Molecular analysis of microbial nitrogen transformation and removal potential in mangrove wetlands under anthropogenic nitrogen input

Microbial colonization and succession on polylactic acid microplastics (PLA MPs) in mangrove forests - the role of environmental conditions and plastic properties

The concerns about possible risks of biodegradable plastics have increased in recent years. In this study, two types of biodegradable polylactic acid (PLA) MPs, 604 (low molecular weight) and 801 (high molecular weight), were incubated in-situ in mangrove ecosystems, across four different environmental matrix - mangrove sediment, mangrove water, mangrove air and beach air for 90 days. The fluorescence staining combined with scanning electron microscopy (SEM) results revealed that microbial colonization (both algae and bacteria) tended to be in the areas of depressions and cavities on MPs, which presumably showed signs of microbial degradation on the surface of the plastics. Over the 90-day incubation period, microbial colonization and succession on the plastics was significantly influenced by both environmental conditions and the properties of the MPs. Microbial colonization on plastic samples in mangrove sediment progressed more rapidly than that in mangrove water. Correspondingly, microbial communities on plastics in sediment showed high similarity to those in the surrounding environment, whereas the opposite was observed in water. Environmental disturbances and nutrient availability in different matrices also led to distinct microbial succession pathways for the two types of MPs. In sediment, which provided the most stable and nutrient-rich environment, divergent succession patterns were observed between 604 and 801 PLA MPs. Conversely, in flowing water and air, where environmental pressures were higher, convergent succession patterns were found. It is worth noting that the relatively stable environmental conditions and limited nutrient sources in mangrove air resulted in the highest enrichment of potential PLA-degrading microorganisms on both types of PLA MPs. Our findings highlighted the critical role of environmental conditions and MP properties in shaping microbial colonization and succession on PLA MPs. These results provided valuable scientific insights into the environmental degradation processes and long-term ecological risks of biodegradable plastics in mangrove coastal ecosystems.

The vertical distribution and metabolic versatility of complete ammonia oxidizing communities in mangrove sediments

Recently discovered complete ammonia-oxidizing (comammox) microorganisms can completely oxidize ammonia to nitrate and play an important role in the nitrogen (N) cycle across various ecosystems. However, little is known about the vertical distribution and metabolic versatility of comammox communities in mangrove ecosystems. Here we profiled comammox communities from deep sediments (up to 5 m) in a mangrove wetland by combining metagenome sequencing and physicochemical properties analysis. Our results showed that the relative abundance of comammox bacteria (23.2 %) was higher than ammonia-oxidizing bacteria (AOB, 12.0 %), but lower than ammonia-oxidizing archaea (AOA, 64.8 %). The abundance of comammox communities significantly (p < 0.01) decreased with the sediment depth, and dissolved organic carbon and total sulfur appeared to be major environmental factors influencing the nitrifying microbial community structure. We also recovered a high-quality metagenome-assembled genome (MAG) of comammox bacteria (Nitrospira sp. bin2030) affiliated with comammox clade A. Nitrospira sp. bin2030 possessed diverse metabolic processes, not only the key genes for ammonia oxidation and urea utilization in the N cycle, but also key genes involved in carbon and energy metabolisms, sulfur metabolism, and environmental adaptation (e.g., oxidative stress, salinity, temperature, heavy metal tolerance). The findings advance our understanding of vertical distribution and metabolic versatility of comammox communities in mangrove sediments, having important implications for quantifying their contribution to nitrification processes in mangrove ecosystems.

Effects of pristine and photoaged tire wear particles and their leachable additives on key nitrogen removal processes and nitrous oxide accumulation in estuarine sediments

Despite growing attention to the environmental pollution caused by tire wear particles (TWPs), the effects of pristine and photoaged TWPs (P-TWPs and A-TWPs) and their TWP leachates (TWPLs; P-TWPL and A-TWPL) on key nitrogen removal processes in estuarine sediments remain unclear. This study explores the responses of the denitrification rate, anammox rate, and nitrous oxide (N2O) accumulation to P-TWP, A-TWP, P-TWPL, and A-TWPL exposure in estuarine sediments, and assesses the potential biotoxic substances present in TWPLs. P-TWPs reduced the denitrification rate by 17.1 ± 10.0 % and increased N2O accumulation by 28.1 ± 18.7 %. The A-TWPs not only reduced the denitrification rate by 31.3 ± 8.3 % and increased N2O accumulation by 43.1 ± 22.0 %, but also decreased the anammox rate by 22.1 ± 13.3 %. A-TWPs further inhibited the denitrification rate by reducing nitrate reductase activity and the abundance of its gene (narG), while simultaneously decreasing hydrazine synthase activity and the abundance of its gene (hzo), thereby slowing the anammox rate. N2O accumulation after exposure to TWPs and TWPLs was positively correlated with the activity ratio of N2O-producing and N2O-consuming enzymes. Zinc (Zn) release in A-TWPL was 48.5 ± 6.9 % higher than that in P-TWPL, which is a crucial reason for the higher biotoxicity produced by A-TWPs. In addition, the abundance of denitrifying and anammox bacteria closely linked to the Zn, manganese, and arsenic concentrations in the TWPLs. This study provides insights into assessing the environmental risks posed by TWPs to estuarine ecosystems.

Meta-analysis: Global patterns and drivers of denitrification, anammox and DNRA rates in wetland and marine ecosystems

Nitrogen cycling is one of the most important biogeochemical processes on Earth, and denitrification, anammox and DNRA processes are important nitrogen cycling processes in estuarine ecosystems. However, due to the large input of anthropogenic nitrogen sources, a large number of environmental problems have now occurred in the estuary. But the global patterns and controlling factors of denitrification, anammox and DNRA rates in wetland marine ecosystems are not yet known. We reached our conclusions through a global synthesis of 546 observation sites from 78 peer-reviewed papers: The three rates were generally higher in areas near wetlands than in coastal areas. The rate of denitrification was highest in the subtropical region the seasonal variability was not significant; and TOC was the main factor controlling denitrification. The rate of anammox was significantly higher in the subtropical region than in the tropical and boreal zones, and the seasonal variability was significant; and at the same time, TN was the main driver of the anammox rate of the wetland ocean. DNRA rates were significantly higher in the tropics than in the subtropics and temperate zones; and the main driver of DNRA rates was temperature. Nitrogen cycle functional genes also had an indirect effect on their rates. With NH4 + -N significantly affecting nirK abundance and TN significantly affecting the gene abundance of nirS; TOC and TN had a greater effect on hzo abundance, which indirectly affected anammox rates; for DNRA, C/N significantly affects the gene abundance of nrfA, which indirectly affects the DNRA rate. Therefore, the findings of this study indicate that physicochemical indicators about N and climatic characteristics have a profound effect on the nitrogen cycling process, which provides a good feedback for studying the role of denitrification and provides a positive impact on global climate and environmental governance.

Loss of microbial functional diversity following Spartina alterniflora invasion reduces the potential of carbon sequestration and nitrogen removal in mangrove sediments-from a gene perspective

Mangrove ecosystems play an important role in carbon (C) sequestration and nitrogen (N) removal. Although Spartina alterniflora has successively invaded native mangrove habitats during the preceding two decades, the effects of this invasion on the microbial functional potential involved in nutrient cycling remain unclear. In this study, metagenomic sequencing was used to investigate microbial C and N cycling in sediments derived from S. alterniflora and three native mangrove species (Kandelia obovata, Avicennia marina, and Aegiceras corniculatum). Greater differences in functional profiles of C and N cycling-related genes were observed between S. alterniflora and mangrove sediments than between different mangrove sediments. Functional diversity was lower in S. alterniflora sediments than in native mangrove sediments. The growth of Thaumarchaeota and Proteobacteria, was enhanced due to their resilience to diversity loss, while the growth of oligotrophs, such as Chloroflexi and Firmicutes, was inhibited in S. alterniflora sediments. Compared to mangrove sediments, the abundance of genes involved in C fixation and methane production was lower in S. alterniflora sediments. However, S. alterniflora significantly increased the gene abundance of pmo which controlled the oxidation process of CH4 to carbon dioxide. Additionally, genes involved in nitrification were enriched, whereas genes involved in N reduction processes, such as denitrification and dissimilatory nitrate reduction to ammonium, N immobilization, and N mineralization, were depleted in S. alterniflora sediments compared to mangrove sediments. Partial least squares regression models demonstrated that the decrease in soil organic C and increase in pH after S. alterniflora invasion induced the loss of microbial functional diversity, which was the main driver of changes in the abundances of genes involved in C and N cycling. Overall, our findings indicate that S. alterniflora invasion modifies the microbial functional profile of nutrient cycling in native mangrove ecosystems and potentially weakens the capacity of mangroves to sequester carbon and remove nitrogen.

Anthropogenic nitrogen pollution impacts saltmarsh resilience with inhibition of seedling establishment and population dispersal

Saltmarsh, a prominent buffer ecosystem, has been identified as an important sink for nitrogen (N) pollutants from marine- and land-based anthropogenic activities. However, how the enriched anthropogenic N impacts saltmarsh sustainability has been neglected due to limited understanding of marsh resilience based on seedling establishment and population dispersal under anthropogenic N inputs. This study combined mesocosm experiments and model simulations to quantify the effects of increased anthropogenic N on the seedling-based vegetation expansion of Spartina alterniflora. The results indicated that seedling survivals, growth rates, and morphological indicators were inhibited by 20.08 %, 37.14 %, and > 35.56 %, respectively, under 1.5 gN/kg anthropogenic N. The sensitivity rate of vegetation expansion was increased by 70 % with 1 gN/kg increased N concentration under the scenario of low seedling density (< 15 m/yr). These findings revealed an important unidentified weakness of the marsh development process to anthropogenic N inputs. Finally, we highlighted the importance of appropriate protection measures to control nutrient pollution in salt marshes. Our study provides new insights for enhancing the resilience and sustainability of saltmarsh ecosystems.

A novel autotrophic denitrification and nitrification integrated constructed wetland process for marine aquaculture wastewater treatment

We undertook a lab-scale evaluation of a novel autotrophic denitrification and nitrification integrated constructed wetland (ADNI-CW) for improved carbon (C), nitrogen (N), and sulfur (S) cycling to treat mariculture wastewater. The process involved an up-flow autotrophic denitrification constructed wetland unit (AD-CW) for sulfate reduction and autotrophic denitrification, and an autotrophic nitrification constructed wetland unit (AN-CW) for nitrification. The 400-day experiment investigated the performance of the AD-CW, AN-CW, and entire ADNI-CW processes under various hydraulic retention times (HRTs), nitrate concentrations, dissolved oxygen levels, and recirculation ratios. Under various HRTs, the AN-CW achieved a nitrification performance exceeding 92%. Correlation analysis of the chemical oxygen demand (COD) revealed that, on average, approximately 96% of COD was removed by sulfate reduction. Under different HRTs, increases in influent NO₃^--N concentrations caused the amount of sulfide to gradually decrease from sufficient to deficient, and the autotrophic denitrification rate also decreased from 62.18 to 40.93%. In addition, when the NO₃^--N load rate was above 21.53 g N/m²·d, the transformation of organic N by mangrove roots may have increased NO₃^--N in the top effluent of the AD-CW. The coupling of N and S metabolic processes mediated by various functional microorganisms (Proteobacteria, Chloroflexi, Actinobacteria, Bacteroidetes, and unclassified_d__Bacteria) enhanced N removal. We intensively explored the effects of changing inputs as culture species developed on the physical, chemical, and microbial changes of CW to ensure a consistent and effective management of C, N, and S. This study lays the foundation for green and sustainable mariculture development.

Study on microbes and antibiotic resistance genes in karst primitive mountain marshes - A case study of Niangniang Mountain in Guizhou, China

Previous research on antibiotic resistance genes and microorganisms centered on those in urban sewage treatment plants, breeding farms, hospitals and others with serious antibiotic pollution. However, at present, there are evident proofs that antibiotic resistance genes (ARGs) indeed exist in a primitive environment hardly without any human's footprints. Accordingly, an original karst mountain swamp ecosystem in Niangniang Mountain, Guizhou, China, including herbaceous swamp, shrub swamp, sphagnum bog and forest swamp, was selected to analyze the physical and chemical parameters of sediments. Moreover, microbial compositions, functions, as well as their connections with ARGs were assayed and analyzed using metagenomic technology. The results showed that there was no significant difference in the dominant microorganisms and ARGs in the four marshes, in which the dominant bacteria phyla were Proteobacteria (37.82 %), Acidobacteriota (22.17 %) and Actinobacteriota (20.64 %); the dominant archaea Euryarchaeota. (1.00 %); and the dominant eukaryotes Ascomycota (0.07 %), with metabolism as their major functions. Based on the ARDB database, the number of ARGs annotated reached 209 including 30 subtypes, and the dominant ARGs were all Bacitracin resistance genes (bacA, 84.77 %). In terms of the diversity of microorganisms and ARGs, the herbaceous swamp ranked the top, and the shrub swamp were at the bottom. Correlation analysis between microorganisms and resistance genes showed that, apart from aac2ic, macB, smeE, tetQ, and tetL, other ARGs were positively correlated with microorganisms. Among them, baca coexisted with microorganisms. Pearson correlation analysis results showed that contrary to ARGs, microorganisms were more affected by environmental factors.

A review of anammox-based nitrogen removal technology: From microbial diversity to engineering applications

The anaerobic ammonium oxidation (anammox) process has the advantages of high efficiency and low energy consumption, so it has broad application prospects in biological denitrification of wastewater. However, the application of anammox technology to existing wastewater treatment is still challenging. The main problems are the insufficient supply of nitrite and the susceptibility of anammox bacteria to environmental factors. In this paper, from the perspective of the diversity of anammox bacteria, the habitats and characteristics of anammox bacteria of different genera were compared. At the same time, laboratory research and engineering applications of anammox technology in treating wastewater from different sources were reviewed, and the progress of and obstacles to the practical application of anammox technology were clarified. Finally, a focus for future research was proposed to intensively study the water quality barrier factors of anammox and its regulation strategies. Meanwhile, a combined process was developed and optimized on this basis.