Communication leads to bacterial heterogeneous adaptation to changing conditions in partial nitrification reactor.

Recently, it is reported that bacterial communication coordinates the whole consortia to jointly resist the adverse environments. Here, we found the bacterial communication inevitably distinguished bacterial adaptation among different species in partial nitrification reactor under decreasing temperatures. We operated a partial nitrification reactor under temperature gradient from 30 °C to 5 °C and found the promotion of bacterial communication on adaptation of ammonia-oxidizing bacteria (AOB) was greater than that of nitrite-oxidizing bacteria (NOB). Signal pathways with single-component sensing protein in AOB can regulate more genes involved in bacterial adaptation than that with two-component sensing protein in NOB. The negative effects of bacterial communication, which were seriously ignored, have been highlighted, and Clp regulator downstream diffusible signal factor (DSF) based signal pathways worked as transcription activators and inhibitors of adaptation genes in AOB and NOB respectively. Bacterial communication can induce differential adaptation through influencing bacterial interactions. AOB inclined to cooperate with DSF synthesis bacteria as temperature declined, however, cooperation between NOB and DSF synthesis bacteria inclined to get weakening. According to the regulatory effects of signal pathways, bacterial survival strategies for self-protection were revealed. This study hints a potential way to govern niche differentiation in the microbiota by bacterial communication, contributing to forming an efficient artificial ecosystem.

Increases in the soil ammonia oxidizing phylotypes and their rechange due to long-term irrigation with wastewater.

Wastewater irrigation is a common practice for agricultural systems in arid and semiarid zones, which can help to overcome water scarcity and contribute with nutrient inputs. Ammonia-oxidizing bacteria (AOB) and archaea (AOA) are key in the transformation of NH4+-N in soil and can be affected by variations in soil pH, EC, N and C content, or accumulation of pollutants, derived from wastewater irrigation. The objective of this study was to determine the changes in the ammonia oxidizing communities in agricultural soils irrigated with wastewater for different periods of time (25, 50, and 100 years), and in rainfed soils (never irrigated). The amoA gene encoding for the catalytic subunit of the ammonia monooxygenase was used as molecular reporter; it was quantified by qPCR and sequenced by high throughput sequencing, and changes in the community composition were associated with the soil physicochemical characteristics. Soils irrigated with wastewater showed up to five times more the abundance of ammonia oxidizers (based on 16S rRNA gene relative abundance and amoA gene copies) than those under rainfed agriculture. While the amoA-AOA: amoA-AOB ratio decreased from 9.8 in rainfed soils to 1.6 in soils irrigated for 100 years, indicating a favoring environment for AOB rather than AOA. Further, the community structure of both AOA and AOB changed during wastewater irrigation compared to rainfed soils, mainly due to the abundance variation of certain phylotypes. Finally, the significant correlation between soil pH and the ammonia oxidizing community structure was confirmed, mainly for AOB; being the main environmental driver of the ammonia oxidizer community. Also, a calculated toxicity index based on metals concentrations showed a correlation with AOB communities, while the content of carbon and nitrogen was more associated with AOA communities. The results indicate that wastewater irrigation influence ammonia oxidizers communities, manly by the changes in the physicochemical environment.

Asymmetries among soil fungicide residues, nitrous oxide emissions and microbiomes regulated by nitrification inhibitor at different moistures.

Carbendazim residue has been widely concerned, and nitrous oxide (N2O) is one of the dominant greenhouse gases. Microbial metabolisms are fundamental processes of removing organic pollutant and producing N2O. Nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) can change soil abiotic properties and microbial communities and simultaneously affect carbendazim degradation and N2O emission. In this study, the comprehensive linkages among carbendazim residue, N2O emission and microbial community after the DMPP application were quantified under different soil moistures. Under 90% WHC, the DMPP application significantly reduced carbendazim residue by 54.82% and reduced soil N2O emission by 98.68%. The carbendazim residue was negatively related to soil ammonium nitrogen (NH4+-N), urease activity, and ratios of Bacteroidetes, Thaumarchaeota and Nitrospirae under 90% WHC, and the N2O emission was negatively related to NH4+-N content and relative abundance of Acidobacteria under the 60% WHC condition. In the whole (60% and 90% WHC together), the carbendazim residue was negatively related to the abundances of nrfA (correlation coefficient = -0.623) and nrfH (correlation coefficient = -0.468) genes. The hao gene was negatively related to the carbendazim residue but was positively related to the N2O emission rate. The DMPP application had the promising potential to simultaneously reduce ecological risks of fungicide residue and N2O emission via altering soil abiotic properties, microbial activities and communities and functional genes. ENVIRONMENTAL IMPLICATION: Carbendazim was a high-efficiency fungicide that was widely used in agricultural production. Nitrous oxide (N2O) is the third most important greenhouse gas responsible for global warming. The 3, 4-dimethylpyrazole phosphate (DMPP) is an effective nitrification inhibitor widely used in agricultural production. This study indicated that the DMPP application reduced soil carbendazim residues and N2O emission. The asymmetric linkages among the carbendazim residue, N2O emission, microbial community and functional gene abundance were regulated by the DMPP application and soil moisture. The results could broaden our horizons on the utilizations DMPP in decreasing fungicide risks and N2O emission.

Soil recalcitrant but not labile organic nitrogen mineralization contributes to microbial nitrogen immobilization and plant nitrogen uptake.

Soil organic nitrogen (N) mineralization not only supports ecosystem productivity but also weakens carbon and N accumulation in soils. Recalcitrant (mainly mineral-associated organic matter) and labile (mainly particulate organic matter) organic materials differ dramatically in nature. Yet, the patterns and drivers of recalcitrant (MNrec) and labile (MNlab) organic N mineralization rates and their consequences on ecosystem N retention are still unclear. By collecting MNrec (299 observations) and MNlab (299 observations) from 57 15N tracing studies, we found that soil pH and total N were the master factors controlling MNrec and MNlab, respectively. This was consistent with the significantly higher rates of MNrec in alkaline soils and of MNlab in natural ecosystems. Interestingly, our analysis revealed that MNrec directly stimulated microbial N immobilization and plant N uptake, while MNlab stimulated the soil gross autotrophic nitrification which discouraged ammonium immobilization and accelerated nitrate production. We also noted that MNrec was more efficient at lower precipitation and higher temperatures due to increased soil pH. In contrast, MNlab was more efficient at higher precipitation and lower temperatures due to increased soil total N. Overall, we suggest that increasing MNrec may lead to a conservative N cycle, improving the ecosystem services and functions, while increasing MNlab may stimulate the potential risk of soil N loss.

Effect of initial ammonium concentration on a one-stage partial nitrification/anammox biofilm system: Nitrogen removal performance and the microbial community.

One-stage partial nitrification coupled with anammox (PN/A) technology effectively reduces the energy consumption of a biological nitrogen removal system. Inhibiting nitrite-oxidizing bacteria (NOB) is essential for this technology to maintain efficient nitrogen removal performance. Initial ammonium concentration (IAC) affects the degree of inhibited NOB. In this study, the effect of the IAC on a PN/A biofilm was investigated in a moving bed biofilm reactor. The results showed that nitrogen removal efficiency decreased from 82.49% ± 1.90% to 64.57% ± 3.96% after the IAC was reduced from 60 to 20 mg N/L, while the nitrate production ratio increased from 13.87% ± 0.90% to 26.50% ± 3.76%. NOB activity increased to 1,133.86 mg N/m2/day after the IAC decreased, approximately 4-fold, indicating that the IAC plays an important inhibitory role in NOB. The rate-limiting step in the mature biofilm of the PN/A system is the nitritation process and is not shifted by the IAC. The analysis of the microbial community structure in the biofilm indicates that the IAC was the dominant factor in changes in community structure. Ca. Brocadia and Ca. Jettenia were the main anammox bacteria, and Nitrosomonas and Nitrospira were the main AOB and NOB, respectively. IAC did not affect the difference in growth between Ca. Brocadia and Ca. Jettenia. Thus, modulating the IAC promoted the PN/A process with efficient nitrogen removal performance at medium to low ammonium concentrations.

Unveiling unique microbial nitrogen cycling and nitrification driver in coastal Antarctica.

Largely removed from anthropogenic delivery of nitrogen (N), Antarctica has notably low levels of nitrogen. Though our understanding of biological sources of ammonia have been elucidated, the microbial drivers of nitrate (NO3-) cycling in coastal Antarctica remains poorly understood. Here, we explore microbial N cycling in coastal Antarctica, unraveling the biological origin of NO3- via oxygen isotopes in soil and lake sediment, and through the reconstruction of 1968 metagenome-assembled genomes from 29 microbial phyla. Our analysis reveals the metabolic potential for microbial N2 fixation, nitrification, and denitrification, but not for anaerobic ammonium oxidation, signifying a unique microbial N-cycling dynamic. We identify the predominance of complete ammonia oxidizing (comammox) Nitrospira, capable of performing the entire nitrification process. Their adaptive strategies to the Antarctic environment likely include synthesis of trehalose for cold stress, high substrate affinity for resource utilization, and alternate metabolic pathways for nutrient-scarce conditions. We confirm the significant role of comammox Nitrospira in the autotrophic, nitrification process via 13C-DNA-based stable isotope probing. This research highlights the crucial contribution of nitrification to the N budget in coastal Antarctica, identifying comammox Nitrospira clade B as a nitrification driver.

Unveiling Microbial Nitrogen Metabolism in Rivers using a Machine Learning Approach.

Microbial nitrogen metabolism is a complicated and key process in mediating environmental pollution and greenhouse gas emissions in rivers. However, the interactive drivers of microbial nitrogen metabolism in rivers have not been identified. Here, we analyze the microbial nitrogen metabolism patterns in 105 rivers in China driven by 26 environmental and socioeconomic factors using an interpretable causal machine learning (ICML) framework. ICML better recognizes the complex relationships between factors and microbial nitrogen metabolism than traditional linear regression models. Furthermore, tipping points and concentration windows were proposed to precisely regulate microbial nitrogen metabolism. For example, concentrations of dissolved organic carbon (DOC) below tipping points of 6.2 and 4.2 mg/L easily reduce bacterial denitrification and nitrification, respectively. The concentration windows for NO3--N (15.9-18.0 mg/L) and DOC (9.1-10.8 mg/L) enabled the highest abundance of denitrifying bacteria on a national scale. The integration of ICML models and field data clarifies the important drivers of microbial nitrogen metabolism, supporting the precise regulation of nitrogen pollution and river ecological management.

Effect of salinity on biological nitrogen removal from wastewater and its mechanism.

The nitrogen discharge from saline wastewater will cause significant pollution to the environment. As a high-efficiency and low-cost treatment method, biological treatment has a promising application prospect in the removal of nitrogen from high-salt wastewater. However, the inhibitory effect of high salt on microorganisms increases the difficulty of its treatment. This review discusses the influence of salinity on the nitrogen removal process, considering both traditional and novel biological techniques. Common methods to enhance the effectiveness of biological nitrogen removal processes and their mechanisms of action in engineering practice and research, including sludge acclimation and inoculation of halophilic bacteria, are also introduced. An outlook on the future development of biological nitrogen removal processes for high-salt wastewater is provided to achieve environmentally friendly discharge of high-salt wastewater.

Effect of ciprofloxacin on the one-stage partial nitrification and anammox biofilm system: A multivariate analysis focusing on size-fractionated organic components.

The impact of ciprofloxacin (CIP) in the partial nitrification and anammox biofilm system was investigated by multivariate analysis, focusing on size-fractionated organic components. The CIP dose of 10 µg/L did not inhibit the total nitrogen (TN) removal efficiency, even though the abundance of antibiotic resistant genes (ARGs) (i.e., qnrD, qnrB, qnrA, qnrS, and arcA) was elevated. However, a gradual higher CIP dosing up to 100 µg/L inhibited the TN removal efficiency, while the abundance of ARGs was still increased. Moreover, both the TN removal efficiency and the abundant ARGs were dwindled at 470 µg/L of CIP. As the CIP dose increased from 0 to 100 µg/L, the abundance of high molecular weight (MW) fractions (14,000 to 87,000 Da; 1000 to 14,000 Da) and humic/fulvic acid-like components in the soluble extracellular polymeric substances (HSS) decreased, with more increases of low MW (84-1000 Da; less than 84 Da) fractions and soluble microbial by-products in soluble extracellular polymeric substances (SMPS). Continuously increasing the CIP dose till 470 µg/L, an inverse trend of the changes of these organic components was noted, along with clear reductions of the microbial diversity and richness, and the abundance of key functional genes responsible for nitrogen removal. The predominance of functional gene amoA (related with ammonia oxidizing bacteria) was more significantly with more distribution of SMPS with relatively low MW and less distribution of HSS with relatively high MW, as well as polymer decomposing microorganisms such as Bryobacteraceae and the unclassified Saprospirales.

Effect of sludge redistribution strategy on stability of partial nitrification-anammox process: Further exploration of the potential value of sludge.

The stability of the two-stage partial nitrification-anammox (PN/A) system was compromised by the inappropriate conversion of insoluble organic matter. In response, a sludge redistribution strategy was implemented. Through the redistribution of PN sludge and anammox sludge in the two-stage PN/A system, a transition was made to the Anammox-single stage PN/A (A-PN/A) system. This specific functional reorganization, facilitated by the rapid reorganization of microbial communities, has the potential to significantly decrease the current risk of suppression. The results of the study showed that implementing the sludge redistribution strategy led to a substantial enhancement in the total nitrogen removal rate (TNRR) by 87.51%, accompanied by a significant improvement of 34.78% in the chemical oxygen demand removal rate (CRR). Additionally, this approach resulted in a remarkable two-thirds reduction in the aeration requirements. High-throughput sequencing revealed that the strategy enriched anammox and ammonia-oxidizing bacteria while limiting denitrifying bacteria, as confirmed by quantitative polymerase chain reaction analysis. Furthermore, the principal component analysis revealed that the location and duration of aeration had direct and indirect effects on functional gene expression and the evolution of microbial communities. This study emphasizes the potential benefits of restructuring microbial communities through a sludge redistribution strategy, especially in integrated systems that encounter challenges with suppression.

The dynamic features and microbial mechanism of nitrogen transformation for hydrothermal aqueous phase as fertilizer in dryland soil.

Hydrothermal aqueous phase (HAP) contains abundant organics and nutrients, which have potential to partially replace chemical fertilizers for enhancing plant growth and soil quality. However, the underlying reasons for low available nitrogen (N) and high N loss in dryland soil remain unclear. A cultivation experiment was conducted using HAP or urea to supply 160 mg N kg-1 in dryland soil. The dynamic changes of soil organic matters (SOMs), pH, N forms, and N cycling genes were investigated. Results showed that SOMs from HAP stimulated urease activity and ureC, which enhanced ammonification in turn. The high-molecular-weight SOMs relatively increased during 5-30 d and then biodegraded during 30-90 d, which SUV254 changed from 0.51 to 1.47 to 0.29 L-1 m-1. This affected ureC that changed from 5.58 to 5.34 to 5.75 lg copies g-1. Relative to urea, addition HAP enhanced ON mineralization by 8.40 times during 30-90 d due to higher ureC. It decreased NO3-N by 65.35%-77.32% but increased AOB and AOA by 0.25 and 0.90 lg copies g-1 at 5 d and 90 d, respectively. It little affected nirK and increased nosZ by 0.41 lg copies g-1 at 90 d. It increased N loss by 4.59 times. The soil pH for HAP was higher than that for urea after 11 d. The comprehensive effects of high SOMs and pH, including ammonification enhancement and nitrification activity inhibition, were the primary causes of high N loss. The core idea for developing high-efficiency HAP fertilizer is to moderately inhibit ammonification and promote nitrification.

A novel derivative synchronous fluorescence method for the rapid, non-destructive and intuitive differentiation of denitrifying bacteria.

It is challenging to differentiate bacteria residing in the same habitat by direct observation. This difficulty impedes the harvest, application and manipulation of functional bacteria in environmental engineering. In this study, we developed a novel method for rapid differentiation of living denitrifying bacteria based on derivative synchronous fluorescence spectroscopy, as exemplified by three heterotrophic nitrification-aerobic denitrification bacteria having the maximum nitrogen removal efficiencies greater than 90%. The intact bacteria and their living surroundings can be analyzed as an integrated target, which eliminates the need for the complex pre-processing of samples. Under the optimal synchronous scanning parameter (Δλ = 40 nm), each bacterium possesses a unique fluorescence spectral structure and the derivative synchronous fluorescence technique can significantly improve the spectral resolution compared to other conventional fluorescence methods, which enables the rapid differentiation of different bacteria through derivative synchronous fluorescence spectra as fast as 2 min per spectrum. Additionally, the derivative synchronous fluorescence technique can extract the spectral signals contributed by bacterial extracellular substances produced in the biological nitrogen removal process. Moreover, the results obtained from our method can reflect the real-time denitrification properties of bacteria in the biological nitrogen removal process of wastewater. All these merits highlight derivative synchronous fluorescence spectroscopy as a promising analytic method in the environmental field.

Impact of salinity and organic matter on the ammonia-oxidizing archaea and bacteria in treating hypersaline industrial wastewater: amoA gene abundance and ammonia removal contributions.

Studies published recently proposed that ammonia-oxidizing archaea (AOA) may be beneficial for hypersaline (salinity > 50 g NaCl L-1) industrial wastewater treatment. However, knowledge of AOA activity in hypersaline bioreactors is limited. This study investigated the effects of salinity, organic matter, and practical pickled mustard tuber wastewater (PMTW) on AOA and ammonia-oxidizing bacteria (AOB) in two sequencing batch biofilm reactors (SBBRs). Results showed that despite observed salinity inhibition (p < 0.05), both AOA and AOB contributed to high ammonia removal efficiency at a salinity of 70 g NaCl L-1 in the two SBBRs. The ammonia removal efficiency of SBBR2 did not significantly differ from that of SBBR1 in the absence of organic matter (p > 0.05). Batch tests and quantitative real-time PCR (qPCR) reveal that salinity and organic matter inhibition resulted in a sharp decline in specific ammonia oxidation rates and amoA gene copy numbers of AOA and AOB (p < 0.05). AOA demonstrated higher abundance and more active ammonia oxidation activity in hypersaline and high organic matter environments. Salinity was positively correlated with the potential ammonia oxidation contribution of AOA (p < 0.05), resulting in a potential transition from AOB dominance to AOA dominance in SBBR1 as salinity levels rose. Moreover, autochthonous AOA in PMTW promoted the abundance and ammonia oxidation activities of AOA in SBBR2, further elevating the nitrification removal efficiency after feeding the practical PMTW. AOA demonstrates greater tolerance to the challenging hypersaline environment, making it a valuable candidate for the treatment of practical industrial wastewater with high salinity and organic content.

Blue-light irradiation induced partial nitrification.

The role of ray radiation from the sunlight acting on organisms has long-term been investigated. However, how the light with different wavelengths affects nitrification and the involved nitrifiers are still elusive. Here, we found more than 60 % of differentially expressed genes (DEGs) in nitrifiers were observed under irradiation of blue light with wavelengths of 440-480 nm, which were 13.4 % and 20.3 % under red light and white light irradiation respectively. Blue light was more helpful to achieve partial nitrification rather than white light or red light, where ammonium oxidization by ammonia-oxidizing archaea (AOA) with the increased relative abundance from 8.6 % to 14.2 % played a vital role. This was further evidenced by the enhanced TCA cycle, reactive oxygen species (ROS) scavenge and DNA repair capacity in AOA under blue-light irradiation. In contrast, nitrite-oxidizing bacteria (NOB) was inhibited severely to achieve partial nitrification, and the newly discovered encoded blue light photoreceptor proteins made them more sensitive to blue light and hindered cell activity. Ammonia-oxidizing bacteria (AOB) expressed genes for DNA repair capacity under blue-light irradiation, which ensured their tiny impact by light irradiation. This study provided valuable insights into the photosensitivity mechanism of nitrifiers and shed light on the diverse regulatory by light with different radiation wavelengths in artificial systems, broadening our comprehension of the nitrogen cycle on earth.

Looking deeper into the effects of scouring and aeration on membrane aerated biofilms: Analysis of nitrogen conversion, oxygen profiles and nitrous oxide emissions.

This study investigated the effects of aeration and scouring strategies on the performance of Membrane Aerated Biofilm Reactors (MABRs) and the distribution of oxygen and nitrous oxide in the biofilm. Four flat sheet MABRs were operated with synthetic feed under different conditions: two with intermittent aeration (iMABR) and two with continuous aeration (cMABR). Scouring was induced by bubbling dinitrogen gas through the reactor bulk at low and high frequencies (LF and HF). In the iMABRs, a partial nitritation biofilm initially developed, but the biofilm adapted to the aeration strategy over time and became nitrifying. The cMABRs directly developed a nitrifying biofilm without a significant phase of partial nitritation. Limiting oxygen availability improved the overall performance with regards to total nitrogen (TN) removal by providing a better environment for anaerobic ammonium oxidation (Anammox) while limiting complete nitrification. Oxygen profiles were measured in the iMABR over time at different biofilms depths, showing that intermittent aeration led to various oxygen concentrations and temporal variations in the oxygen availabilities at different depths of the biofilm. Also, N2O emissions from the MABRs differed greatly between the different systems, but still remained lower compared to other reactor configurations for nitrogen removal, making the MABR technology a worthy alternative. The results showed large differences between the operating strategies of the MABRs and can help to gain more insight into the specific properties of MABRs for nitrogen removal.

Understanding vermicompost and organic manure interactions: impact on toxic elements, nitrification activity, comammox Nitrospira inopinata, and archaea/bacteria.

Vermicompost is a substantial source of nutrients, promotes soil fertility, and maintains or increases soil organic matter levels. Potentially toxic elements (PTEs) in vermicompost impact on nitrification activity. However, it is yet unknown how vermicompost affects nitrifying bacteria and archaea, comammox Nitrospira inopinata (complete ammonia oxidizers), net nitrification rates (NNRs), and PTEs. The effects of vermicompost application on NNRs, potential nitrification rates (NPs), PTEs, and the abundances of comammox N. inopinata bacteria, nitrite-oxidizing bacteria (NOB), and ammonia-oxidizing bacteria (AOB)/archaea (AOA) were studied. NNRs and NPs were significantly higher (p < 0.05) in fresh cow-dung vermicompost (stored for 40 days) as compared with other organic manure. The level of PTEs (Cu2+, Fe2+, Pb2+, Cd2+, and Zn2+) was significantly lower (p < 0.05) in vermicompost as compared with compost of waste material with Trichoderma and cow dung. Comammox N. inopinata, NOB, AOB, and AOA were significantly higher (p < 0.05) in stored cow-dung vermicompost (more than 1 year) as compared with other organic manure. The results of the scatterplot matrix analysis suggested that Fe2+, total nitrogen (TN), soil organic carbon (SOC), and total carbon (TC) were linearly correlated (p < 0.001) with NNRs and NPs in vermicompost and organic manure. Similarly, comammox N. inopinata bacteria, NOB, AOB, and AOA were linearly correlated (p < 0.001) with NNR and NP. These results indicated that vermicompost promoted nitrification activity by increasing microbial diversity and abundance, supplying nutrients and organic matter for microbial growth, and facilitating complex microbial interactions. It may be concluded that the influence of vermicompost, which played a great role in PTE concentration reduction, increased chemical, and biological properties, increased the growth rate of nitrifying bacteria/archaea and the nitrogen cycle.

Fungal community diversity and their contribution to nitrogen cycling in in-situ aerated landfills: Insights from field and laboratory studies.

The application of in-situ aeration technology in landfills has been reported to promote fungal growth, but the community diversity and function of fungi in the aerated landfill system remain unknown. This study firstly investigated an in-situ aerated remediation landfill site to characterize the fungal community diversity in refuse. And to further reveal the fungal involvement in the nitrogen cycling system, laboratory-scale simulated aerated landfill reactors were then constructed. The results in the aerated landfill site showed a significant correlation between fungal community structure and ammonia nitrogen content in the refuse. Dominant fungi in the fungal community included commonly found environmental fungi such as Fusarium, Aspergillus, Gibberella, as well as unique fungi in the aerated system like Chaetomium. In the laboratory-scale aerated landfill simulation experiments, the fungal system was constructed using bacterial inhibitor, and nitrogen balance analysis confirmed the significant role of fungal nitrification in the nitrogen cycling process. When ammonia nitrogen was not readily available, fungi converted organic nitrogen to nitrate, serving as the main nitrification mechanism in the system, with a contribution rate ranging from 62.71 % to 100 % of total nitrification. However, when ammonia nitrogen was present in the system, autotrophic nitrification became the main mechanism, and the contribution of fungal nitrification to total nitrification was only 15.96 %. Additionally, fungi were capable of directly utilizing nitrite for nitrate production with a rate of 4.65 mg L-1 d-1. This research article contributes to the understanding of the importance of fungi in the aerated landfill systems, filling a gap in knowledge.

The effect of nitrogen input on N2O emission depends on precipitation in a temperate desert steppe.

Nitrous oxide (N2O) is the third most important greenhouse gas, and can damage the atmospheric ozone layer, with associated threats to terrestrial ecosystems. However, to date it is unclear how extreme precipitation and nitrogen (N) input will affect N2O emissions in temperate desert steppe ecosystems. Therefore, we conducted an in-situ in a temperate desert steppe in the northwest of Inner Mongolia, China between 2018 and 2021, in which N inputs were combined with natural extreme precipitation events, with the aim of better understanding the mechanism of any interactive effects on N2O emission. The study result showed that N2O emission in this desert steppe was relatively small and did not show significant seasonal change. The annual N2O emission increased in a non-linear trend with increasing N input, with a much greater effect of N input in a wet year (2019) than in a dry year (2021). This was mainly due to the fact that the boost effect of high N input (on June 17th 2019) on N2O emission was greatly amplified by nearly 17-46 times by an extreme precipitation event on June 24th 2019. In contrast, this greatly promoting effect of high N input on N2O emission was not observed on September 26th 2019 by a similar extreme precipitation event. Further analysis showed that soil NH4+-N content and the abundance of ammonia oxidizing bacteria (amoA (AOB)) were the most critical factors affecting N2O emission. Soil moisture played an important indirect role in regulating N2O emission, mainly by influencing the abundance of amoA (AOB) and de-nitrification functional microorganisms (nosZ gene). In conclusion, the effect of extreme precipitation events on N2O emission was greatly increased by high N input. Furthermore, in this desert steppe, annual N2O flux is co-managed through soil nitrification substrate concentration (NH4+-N), the abundance of soil N transformation functional microorganisms and soil moisture. Overall, it was worth noting that an increase in extreme precipitation coupled with increasing N input may significantly increase future N2O emissions from desert steppes.

Contrasting response of comammox Nitrospira, ammonia oxidising bacteria, and archaea to soil pH and nitrogen inputs.

This study aimed to investigate the effect of soil pH change, and nitrogen amendment on ammonia oxidiser abundance and comammox Nitrospira community composition. The experimental design used soil mesocosms placed in a temperature-controlled incubator for 90 days. A Templeton silt loam was used as its physiochemical properties are typical of the region's dairy farms. The results showed that comammox Nitrospira clade B preferred the natural (pH 6.1-6.2) soil pH with no applied nitrogen. Furthermore, synthetic urine (N700) decreased the abundance of comammox Nitrospira clade B. This may have been because the large amounts of available ammonia in the N700 treatments inhibited the growth of comammox Nitrospira. These results suggest that while comammox Nitrospira clade B are present in New Zealand dairy farm soils, but their role in nitrification in the very high nitrogen environment under a urine patch in grazed pastures may be limited. Further research is needed to confirm this. In contrast to comammox, the AOB community (dominated by Nitrosospira) responded positively to the application of synthetic urine. The response was greatest in the high pH soil (7.1), followed by the natural and then the low pH (4.9) soils. This may be due to the difference in ammonia availability. At high pH, the ammonia/ammonium equilibrium favours ammonia production. Calculated ammonia availability in the N700 treatments accurately predicted the AOB amoA gene abundance. Interestingly, the AOA community abundance (which was predominantly made up of Thaumarchaeota group I.1b clade E) seemed to prefer the natural and high pH soils over the low pH. This may be due to the specific lineage of AOA present. AOA did not respond to the application of nitrogen.

Continuous planting of euhalophyte Suaeda salsa enhances microbial diversity and multifunctionality of saline soil.

Halophyte-based remediation emerges as a novel strategy for ameliorating saline soils, offering a sustainable alternative to conventional leaching methods. While bioremediation is recognized for its ability to energize soil fertility and structure, the complex interplays among plant traits, soil functions, and soil microbial diversity remain greatly unknown. Here, we conducted a 5-year field experiment involving the continuous cultivation of the annual halophyte Suaeda salsa in saline soils to explore soil microbial diversity and their relationships with plant traits and soil functions. Our findings demonstrate that a decline in soil salinity corresponded with increases in the biomass and seed yield of S. salsa, which sustained a consistent seed oil content of approximately 22% across various salinity levels. Significantly, prolonged cultivation of halophytes substantially augmented soil microbial diversity, particularly from the third year of cultivation. Moreover, we identified positive associations between soil multifunctionality, seed yield, and taxonomic richness within a pivotal microbial network module. Soils enriched with taxa from this module showed enhanced multifunctionality and greater seed yields, correlating with the presence of functional genes implicated in nitrogen fixation and nitrification. Genomic analysis suggests that these taxa have elevated gene copy numbers of crucial functional genes related to nutrient cycling. Overall, our study emphasizes that the continuous cultivation of S. salsa enhances soil microbial diversity and recovers soil multifunctionality, expanding the understanding of plant-soil-microbe feedback in bioremediation.IMPORTANCEThe restoration of saline soils utilizing euhalophytes offers a viable alternative to conventional irrigation techniques for salt abatement and soil quality enhancement. The ongoing cultivation of the annual Suaeda salsa and its associated plant traits, soil microbial diversity, and functionalities are, however, largely underexplored. Our investigation sheds light on these dynamics, revealing that cultivation of S. salsa sustains robust plant productivity while fostering soil microbial diversity and multifunctionality. Notably, the links between enhanced soil multifunctionality, increased seed yield, and network-dependent taxa were found, emphasizing the importance of key microbial taxa linked with functional genes vital to nitrogen fixation and nitrification. These findings introduce a novel understanding of the role of soil microbes in bioremediation and advance our knowledge of the ecological processes that are vital for the rehabilitation of saline environments.