2O emissions is still unclear. Here, we collected rhizosphere and bulk soils with thirty years of different fertilization strategies, i.e., non-fertilization (CK), chemical N, P, and K application (NPK), and NPK plus pig manure application (NPKM), respectively, to test changes in nitrification potential rate (PNR), N2O emission fluxes, abundance of ammonia oxidizers and their significant drivers. The result showed that NPKM significantly increased soil C and N levels, the proportion of soil middle-size particles (40.35–148.00 μm class), and soil PNR, but decreased soil N2O emissions, especially in the drying time of paddy (P < 0.05), compared to NPK fertilization. NPKM had the highest values of AOA, AOB, and comammox clade A amoA gene copy numbers (P < 0.05), but clade B was increased by the NPK in the rhizosphere soil. Furthermore, fertilization showed greater effects on ammonia oxidizers (except for clade B) than the rhizosphere effect. Mantel test showed that SOM, TP, pH, NH4+, and NO3− were main abiotic factors causing the niche separation among ammonia oxidizers. Linear regression analysis and structural equation model (SEM) showed that both PNR and N2O emission fluxes were significantly associated with the abundance of AOB and comammox clade A (P < 0.05). Therefore, our results underline the importance of AOB together with comammox clade A in nitrification and N2O production in long-term organic fertilized paddy fields, which could provide new ideas for the mitigation of N2O emission by adopting organic fertilization scenarios in Chinese paddy fields.

Distinguished denitrifying phosphorus removal in the high-rate anoxic/microaerobic system for sewage treatment

This study re-evaluated the role of anoxic and anaerobic zones during the enhanced biological phosphorus (P) removal process by investigating the potential effect of introducing an anoxic zone into a high-rate microaerobic activated sludge (MAS) system (1.60–1.70 kg chemical oxygen demand (COD) m−3 d−1), i.e., a high-rate anoxic/microaerobic (A/M) system for sewage treatment. In the absence of a pre-anaerobic zone, introducing an anoxic zone considerably reduced effluent NOx−-N concentrations (7.2 vs. 1.5 mg L−1) and remarkably enhanced total nitrogen (75% vs. 89%) and total P (18% vs. 60%) removal and sludge P content (1.48% vs. 1.77% (dry weight)) due to further anoxic denitrifying P removal in the anoxic zone (besides simultaneous nitrification and denitrification in the microaerobic zone). High-throughput pyrosequencing demonstrated the niche differentiation of different polyphosphate accumulating organism (PAO) clades (including denitrifying PAO [DPAO] and non-DPAO) in both systems. Introducing an anoxic zone considerably reduced the total PAO abundance in sludge samples by 42% and modified the PAO community structure, including 17–19 detected genera. The change was solely confined to non-DPAOs, as no obvious change in total abundance or community structure of DPAOs including 7 detected genera was observed. Additionally, introducing an anoxic zone increased the abundance of ammonia-oxidizing bacteria by 39%. The high-rate A/M process provided less aeration, higher treatment capacity, a lower COD requirement, and a 75% decrease in the production of waste sludge than the conventional biological nutrient removal process.

Nitrification inhibitor chlorate and nitrogen substrates differentially affect comammox Nitrospira in a grassland soil.

Through the combined use of two nitrification inhibitors, Dicyandiamide (DCD) and chlorate with nitrogen amendment, this study aimed to investigate the contribution of comammox Nitrospira clade B, ammonia oxidizing bacteria (AOB) and archaea (AOA) to nitrification in a high fertility grassland soil, in a 90-day incubation study. The soil was treated with nitrogen (N) at three levels: 0 mg-N kg-1 soil, 50 mg-N kg-1 soil, and 700 mg-N kg-1 soil, with or without the two nitrification inhibitors. The abundance of comammox Nitrospira, AOA, AOB, and nitrite oxidising bacteria (NOB) was measured using qPCR. The comammox Nitrospira community structure was assessed using Illumina sequencing. The results showed that the application of chlorate inhibited the oxidation of both NH4+ and NO2- in all three nitrogen treatments. The application of chlorate significantly reduced the abundance of comammox Nitrospira amoA and nxrB genes across the 90-day experimental period. Chlorate also had a significant effect on the beta diversity (Bray-Curtis dissimilarity) of the comammox Nitrospira clade B community. Whilst AOB grew in response to the N substrate additions and were inhibited by both inhibitors, AOA showed litle or no response to either the N substrate or inhibitor treatments. In contrast, comammox Nitrospira clade B were inhibited by the high ammonium concentrations released from the urine substrates. These results demonstrate the differential and niche responses of the three ammonia oxidising communities to N substrate additions and nitrification inhibitor treatments. Further research is needed to investigate the specificity of the two inhibitors on the different ammonia oxidising communities.

The different responses of AOA and AOB communities to irrigation systems in the semi-arid region of Northeast China.

Ammonia oxidation is the rate-limiting step in nitrification and the key step in the nitrogen (N) cycle. Most soil nutrients and biological indicators are extremely sensitive to irrigation systems, from the perspective of improving soil fertility and soil ecological environment, the evaluation of different irrigation systems and suitability of selection, promote crop production and soil quality, study the influence of the soil microenvironment contribute to accurate evaluation of irrigation farmland soil health. Based on the amoA gene, the abundance and community diversity of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) and their responses to soil physicochemical factors and enzyme activities were studied in semi-arid areas of Northeast China. The study consisted of three irrigation systems: flood irrigation (FP), shallow buried drip irrigation (DI), and mulched drip irrigation (MF). The results showed that DI and MF significantly increased the contents of alkaline hydrolyzed nitrogen (AN), nitrate nitrogen (NO3--N), soil moisture, and the activities of ammonia monooxygenase (AMO) and hydroxylamine oxidase (HAO). Compared with FP, DI significantly increased the abundance of soil AOA and AOB, while MF significantly increased the abundance of soil AOB. Irrigation systems significantly affected the community composition of ammonia-oxidizing microorganisms (AOM). Also, AN and soil moisture had the greatest influence on the community composition of AOA and AOB, respectively. The AOB community had better stability and stress resistance. Moreover, the symbiotic network of AOB in the three irrigation systems was more complex than that of AOA. Compared with FP, the AOA community under treatment DI had higher complexity and stability, maintaining the versatility and sustainability of the ecosystem, while the AOB community under treatment MF had higher transfer efficiency in terms of matter and energy. In conclusion, DI and MF were more conducive to the propagation of soil AOM in the semi-arid area of Northeast China, which can provide a scientific basis for rational irrigation and N regulation from the perspective of microbiology.

Wheat straw and microbial inoculants have an additive effect on N2O emissions by changing microbial functional groups

AbstractStraw‐decomposing microbial inoculants (MIs) have been increasingly applied to straw‐amended soils. However, the interactive effects and underlying microbial mechanisms of straw and decomposing MIs on nitrous oxide (N2O) emissions remain unclear. Here, a pot experiment with an Aquic Inceptisol was conducted to determine soil N2O emissions and the abundance and composition of microbial functional genes under six amendments: wheat straw (W), Bacillus subtilis MI (B), Streptomyces rochei MI (S), a combination of straw and B. subtilis MI (WB), a combination of straw and S. rochei MI (WS), and a control without wheat straw or MI (C). Compared with the control, the amendments of straw, decomposing MIs, and their combinations decreased soil N2O emissions by 43%, 22–30%, and 46–60%, respectively. Mechanistically, the positive relationship between ammonia‐oxidizing bacteria (AOB) and soil potential nitrification rate (PNR), along with decreased AOB abundance (−36%) following straw and decomposing MI amendments, further suggested that AOB predominated soil nitrification and was responsible for the suppressed nitrification. In addition, straw amendment increased nirK gene abundance (by 48%) and potential denitrification rate (by 11%), while the increase in nosZI gene abundance (+25%) involved in N2O consumption contributed to the decrease in N2O emissions. Overall, the additive effect of straw and decomposing MIs on soil N2O emissions was associated with two amendment‐induced changes in the abundance and composition of AOB and straw‐stimulated the abundance of the nosZI gene. Our results revealed the potential for mitigating N2O emissions following the amendments of straw and MI by influencing soil N2O‐related microbial groups.

Urban and agricultural land use led to niche differentiation of AOA, AOB and comammox along the Beiyun River continuum

River ecological health has been severely threatened by anthropogenic land-use pressures. Here, by combining remote sensing and molecular biology methods, we evaluated the impact of land-use activities on nitrification, a fundamental ecological process in rivers, which is conducted by ammonia-oxidising archaea (AOA) and ammonia-oxidising bacteria (AOB), or the newly discovered complete ammonia oxidisers (comammox). We explored the relationships of the abundance, activity, and diversity of AOA, AOB, and comammox in river sediments with land-use pressure by proposing a quantitative land use pattern index (LPI) over a 184 km continuum along the Beiyun River in North China. We found that comammox dominated nitrification in the forestry upstream (67.07 % in summer, 56.40 % in winter), while AOB became the major player in the urban middle (56.51 % in summer, 53.08 % in winter) and agricultural downstream reaches (62.98 % in summer, 50.74 % in winter). In addition, urban and agricultural land use lowered the α diversity of AOA and comammox, as well as simplified their co-occurrence networks, but promoted AOB diversity and complicated their networks. The structural equation model illustrated that the key drivers affecting the key taxa and activities were ammonia, and C/N for AOB, and total organic matter, and pH for comammox. We thus conclude that watershed urban and agricultural land use drive the niche differentiation of AOA, AOB, and comammox, specifically leading to a robust AOB community but weakened AOA and comammox communities. Our study connects the macro and micro worlds and provides a new paradigm for studying the variation in microbial communities as well as the potential ecological consequences under the increased anthropogenic land-use pressures in the Anthropocene.

Effects of 3-year biochar application on carbon sequestration, nitrogen retention and nitrate leaching of fluvo-aquic soil profiles in vegetable rotation fields

The impacts of biochar application on the carbon (C) and nitrogen (N) cycles in soil profiles in vegetable fields have rarely been reported. A three-year field experiment (CK, control; BC, biochar; N, nitrogen fertilizer; BCN, biochar and nitrogen fertilizer) was conducted in fluvo-aquic soil with a wild cabbage-Chinese cabbage rotation to investigate biochar effects on soil organic carbon (SOC) sequestration, N retention, and nitrate (NO3−) leaching in the soil profile (topsoil, 0–20 cm; subsoil, 20–50 cm; third-layer soil, 50–100 cm). The results showed that the biochar-induced increase in topsoil SOC under N fertilization was greater for Chinese cabbage season than for wild cabbage season. Excluding biochar-N, biochar application caused an extra increase in topsoil total nitrogen (TN) under N fertilization. Biochar decreased the NO3−-N concentration of third-layer soil solution, particularly under N fertilization, indicating that biochar reduced the potential source of NO3− leaching. Under N fertilization, biochar reduced the abundances of carbon-degrading bacteria (Streptomyces, Bacillus, Mycobacterium, and Sphingomonas) and genes (sga, xylA, lig, and pgu) in the topsoil, as well as the abundances of ammonia-oxidizing bacteria (Nitrosospira and Nitrosomonas) and gene (amoA) in the third-layer soil. However, biochar increased the abundance of ammonia-assimilating bacteria (Rhodococcus) and gene (glnA) in the topsoil. Biochar inhibited the microbial function associated with C degradation by affecting soil TN, thus enhancing topsoil SOC sequestration. Biochar promoted the soil microbial function related to ammonia assimilation by affecting dissolved organic carbon (DOC), subsequently enhancing ammonia assimilation. Moreover, biochar initially inhibited ammonia oxidation in the third-layer soil by increasing soil DOC, subsequently affecting nitrite oxidation and ultimately reducing soil NO3− leaching. Biochar significantly increased the N use efficiency of vegetables in the last two years. This study provides insights into biochar effects on the changes in soil microbial function, which promoted SOC sequestration, enhanced N retention and mitigated nitrate leaching in a vegetable rotation field.

Mitigation of N2O emissions in water-saving paddy fields: Evaluating organic fertilizer substitution and microbial mechanisms

Water-saving irrigation strategies can successfully alleviate methane emissions from rice fields, but significantly stimulate nitrous oxide (N2O) emissions because of variations in soil oxygen level and redox potential. However, the relationship linking soil N2O emissions to nitrogen functional genes during various fertilization treatments in water-saving paddy fields has rarely been investigated. Furthermore, the mitigation potential of organic fertilizer substitution on N2O emissions and the microbial mechanism in rice fields must be further elucidated. Our study examined how soil N2O emissions were affected by related functional microorganisms (ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), nirS, nirK and nosZ) to various fertilization treatments in a rice field in southeast China over two years. In this study, three fertilization regimes were applied to rice cultivation: a no nitrogen (N) (Control), an inorganic N (Ni), and an inorganic N with partial N substitution with organic manure (Ni+No). Over two rice-growing seasons, cumulative N2O emissions averaged 0.47, 4.62 and 4.08 kg ha−1 for the Control, Ni and Ni+No treatments, respectively. In comparison to the Ni treatment, the Ni+No fertilization regime considerably reduced soil N2O emissions by 11.6% while maintaining rice yield, with a lower N2O emission factor (EF) from fertilizer N of 0.95%. Nitrogen fertilization considerably raised the AOB, nirS, nirK and nosZ gene abundances, in comparison to the Control treatment. Moreover, the substitution of organic manure for inorganic N fertilizer significantly decreased AOB and nirS gene abundances and increased nosZ gene abundance. The AOB responded to N fertilization more sensitively than the AOA. Total N2O emissions significantly correlated positively with AOB and nirS gene abundances while having a negative correlation with nosZ gene abundance and the nosZ/nirS ratio across N-fertilized plots. In summary, we conclude that organic manure substitution for inorganic N fertilizer decreased soil N2O emissions primarily by changing the soil NO3−-N, pH and DOC levels, thus inhibiting the activities of ammonia oxidation in nitrification and nitrite reduction in denitrification, and strengthening N2O reduction in denitrification from water-saving rice paddies.

The addition of discrimination inhibitors stimulations discrimination potential and N2O emissions were linked to predation among microorganisms in long term nitrogen application and straw returning systems.

Ammonia oxidizing archaea (AOA) and ammonia oxidizing bacteria (AOB) have been proven to be key microorganisms driving the ammonia oxidation process. However, under different fertilization practices, there is a lack of research on the impact of interaction between predators and AOA or AOB on nitrogen cycling at the multi-trophic level. In this study, a network-oriented microscopic culture experiment was established based on four different long-term fertilization practices soils. We used the nitrification inhibitors 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxide-3-oxyl (PTIO) and 3, 4-Dimethylpyrazole phosphate (DMPP) inhibited AOA and AOB, respectively, to explore the impact of interaction between protists and AOA or AOB on nitrogen transformation. The results showed that long-term nitrogen application promoted the potential nitrification rate (PNR) and nitrous oxide (N2O) emission, and significantly increased the gene abundance of AOB, but had no obvious effect on AOA gene abundance. DMPP significantly reduced N2O emission and PNR, while PTIO had no obvious effect on them. Accordingly, in the multi-trophic microbial network, Cercozoa and Proteobacteria were identified as keystone taxa of protists and AOB, respectively, and were significantly positively correlated with N2O, PNR and nitrate nitrogen. However, Nitrososphaerota archaeon as the keystone species of AOA, had an obvious negative linkage to these indicators. The structural equation model (SEM) showed that AOA and AOB may be competitors to each other. Protists may promote AOB diversity through direct trophic interaction with AOA. The interaction pattern between protists and ammonia-oxidizing microorganisms significantly affects potential nitrification rate and N2O emission, which has important implications for soil nitrogen cycle.

High efficiency and stable partial nitration achieved via gel immobilization

Long-term high efficiency and stable partial nitrification (PN) performance was achieved using gel-immobilized partial nitrifying bacteria. The PN characteristics of the filler under high and low ammonia nitrogen concentrations and low temperature were comprehensively studied and the rapid reactivation was achieved after reactor breakdown or long stagnation period. The results showed that the maximum ammonia oxidation rate was 66.8 mg•(L•h)−1 and the nitrite accumulation rate was above 95 % for the filler. Efficient and stable PN performance depends on the high abundance of ammonia-oxidizing bacteria (AOB) inside the filler and dynamically microbial community. In addition, the oxygen-limited zone and competition between the microorganisms inside the filler effectively inhibited the growth of nitrite oxidizing bacteria, and the sludge outside the filler assisted in this process, which supported the dominant position of AOB in fillers. This study provides a reliable technology for the practical application of the PN nitrogen removal process.

Assessing the effectiveness of 3, 4-dimethylpyrazole phosphate (DMPP) inhibitor in mitigating N2O emissions from contrasting Cd-contaminated soils

Improving nitrogen use efficiency of chemical fertilizers is essential to mitigate the negative environmental impacts of nitrogen. Nitrification, the conversion of ammonium to nitrate via nitrite by soil microbes, is a prominent source of nitrogen loss in soil systems. The effectiveness of nitrification inhibitors in reducing nitrogen loss through inhibition of nitrification is well-documented, however, their efficacy in heavy metals-contaminated soils needs thorough investigations. The current study assessed the efficacy of nitrification inhibitor 3, 4-dimethylpyrazole phosphate (DMPP) in reducing nitrous oxide (N2O) emissions in cadmium (Cd) contaminated paddy and red soils under lab-controlled environment. Obtained results indicated the substantial reduction in N2O emissions with DMPP in paddy and red soil by 48 and 35 %, respectively. However, Cd contamination resulted in reduced efficacy of DMPP, thus decreased the N2O emissions by 36 and 25 % in paddy and red soil, respectively. It was found that addition of DMPP had a significant effect on the abundance of ammonia oxidizing bacteria (AOB) and archaea (AOA). Notably, the reduction in N2O emissions by DMPP varied with the abundance of AOB. Moreover, Cd pollution resulted in a significant (P < 0.05) reduction in the abundance of archaeal and bacterial amoA genes, as well as bacterial nirK, nirS, and nosZ genes. The combined treatment of Cd and DMPP had a detrimental impact on denitrifiers, thereby influencing the overall efficiency of DMPP. These findings provide novel insights into the application of DMPP to mitigate nitrification and its potential role in reducing N2O emissions in contaminated soils.