Search Results (74)

Nitrous oxide (N₂O) is a major greenhouse gas, and terrestrial ecosystems are among the primary sources of its emissions. Biochar is recognized as an effective soil amendment for mitigating N₂O emissions, but its long-term residual effects and microbial mechanisms in subtropical plantations remain unclear. Therefore, this study evaluated the residual effects of Eucalyptus-derived biochar on soil N₂O emissions six years after a single application and explored associations with nitrogen cycle functional genes. A field experiment was conducted in a Eucalyptus plantation in northern Guangxi with biochar applied at six rates (0–6% w/w). Soil N₂O fluxes were measured in the fifth and sixth years (2022–2023); soil chemical parameters, soil enzyme activities, and N₂O-related microbial functional genes (amoA, nirK, nirS and nosZ) abundance were analyzed. Biochar application significantly reduced ammonium nitrogen content but enhanced nitrate nitrogen content. Urease, protease, and sucrase activities increased, while nitrate reductase, nitrite reductase, and hydroxylamine reductase activities decreased. Furthermore, quantitative analysis revealed substantial variations in functional gene abundances. The abundance of ammonia-oxidizing archaea (AOA-amoA) exhibited a unimodal response, whereas ammonia-oxidizing bacteria (AOB-amoA) showed a robust dose-dependent accumulation. Notably, annual N₂O emissions were suppressed by up to 35.2%, driven by a 3.4-fold increase in nosZ gene abundance and a significant reduction in the (nirK + nirS)/nosZ ratio. This mitigation was attributed to enhanced N₂O consumption by nosZ-harboring denitrifiers and reduced heterotrophic ammonia oxidation. Overall, these findings highlight the pivotal role of long-term organic amendments in steering nitrogen transformation pathways, providing a theoretical basis for sustainable soil management in subtropical plantations. Full article

Future climate models indicate an enhanced severity of regional drought and more frequent rewetting events, which may cause cascading impacts on the nitrogen cycle and nitrous oxide (N₂O) emissions, and the underlying microbial mechanism remains largely unknown. Here we conducted an incubation study on the impact of different soil moisture statuses on N₂O producers and N₂O reducers following the application of different fertilizer types (urea and manure) on a neutral vegetable soil. The different soil moisture treatments included 100% field capacity, drought, and rewetting (50% to 100% field capacity). Results showed that the N₂O emissions significantly decreased under drought conditions. Only ammonia-oxidizing archaea (AOA) and fungal nirK were well adapted to drought stress in the control soil. Different fertilizers modulated the resilience of the functional guilds. Ammonia-oxidizing bacteria (AOB), nirK-type denitrifying bacteria and nosZ clade (both I and II) showed significant resilience in both fertilized and non-fertilized soils in response to soil rewetting. Soil rewetting also changed the underlying microbial mechanisms of N₂O emissions. The results show a more significant negative relationship between N₂O emissions and nosZI clade at 100% field capacity, as well as nosZII clade after soil rewetting. We highlight the significant role of the nosZII clade following soil rewetting events, which might be one factor that led to relatively lower N₂O emissions compared to those at 100% field capacity. Our results provide new insights into developing mitigation strategies by fostering nosZII, which should be studied further in other cropland ecosystems or vegetable systems with frequent irrigation. Full article

Water scarcity is driving increased use of treated wastewater in agriculture while also leading to an increase in concerns about the presence of active pharmaceutical active compounds (PhACs) and their impact on soil ecosystems. This study provides novel field-scale evidence on the combined impact of tertiary-treated wastewater (TWW) irrigation and short-term tomato/wheat crop succession on soil microbial communities, nitrogen-cycling functional groups, and crop productivity. Over two consecutive years in southern Italy, TWW was compared with freshwater (FW) using integrated chemical, microbiological, and metagenomic approaches. TWW irrigation significantly increased tomato and wheat yields (+14% and +20%, respectively) without negatively affecting crop quality. Several PhACs were detected in soil and showed moderate accumulation under TWW, particularly sitagliptin and flecainide, which reached 10 ng/g. However, limited effects were observed in terms of total microbial abundance, nitrogen-cycle gene markers, or overall microbiome structure. The fungal population of Bionectria was found to be a potential biomarker since it was negatively affected by TWW (−56%). In contrast, time and crop succession emerged as the primary driver of microbial dynamics, inducing marked shifts in bacterial and fungal community composition and diversity, with wheat promoting higher diversity than tomato. Nitrogen-fixing bacteria were higher in tomato crop seasons. Ammonia oxidizing increased in the wheat crop season, while denitrifiers were more influenced by sampling time. These findings demonstrate that, under compliant treatment conditions, TWW reuse can enhance crop productivity with limited short-term ecological risks, supporting sustainable agricultural water management. Full article

In permanently submerged coastal wetlands, interactions between biogeochemical processes and microbial communities strongly influence greenhouse gas (GHG) fluxes. To improve our understanding of how redox-driven processes shape GHG dynamics in these ecosystems, we investigated the relationships among iron (Fe) pools, microbial dynamics, and the potential GHG production in subaqueous soils from an interdunal wetland in San Vitale Park (Italy), permanently submerged and affected by seasonal oscillations of the saline water table. Two subaqueous soil columns (WAS-2 and WAS-4), collected from similar settings, were analyzed. Surface layers of WAS-4 showed higher salinity and carbonate content, whereas WAS-2 was characterized by overall higher Fe concentrations. Distinct vertical distributions of organic matter and sulfur (S) were shown along depth. Laboratory incubations revealed that nitrous oxide (N₂O) production was up to ten times higher in WAS-2 than in WAS-4, with peaks in the top 13–14 cm, consistent with more active nitrification-denitrification in surface layers. Methane (CH₄) and carbon dioxide (CO₂) fluxes decreased with depth, reflecting reduced availability of labile carbon. Methanomicrobiales dominated CH₄-producing layers, indicating hydrogenotrophic methanogenesis, while amoA-carrying Nitrosomonadales and Thaumarchaeota, occurred in shallow, organic-rich layers where ammonia supported nitrification and denitrification. Denitrifiers mainly belonged to α- and β-Proteobacteria, consistent with their direct contribution to N₂O peaks. Spearman’s correlations showed N₂O positively correlated to sulfur and labile carbon (C), supporting denitrification under moderately reducing conditions. CH₄ and CO₂ positively correlated with organic C (Corg), total nitrogen (TN), and reactive Fe forms, reflecting redox-mediated microbial respiration and methanogenesis. Trace elements (B, Cr, Cu, Ni) acted as micronutrients or inhibitors depending on concentration. Canonical correspondence analysis indicated depth-structured links among gas fluxes, soil chemistry (Corg, TN, S/C, CaCO₃, P), and microbial distributions: surface layers, rich in labile C and nutrients, supported active bacteria and archaea involved in decomposition, nitrification, and denitrification, whereas deeper layers hosted oligotrophic archaea adapted to inorganic substrates. Overall, Fe pools appeared to be associated with soil processes relevant to GHG dynamics, although the extent of their regulatory role remains uncertain due to potential alterations of redox-sensitive Fe fractions during sample handling. These results contribute to broader efforts to predict GHG emissions in submerged wetland soils by linking redox stratification, inorganic chemistry, and microbial functional groups. Full article

Nutrient additions including nitrogen (N) and phosphorus (P) are widely considered as an important strategy for enhancing grassland productivity. However, the effects of these nutrients additions on soil nitrous oxide (N₂O) emissions and the underlying mechanisms remain debated. We conducted a two-year field experiment in an alpine grassland on Kunlun Mountain in northwestern China to assess the effects of N and P additions on N₂O emissions, in relation with nitrifying enzyme activity (NEA), denitrifying enzyme activity (DEA), and key functional genes abundance responsible for nitrification (amoA and Nitrobacter-like nxrA) and denitrification (narG, nirS, nirK and nosZ). Compared to the Control without nutrient addition (CK), N addition alone substantially increased cumulative N₂O emission (ƩN₂O) by 2.0 times. In contrast, P addition or combined N and P (N+P) addition did not significantly affect ƩN₂O, though both treatments significantly increased plant aboveground biomass. Such results indicate that P addition may mitigate N-induced N₂O emission, likely by reducing soil N availability through enhanced plant and microbial N uptake. Compared to CK, N or N+P addition significantly elevated NEA but did not affect DEA. Structural equation modeling (SEM) indicated that NEA was directly influenced by the gene abundances of ammonia-oxidizing bacteria (AOB) and Nitrobacter-like nxrA but not by ammonia-oxidizing archaea (AOA). However, SEM also revealed that soil environmental variables including soil temperature, pH, and water-filled pore space (WFPS) had a stronger direct influence on N₂O emissions than the abundances of nitrifiers. These results demonstrate that soil environmental conditions play a more significant role than functional gene abundances in regulating N₂O emissions following N and P additions in semi-arid alpine grasslands. This study highlights that the N+P application can potentially decrease N₂O emissions than N addition alone, while increasing productivity in the alpine grassland ecosystems. Full article

Reducing the generation of excess sludge and achieving resource recovery are crucial for enhancing the economic efficiency and environmental sustainability of wastewater treatment plants (WWTPs). This study utilizes ultrasonic cavitation technology to transform organic matter into excess sludge to achieve sludge reduction and carbon source recovery. To this end, we systematically investigated the effects of various ultrasonic cavitation conditions on sludge reduction, organic matter conversion, and denitrification efficiency. The results showed that the optimal sludge reduction effect occurs at an original mixed liquid suspended solids (MLSS) of 10 g/L, under neutral and non-aerated conditions, reaching 15.07%. Ultrasonic cavitation treatment significantly enhanced the conversion efficiency of organic matter in the sludge, greatly increasing the concentration of organic matter in the supernatant, with soluble chemical oxygen demand (SCOD) maintained around 900 mg/L, thereby significantly improving the denitrification process. Furthermore, through magnetic-nanoparticle mediated isolation (MMI) and metagenomic sequencing analysis, the dominant denitrifying bacteria and their functional genes that utilize organic matter in the supernatant of ultrasonically treated sludge as a carbon source were identified. Finally, long-term pilot-scale operations further validated the practical application potential of ultrasonic cavitation technology for excess sludge reduction and resource utilization. Full article

The widespread occurrence of nano-plastics (NPs) in aquatic environments poses emerging challenges to the pollutant removal performance and ecological stability of constructed wetlands (CWs). This study investigates the performance of calcium-modified (Ca-MBF) and manganese-modified basalt fiber (Mn-MBF) bio-nests as novel substrates to mitigate NP-induced inhibition of CWs. Laboratory-scale CWs were operated for 180 days to evaluate substrate-associated enzyme activities, microbial community structure, and functional gene profiles. Results showed that Mn-MBF bio-nests enhanced the activities of dehydrogenase (DHA), urease (UR), ammonia monooxygenase (AMO), nitrite oxidoreductase (NOR), nitrate reductase (NAR), nitrite reductase (NIR), and phosphatase (PST) by 86.2%, 65.5%, 127.0%, 62.8%, 131.5%, 65.3%, and 107.0%, respectively, compared with the control. In contrast, Ca-MBF bio-nests increased these enzyme activities by 48.6%, 53.5%, 67.0%, 30.6%, 95.0%, 45.3%, and 54.6%, respectively. MBF bio-nests also enhanced microbial diversity, enriched denitrifying and phosphorus-removing bacteria (e.g., Thauera, Plasticicumulans), and promoted extracellular polymeric substance secretion. Functional gene prediction indicated elevated abundances of nitrogen cycle-related genes, thereby enhancing nitrification, denitrification, and phosphorus removal processes. These synergistic effects collectively improved nitrification, denitrification, and phosphorus removal efficiency, with Mn-MBF showing superior performance. This study highlights MBF bio-nests as a sustainable strategy to enhance the resilience and long-term operational stability of CWs in environments impacted by nano-plastic pollution. Full article

The Sanniang Bay (SNB) and Dafeng River Estuary (DFR) in the Northern Beibu Gulf, China, are critical habitats for the Indo-Pacific humpback dolphin (Sousa chinensis). However, whether and how the decreased dissolved oxygen (DO) has happened in bottom seawater remains poorly understood. This study investigated DO depletion and microbial community responses using a multidisciplinary approach. High-resolution spatiotemporal sampling (16 stations across four seasons) was combined with functional annotation of prokaryotic taxa (FAPROTAX) to characterize anaerobic metabolic pathways and quantitative PCR (qPCR) targeting dsrA and dsrB genes to quantify sulfate-reducing bacteria. Partial least-squares path modeling (PLS-PM) was employed to statistically link environmental variables (seawater properties and nutrients) to microbial community structure. Results revealed pronounced bottom DO declining to 5.44 and 7.09 mg L⁻¹, a level approaching sub-optimal state (4.0–4.8 mg L⁻¹) in September. Elevated chlorophyll-a (Chl-a) near the SDH coincided with anaerobic microbial enrichment, including sulfate reducers (dsrA/dsrB abundance: SNB > DFR). PLS-PM identified seawater properties (turbidity, DO, pH) and nitrogen as key drivers of anaerobic taxa distribution. Co-occurrence network analysis further demonstrated distinct microbial modules in SNB (phytoplankton-associated denitrifiers) and DFR (autotrophic sulfur oxidizers, nitrogen fixation, and denitrification). These findings highlight how environmental factors drive decreased DO, reshaping microbial networks and threatening coastal ecosystems. This work underscores the need for regulating aquaculture/agricultural runoff to limit eutrophication-driven hypoxia and temporarily restrict human activities in SNB during peak hypoxia (September–October). Full article

The use of Auxenochlorella pyrenoidosa (formerly Chlorella pyrenoidosa) and its intracellular substances (ISs) to promote biofloc development has been extensively studied. To identify the key components of the ISs of A. pyrenoidosa that drive biofloc formation, algal-extracted polysaccharides (AEPSs) and algal-extracted proteins (AEPTs) were isolated from the ISs. In this study, we established four groups: ISs, AEPSs, AEPTs, and tap water (TW, control), to investigate the effects of AEPSs and AEPTs on biofloc formation dynamics, water quality parameters, and microbial community composition. The results indicated no significant differences were observed between the ISs and AEPSs groups during the cultivation period. AEPSs significantly enhanced flocculation efficiency, achieving a final floc volume of 60 mL/L. This enhancement was attributed to the selective promotion of floc-forming microbial taxa, such as Comamonas, which can secrete procoagulants like EPS, and Pseudomonas and Enterobacter, which have denitrification capabilities. Water quality monitoring revealed that both AEPSs and AEPTs achieved nitrogen removal efficiencies exceeding 50% in the biofloc system, with AEPSs outperforming AEPTs. This is closely related to the fact that the microorganisms with increased flocculation contain numerous nitrifying and denitrifying bacteria. So, the intracellular polysaccharides were the key component of the ISs of A. pyrenoidosa that drive biofloc formation. These findings provide critical insights into the functional roles of algal-derived macromolecules in biofloc dynamics and their potential applications in wastewater treatment. Full article

With the growing problem of global water pollution, nitrogen pollution has become a key factor affecting aquatic ecosystems and human health. The biological sponge iron system (BSIS) has gained attention as a research hotspot due to its efficient denitrification capability. This study focused on the changes in microbial community structure and the relative abundance and interrelationships of nitrogen cycle-related functional bacteria at different operational stages of the BSIS with a sponge iron (SFe) dosage of 90 g/L. The results showed that as the operation time of the reactor extended, the relative abundance of denitrifying genera such as Saccharimonadales, Arenimonas, and Acinetobacter significantly increased, while the relative abundance of Proteobacteria showed a trend of initial increase followed by a decrease. The relative abundance of nitrifying bacteria exhibited a more complex variation, whereas the abundance of denitrifying bacteria showed a continuous upward trend. In addition, there were complex interrelationships among different denitrifying bacteria, such as a positive correlation between Saccharimonadales and Acetobacteraceae, and a negative correlation between Rhodothermus and Pseudoxanthomonas. This study not only revealed the changes in the relative abundance and interrelationships of microbial communities and nitrogen cycle-related functional bacteria over time with an SFe dosage of 90 g/L, but also provided a new perspective for understanding the intrinsic mechanism of enhanced biological denitrification by sponge iron. These findings are of great significance for optimizing the operating parameters of the BSIS, improving denitrification efficiency, and promoting the practical application of this technology in the field of environmental engineering. Full article

Although nitric oxide (NO) production in bacteria has traditionally been associated with denitrification or stress responses in model or symbiotic organisms, functionally validated L-arginine-dependent nitric oxide synthase (bNOS) activity has not been documented in free-living, non-denitrifying soil bacteria. This paper reports Paenibacillus nitricinens sp. nov., a bacterium isolated from rainforest soil capable of synthesizing NO via a bNOS under aerobic conditions. A bnos-specific PCR confirmed gene presence, while whole-genome sequencing (6.7 Mb, 43.79% GC) revealed two nitrogen metabolism pathways, including a bnos-like gene. dDDH (<70%) and ANI (<95%) values with related Paenibacillus strains support the delineation of this isolate as a distinct species. Extracellular and intracellular NO measurements under aerobic conditions showed a dose-dependent response, with detectable production at 0.1 µM L-arginine and saturation at 100 µM. The addition of L-NAME reduced NO formation, confirming enzymatic mediation. The genomic identification of a bnos-like gene strongly supports the presence of a functional pathway. The absence of canonical nitric oxide reductase (Nor) genes or other typical denitrification-related enzymes reinforces that NO production arises from an alternative, intracellular enzymatic mechanism rather than classical denitrification. Consequently, P. nitricinens expands the known repertoire of microbial NO synthesis and suggests a previously overlooked source of NO flux in well-aerated soils. Full article

With the rapid development of the global aquaculture industry, the issue of effluent pollution from aquaculture has become increasingly severe. Effective management of aquaculture effluent is an urgent requirement for the sustainable development of the aquaculture industry, with a key focus on the efficient removal of nitrogen. Heterotrophic bacteria assimilation technology offers advantages such as high efficiency and resource recovery; however, its application in effluent treatment remains limited. Therefore, this study aimed to identify the optimal carbon source for the heterotrophic bacteria assimilation process and to optimize its operating parameters using response surface methodology (RSM). The results revealed that the sucrose group achieved the highest total ammonia nitrogen (TAN) removal rate of 85.1%, significantly outperforming molasses (77.0%) and glucose (62.9%), with microbial biomass also significantly higher than in the other groups. Metagenomic analysis indicated that sucrose promotes the formation of efficient denitrifying microbial communities by enriching the phylum Bacteroidota and the denitrifying functional bacteria Xanthomarina, thereby significantly enhancing denitrification efficiency. The optimal carbon source was determined to be sucrose. Using the optimal parameters of microbial biomass at 1.7 g/L, a hydraulic retention time of 36 h, and a chemical oxygen demand-to-total nitrogen (COD/TN) ratio of 26, the removal rates of total nitrogen (TN), TAN, and nitrite nitrogen (NO₂⁻-N) exceeded 85%, while the removal rate of nitrate nitrogen (NO₃⁻-N) surpassed 60%. A significant interaction was observed between microbial biomass and hydraulic retention time, which notably affected denitrification efficiency (p < 0.05). This study provides theoretical support for the harmless and resourceful treatment of aquaculture effluent, contributing to the green and sustainable development of the aquaculture industry. Full article

The Anaerobic–Swing Aerobic–Anoxic–Oxic (ASAO) process was developed to tackle problems such as temperature sensitivity during the Anaerobic–Oxic–Anoxic (AOA) process. By introducing a swing zone (S zone) with adjustable dissolved oxygen (DO), during the 112-day experimentation period, the ASAO system achieved removal rates of 88.18% for total inorganic nitrogen (TIN), 78.23% for total phosphorus (TP), and 99.78% for ammonia nitrogen. Intermittent aeration effectively suppressed nitrite-oxidizing bacteria (NOB), and the chemical oxygen demand (COD) removal rate exceeded 90%, with 60% being transformed into internal carbon sources like polyhydroxyalkanoates (PHAs) and glycogen (Gly). The key functional microorganisms encompassed Dechloromonas (denitrifying phosphorus-accumulating bacteria), Candidatus Competibacter, and Thauera, which facilitated simultaneous nitrification–denitrification (SND) and anaerobic ammonium oxidation (ANAMMOX). The enrichment of Candidatus Brocadia further enhanced the ANAMMOX activity. The flexibility of DO control in the swing zone optimized microbial activity and mitigated temperature dependence, thereby verifying the efficacy of the ASAO process in enhancing the removal rates of nutrients and COD in low-C/N wastewater. The intermittent aeration strategy and the continuous low-dissolved-oxygen (DO) operating conditions inhibited the activity of nitrite-oxidizing bacteria (NOB) and accomplished the elimination of NOB. Full article

Anaerobic ammonium oxidation (anammox) technologies have attracted substantial interest due to their advantages over traditional biological nitrogen removal processes, including high efficiency and low energy demand. Currently, multiple side-stream applications of the anammox coupling process have been developed, including one-stage, two-stage, and three-stage systems such as completely autotrophic nitrogen removal over nitrite, denitrifying ammonium oxidation, simultaneous nitrogen and phosphorus removal, partial denitrification-anammox, and partial nitrification and integrated fermentation denitritation. The one-stage system includes completely autotrophic nitrogen removal over nitrite, oxygen-limited autotrophic nitrification/denitrification, aerobic de-ammonification, single-stage nitrogen removal using anammox, and partial nitritation. Two-stage systems, such as the single reactor system for high-activity ammonium removal over nitrite, integrated fixed-film activated sludge, and simultaneous nitrogen and phosphorus removal, have also been developed. Three-stage systems comprise partial nitrification anammox, partial denitrification anammox, simultaneous ammonium oxidation denitrification, and partial nitrification and integrated fermentation denitritation. The performance of these systems is highly dependent on interactions between functional microbial communities, physiochemical parameters, and environmental factors. Mainstream applications are not well developed and require further research and development. Mainstream applications demand a high carbon/nitrogen ratio to maintain levels of nitrite-oxidizing bacteria, high concentrations of ammonium and nitrite in wastewater, and retention of anammox bacteria biomass. To summarize various aspects of the anammox processes, this review provides information regarding the microbial diversity of different genera of anammox bacteria and the engineering aspects of various side streams and mainstream anammox processes for wastewater treatment. Additionally, this review offers detailed insights into the challenges related to anammox technology and delivers solutions for future sustainable research. Full article

This study investigates the nitrogen removal pathways and microbial community dynamics in a novel system coupling simultaneous nitrification and denitrification (SND) with sulfur autotrophic denitrification (SAD) for the treatment of mariculture tailwater. High-throughput sequencing and predictive functional analysis were employed to examine microbial compositions and their functional roles across varying carbon-to-nitrogen (C/N) ratios. The results revealed that SND occurred in the aerobic stage, with Nitrosomonas and Nitrospira facilitating nitrification, while Denitromonas and Paracoccus drove denitrification. In the anaerobic stage, SAD was the primary nitrogen removal process, with sulfur metabolism supported by Thiobacillus and Desulfobacteria. Increasing C/N ratios enriched denitrifying bacteria, enhancing nitrogen removal performance, but reduced nitrifying activity. Functional gene analysis demonstrated the upregulation of denitrification genes (napAB, nirS, norBC, nosZ) with higher carbon inputs, while sulfur metabolism genes (sqr, soxB, dsrAB) confirmed the critical role of sulfur cycling in SAD. The integration of SND and SAD pathways, supported by carbon addition, achieved efficient nitrogen removal, while promoting sulfur bioavailability. Under C/N ratios of 1.2, the nitrate nitrogen (NO₃⁻-N) removal efficiencies reached 93.48%, respectively, while the total nitrogen (TN) removal efficiencies were 95.06%. Ammonia nitrogen (NH₄⁺-N) removal efficiency consistently exceeded 95%, stabilizing at 99.00% in the steady-state operation. This research provides a comprehensive understanding of the microbial and functional mechanisms underlying SND–SAD systems, offering an innovative solution for sustainable mariculture tailwater management. Full article