Abundance Of Anammox Bacteria Research Articles

Insights into the effects of exogenous folate on the recovery of SPNA system after starvation: Performance, microbial community and metabolism

To investigate the effects of folate addition on the recovery process of the single-stage partial nitritation-anammox (SPNA) system, two continuous stirred tank reactors (CSTRs), named R1 (adding folate) and R2 (control group), were operated for 105 days at room temperatures. The highest nitrogen removal rate (NRR) observed in R1 was 0.47 kg N/(m3·d) with the addition of 3.0 mg/L folate. Additionally, the activities of HZO and HZS in R1 were higher than those in R2. The relative abundance of Candidatus Brocadia reached 23.7% in R1 and 18.2% in R2. Moreover, the relative abundance of nitrogen metabolism genes and carbon metabolism genes increased with folate addition. However, 3.0 mg/L folate addition reduced the relative abundance of nirK/S and the activity and growth of ammonia-oxidizing bacteria, which was not conducive to continually improving the NRR. This study provided a novel perspective on improving the activity and abundance of anammox bacteria during the restoration process.

Rapid establishment of municipal sewage partial denitrification-anammox for nitrogen removal through inoculation with side-stream anammox biofilm without domestication

Mainstream partial denitrification anammox was achieved through inoculation of side-stream mature partial nitritation anammox biofilm without domestication. The contribution of anammox to nitrogen removal was 29.4 %. Moreover, prolonging anoxic hydraulic retention time and introducing side-stream nitrite under different carbon/nitrogen ratios enriched anammox bacteria. The abundance of anammox bacteria increased by ∼ 10 times ((2.19 ± 0.17) × 1012 copies gene / g dry sludge) with a total relative abundance of 18.51 %. During 258 days of operation, the contribution of anammox to nitrogen removal gradually increased to 68.8 %. The total nitrogen in the effluent decreased to 8.84 mg/L with a total nitrogen removal efficiency of 76.4 % under a carbon/nitrogen ratio of 3. This paper proposes a novel way to rapidly achieve mainstream partial denitrification anammox via inoculation with side-stream mature partial nitritation anammox biofilm. This method achieves advanced nitrogen removal from municipal wastewater, even under low carbon/nitrogen ratios.

Insights into the roles of EDTA in enhancing the bioavailability of Fe(Ⅲ) and stabilizing the anammox granular sludge system

The adsorption and utilization of Fe(Ⅲ) can be impeded by precipitation in anaerobic reactors. In this study, we investigated whether the bioavailability of Fe(Ⅲ) can be enhanced by EDTA-Fe(Ⅲ), thereby improving the stability of anammox system. Fe(Ⅲ) and EDTA-Fe(Ⅲ) were added to two parallel up-flow anaerobic sludge blanket (UASB) reactors, respectively. After 186 days of operation, when the nitrogen loading rate (NLR) was 0.8 g-N/L/d, the nitrogen removal rate (NRR) of R2 was stable at 0.675 g-N/L/d, which was higher than that of R1 at 0.557 g-N/L/d. The anammox activity of R2 reached its peak in phase Ⅲ (158.55 ± 4.53 mg-N/g-VSS/d), while the anammox activity of R1 was only 28.37 ± 5.96 mg-N/g-VSS/d. Moreover, in phase Ⅱ-Ⅴ, the bioavailability of Fe(Ⅲ) in R2 was increased by 15.63%, 38.37%, 65.90%, and 39.63%, respectively, compared with R1. The results showed that EDTA-Fe(Ⅲ) can prevent precipitation encasing anammox granular sludge, which can enhance substrate transport and Fe(Ⅲ) adsorption utilization. High throughput sequencing suggested that EDTA-Fe(Ⅲ) could better increase the abundance of anammox bacteria (AnAOB). In conclusion, this research proved that EDTA could increase the bioavailability of Fe(Ⅲ) and thereby ensuring the stability of the reactors.

Rhizosphere-Associated Anammox Bacterial Diversity and Abundance of Nitrogen Cycle-Related Functional Genes of Emergent Macrophytes in Eutrophic Wetlands.

Rhizospheric microbial community of emergent macrophytes plays an important role in nitrogen removal, especially in the eutrophic wetlands. The objective of this study was to identify the differences in anammox bacterial community composition among different emergent macrophytes and investigate revealed the the main factors affecting on the composition, diversity, and abundance of anammox bacterial community. Results showed that the composition, diversity, and abundance of the anammox community were significantly different between the vegetated sediments of three emergent macrophytes and unvegetated sediment. The composition of the anammox bacterial community was different in the vegetated sediments of different emergent macrophytes. Also, the abundance of nitrogen cycle-related functional genes in the vegetated sediments was found to be higher than that in the unvegetated sediment. Canonical correspondence analysis (CCA) and structural equation models analysis (SEM) showed that salinity and pH were the main environmental factors influencing the composition and diversity of the anammox bacterial community and NO2--N indirectly affected anammox bacterial community diversity by affecting TOC. nirK-type denitrifying bacteria abundance had significant effects on the bacterial community composition, diversity, and abundance of anammox bacteria. The community composition of anammox bacteria varies with emergent macrophyte species. The rhizosphere of emergent macrophytes provides a favorable environment and promotes the growth of nitrogen cycling-related microorganisms that likely accelerate nitrogen removal in eutrophic wetlands.

Functional differentiation of size-fractionated biomass in the mixotrophic mainstream UASB-anammox process

The soluble organic matter in sewage is one of the major obstacles to the stable operation of mainstream anammox, which would induce the excessive proliferation of heterotrophic bacteria. Given its excellent volumetric nitrogen removal rate (>2.0 kg N m−3 d−1) in mainstream treatment at 15 °C, the physicochemical properties and microbial ecology of size-fractionated aggregates in mixotrophic anammox-UASB system were investigated to develop strategies for population management. The presence of glucose or acetate (COD/N = 1.0) decreased the contribution of anammox by approximately 30 %, thereby causing the increase of effluent TN concentrations to over 12 mg N L−1, in which NH4+-N accounted for ∼85 %. Interestingly, the relative abundance of anammox bacteria were increased from 1.0 % in flocs (<0.2 mm) to 34.9 % in big granules (>0.8 mm) of the acetate-fed reactor, while the abundance of denitrifying bacteria was decreased from 74.0 % in flocs to 12.0 % in big granules. Similar trend was also observed for the glucose-fed reactor. As a result, the expressions of anammox functional genes, specific anammox activity, extracellular polymeric substances and heme c contents were all increased with the increase of particle sizes. Notably, in contrast to the glucose-fed biomass, the acetate-fed biomass showed significant potential of denitratation. Accordingly, the screen with a size of around 0.2 mm may be an effective tool to uncouple the retention times of denitrifying bacteria and anammox bacteria. These results provided direct evidences for functional differentiation of size-fractionated biomass and would guide us to balance their functions for a satisfactory effluent quality.

Cultivation of the coupling bacteria for simultaneous autotrophic nitrogen and sulfur removal and its remediation effect on the river sediment

The coupling bacteria for simultaneous autotrophic nitrogen and sulfur removal was cultivated by supplying sulfide to an Anammox biofilter treating low-strength wastewater. The results showed that sulfide-driven autotrophic denitrification (SAD) was successfully induced, and the total nitrogen (TN) removal increased from 83.0% to 94.4% when the sulfide concentration was increased to 25 mg L−1, with complete sulfide removal. Mass balance analysis suggested that 30.5% of the generated nitrate was reduced to nitrite while the rest was converted to nitrogen gas. The relative abundance of Anammox bacteria (Candidatus Kuenenia) increased from 9.16% to 18.8%, and the SAD bacteria (Thiobacillus) increased from 0.07% to 2.00%, both contributing collaboratively to nitrogen and sulfur removal. The coupling bacteria demonstrated a significant remediation effect on river sediment, increasing the TN removal activity by 10 times with a sludge addition ratio of 1:20. The results provide indications for enhancing the nitrogen and sulfur cycle in aquatic environments.

Optimization of two CSTRs using granular sludges dominated by Ca. Jettenia asiatica and Ca. Brocadia sinica

Two CSTRs using granules dominated by Ca. Jetteni asiatica (R1) and Ca. Brocadia sinica (R2) were operated depending on influent T-N concentrations and HRT. R1 achieved the highest NRR of 1.64 kgN/m3/day at HRT 8 h and T-N 600 mg/L, while R2 obtained the highest NRR of 2.05 kgN/m3/day at HRT 4 h and T-N 400 mg/L. The both reactors achieved high performance in high T-N concentration with the increasing of HRT in relatively short time. The sufficient T-N concentration and favorable short HRT were giving significant effects in promoting biomass increment and maintaining high removal in R1 and R2. In R1, granules larger than 2 mm accounted for over 60 %, while in R2 granules in the range of 1-2 mm comprised approximately 60 %. Granules in R1 were relatively harder and denser, and the surface of granules in R1 appeared rough, whereas the surface of granules in R2 seemed smoother. The abundance of anammox bacteria were much improved in both R1 and R2, operating under optimal operational conditions, showed significant improvement. The distribution of Ca. Brocadia sinica increased from 2.6 % to 42.0 % for R1 and from 9.1 %, to 90.5 % for R2, while there was little change in Ca. Jettenia asiatica. In this study, while the optimal HRT and nitrogen concentration as influent varied depending on the dominant anammox bacteria and granule characteristics in the inoculum, Ca. Brocadia sinica appears to play a significant role in nitrogen removal.

Enhanced resuscitation of anammox granular sludge by adding folate: A perspective from the growth factor

Quick resuscitation of preserved anammox granular sludge (AnGS) is crucial for its engineering applications. In this study, the stimulation effect and its mechanism of folate addition on resuscitation of AnGS after the long-term cryopreservation were investigated. The folate addition was found to enhance the recovery of AnGS activity to 76.4% of the original level on the 8th day, which was 28.1% higher than the folate-free group (CK). The folate addition could also promote the community recovery of AnGS, in which the live cells and abundance of anammox bacteria (AnAOB) were 10.2% and 14.0% higher than those in the CK in the early phase of resuscitation. Besides, the folate addition was revealed to stimulate the AnAOB recovery of AnGS, with higher activity and cell number by 58.7% and 40.9% than those in the CK. Furthermore, the mechanism of folate stimulation was proposed on the resuscitation of preserved AnGS. The exogenous folate addition could enhance the CO2 fixation capacity of AnAOB, which further accelerated both activity and cell number recovery of AnAOB, leading to the strong stimulation effect on the resuscitation of AnGS. These findings could offer valuable insights for optimizing and innovating the preservation technology of AnGS.

Partial denitrification-anammox granular sludge domesticated from high-strength anammox granules and the high-efficiency performance in treating low-nitrogen wastewater

Partial denitrification (PD) is an effective approach to supply nitrite for the anaerobic ammonium oxidation (anammox) reaction, and the PD-anammox process can achieve nearly 100 % nitrogen removal when denitratation, denitritation and anammox processes are well balanced. However, most of the previous studies initiated the PD-anammox process by a mixed inoculation of denitrification and anammox sludges, leading to low anammox bacteria abundance and a risk of unstable operation in the long-term. To address this, this study used high-strength anammox granules as seed sludge for rapid PD-anammox process start-up. During the continuous operation, nitrogen removal efficiencies of 97.6 ± 1.6 % and 91.0 ± 2.0 % were attained under influent conditions of 159.4 ± 3.4 mg N/L and 78.1 ± 3.5 mg N/L, respectively. In addition, the nitrite conversion rate of the sludge reached 5.34 ± 0.37 g N/g VSS/d during the operation, and the anammox activity was stable at 0.27–0.41 g N/g VSS/d, indicating a synergistic PD-anammox relationship. Furthermore, PD bacteria were efficiently enriched in the reactor within a short period of time, with Thauera accounting for 7.6 % of the relative abundance. Notably, the abundances of dominating anammox bacteria, Ca. Brocadia and Ca. Kuenenia were 16.6 % and 4.9 %, respectively, which were among the highest of the reported PD-anammox processes. High anammox microbial abundance is conducive to ensuring the dominance and stability of the anammox reaction, enabling efficient nitrite conversion and nitrogen removal throughout the continuous operation. Finally, nitrogen removal pathways based on mass balance were proposed to clarify the fate of different nitrogen compounds in the PD-anammox system.

Quantitative effect of adding percentages of anammox granules on the start-up process and microbial community analysis

The anaerobic ammonium oxidation (anammox) process is challenging due to its long start-up duration and high demand for mature anammox seed sludge. However, adding a small amount of anammox sludge to the inoculum can be a reasonable solution. This study investigated the effect of adding percentage of anammox granules (0, 1, 2, 4, and 8%) in the seed sludge on the anammox start-up process. The anammox process was achieved in all five reactors after 55, 6, 5, 3 and 0 days. Increasing the adding percentage effectively shortened the duration of lag phase and cell lysis, but had little effect on the final nitrogen removal performance, except for 4% adding percentage. Families of Brocadiaceae, Burkholderiaceae, Ignavibacteriaceae, SJA-28, and Rhodocyclaceae were dominant, with a core microbiota of eight operational taxonomic unites (OTUs), and Candidatus Brocadia fulgida became the dominant anammox species. Seven synergistic members with anammox bacteria were identified by correlation network analysis. Major potential functional groups involved in C and N cycle were also observed by FAPROTAX. Together with the qPCR and sequencing results, it was suggested that more than 2% of adding percentages would result in a short lag phase, rapid growth rate in elevation stage, high final performances, and anammox bacteria abundance comparable to that in the anammox seed sludge. This crucial finding indicated the feasibility of economical and rapid start-up of the anammox process with a minimum amount of anammox seed sludge.

Performance optimization and nitrogen removal mechanism of up-flow partial denitrification/anammox process

This study aimed to remediate the problems of sludge floating and uneven mass transfer in up-flow partial denitrification/anammox (PDA) reactors and dissect the nitrogen removal mechanism. Two up-flow PDA reactors were operated, whereby in R1 combined biological carriers were added, while in R2 mechanical stirring was applied, the reactors were inoculated with PD sludge and anammox sludge. Results showed the TN removal rates at the end of the operation were 89% (R1) and 92% (R2). The addition of both strategies suppressed the occurrence of sludge upwelling and deterioration of settling performance, even when the granule diameter of the granular zone in R1 and R2 reached 1.921 and 2.006 mm, respectively. 16SrRNA sequencing revealed R1 had a higher abundance of anammox bacteria (AAOB, 14.53%-R1, 9.06%-R2, respectively), and R2 had a higher quantity of denitrifying bacteria (61.92%-R1, 67.11%-R2, respectively). And the nitrogen removal was contributed by anammox and denitrification in combination, with contributions of 82.17%, 17.83% (R1), and 85.07%, 14.93% (R2), respectively. In summary, both strategies prevented sludge flotation and uneven nitrogen mass transfer. However, mechanical agitation had a more substantial positive effect on the performance of PDA than the addition of biocarriers because it achieved a more adequate mass transfer.

Microbial interactions play a keystone role in rapid anaerobic ammonium oxidation sludge proliferation and biofilm formation

Two mature anaerobic ammonium oxidation (anammox) consortia with high/low relative abundance of anammox bacteria were inoculated for the rapid sludge proliferation and biofilm formation in this study, named up-flow anaerobic sludge blanket reactor (UASB1) (high) and UASB2 (low), respectively. Results showed that the nitrogen removal efficiency of UASB2 reached 90.94% after the 120-day operation, which was 13% higher than that of UASB1. Moreover, its biomass amounts were 22.18% (biofilm) and 40.96% (flocs) higher than that of UASB1, respectively. Ca. Kuenenia possessed relative abundances of 29.32% (flocs), 27.42% (biofilm) and 31.56% (flocs), 35.20% (biofilm) in the UASB1 and UASB2, respectively. The relative abundances of genes involved in anammox transformation (hzs, nir) and carbon metabolism (fdh, lgA/B/C, acs) were higher in the UASB2, indicating that Ca. Kuenenia might produce acetate and glycogen to enhance microbial interactions. These findings emphasized the importance of microbial interactions in anammox sludge proliferation and biofilm formation.

Implemented impediment of extracellular electron transfer–dependent anammox process :Unstable nitrogen removal efficiency and decreased abundance of anammox bacteria

The present study investigates the extracellular electron transfer (EET)–dependent anammox process as a promising approach for sustainable wastewater treatment. The study examines the performance and metabolic pathway of the EET–dependent anammox process in comparison to the nitrite–dependent anammox process. The EET–dependent reactor successfully achieved nitrogen removal with a maximum removal efficiency of 93.2%, although it exhibited a lower ability to sustain high nitrogen removal load when compared to the nitrite–dependent anammox process, which poses opportunity and challenge for ammonia–wastewater treatment under applied voltage conditions. Nitrite was identified as a critical factor responsible for the changes in microbial community structure, resulting in a significant reduction in nitrogen removal load in the absence of nitrite. The study further suggests that the Candidatus Kuenenia species could dominate the EET–dependent anammox process, while nitrifying and denitrifying bacteria also contribute to the nitrogen removal in this system.

Performance changes in the anammox process under the stress of rare-earth element Ce(III) and the evolution of microbial community and functional genes

The high Ce(III) content in ionic rare-earth tailings wastewater has hindered the application of anammox process in this field. Here, the effect of Ce(III) on the performance of anammox processes was investigated, and the evolution of microbial communities and functional genes was explored using metagenomic sequencing. The results showed that the reactor nitrogen removal rate decreased when the Ce(III) concentration reached 25 mg/L, although ammonia nitrogen removal (92.31%) and nitrogen removal efficiency (81.33%) remained at a high level; however, both showed a significant decreasing trend. The relative abundance of anammox bacteria increased continuously from P1–P5, reaching 48.81%, whereas the relative abundance of Candidatus jettenia reached 33.71% at P5, which surpassed that of Candidatus brocadia as the most abundant anammox bacteria, and further analysis of functional genes and metabolic pathways revealed that Candidatus brocadia was richer in biochemical metabolic genes, whereas Candidatus jettenia had richer efflux genes.

Biological carbon promotes the recovery of anammox granular sludge after starvation

This article adopts the strategy of adding biochar and increasing HRT to accelerate the performance and particle morphology recovery of anaerobic ammonia oxidation granular sludge stored at room temperature for 68 days. The results showed that biochar accelerated the death of heterotrophic bacteria, shortened the cell lysis and lag period of the recovery process by 4 days, and it only took 28 days for the nitrogen removal performance of the reactor to recover to the original level, and 56 days for re-granulation. Biochar promoted the secretion of EPS (56.96 mg gVSS−1), and the sludge volume and nitrogen removal performance of the bioreactor remain stable. Biochar also accelerated the growth of Anammox bacteria. The abundance of Anammox bacteria in the biochar reactor reached 38.76% on the 28th day. The high abundance of functional bacteria and the optimized community structure of biochar made system (Candidatus_Kuenenia: 38.30%) more risk-resistant than control reactor.

Microbial community structure and nitrogen conversion rate of size-fractionated granules in partial denitrification and anammox reactor

Granule-based partial denitrification and anammox (PDA) process is affected by microbial community. To reveal how the nitrogen conversion rate varies with microbial composition caused by the granule size, PDA granules were divided into five sizes (<0.2, 0.2–0.5, 0.5–0.9, 0.9–1.6, and 1.6–2.0 mm). The abundance of anammox bacteria (dominated by Candidatus Brocadia) increased with particle size and peaked at 14.6% for 0.9–1.6 mm. In contrast, the abundance of denitrifiers (dominated by Thauera) decreased from 83.3% to 23.5% when granule size increased from <0.2 mm to 0.5–0.9 mm, but increased to 48.1% with further increases in particle size to 1.6–2.0 mm. The nitrogen conversion rate was affected by the microbial composition in granules. Nitrogen was autonomously removed in the granules of 0.9–2.0 mm. However, nitrite was accumulated in granules of <0.9 mm. Nitrite cross-feeding occurred inside and between granules. The findings provide a reference for the regulation of granule-based PDA systems.

Achieving advanced nitrogen removal from low-carbon municipal wastewater using partial-nitrification/anammox and endogenous partial-denitrification/anammox

To achieve advanced nitrogen removal from low-carbon wastewater, a partial-nitrification/anammox and endogenous partial-denitrification/ anammox (PN/A-EPD/A) process was developed in a sequential batch biofilm reactor (SBBR). Advanced nitrogen was achieved with the effluent total nitrogen (TN) of 3.29 mg/L when the influent COD/TN and the TN were 2.86 and 59.59 mg/L, respectively. This was attributed to a stable PN/A-EPD/A, which was achieved through the integration of four strategies, including treating the inoculated sludge with free nitrous acid, inoculating anammox biofilm, discharging excess activated sludge and residual ammonium at the end of oxic stage. The 16S rRNA high-throughput sequencing results demonstrated that anammox bacteria coexisted with ammonia oxidizing bacteria, nitrite oxidizing bacteria, denitrifying glycogen accumulating organisms (DGAOs) and denitrifying phosphorus accumulating organisms (DPAOs) in biofilms. The abundance of anammox bacteria in the inner layer of the biofilm is higher, while that of DGAOs and DPAOs is higher in the outer layer.

Linking morphological features to anammox communities in a partial nitritation and anammox (PN/A) biofilm reactor

Partial nitritation/anammox (PN/A) has been recognized as a cost-efficient process for wastewater nitrogen removal. The addition of carriers could help achieve biomass retention and enhance the treatment efficiency by forming the dense biofilm. However, accurately determining the abundance of anammox bacteria (AnAOB) to evaluate the biofilm development still remains challenging in practice without access to specialized facilities and experimental skills. In this study, we explored the feasibility of utilizing the morphological features of anammox biofilm as an indication of the biofilm development progression, and its correlation with microbial communities was also revealed. The time-series biofilms from an integrated fixed-film activated sludge (IFAS) system with stable PN/A performance were sampled representing the different biofilm development stages. The biofilm morphological features including color and texture were respectively quantified by red (R) coordinate and Local binary pattern (LBP) descriptor via image processing. Hierarchy clustering analysis proved that the extracted morphological descriptors could well distinguish the different stages (colonization, succession, and maturation) of biofilm development. The microbial community dynamics of time-series anammox biofilms were investigated using the amplicon sequence variant (ASV) analysis. Candidatus Brocadia, as the typical AnAOB, dominated in the whole communities of 16.3%–20.0%, moreover, the biofilm development was found to be driven by distinct Brocadia species. Linear regression evidenced that the Brocadia abundance could be directly correlated to the value of R and LBP, and the total variation of microbial communities could be significantly explained by the morphological features via redundancy analysis. This study demonstrates a new way to monitor the biofilm development by extracting the visible features of anammox aggregates, which can help facilitate the automated control of anammox-based bioprocess.

Achieving robust and highly efficient nitrogen removal in a mainstream anammox reactor by introducing low concentrations of readily biodegradable organics.

In this study, an anammox reactor was operated to treat low-strength (NH4+ + NO2-, 25-35 mg/L) wastewater without (phase I) or with (phase II) readily biodegradable chemical oxygen demand (rbCOD). In phase I, although efficient nitrogen removal was achieved at the beginning, nitrate accumulated in the effluent after long-term operation (75 days), resulting in a decrease in the nitrogen removal efficiency to 30%. Microbial analysis revealed that the abundance of anammox bacteria decreased from 2.15 to 1.78%, whereas that of nitrite-oxidizing bacteria (NOB) increased from 0.14 to 0.56%. In phase II, rbCOD, in terms of acetate, was introduced into the reactor with a carbon/nitrogen ratio of 0.9. The nitrate concentration in the effluent decreased within 2 days. Advanced nitrogen removal was achieved in the following operation, with an average effluent total nitrogen of 3.4 mg/L. Despite the introduction of rbCOD, anammox pathway still dominated to the nitrogen loss. High-throughput sequencing indicated that high anammox abundance (2.48%) further supports its dominant position. The improvement in nitrogen removal was attributed to the enhanced suppression of NOB activity, simultaneous nitrate polishing through partial denitrification and anammox, and promotion of sludge granulation. Overall, the introduction of low concentrations of rbCOD is a feasible strategy for achieving robust and efficient nitrogen removal in mainstream anammox reactors.

Global variations and controlling factors of anammox rates.

Soil anammox is an environmentally-friendly way to eliminate reactive nitrogen (N) without generating nitrous oxide. Nevertheless, the current earth system models have not incorporated the anammox due to the lack of parameters in anammox rates on a global scale, limiting the accurate projection for N cycling. A global synthesis with 1212 observations from 89 peer-reviewed papers showed that the average anammox rate was 1.60 ± 0.17 nmol N g-1 h-1 in terrestrial ecosystems, with significant variations across different ecosystems. Wetlands exhibited the highest rate (2.17 ± 0.31 nmol N g-1 h-1 ), followed by croplands at 1.02 ± 0.09 nmol N g-1 h-1 . The lowest anammox rates were observed in forests and grasslands. The anammox rates were positively correlated with the mean annual temperature, mean annual precipitation, soil moisture, organic carbon (C), total N, as well as nitrite and ammonium concentrations, but negatively with the soil C:N ratio. Structural equation models revealed that the geographical variations in anammox rates were primarily influenced by the N contents (such as nitrite and ammonium) and abundance of anammox bacteria, which collectively accounted for 42% of the observed variance. Furthermore, the abundance of anammox bacteria was well simulated by the mean annual precipitation, soil moisture, and ammonium concentrations, and 51% variance of the anammox bacteria was accounted for. The key controlling factors for soil anammox rates differed from ecosystem type, e.g., organic C, total N, and ammonium contents in croplands, versus soil C:N ratio and nitrite concentrations in wetlands. The controlling factors in soil anammox rate identified by this study are useful to construct an accurate anammox module for N cycling in earth system models.