Manganese oxides in Phragmites rhizosphere accelerates ammonia oxidation in constructed wetlands

Plant-microbe involvement: How manganese achieves harmonious nitrogen-removal and carbon-reduction in constructed wetlands

Carbon deficits in inflow frequently lead to inefficient nitrogen removal in constructed wetlands (CWs) treating tailwater. Solid carbon sources, commonly employed to enhance denitrification in CWs, increase carbon emissions. In this study, MnO2 was incorporated into polycaprolactone substrates within CWs, significantly enhancing NH4+-N and NO3--N removal efficiencies by 48.26-59.78 % and 96.84-137.23 %, respectively. These improvements were attributed to enriched nitrogen-removal-related enzymes and increased plant absorption. Under high nitrogen loads (9.55 ± 0.34 g/m3/d), emissions of greenhouse gases (CO2, CH4, and N2O) decreased by 147.23-202.51 %, 14.53-86.76 %, and 63.36-87.36 %, respectively. N2O emissions were reduced through bolstered microbial nitrogen removal pathways by polycaprolactone and MnO2. CH4 accumulation was mitigated by the increased methanotrophs and dampened methanogenesis, modulated by manganese. Additionally, manganese-induced increases in photosynthetic pigment contents (21.28-64.65 %) fostered CO2 sequestration through plant photosynthesis. This research provides innovative perspectives on enhancing nitrogen removal and reducing greenhouse gas emissions in constructed wetlands with polymeric substrates.

Root-mediated acidification, phosphatase activity and the phosphorus-cycling microbial community enhance phosphorus mobilization in the rhizosphere of wetland plants

Rhizoremediation of wetland plants is an environmentally friendly strategy for sediment phosphorous (P) removal, the basic underlying principle of which is the complex interactions between roots and microorganisms. This study investigated the immobilization and mobilization mechanisms of P in the rhizosphere of wetland plants using high-resolution spatial visualization techniques and metagenomic sequencing. Two-dimensional visualization of the spatial distribution of P, iron (Fe) and manganese (Mn) indicated that the sequestration of Fe-oxides rather than Mn-oxides caused the depletion of labile P, resulting in an increase in the Fe-adsorbed P fraction. Plants altered the rhizospheric environments and P-cycling microbial community to mobilize low-availability P from sediments. Mineral P solubilization and organic P mineralization were enhanced by local acidification and increased phosphatase activity, respectively. Microbial P mobilization also increased with increasing relative abundances of P solubilization and mineralization genes (gcd and phnW) and decreasing P transportation genes (ugpA, ugpB, and pit) genes in the rhizosphere. These processes led to the remobilization of 10.04 % of inorganic P, and 15.23 % of organic P, in the rhizosphere during the incubation period. However, the resupply of P via the above processes did not compensate for the depletion of rhizospheric P via root uptake and mineral sequestration. Our results provide novel insights into the mechanisms of rhizospheric P cycling, which will help to inform future phytoremediation strategies.

Molecular transformation of dissolved organic matter in manganese ore-mediated constructed wetlands for fresh leachate treatment

The organic matter (OM) and nitrogen in Fresh leachate (FL) from waste compression sites pose environmental and health risks. Even though the constructed wetland (CW) can efficiently remove these pollutants, the molecular-level transformations of dissolved OM (DOM) in FL remain uncertain. This study reports the molecular dynamics of DOM and nitrogen removal during FL treatment in CWs. Two lab-scale vertical-flow CW systems were employed: one using only sand as substrates (act as a control, CW-C) and the other employing an equal mixture of manganese ore powder and sand (experimental, CW-M). Over 488 days of operation, CW-M exhibited significantly higher removal rates for chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), and dissolved organic matter (represented by dissolved organic carbon, DOC) at 98.2 ± 2.5%, 99.2 ± 1.4%, and 97.9 ± 1.9%, respectively, in contrast to CW-C (92.8 ± 6.8%, 77.1 ± 28.1%, and 74.7 ± 9.5%). The three-dimensional fluorescence excitation-emission matrix (3D-EEM) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses unveiled that the influent DOM was predominantly composed of readily biodegradable protein-like substances with high carbon content and low unsaturation. Throughout treatment, it led to the degradation of low O/C and high H/C compounds, resulting in the formation of DOM with higher unsaturation and aromaticity, resembling humic-like substances. CW-M showcased a distinct DOM composition, characterized by lower carbon content yet higher unsaturation and aromaticity than CW-C. The study also identified the presence of Gammaproteobacteria, reported as Mn-oxidizing bacteria with significantly higher abundance in the upper and middle layers of CW-M, facilitating manganese cycling and improving DOM removal. Key pathways contributing to DOM removal encompassed adsorption, catalytic oxidation by manganese oxides, and microbial degradation. This study offers novel insights into DOM transformation and removal from FL during CW treatment, which will facilitate better design and enhanced performance.

Microbial community structure in a constructed wetland based on a recirculating aquaculture system: Exploring spatio-temporal variations and assembly mechanisms

The diversity, composition and performance of microbial communities within constructed wetlands (CW) were markedly influenced by spatio-temporal variations. A pilot-scale integrated vertical-flow constructed wetland (IVCW) as the biological purification unit within a recirculating aquaculture system (RAS) was established and monitored in this study. The investigation aimed to elucidate the responses of community structure, co-occurrence networks, and assembly mechanisms of the microbial community to spatial and temporal changes. Spatially, all a-diversity indices and microbial networks complexity were significantly higher in the upstream pool of the IVCW than in the downstream pool. Temporally, the richness increased over time, while the evenness showed a decreasing trend. The number of nodes and edges of microbial networks increased over time. Notably, the stable pollutant removal efficiencies were observed during IVCW operations, despite a-diversity and bacterial community networks exhibited significant variations across time. Functional redundancy emerged as a likely mechanism contributing to the stability of microbial ecosystem functions. Null model and neutral model analyses revealed the dominance of deterministic processes shaping microbial communities over time, with deterministic influences being more pronounced at lower a-diversity levels. DO and inorganic nitrogen emerged as the principal environmental factor influencing microbial community dynamics. This study provides a theoretical foundation for the regulation of microbial communities and environmental factors within the context of IVCW.

Manganese Nanoparticles: Synthesis, Mechanisms of Influence on Plant Resistance to Stress, and Prospects for Application in Agricultural Chemistry

Manganese (Mn) is an important microelement for the mineral nutrition of plants, but it is not effectively absorbed from the soil and mineral salts added thereto and can also be toxic in high concentrations. Mn nanoparticles (NPs) are less toxic, more effective, and economical than Mn salts due to their nanosize. This article critically reviews the current publications on Mn NPs, focusing on their effects on plant health, growth, and stress tolerance, and explaining possible mechanisms of their effects. This review also provides basic information and examples of chemical, physical, and ecological ("green") methods for the synthesis of Mn NPs. It has been shown that the protective effect of Mn NPs is associated with their antioxidant activity, activation of systemic acquired resistance (SAR), and pronounced antimicrobial activity against phytopathogens. In conclusion, Mn NPs are promising agents for agriculture, but their effects on gene expression and plant microbiome require further research.

Simultaneous remediation of diesel-polluted soil and promoted ryegrass growth by non-thermal plasma pretreatment

The remediation of petroleum-polluted soil has garnered significant global attention. In this study, a pot-culture experiment was conducted to assess the feasibility of using non-thermal plasma (NTP) as an efficient and economic-friendly pretreatment method in the phytoremediation of diesel-polluted soil. The remediation effectiveness was evaluated via both the removal of diesel and the ryegrass growth. Specifically, at the 50th d of ryegrass growth, the increase of diesel removal efficiency with NTP pretreatment ranged from 16 % to 30 %. Moreover, both clean and diesel-polluted soils pretreated by NTP promoted the growth of ryegrass in shoot lengths and biomass especially after the 35th d. It was found that nitrate nitrogen fixed by NTP not only stimulated the nitrate reductase activities in leaves and promoted plant growth, but also was transformed to more ammonia nitrogen for organism life activity. Subsequent investigation proved that the related nitrogen-metabolism activities of microbes were enriched in rhizosphere soils with NTP pretreatment. Furthermore, NTP treatment increased the abundance of beneficial microbial communities in diesel soil rhizosphere on the 42nd d of growth period. In addition, changes in the proportions of soil dissolved organic matter indicated enhanced nutrient cycling in soils with NTP pretreatment. These promotional effects underscored the contribution of NTP pretreatment in rapidly detoxifying diesel-contaminated soil within 10 min and accelerated the establishment of ryegrass ecosystem. This study provides valuable insights into the role of nitrogen fixation and offers an efficient and promising advanced approach for the phytoremediation of diesel-polluted soil with NTP pretreatment.

Role of n-DAMO in Mitigating Methane Emissions from Intertidal Wetlands Is Regulated by Saltmarsh Vegetations

Coastal wetlands are hotspots for methane (CH4) production, reducing their potential for global warming mitigation. Nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) plays a crucial role in bridging carbon and nitrogen cycles, contributing significantly to CH4 consumption. However, the role of n-DAMO in reducing CH4 emissions in coastal wetlands is poorly understood. Here, the ecological functions of the n-DAMO process in different saltmarsh vegetation habitats as well as bare mudflats were quantified, and the underlying microbial mechanisms were explored. Results showed that n-DAMO rates were significantly higher in vegetated habitats (Scirpus mariqueter and Spartina alterniflora) than those in bare mudflats (P < 0.05), leading to an enhanced contribution to CH4 consumption. Compared with other habitats, the contribution of n-DAMO to the total anaerobic CH4 oxidation was significantly lower in the Phragmites australis wetland (15.0%), where the anaerobic CH4 oxidation was primarily driven by ferric iron (Fe3+). Genetic and statistical analyses suggested that the different roles of n-DAMO in various saltmarsh wetlands may be related to divergent n-DAMO microbial communities as well as environmental parameters such as sediment pH and total organic carbon. This study provides an important scientific basis for a more accurate estimation of the role of coastal wetlands in mitigating climate change.

Simultaneously enhanced autotrophic-heterotrophic denitrification in iron-based ecological floating bed by plant biomass: Metagenomics insights into microbial communities, functional genes and nitrogen metabolic pathways

In this study, the ecological floating bed supporting with zero-valent iron (ZVI) and plant biomass (EFB-IB) was constructed to improve nitrogen removal from low-polluted water. The effects of ZVI coupling with plant biomass on microbial community structure, metabolic pathways and functional genes were analyzed by metagenomic sequencing, and the mechanism for nitrogen removal was revealed. Results showed that compared with mono-ZVI system (EFB-C), the denitrification efficiencies of EFB-IB were effectively enhanced, with the higher average NO3--N removal efficiencies of 22.60-59.19%. Simultaneously, the average NH4+-N removal efficiencies were 73.08-91.10%. Metagenomic analyses showed that EFB-IB enriched microbes that involved in iron cycle, lignocellulosic degradation and nitrogen metabolism. Plant biomass addition simultaneously increased the relative abundances of autotrophic and heterotrophic denitrifying bacteria. Network analysis showed the cooperation between autotrophic and heterotrophic denitrifying bacteria in EFB-IB. Moreover, compared with EFB-C, plant biomass addition increased the relative abundances of genes related to iron cycle, lignocellulose degradation and glycolysis processes, ensuring the production of autotrophic and heterotrophic electron donors. Therefore, the relative abundances of key enzymes and functional genes related to denitrification were higher in EFB-IB, being beneficial to the NO3--N removal. Additionally, the correlation analysis of nitrogen removal and functional genes verified the synergistic mechanism of iron-based autotrophic denitrification and plant biomass-mediated heterotrophic denitrification in EFB-IB. In summary, plant biomass has excellent potential to improve the nitrogen removal of iron-based EFB from low-polluted water.

Biological Oxidation of Manganese Mediated by the Fungus Neoroussoella solani MnF107

Manganese oxides are highly reactive minerals and influence the geochemical cycling of carbon, nutrients, and numerous metals in natural environments. Natural Mn oxides are believed to be dominantly formed by biotic processes. A marine Mn-oxidizing fungus Neoroussoella solani MnF107 was isolated and characterized in this study. SEM observations show that the Mn oxides are formed on the fungal hyphal surfaces and parts of the hypha are enveloped by Mn oxides. TEM observations show that the Mn oxides have a filamentous morphology and are formed in a matrix of EPS enveloping the fungal cell wall. Mineral phase analysis of the fungal Mn oxides by XRD indicates that it is poorly crystalline. Chemical oxidation state analysis of the fungal Mn oxides confirms that it is predominantly composed of Mn(IV), indicating that Mn(II) has been oxidized to Mn (IV) by the fungus.

The evolution of nitrogen transformation microorganism consortium under continued manganese domestication conditions

Manganese redox-stimulated bioremediation of nitrogen wastewater is receiving increasing attention. However, the nitrogen metabolic capacity and community evolution during manganese-mediated nitrogen transformation process under continued manganese domestication conditions are ambiguous. In this study, nitrogen- metabolizing microbial consortiums were incubated with synthesized Mn-humic acid complex (Mn-HA) for one month (M1), three months (M2) and six months (M3), respectively. During the Mn-HA incubation period, Bio-MnOx accompanying with bacterial consortiums (MnOB consortiums) with high TIN removal capacities were obtained. The TIN removal rates in M1, M2 and M3 were 0.220, 1.246 and 4.237 mg·L-1·h-1, respectively, which were 15.961, 90.006 and 1550.006 times higher than CK (Control Check group, no Mn-HA added group) (0.014 mg·L-1·h-1), respectively. Functional genes (amoA, AMX and narG) were most abundant in M3, which was associated with the highest nitrogen removal rate in M3. MnOB1 (bacterial consortium in M1), including Geobactor, Geothrix, Anaeromyxobacter and Bacillus, may be responsible for the Mnammox-NDMO (MnOx reduction coupled to ammonium oxidation - nitrate/nitrite-dependent low-valent Mn oxidation) process. MnOB3 (bacterial consortium in M2) enriched nitrifying bacteria Ellin6067, and denitrifying bacteria Denitratisoma, which dominated nitrogen transformation. MnOB6 (bacterial consortium in M3) enriched denitrifiers Denitratisoma, nitrifiers Ellin6067 and potential anammox bacteria SM1A02, Candidatus_Brocadia. Combined with the reduced abundance of Nitrospirae, a short-cut partial nitrification and denitrification (PND) or partial nitrification, denitrification and anammox (PNDA) could occurred in M2 and M3. It is suggested that community may have evolved into an energetically efficient short-cut nitrification, denitrification and anammox consortium to replace the full-range nitrification and denitrification community in M1 and CK under the continued manganese domestication conditions. Enhanced metabolic pathways of hydroxylamine oxidation and the nitric oxide reduction may confirm that PND or PNDA occurred in M2 and M3.

Microbe-mediated simultaneous nitrogen reduction and sulfamethoxazole/N-acetylsulfamethoxazole removal in lab-scale constructed wetlands

Constructed wetlands (CWs) are increasingly used to treat complex pollution such as nitrogen and emerging organic micropollutants from anthropogenic sources. In this study, the denitrification, anaerobic ammonium oxidation, dissimilatory nitrate reduction to ammonium, and nitrous oxide release rates following exposure to the frequently detected sulfonamides sulfamethoxazole (SMX) and its human metabolite, N-acetylsulfamethoxazole (N-SMX), were investigated in lab-scale CWs. Over a period of 190 d, the denitrification rates were noticeably inhibited in the SMX and N-SMX groups at week 5. Subsequently, the denitrification rates recovered, accompanied by an increase in the relevant nitrogen reduction and antibiotic resistance genes (ARGs). The composition of the microbial community also changed during this process. After the denitrification rates recovered, Burkholderia_Paraburkholderia and Gordonia exhibited a significant positive correlation with SMX exposure, which simultaneously reduced nitrate concentrations and degraded antibiotics. Burkholderia_Paraburkholderia is a key carrier of ARGs. Finally, nitrogen reduction (> 90%) and antibiotic removal (> 80%) also recovered in both SMX- and N-SMX-exposed lab-scale CWs during the operation, which revealed the interaction of SMX or N-SMX removal and nitrogen reduction.

Microalgae-based constructed wetland system enhances nitrogen removal and reduce carbon emissions: Performance and mechanisms

Combination of constructed wetlands (CWs) and microalgae-based technologies has been proved as effective wastewater treatment option; however, little attention was paid to investigate the optimal combination ways. This study showed that the integrated system (IS) connecting microalgal pond with CWs exhibited improved pollutant-removal efficiencies and preferred carbon reduction effects compared to other alternatives such as coupled system or independent CWs. Microbial analysis demonstrated that core microorganisms (e.g., Acinetobacter and Thermomonas) of the IS were mostly associated with carbon, nitrogen, and energy metabolism. Based on co-occurrence networks, microbial quantity with denitrification function in the IS accounted for 71.01 % of the microorganism related to nitrogen metabolism, which was higher than that of 48.84 % in the independent CWs, indicating that the presence of microalgae in IS played important role in promoting biological denitrification. These findings provide insights into the microbial mechanism and highlights the complementary effects between microalgae and CWs.

Exploring the resilience of constructed wetlands to harmful algal blooms disturbances: A study on microbial response mechanisms

Constructed wetlands (CWs) have emerged as a promising environmentally sustainable technique for wastewater treatment. However, the susceptibility of CWs to disturbances caused by harmful algal blooms (HABs) raises concerns. This study aimed to investigate the impact of HABs on the pollutants' removal performance of CWs and the response of rhizosphere microbial community. Results revealed that CWs possessed an adaptive capacity that enabled them to recover caused by HABs. The rhizosphere was found to stimulate the occurrence of Acinetobacter, which played a critical role to help resist HABs disturbance. This study also observed an increased dissimilatory nitrate reduction metabolic pathway which promoted denitrification and enhanced the nitrogen removal efficiency of CWs. Additionally, the structural equation model further suggested that dissolved oxygen exerted a significant influence on the microbial activities and then affected the pollutants removal performance. Overall, our findings shed light on the mechanism for CW stability maintenance during HABs disturbance.

Enrichment and response of iron-metabolizing microorganisms and metabolic genes in the contaminated area of stratified stacking coal gangue dumps, Northern China

In the Xishan coalfield of northern China, the stratified stacking of soil and gangue was applied to limit the acid pollution from high-sulfur coal gangue. In this study, we found that stratified stacking can effectively neutralize the acidity, with the pH value of gangue-leaching water being 6.02-8.13. In contrast to the acidic contaminated area, most of the microorganisms in the study area sediment were neutrophilic, with the main genera being Arthrobacter, Pseudorhodobacter, Pseudomonas, and Rhodoferax. A variety of iron- and sulfur-metabolizing bacteria was discovered in the gangue-leaching sediment, with the total relative abundance ranging from 4.20 to 23.75%, of which the iron-reducing bacteria (FeRB) accounted for the highest percentage. The distributions of these functional microorganisms in the samples were significantly influenced by Fe and S. The co-occurrence network analysis revealed a significant positive correlation between the iron- and sulfur-metabolizing bacteria in the sediment (93.75%), indicating a strong reciprocal symbiotic relationship between these bacteria. The iron and sulfur metabolism genes in the sediment were predicted and compared based on the Tax4Fun functional prediction method. Results showed that functional genes related to iron metabolism were highly expressed in the gangue-leaching sediment. This study enhances the understanding of iron and sulfur metabolism in gangue-leaching contaminated areas.

Effects of two plant species combined with slag-sponges on the treatment performance of contaminated saline water in constructed wetland

Constructed wetland (CW), an ecological water treatment system, can purify and repair the damaged saline water body in an open watershed, but its repairing function is limited at low temperature under salt stress. In this study, two different plant species with slag-sponge layer were operated to enhance the purification effect of CW on the damaged saline water body. The results showed that the combination of Scirpus mariqueter and slag-sponges in CW had a better purification effect especially under the condition of salinity of 10‰ (S = 10) with a respective removal efficiency of 91.04% of total nitrogen, 80.07% of total phosphorus, and 93.02% of COD in high temperature (25 ~ 35 °C). Furthermore, ecological traits (enzyme activity and amino acids) of plants, the abundance and distribution of functional microorganisms on the surface of slag-sponges, and the microbial state on the substrate surface of the denitrifying zone of CW were analyzed to explain how exactly the combinations worked. It was found that the enrichment of functional microorganisms in slag-sponge and the anaerobic zone of plants have improved the nitrogen and phosphorus removal. Plants maintained high enzyme activities and the ability to synthesize key amino acids under salt stress to ensure the growth and reproduction of plants and achieve the assimilation function. Scirpus mariqueter combined with slag-sponges in CW effectively improved the purification effect of damaged saline water, indicating that it is an ecological and green saline water treatment way.

Enhancement of micropollutant biotransformation by adding manganese sand in constructed wetlands

Recent investigations have shown that the addition of manganese (Mn) sand to constructed wetlands (i.e., Mn-amended CWs) can improve the performance of organic micropollutants (MPs) removal. In addition to the direct oxidation and adsorption of Mn oxides, the indirect role of Mn oxides in MP biotransformation is crucial to the removal of MPs but has seldom been referred to. Herein, we constructed lab-scale CWs with or without the addition of natural Mn sand (∼35% Mn oxides) to decipher the influence of Mn oxides on the biotransformation of the six selected MPs which commonly existed in the wastewater. The experimental results showed that the addition of Mn sand to CWs can improve the removal of MPs (8.48% atrazine, 13.16% atenolol, and 6.27% sulfamethoxazole [pairwise Wilcoxon test p < 0.05]). Combining the detection of transformation products and metagenomic sequencing, we found that the enhanced removal of atrazine in the Mn-amended CWs was mainly due to the bioaugmented hydroxylation process. The enrichment of biotransformation-related genes and associated microbes of atenolol and sulfamethoxazole in Mn-amended CWs indicated that the addition of Mn sand to CWs can strengthen the biotransformation of MPs. Furthermore, we found that these MP-biodegrading microbes were widely present in the full-scale CWs. Overall, our research provides fundamental information and insights for further application of Mn-amended CWs in MP removal.

Coupled mixotrophic denitrification and utilization of refractory organics driven by Mn redox circulation for significantly enhanced nitrogen removal

Coupled mixotrophic denitrification and degradation of organics driven by redox transition of Mn for nitrogen removal has attracted much attention. Herein, this study explored the removal performance and mechanisms for nitrogen and refractory organics from secondary effluent in up-flow MnOx biofilter. Results showed that the removal of organics and nitrate was significantly enhanced by the synergistic process of heterotrophic denitrification and Mn(II)-driven autotrophic denitrification (MnAD), which were originated from the facilitation of Mn circulation. But nitrate removal was closely related to the types of carbon source and Mn(II) concentration. Single small molecular carbon source (glucose) performed better than mixed carbon source (humic acid and glucose) in nitrate removal process (74.8% in stage 1-2 vs. 54.1% in stage 3-5). And raising external Mn(II) concentration increased the contribution of MnAD (60.2% in stage 5 vs. 46.5% in stage 3) to nitrate removal. Furthermore, the relationship between Mn/N transformation and microbial community structure shifts revealed that the redox transition between Mn(II) and Mn(IV) promoted the enrichment of denitrogenation bacteria and functional genes, thus contributing to pollutants removal. Our studies expand the knowledge of MnOx-mediated pollutants removal processes and support the potential application of MnOx for removal of residual refractory organics and nitrogen.

A review: Manganese-driven bioprocess for simultaneous removal of nitrogen and organic contaminants from polluted waters

Water pollutants, such as nitrate and organics have received much attention for their harms to ecological environment and human health. The redox transformation between Mn(Ⅱ) and Mn(Ⅳ) for nitrogen and organics removal have been recognized for a long time. Mn(Ⅱ) can act as inorganic electron donor to drive autotrophic denitrification so as to realize simultaneous removal of Mn(Ⅱ), nitrate and organic pollutants. Mn oxides (MnOx) also play an important role in the adsorption and degradation of some organic contaminants and they can change or create new oxidation pathways in the nitrogen cycle. Herein, this paper provides a comprehensive review of nitrogen and organic contaminants removal pathways through applying Mn(Ⅱ) or MnOx as forerunners. The main current knowledge, developments and applications, pollutants removal efficiency, as well as microbiology and biochemistry mechanisms are summarized. Also reviewed the effects of factors such as the carbon source, the environmental factors and operation conditions have on the process. Research gaps and application potential are further proposed and discussed. Overall, Mn-based biotechnology towards advanced wastewater treatment has a promising prospect, which can achieve simultaneous removal of nitrogen and organic contaminants, and minimize sludge production.

Nitrogen, manganese, iron, and carbon resource acquisition are potential functions of the wild rice Oryza rufipogon core rhizomicrobiome

BACKGROUND

The assembly of the rhizomicrobiome, i.e., the microbiome in the soil adhering to the root, is influenced by soil conditions. Here, we investigated the core rhizomicrobiome of a wild plant species transplanted to an identical soil type with small differences in chemical factors and the impact of these soil chemistry differences on the core microbiome after long-term cultivation. We sampled three natural reserve populations of wild rice (i.e., in situ) and three populations of transplanted in situ wild rice grown ex situ for more than 40 years to determine the core wild rice rhizomicrobiome.

RESULTS

Generalized joint attribute modeling (GJAM) identified a total of 44 amplicon sequence variants (ASVs) composing the core wild rice rhizomicrobiome, including 35 bacterial ASVs belonging to the phyla Actinobacteria, Chloroflexi, Firmicutes, and Nitrospirae and 9 fungal ASVs belonging to the phyla Ascomycota, Basidiomycota, and Rozellomycota. Nine core bacterial ASVs belonging to the genera Haliangium, Anaeromyxobacter, Bradyrhizobium, and Bacillus were more abundant in the rhizosphere of ex situ wild rice than in the rhizosphere of in situ wild rice. The main ecological functions of the core microbiome were nitrogen fixation, manganese oxidation, aerobic chemoheterotrophy, chemoheterotrophy, and iron respiration, suggesting roles of the core rhizomicrobiome in improving nutrient resource acquisition for rice growth. The function of the core rhizosphere bacterial community was significantly (p < 0.05) shaped by electrical conductivity, total nitrogen, and available phosphorus present in the soil adhering to the roots.

CONCLUSION

We discovered that nitrogen, manganese, iron, and carbon resource acquisition are potential functions of the core rhizomicrobiome of the wild rice Oryza rufipogon. Our findings suggest that further potential utilization of the core rhizomicrobiome should consider the effects of soil properties on the abundances of different genera. Video Abstract.

Successional dynamics of microbial communities in response to concentration perturbation in constructed wetland system

Constructed wetlands (CWs) are widely considered as resilient systems able to adapt to environmental perturbations. Little attention has been paid, however, to microbial dynamics when CWs withstand and recover from external shock. To understand the resilience of CWs, this study investigated rhizosphere microbial dynamics when CWs were subjected to influent COD perturbation (200 mg/L-1600 mg/L). Results demonstrated that CWs had strong adaptability to different influent perturbations, characterized by transitions from fluctuating to stable pollutant removal. Microbial analysis showed that rhizosphere microorganisms competed for niches in response to increased COD concentrations, and Trichococcus played key roles in resisting concentration perturbations. Structural equation modeling indicated that rhizosphere community succession and microbial energy metabolism were shaped by pH and DO. These findings provide insights into the mechanism for CW stability maintenance when facing concentration perturbations.

New insight into ammonium oxidation processes and mechanisms mediated by manganese oxide in constructed wetlands

Manganese oxide (MnOx) mediated ammonium (NH₄⁺) oxidation in wetlands is receiving increased interest; however, the biochemical mechanisms of this process are vague due to only few studies have focused on terrestrial ecosystems. In this study, three subsurface flow constructed wetlands (CWs), high/low content of Mn-sand CW (HMn-CW/LMn-CW) and quartz sand CW (C-CWs), were set up to explore the extent of ammonium nitrogen (NH₄⁺-N) removal and underlying mechanisms. According to the surface characteristics of Mn-sand, MnOx nanospheres were loaded as birnessite on the sand, while changes of the Mn/N contents indicated involvement of Mn-sand in NH₄⁺-N removal. During the 120-day operation, higher extent of NH₄⁺-N removal with decreased nitrous oxide (N₂O) emission was achieved in the HMn-CW (76%) than in the LMn-CW (73%) and C-CW (67%). According to the distribution of nitrogen compounds and Mn²⁺, Mn-sand in the HMn-CW delayed oxidation of NH₄⁺ and production of nitrate and nitrite. High abundance of Zooloea and Psychrobacter was observed in the Mn-sand layer of HMn-CW, corresponding to a higher observed NH₄⁺-N removal. NH₄⁺ oxidation to hydroxylamine and then to nitrite was enhanced in HMn-CW due to ammonia monooxygenase genes being promoted. The decrease of N₂O emission was closely related to the genus TM7a, verified by Pearson correlation analysis. Our findings expand the knowledge of MnOx-mediated NH₄⁺ oxidation in wetlands and support the potential application of manganese oxide for effective nitrogen removal in CWs.

Mn(II) Sorption on Stream Sediments Sampled in Manganese Mining Area: Dynamics and Mechanisms

The stream sediments that have been impacted by manganese (Mn) containing wastewater for decades contain not only abundant microorganisms but also organic/inorganic substances. To achieve effective treatment of manganese (Mn)-containing effluent and recovery of Mn from water/sediments, the Mn(II) sorption behaviors and mechanism on sediments of a stream in Mn mining areas were studied. In addition, the study analyzed the effects of various factors (initial concentration, solution pH, sediment dose, contact time, and coexisting cations) on the Mn sorption efficiency of Daxin sediments, and explored the contribution of microbial activity in the sediment sorption of Mn(II). The results showed that the sorption process of Mn(II) on the sediments was consistent with the Elovich and Freundlich models, and the removal of heavy metals was maximum at 40 °C (62.47–98.93%), pH = 8 (77.51%), initial concentration of 1 mmol·L−1 (95.37%) and sediment dosing of 12 g·L−1 (98.93%). The addition of 50 mM NaN3 inhibited the microbial activity in the Daxin sediment, reducing the sorption and removal rates of Mn(II) by 0.605 mg·g−1 and 8.92%, respectively. After sorption, the proportion of the Fe–Mn oxidation(iron–manganese) state in Daxin sediments decreased from 54% to 43%, while the proportion of the exchangeable state increased by 10.80%. Microorganisms in the sediment had a positive effect on inhibiting heavy metal migration and reducing the bioavailability of contaminants in the soil. Through this study, we hope to further understand the sorption and desorption mechanism of manganese by stream sediments in manganese ore areas, so as to provide a guide on the management and recovery of Mn from stream sediments in manganese mining areas.