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Denitrifying anaerobic methane oxidation (DAMO) and associated microbial diversity and abundance in the marsh sediments of Chongming eastern intertidal flat, the Yangtze Estuary, were investigated using carbon-isotope tracing and molecular techniques. Co-existence of nitrate-DAMO archaea and nitrite-DAMO bacteria was evidenced, with higher biodiversity of DAMO archaea than DAMO bacteria. Abundance of DAMO archaeal mcrA gene and DAMO bacterial pmoA gene ranged from 4.2 × 10 3 to 3.9 × 10 10 copies g -1 and from 4.5 × 10 5 to 6.4 × 10 6 copies g -1 , respectively. High DAMO potential was detected, ranging from 0.6 to 46.7 nmol 13 CO 2 g -1 day -1 for nitrate-DAMO and from 1.3 to 39.9 nmol 13 CO 2 g -1 day -1 for nitrite-DAMO. In addition to playing an important role as a CH 4 sink, DAMO bacteria also removed a substantial amount of reactive nitrogen (29.4 nmol N g -1 day -1 ) from the intertidal sediments. Overall, these results indicate the importance of DAMO bioprocess as methane and nitrate sinks in intertidal marshes., (Copyright © 2019. Published by Elsevier Ltd.)

Aquatic environments are hot spots of nitrogen (N) cycling and nitrous oxide (N2O) emission. Understanding key N biogeochemical processes and N2O dynamics is critical for uncovering the responses of aquatic environments to human activities. In this study, we summarized the development of techniques and approaches for determination of N cycling processes and N2O sources in aquatic environments of China. We also reviewed the main N transformation processes and associated biogeochemical controls in aquatic environments of China (e.g., constructed wetlands, paddy fields, lakes, rivers, aquaculture ponds, and estuaries and coasts). In addition, we further synthesized N2O dynamics in these aquatic environments. The results suggested that N cycling processes have been greatly concerned in various aquatic environments of China, whereas more comprehensive analyses of N cycling processes are still sparse for projecting N fates and dynamics in response to changing environments, largely limiting the implementation of N management strategy of China. Aquatic environments of China may be the important sources of atmospheric N2O, but the production and consumption processes of N2O need to be further studied for effective greenhouse gas mitigation. We also argued that it is urgently necessary to incorporate microbial traits into biogeochemical ecosystem modeling to improve the estimation reliability of N cycling and N2O dynamics. This review highlights the importance of N cycling and N2O dynamics, as well as associated environmental implications, and presents the directions of future research on N cycling in aquatic environments of China. [ABSTRACT FROM AUTHOR]

Nitrate overloading in estuarine and coastal regions can lead to various environmental problems. However, limited information is available about nitrate reduction processes and their associated contributions to nitrogen removal in estuary environments. In this study, stable isotope tracing, high-throughput sequencing, and qPCR methods were used to explore the effects of different nitrate concentrations (CK, 100 μM, 200 μM, 400 μM, and 600 μM) on the nitrate reduction rates, microbial abundances, and community structures in wetland sediments from the Yellow River estuary. With nitrate concentration increasing, the denitrification rate increased from 1.08 to 5.97 nmol N g−1 h−1, while the anaerobic ammonium oxidation rates decreased from approximate 1.25 to 0.42 nmol N g−1 h−1. Diversity analyses based on high-throughput sequencing data indicated that the Shannon indexes were lower in the 400 and 600 μM nitrate-addition treatments than other treatments, and the 600 μM nitrate treatment has the lowest α-diversity. The β-diversity results showed that the bacterial community compositions were different between the ≤ 200 μM and ≥ 400 μM nitrate concentration treatments. The nitrate concentration can be divided into high (≥ 400μM) and low (≤ 200) groups based on multiple regression analyses. The co-occurrence network revealed that there was a large difference in the bacterial relationship between the two groups. Linear discriminant effect analysis showed that Gammaproteobacteria, Bacilli, and Actinobacteria were the indicator taxa in the high nitrate concentration group. Overall, these results indicate that nitrate is a key factor to influence the nitrate reduction rates and related microbial communities in estuarine environments. [ABSTRACT FROM AUTHOR]

Complete ammonia oxidizers (comammox), as novel microbial communities, are predicted to play an important role in the nitrogen cycle. Here we reported the presence of complete nitrification in tidal sediments and examined the diversity and abundance of comammox in natural ecosystems. Metagenome and metatranscriptome of the enrichment culture from tidal sediments harbored the genes of comammox. Near-complete comammox AmoA/B/C- and Hao-like sequences showed close relationships to the known comammox (with sequence identity from 79 to 99%) rather than classical betaproteobacterial ammonia-oxidizing bacteria (β-AOB) (57 to 66%) and ammonia-oxidizing archaea (AOA) (24 to 38%). To analyze the diversity of comammox in natural environments, a new primer set targeting clade A comammox Nitrospira (COM-A) amoA genes was designed based on sequences obtained in this study and sequences from published database. In silico evaluation of the primers showed the high coverage of 89 and 100% in the COM-A amoA database. Application of the primers in six different ecosystems proved their strong availability. Community composition of COM-A suggested a relatively higher diversity than β-AOB in similar environments. Quantification results showed that COM-A amoA genes accounted for about 0.4-5.6% in total amoA genes. These results provide novel insight into our perception of the enigmatic comammox and have significant implications for profound understanding of complex nitrification process. [ABSTRACT FROM AUTHOR]

Marine benthic nitrogen (N) cycling may vary widely across space and seasons; it is thus needed to make high‐resolution estimations of these important ecosystem processes with a reasonable number of variables. In this study, we determined the benthic denitrification and anammox potentials in two basins, the Bohai Sea and the North Yellow Sea of China in May and November, and evaluated models in predicting these functions with environmental factors and/or microbial gene‐based functional traits. We found that denitrification generally dominated the N loss (54–98%), and that the denitrification rate varied greatly between basins and seasons. The anammox rate was generally higher in the Bohai Sea than in the North Yellow Sea in both seasons, and it made a greater contribution in November (22%) than in May (16%). Among the measured environmental factors, chlorophyll a in bottom waters and sedimentary organic carbon content were the most influential for predicting denitrification and anammox rates, respectively. On the other hand, the alpha diversities and gene abundances of involved bacteria were poorly correlated with the function potentials, indicating that these functional traits could not well explain the functions alone. Upon the incorporation of two gene copy number ratios [nosZ/(nirS + nirK) and nirK/bacterial 16S rRNA genes] into the environmental factor‐parameterized models, however, we found that the predictive powers of the regression models for total N loss, denitrification and anammox rates, and contributions of anammox increased substantially, indicating that taking microbial functional traits into account could make estimations of these N‐cycling functions in coastal ecosystems more accurate. Key Points: Benthic N2 productions via denitrification and anammox varied greatly across seasons and at a basin‐wide scaleBottom water chlorophyll a and sediment organic carbon were the main environmental factors underlying the biogeography of benthic N lossAdding proper functional traits into models improved the predictability for benthic denitrification and anammox functions [ABSTRACT FROM AUTHOR]

Urbanizations have increased the loadings of reactive nitrogen in urban riverine environments. However, limited information about dissimilatory nitrate reduction processes and associated contributions to nitrogen removal is available for urban riverine environments. In this study, sediment slurry experiments were conducted with nitrogen isotope-tracing technique to investigate the potential rates of denitrification, anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA) and their contributions to nitrate reduction in sediments of urban river networks, Shanghai. The potential rates of denitrification, anammox and DNRA measured in the study area ranged from 0.193 to 98.7 nmol N g −1 h −1 dry weight (dw), 0.0387–23.7 nmol N g −1 h −1 dw and 0–10.3 nmol N g −1 h −1 dw, respectively. Denitrification and DNRA rates were higher in summer than in winter, while anammox rates were greater in winter than in summer for most sites. Dissolved oxygen, total organic carbon, nitrate, ammonium, sulfide, Fe(II) and Fe(III) were found to have significant influence on these nitrate reduction processes. Denitrification contributed 11.5–99.5%% to total nitrate reduction, as compared to 0.343–81.6% for anammox and 0–52.3% for DNRA. It is estimated that nitrogen loss of approximately 1.33 × 10 5 t N year −1 was linked to both denitrification and anammox processes, which accounted for about 20.1% of total inorganic nitrogen transported annually into the urban river networks of Shanghai. Overall, these results show the potential importance of denitrification and anammox in nitrogen removal and provide new insight into the mechanisms of nitrogen cycles in urban riverine environments. [ABSTRACT FROM AUTHOR]

Biochar has the potential to remediate heavy metals in agricultural soil and mitigate nitrous oxide (N 2 O) emissions; however, the effects of biochar on heavy metal remediation, the soil microbial community and N 2 O emissions are not completely understood. In this study, we conducted a pot experiment in which Glycine max L. (soybean) was cultivated in two cadmium (Cd)-contaminated soils (low, 3.14 mg kg−1; high, 10.80 mg kg−1) to investigate the effects of biochar on the bioremediation of Cd, N 2 O emissions and the rhizosphere microbial community structure. The bioaccumulation of Cd in the plant shoots and roots increased with all biochar addition rates (0%, 1%, 5% and 10%); unexpectedly, the translocation capacity of Cd to the edible parts of the plant significantly decreased to 0.58 mg kg−1, which was close to the edible threshold (0.4 mg kg−1). The abundance and activities of functional marker genes of microbial nitrification (amoA) and denitrification (nirK, nirS and nosZ) were quantified with quantitative PCR, and we found that biochar addition reduced the precursor production of rhizoshpere N 2 O by inhibiting the transcription of the nirK gene. In addition, the nitrogenase activity during anthesis (S) was significantly (P < 0.05) increased with 1% (v/v) biochar addition. Noticeably, biochar addition only changed the microbial community structure in the very first stage before eventually stabilize. This study highlighted that biochar has the potential ability to maintain the quality of agricultural crops, remediate Cd-contaminated soils and may help reduce N 2 O emissions without disturbing the microbial community. Image 1 • Biochar increased nitrogenase activity of soybean planted in Cd-polluted soil. • Cd translocation to the edible parts of soybean was reduced by biochar amendment. • Biochar inhibited the transcription efficiency of the gene nirK. • A short-term impact of biochar on microbial community was observed. [ABSTRACT FROM AUTHOR]

Coupling of nitrogen removal processes with nitrification (NR n) are vital synergistic nitrogen elimination mechanisms in aquatic environments. However, the effects of antibiotics on NR n are not well known. In the present work, 20-day continuous-flow experiments combined with 15N tracing techniques and quantitative PCR were performed to simulate the impact of sulfamethoxazole (SMX, a sulfonamide antibiotic) with near in situ concentration on NR n processes in sediments of Yangtze Estuary. Results showed that SMX with near in situ concentration significantly decreased NR n , NR w (uncoupling of nitrogen removal processes with nitrification) and actual nitrogen removal rates via inhibiting nitrogen transformation functional genes (AOB, narG , nirS , nosZ) and anammox 16S rRNA gene, while the coupling links between nitrification and nitrogen removal processes were not broken by the exposure. The proportion of NR n in total nitrogen removal processes decreased by approximately 10% with SMX addition, due to the different inhibition on AOB, denitrifying genes and anammox 16S rRNA gene. N 2 O production and nitrite accumulation remarkably increased with SMX addition under simultaneous nitrification and denitrification, and they strongly correlated with each other. The more severely inhibition on nirS gene (13.6–19.8%) than Nitrospira nxrB gene (0.3–8.2%) revealed that the increased nitrite accumulation with SMX addition mainly occurred in heterotrophic denitrification, suggesting that the increased N 2 O production was dominated by the heterotrophic nitrite reduction. Moreover, we estimated that the ratio of external inorganic N eliminated by actual nitrogen removal can upgrade to 6.4–7.4% under circumstances of no inhibition by SMX. This study revealed the effects of SMX with near in situ concentration on NR n processes and illustrated the microbial mechanism on functional genes level. Our results highlighted the inhibitory effects of SMX on NR n may contribute to reactive N retention and N 2 O production in estuarine and coastal ecosystems. Image 1 • SMX inhibits coupled, uncoupled and actual nitrogen removal rates. • SMX decreased the ratio of coupled nitrogen removal in total nitrogen removal. • Nitrification, denitrification and anammox functional genes were affected. • SMX increased N 2 O emission due to the increased heterotrophic nitrite reduction. SMX inhibited NR n rates and decreased NR n ratio in total nitrogen removal via suppressing AOB, denitrifying genes and anammox 16S rRNA gene. [ABSTRACT FROM AUTHOR]

Denitrifying anaerobic methane oxidation (DAMO), consisting of nitrite-dependent DAMO (nitrite-DAMO) and nitrate-dependent DAMO (nitrate-DAMO), has recently been discovered and considered an important link between carbon and nitrogen cycles. In this work, we investigated biodiversity, abundance, and potential methane (CH 4) oxidation activity of nitrite-DAMO bacteria and nitrate-DAMO archaea in intertidal marsh soil cores, based on molecular and stable isotope tracing methods. Results evidenced the co-occurrence and vertical stratification of DAMO bacteria and archaea in intertidal marsh soils, with higher biodiversity of DAMO archaea compared with DAMO bacteria. The abundance of DAMO bacterial pmoA gene (8.2 × 105–3.0 × 107 copies g−1 dry soil) was approximate to that of DAMO archaeal mcrA gene (3.0 × 105–3.9 × 107 copies g−1 dry soil) in the intertidal marsh soil cores. Stable isotope experiments showed that DAMO bacteria and archaea were both active in the intertidal marshes, with CH 4 oxidation potential of 0.1–3.8 nmol 13CO 2 g−1 dry soil day−1 and 0.1–4.1 nmol 13CO 2 g−1 dry soil day−1, respectively. The relative importance (including the abundance and CH 4 oxidation activity) of DAMO bacteria and archaea showed significant vertical variations, with more contribution by DAMO bacteria at the soil-tidal water interface and soil-groundwater interface layers of the soil cores, which are largely due to the influence of tidal dynamics. In addition to playing an important role as CH 4 sink, DAMO process was also a non-negligible pathway of nitrogen removal in intertidal marsh soils, with an estimated nitrogen removal rate of 0.4–10.1 nmol N g−1 dry soil day−1. Overall, these results illustrated the occurrence and environmental significance of DAMO bioprocess in intertidal marshes. Unlabelled Image • Co-occurrence of DAMO bacteria and archaea in intertidal marsh soils is evidenced. • DAMO microbes play an important role as CH 4 sink in intertidal marsh soils. • Tidal dynamics control depth distributions of DAMO microbial abundance and activity. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (AgNPs) are the most common materials in nanotechnology-based consumer products. Due to wide application of AgNPs, their potential environmental impact is a current and highly topical focus of concern. Nitrification is one of the most susceptible processes to AgNPs in the nitrogen cycle, but effects of AgNPs on nitrification in aquatic environments are not well understood. Here, we report the AgNP impacts on nitrification and associated nitrous oxide (N2O) production in estuarine sediments. AgNPs inhibited nitrification rates, which decreased exponentially with increasing AgNP concentrations. The response of nitrifier N2O production to AgNPs exhibited low-dose (<534, 1476, 2473 μg L-1 for 10, 30, and 100 nm AgNPs, respectively) stimulation and high-dose inhibition (hormesis effect). Compared with control, N2O production could be enhanced by >100% at low doses. This result was confirmed by metatranscriptome studies showing upregulation of nitric oxide reductase (norQ) gene expression in the low-dose treatment. Isotopomer analysis revealed that hydroxylamine oxidation was the main N2O production pathway, and its contribution to N2O emission was enhanced when exposed to low-dose AgNPs. This study highlights molecular underpinnings of AgNP effects on nitrification activity and demonstrates that the release of AgNPs into the environment should be controlled because they interfere with nitrifying communities and stimulate N2O emission. [ABSTRACT FROM AUTHOR]

Coastal wetlands, being a multifaceted and crucial global ecosystem, are facing significant impacts from diverse environmental alterations, particularly soil salinization. Concurrently, the escalation of extreme climate events, such as global warming, presents complex challenges for the protection and restoration efforts. Previous researches concerning microbial communities in the context of climate with continous line numbering change have predominantly concentrated on their structural aspects, with limited attention given to establishing relationships between community structure and functional attributes. In this study, a two-year investigation was conducted on conventional coastal wetland ecosystems, considering variations in salinity and seasonal temperature. Utilizing high-throughput 16S rRNA sequencing, isotope technology, and other methods to explore the bacterial community, nitrogen cycling functional groups, and nitrogen reduction process. This research aims to assess the holistic impacts of significant global environmental changes on microbial communities. The results suggest that salinity, acting as an environmental filter, has a significant impact on the microbial community composition. It leads to a decrease in species abundance, an increase in deterministic processes and the nesting of community succession, while also reducing the stability of microbial ecological networks. The mechanism by which soil salinity impacts bacterial communities involves three main aspects: direct effects, positive climate regulation, and negative regulation of soil properties. Surprisingly, soil salinity exerts a mild inhibitory influence on microbial functional genes and metabolic activity. The primary factors involved in the nitrogen reduction process include electron donors/acceptors, types of nitrogen sources, and organic carbon. The three processes are interconnected due to the impact of environmental factors and signal transmission among microbial populations. This study offers a novel scientific framework for the rehabilitation and enhancement of saline-alkali coastal ecosystems in the face of impending global changes. It achieves this by investigating the varied response patterns exhibited by microbial communities and ecological functional metabolism under salinity-induced stress. [Display omitted] • We conducted large-scale study on coastal wetland ecosystems to evaluate the different impacts of salt stress, seasonal temperature changes, and other factors on microbial communities and ecological functions. • Salt stress, as the main factor, strongly affects the microbial community in coastal wetlands and makes them unable to resist complex and drastic environmental changes, but has a weak inhibitory effect on microbial functional genes and metabolic activity. • The process of nitrogen reduction is coupled with the interaction of environmental factors and signal transmission between microbial populations, and is more influenced by electron donors/acceptors, nitrogen source types, and organic matter. [ABSTRACT FROM AUTHOR]

• NO2−/NO3−-dependent anaerobic CH4 oxidation (n-DAMO) microbes are active in estuarine and intertidal wetlands • n-DAMO bacteria contribute more to CH4 oxidation than n-DAMO archaea • Abundance and role of n-DAMO microbes vary across estuarine habitats with different salinities • n-DAMO microbial dynamics are associated closely with sediment characteristics Nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) is a crucial link between carbon and nitrogen cycles in estuarine and coastal ecosystems. However, the factors that affect the heterogeneous variability in n-DAMO microbial abundance and activity across estuarine and intertidal wetlands remain unclear. This study examined the spatiotemporal variations in n-DAMO microbial abundance and associated activity in different estuarine and intertidal habitats via quantitative PCR and 13C stable isotope experiments. The results showed that Candidatus ' Methylomirabilis oxyfera ' (M. oxyfera)-like DAMO bacteria and Candidatus ' Methanoperedens nitroreducens ' (M. nitroreducens)-like DAMO archaea cooccurred in estuarine and intertidal wetlands, with a relatively higher abundance of the M. oxyfera -like bacterial pmoA gene (4.0 × 106-7.6 × 107 copies g−1 dry sediment) than the M. nitroreducens -like archaeal mcrA gene (4.5 × 105-9.4 × 107 copies g−1 dry sediment). The abundance of the M. oxyfera -like bacterial pmoA gene was closely associated with sediment pH and ammonium (P <0.05), while no significant relationship was detected between M. nitroreducens -like archaeal mcrA gene abundance and the measured environmental parameters (P >0.05). High n-DAMO microbial activity was observed, which varied between 0.2 and 84.3 nmol 13CO 2 g−1 dry sediment day−1 for nitrite-DAMO bacteria and between 0.4 and 32.6 nmol 13CO 2 g−1 dry sediment day−1 for nitrate-DAMO archaea. The total n-DAMO potential tended to be higher in the warm season and in the upstream freshwater and low-salinity estuarine habitats and was significantly related to sediment pH, total organic carbon, Fe(II), and Fe(III) contents (P <0.05). In addition to acting as an important methane (CH 4) sink, n-DAMO microbes had the potential to consume a substantial amount of reactive N in estuarine and intertidal environments, with estimated nitrogen elimination rates of 0.5-224.7 nmol N g−1 dry sediment day−1. Overall, our investigation reveals the distribution pattern and controlling factors of n-DAMO bioprocesses in estuarine and intertidal marshes and gains a better understanding of the coupling mechanisms between carbon and nitrogen cycles. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Anaerobic ammonium oxidation (anammox) is an important bioprocess for nitrogen removal and has been studied in estuarine environments. However, knowledge on anammox bacterial community dynamics and related controlling factors remains limited in these ecosystems. In this study, the community compositions, abundance, and activity of anammox bacteria in the surface sediments from the Indus Estuary were investigated along a salinity gradient, considering the links between the anammox bacterial community dynamics and environmental variables. The potential importance of anammox was also estimated for nitrogen removal. High anammox bacterial diversity was detected in the sediments of the Indus Estuary, including Kuenenia , Brocadia , Scalindua , Jettenia , and a novel anammox-like cluster. Kuenenia was identified as the dominant anammox bacteria in most samples. Anammox bacterial diversity was significantly correlated with sediment NO 3 −, while the distribution of anammox bacterial community was significantly related to temperature and sediment sulfide (P < 0.05). The anammox bacterial abundance based on the 16S rRNA gene varied between 1.64 × 106 copies g−1 and 8.21 × 108 copies g−1, and was significantly correlated with sediment Fe(II). Based on an 15N isotope-tracing technique, potential anammox rates were found in the range 0.01–0.32 μ mol N kg−1 h−1, and were controlled mainly by salinity, Fe(II), and TOC. It was estimated that the anammox bacteria contributed about 21.9% to the total nitrogen loss, on average. These results show the importance of anammox bacteria for nitrogen transformation and removal in estuarine and coastal environments. Image 1 • High diversity of anammox bacteria was detected in the estuarine environments. • Anammox bacterial diversity was associated with sediment NO 3 − • Distribution of anammox bacteria was related to temperature and sediment sulfide. • Anammox bacteria played an important role in nitrogen removal. [ABSTRACT FROM AUTHOR]

Wetland ecosystems are hotspots for nitrogen cycling, while the community dynamics of nitrification-driving microbes include ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), complete ammonia oxidizer (comammox) Nitrospira, and nitrite-oxidizing bacteria were not well-studied. In this study, we investigated the nitrification process in typical inland and coastal wetlands in northern China and found a high diversity of ammonia oxidizers. To simulate the freezing-thawing state under natural environment, the soil samples were first frozen at −20 °C for two months, and then gradually thawed at 4 °C. Further microcosm incubation combined with 13C-DNA-stable isotope probing analyses showed that after the freeze–thaw cycle, only the activities of AOA and comammox Nitrospira clade B recovered. The results indicated that these two groups of nitrifiers were more freeze–thaw resistant, which is in line with literature showing that AOA and comammox Nitrospira clade B were relatively more abundant than their counterparts in low-temperature environments. We tested, for the first time, the cold-shock resilience of nitrifying microbes in wetland soils and spotted candidates driving nitrification under fluctuating temperatures. [Display omitted] • Wetland ecosystems are hotspots for nitrogen cycling. • Nitrification process in inland and coastal wetlands in northern China is studied. • Ammonia-oxidizing archaea & comammox Nitrospira clade B are active ammonia oxidizers. • These two groups of nitrifiers are more adapted to low-temperature environments. [ABSTRACT FROM AUTHOR]

• Feammox activities were widespread across the estuarine and coastal wetlands of China. • Feammox rates at the subtropical sites were generally higher than at the temperate sites. • Spatial variations of diversities and abundances of Fe reducing bacteria were similar to Feammox rates. • Sediment characteristics and geographical factors affected Feammox via altering relevant bacterial abundance. Anaerobic ammonium oxidation coupled with ferric iron reduction (Feammox) is a newly identified microbial nitrogen (N) removal process in natural ecosystems. However, little is known about the distributions of Feammox activity and their environmental drivers across estuarine and coastal wetlands at a continental scale. In this study, we determined the potential Feammox rates and related microbial diversities and abundances along the estuarine and coastal wetlands of China encompassing subtropical to temperate climate zones. Measured potential Feammox activity ranged from 0.05 to 0.23 mg N kg−1 d-1, and the process rates at the subtropical sites were generally higher than at the temperate sites. Partial least squares path model (PLS-PM) showed that the abundance of Fe reducing bacteria significantly and directly affected the potential Feammox rates, while sediment characteristics (mainly including sediment water content, Fe(III), TOC and NO 3 –) and geographical factors (longitude and latitude) had an indirect effect on the process rates. The N loss via the Feammox was approximately 1.72–7.89 kg N ha−1 year−1, accounting for 0.41–1.91 % of multi-annual average land-based inorganic N transported into the estuarine and coastal wetlands of China. Overall, this study reveals the distribution patterns and controlling factors of the Feammox process in estuarine and coastal wetlands of China, and provides a valuable database for N management in estuarine and coastal ecosystems. [ABSTRACT FROM AUTHOR]

As the important benthic animal in coastal wetlands, crab bioturbation may significantly affect the nitrogen (N) budgets by regulating microbial N transformation processes. However, the response of interaction between different microbial N processes to crab bioturbation remains poorly understood. Here, a 30-day microcosmic experiment was conducted using sediment collected from the Yangtze Estuary wetland, followed by the determination of temporal variations of physicochemical parameters, N removal (denitrification plus anammox, which is defined as N 2 production) and retention rates (nitrate dissimilatory reduction to ammonium, DNRA) as well as relevant gene abundances in response to different crabs densities. The results showed that crab bioturbation simultaneously promoted the rates of N 2 production and DNRA processes. These two process rates were positively associated with the intensity of crab bioturbation, which was supported by molecular analysis of relevant functional gene abundance. Crab bioturbation was more beneficial to DNRA than N 2 production. Due to this disproportionate stimulation, crab bioturbation increased the importance of DNRA, indicating that N retention was becoming more significant under crab bioturbation in estuarine and coastal wetlands. The variations of sediment total organic carbon and oxygen availability driven by crab bioturbation were the critical factors mediating the changes in microbial N removal and retention. Overall, our findings highlighted that crab bioturbation can affect the N budgets in estuarine and coastal wetlands by altering the competition between microbial N removal and retention. • Crab bioturbation promoted both microbial N removal and retention process rates. • The increase is higher for N retention than N removal rates under the crab bioturbation. • Substrate contents, oxygen levels and relevant gene abundance control N removal and retention. • Crab activity affects the competition between N removal and retention, and decreases N loss capacity. [ABSTRACT FROM AUTHOR]

Estuarine antibiotic residues are profoundly impacting microbial nitrogen (N) cycling and associated N 2 O production, but the response of N 2 O production pathways to antibiotics remains poorly understood. Here, 15N–18O labeling technique combined with molecular methods were used to investigate the impacts of sulfamethoxazole on the contribution of ammonia oxidation (nitrifier nitrification, nitrifier denitrification, and nitrification-coupled denitrification) and heterotrophic denitrification (HD) to N 2 O production in estuarine sediments. Results showed that environmental concentration of sulfamethoxazole (4 ng/g) promoted the total N 2 O production by 17.1% through nitrifier denitrification. Environmentally relevant (40–4000 ng/g) and irrelevant (40,000 ng/g) concentration of sulfamethoxazole drove nitrification denitrification to gradually lose the dominant role in total N 2 O production and ammonia oxidation-derived N 2 O, replaced by HD and nitrifier nitrification, while total N 2 O production were inhibited. Furthermore, when HD dominated the total N 2 O production, the HD-derived N 2 O increased by 63.6% with sulfamethoxazole concentration reaching 40,000 ng/g. The mechanistic investigation further showed that nitrifying bacteria were more susceptible to sulfamethoxazole than nitrifying archaea and denitrifiers. The increased expression of nirS gene carried by non-dominant denitrifiers improved the ratio of nirS : nosZ and hence increased HD-derived N 2 O under high sulfamethoxazole stresses. Overall, our results provide a comprehensive view into how antibiotics regulate N 2 O production and its pathways in estuarine sediments. [Display omitted] • Environmental dose of SMX enhanced the N 2 O production via ND. • Environmentally relevant and irrelevant dose of SMX altered N 2 O production avenues. • SMX altered the keystone species involved in N 2 O production from HD. • SMX increased N 2 O production from HD when HD dominated the total N 2 O production. • Nitrifying bacteria were more vulnerable to SMX than archaea and denitrifiers. [ABSTRACT FROM AUTHOR]

• The presence of MPs significantly altered sedimentary nitrogen turnover. • Biodegradable MPs impacted bacterial community more profoundly. • Nitrogen cycling functional microbes had different responses to MPs. • Petroleum-based and biodegradable MPs promoted N 2 O production via varied avenues. • Biodegradable MPs have a greater potential to enhance global warming. Increasing microplastics (MPs) pollution in estuaries profoundly impacts microbial ecosystems and biogeochemical processes. Nitrous oxide (N 2 O), a powerful greenhouse gas, is an important intermediate product of microbial nitrogen cycling. However, how MPs regulate N 2 O production and its pathways remain poorly understood. Here, impacts of traditional petroleum-based and emerging biodegradable MPs on microbial N 2 O production and its pathways were studied through dual-isotope (15N–18O) labeling technique and molecular methods. Results indicated that both traditional petroleum-based and emerging biodegradable MPs promoted sedimentary N 2 O production, whereas pathways varied. Biodegradable polylactic acid (PLA) MPs displayed greater promotion of N 2 O production than petroleum-based MPs, polyvinyl chloride (PVC) and polyethylene (PE), of which PLA promoted through nitrifier nitrification (NN) and heterotrophic denitrification (HD), PE through nitrifier denitrification and HD, and PVC through NN. By combining the analysis of N 2 O production rates with sediment chemical and microbiological properties, we demonstrated that the enrichment of nitrifying and denitrifying bacteria, as well as related functional genes directly and/or indirectly increased N 2 O production primarily by interacting with carbon and nitrogen substrates. Different response of nitrogen cycling microbes to MPs led to the difference in N 2 O increase pathways, of which nitrifying bacteria significantly enriched in all MPs treatments due to the niches provided by MPs. However, part of denitrifying bacteria significantly enriched in treatments containing PLA and PE MPs, which may serve as organic carbon substrates. This work highlights that the presence of MPs can promote sedimentary N 2 O production, and the emerging biodegradable MPs represented by PLA may have a greater potential to enhance estuarine N 2 O emissions and accelerate global climate change. [Display omitted] [ABSTRACT FROM AUTHOR]