Reed restoration decreased nutrients in wetlands with dredged sediments: Microbial community assembly and function in rhizosphere

Non-synergistic effects of microplastics and submerged macrophytes on sediment microorganisms involved in carbon and nitrogen cycling

Submerged macrophyte communities play a crucial role in regulating sediment carbon and nitrogen cycling in lake ecosystems. However, their interactions with emerging pollutants such as polystyrene microplastics (PS-MPs) remain poorly understood. In this study, we employed metagenomic analysis to examine the combined effects of submerged macrophyte communities and PS-MPs on sediment microbial communities, focusing on microbial populations, functional genes, and metabolic pathways involved in carbon and nitrogen cycling. Our results revealed a non-synergistic interaction between macrophyte communities and PS-MPs in shaping sediment biogeochemical processes. While increasing PS-MPs concentrations (from 0.5 to 2.5 % w/w) significantly enhanced microbial diversity (species richness increased from 533 to 1301), the presence of macrophytes moderated this response. Notably, we observed differential selective pressures on functional genes involved in key carbon and nitrogen cycling steps, particularly amoAB and amoC, nirS, and nirK, indicating distinct shifts in microbial functional groups. Furthermore, we identified complex substrate-pathway interactions: nitrate and ammonium differentially influenced fermentation and methanogenesis, while inorganic carbon positively regulated nitrate dissimilatory reduction. These findings provide novel insights into the regulatory mechanisms of submerged macrophytes in sediment biogeochemical cycling under microplastic stress, highlighting their potential role in maintaining ecosystem functions in contaminated aquatic environments.

Distinct Assembly Patterns of Soil Bacterial and Fungal Communities along Altitudinal Gradients in the Loess Plateau's Highest Mountain

A critical issue in microbial ecology is quantifying the relative contributions of deterministic and stochastic processes to microbial community assembly, and predicting ecosystem function by understanding the ecological processes of community composition is an integral part. However, the mechanisms driving microbial community assembly along altitudinal gradients in mountain ecosystems remain largely unexplored. Here, we used high-throughput sequencing to examine the structural characteristics and diversity maintenance mechanisms of soil bacterial and fungal communities along an altitudinal gradient (2632-3661 m) in Mahan Mountain, the highest peak of the Loess Plateau. Proteobacteria, Acidobacteriota and Actinobacteriota dominated the bacterial communities, while Ascomycota, Basidiomycota and Mortierellomycota were the predominant fungal groups. Although elevation did not significantly affect bacterial and fungal alpha diversity, notable shifts in community structure were observed along the altitudinal gradients. Bacterial communities were predominantly shaped by deterministic processes, leading to pronounced structural and compositional differentiation across altitudes. In contrast, fungal community assembly was primarily determined by a combination of deterministic and stochastic processes, leading to small pronounced structural divergence. The interplay of topography, climate, and soil conditions influenced the altitudinal distribution and community structure of soil bacteria in this mountain ecosystem.

Habitat preference drives the community composition, beta diversity and assembly processes of benthic diatoms: A case study of a wetland cluster in a cold region

The loss of biodiversity in urban wetlands has become increasingly severe due to urbanization. Based on their attachment patterns, benthic diatoms can be divided into several types according to habitat (i.e., epilithic, epiphytic, and epipelic). Diatoms are often used as ecological indicators due to their sensitivity to environmental changes. However, details concerning the composition, temporal dynamics, and assembly mechanisms of benthic diatom communities in urban wetland habitats remain unclear. In this study, we systematically evaluated the composition and seasonal dynamics of benthic diatoms among three different habitats and validated the applicability of eDNA for studies of diatoms. The relationship between the taxonomic and functional diversity of diatom communities was examined, and the assembly mechanisms of diatom communities were explored. An analysis of 249 benthic diatom samples and 27 water samples from nine sites over eight months revealed differences in the composition of diatom communities among epilithic, epiphytic, and epipelic habitats. In diatoms from different hydrological periods, the contribution of turnover to total taxonomic beta diversity was much larger than that of nestedness, while the nestedness components of functional diversity were comparatively large. Nutrients, total dissolved solids, and water temperature were the main variables that affected the taxonomic and functional beta diversity of the benthic diatom communities. The results suggested that benthic diatom community assembly in the three habitats and eDNA was primarily driven by deterministic processes. This study has demonstrated how habitat preference affects the composition, beta diversity and assembly processes of benthic diatom communities and provided novel insights into the conservation of biodiversity in urban wetlands.

Manganese-modified reed biochar decreased nutrients and methane release from algae debris-contaminated sediments

Biochar is one of the ways for carbon storage, pollution control and biosolid reuse. Aquatic plant reeds are widely used in nutrient removal in wetlands and have huge biomass. Nonetheless, little is known regarding the effects of reed-based biochar on sediments. In this study, reed-based biochar (BC) modified with or without Mn-oxidizers (MBC) was prepared to investigate their impacts on nutrient removal, methane (CH4) emission fluxes, and CH4 concentration and microbial community in sediments for 20 days. We found that BC and MBC significantly reduced CH4 emission fluxes by 56.84 ± 10.47% and 69.95 ± 0.76% (p < 0.05) compared to control (CK), respectively. In addition, BC and MBC had a higher efficiency of nutrient removal, and the removal rate increased by 4.4% for NH4+-N and 10.13% for TN in BC and by 3.21%, 8.43% and 18.29% for NH4+-N, TN and TP in MBC, respectively. Proteobacteria, Chloroflexi, Bacteroidota, Firmicutes, Desulfobacterota and Acidobacteriota were the predominant phyla in sediments and might contribute to nutrient removal. Network analysis revealed that biochar addition promoted interspecific competition in sediments, which could be more beneficial for enhancing the stability of microbial community structures. The decreased mcrA (CH4 bioproduction) abundance but increased pomA (CH4 oxidation) abundance was detected in BC and MBC compared to CK, explaining biochar-reduced CH4 emissions. This study highlights that reed straw-based biochar can be used in the in-situ remediation of polluted sediments and provides a choice for carbon storage and pollution control for managers.

Pollutant accumulation characteristics of substrates and mechanism of microbial action in different ecological ditches

Ecological ditches serve as one of the important measures for the concentrated infiltration of stormwater in the construction process of sponge cities. Prolonged concentrated infiltration of stormwater can lead to the accumulation of pollutants and pollution risks in the substrate of ecological ditches. In this study, two different substrate ecological ditches were constructed, namely, a combined substrate ecological ditch with zeolite + ceramsite (EA), and a biological substrate ecological ditch (EB). The accumulation characteristics of pollutants and microbial mechanisms in the ecological ditches were evaluated by simulating the cumulative rainfall test for three years. Results showed that there was serious total nitrogen (TN) contamination in both EA and EB substrates, with mean values of 718.6 and 802.7 mg/kg, respectively. The average contents of potentially toxic elements (Cu, Pb, and Zn) in EA and EB substrates were higher than the background values of soil elements in China, and Cu posed considerable ecological risks to the environment. Proteobacteria was the dominant phylum and accounted for 32.85-41.33% in two ditches; the total number of denitrifying functional bacterial genera in the EB increased by 1.53% than EA, which proved that the biological substrate was more favourable for the growth of denitrifying microorganisms. The accumulation characteristics of pollutants and microbial mechanisms in the ecological ditches with different substrates above provide a reference for extending the service life of ecological ditch facilities.

Vertical distribution and influencing factors of soil PAHs under different ecosystem habitats in the Liaohe River Estuary Wetlands, Northeastern China

The vertical distribution, sources and influencing factors of polycyclic aromatic hydrocarbons (PAHs) in soil across ecosystem habitats were investigated around the Liaohe River Estuary (LRE) Wetland. The concentration of Ʃ16PAHs ranged from 41.0 to 435.4 ng g-1 dw, with a predominance of low molecular weight PAHs. Overall, PAHs and physicochemical properties of soil decreased with depth. Vegetation was found to increase soil PAHs. Additionally, soil physicochemical properties also regulated PAHs concentration, particularly for PAHs with high molecular weight. Among the habitats, total organic carbon was the key influencing factor for Suaeda heteroptera, while specific surface area was crucial for Phragmites australis. Results of characteristic ratio method and principal component analysis revealed that PAHs in LRE primarily originate petroleum, coal and biomass combustion. In summary, vegetation colonization significantly affected the distribution, sources, and controlling factors of PAHs. These findings are meaningful for management of soil PAHs across various ecosystem habitats.

Interactions between SDBS and Hydrilla verticillata - epiphytic biofilm in wetland receiving STPs effluents: Nutrients removal and epiphytic microbial assembly

The fate and effects of sodium dodecyl benzene sulfonate (SDBS) in sewage treatment plants effluents on nutrients and submerged macrophytes are far from clear in wetlands. This study conducted a 24-day experiment to investigate changes in nutrients and epiphytic biofilm of Hydrilla verticillata in wetlands receiving effluents with 0.5, 2 and 5 mg L-1 SDBS. The decrease of SDBS in overlying water followed pseudo-first-order kinetic equation, with over 80 % of SDBS removal achieved. 2 and 5 mg L-1 SDBS decreased nutrient removal efficiency, induced oxidative stress response and damaged cells of H. verticillata. SDBS altered bacterial and eukaryotic community diversity. 0.5 mg L-1 SDBS can promote carbon fixation and methane oxidation of microorganisms. Network analysis revealed that 0.5 mg L-1 SDBS decreased the stability of epiphytic ecosystems. Mantel tests indicated significant influences of SDBS, temperature, and total nitrogen on epiphytic microbial communities.

Occurrence, risk assessment and source apportionment of perfluoroalkyl acids in the river of a hill-plain intersection region: The impacts of land use and river network structure

Studying the impacts of land use and river network structure on perfluoroalkyl acids (PFAAs) footprint in rivers is crucial for predicting the fate of PFAAs in aquatic environments. This study investigated the distribution, ecological risks, sources and influence factors of 17 PFAAs in water and sediments of rivers from hills to plain areas. The results showed that the detection frequencies were higher for short-chain PFAAs than long-chain PFAAs in water, whereas an opposite pattern was found in sediments. The concentration of ∑PFAAs ranged from 59.2 to 414 ng/L in water and from 1.4 to 60.1 ng/g in sediments. Perfluorohexanoic acid and perfluorooctanoic acid were identified as the main pollutants in the river. The average concentrations of PFAAs were higher in the aquaculture areas (water: 309.8 ng/L; sediments: 43.27 ng/g) than in residential areas (water: 206.03 ng/L; sediments: 11.7 ng/g) and farmland areas (water: 123.12 ng/L; sediments: 9.4 ng/g). Environmental risk assessment showed that PFAAs were mainly low risk or no risk in water, but were moderate risk and even high risk in sediments, especially for perfluorooctane sulfonate. Source apportionment found that PFAA sources were mostly from industry, wastewater discharge, and surface runoff. Dissolved oxygen, chemical oxygen demand, water system circularity, network connectivity and organic matter were significantly correlated to PFAA concentration, indicating that the physicochemical properties and river network might directly influence the environmental behavior of PFAAs. The built-up area was positively correlated with PFAAs. These findings indicated that a comprehensive understanding of the influences of land use and river network structure on PFAAs in rivers is essential for managers to formulate effective PFAA control strategies.

Glufosinate-ammonium increased nitrogen and phosphorus content in water and shaped microbial community in epiphytic biofilm of Hydrilla verticillata

Glufosinate-ammonium (GLAM) can be released into adjacent water bodies with rainfall runoff and return water from farmland irrigation. However, impacts of GLAM on aquatic organisms remain unclear. In this study, changes in water quality, plant physiological parameters and epiphytic microbial community were investigated in wetlands with Hydrilla verticillata exposed to GLAM for 24 days. We found GLAM addition damaged cell and reduced chlorophyll a content in Hydrilla verticillata leaves, and increased ammonium and phosphorus in water (p < 0.001). The α-diversity increased in bacterial community but decreased in eukaryotic community with GLAM exposure. Neutral community models explained 62.3 % and 55.0 % of the variance in bacterial and eukaryotic communities, respectively. Many GLAM micro-biomarkers were obtained, including some clades from Proteobacteria, Bacteroidete, Actinobacteriota, Phragmoplastophyta, Annelida and Arthropoda. Redundancy analysis revealed that GLAM concentration was positively correlated to Flavobacterium, Gomphonema and Closterium but negatively to Methyloglobulus and Methylocystis. Network analysis revealed that 15 mg/L GLAM disturbed the interactions among phytoplankton, protozoa, metazoan and bacteria and reduced the stability of the microbial communities compared to 8 mg/L GLAM. GLAM shaped the nitrogen and phosphorus cycle related bacterial genes. This study highlights that herbicides are non-neglectable factors affecting the efficiency of aquatic ecological restoration in agricultural areas to control agricultural non-point source pollution.

Chlormequat inhibits Vallisneria natans growth and shapes the epiphytic biofilm microbial community

Submerged macrophytes can overgrow and negatively affect freshwater ecosystems. This study aimed to investigate the use of chlormequat (CQ) to regulate submerged Vallisneria natans growth as well as its impact on the microbial community of epiphytic biofilms. V. natans height under CQ dosages of 20, 100, and 200 mg/L decreased within 21 days by 12.57%, 30.07%, and 44.62%, respectively, while chlorophyll content increased by 1.94%, 20.39%, and 38.83%. At 100 mg/L, CQ reduced the diversity of bacteria in the biofilm attached to V. natans leaves but increased the diversity of the eukaryotic microbial community. CQ strongly inhibited Cyanobacteria; compared with the control group, the treatment group experienced a significant reduction from 36.54% to 2.61%. Treatment significantly inhibited Gastrotricha and Rotifera, two dominant phyla of eukaryotes in the leaf biofilm, reducing their relative abundances by 17.41% and 6.48%, respectively. CQ significantly changed the leaf biofilm microbial community correlation network. The treatment group exhibited lower modularity (2.012) compared with the control group (2.249); however, the central network of the treated group contained a higher number of microbial genera (13) than the control group (4), highlighting the significance of eukaryotic genera in the network. The results obtained from this study provide invaluable scientific context and technical understanding pertinent to the restoration of submerged macrophytes within aquatic ecosystems. PRACTITIONER POINTS: Chlormequat reduced the plant height but increased leaf chlorophyll content. Chlormequat reduced biofilm bacterial diversity but increased eukaryotic diversity. Chlormequat affected the bacterial-fungal association networks in biofilms.

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.

Ecological role of reed belts in lakeside zone: Impacts on nutrient retention and bacterial community assembly during Hydrilla verticillata decomposition

Reed belts acting as basic nutrient filters are important parts of lake buffer riparian zones. However, little is known about their impacts on nutrient release and bacterial community during plant litter decomposition. In this study, a field experiment was conducted in west-lake Taihu to monitor the changes in nutrients, bacterial enzymatic activities, and bacterial community in plant debris during Hydrilla verticillata (H. verticillata) decomposition in open water (HvC) and reed belts (HvL) area for 126 days. We found that there was lower temperature but higher nutrient concentrations in overlying water in HvL than HvC. Partial least squares path modeling revealed that environmental parameters in overlying water had important impacts on bacterial activities and nutrient release (such as alkaline phosphatase, cellulase, and soluble sugar) and therefore affected dissolved organic matter components in plant debris. According to Illumina sequencing, 46,003 OTUs from 10 dominant phyla were obtained and Shannon index was higher in HvL than HvC at the same sampling time. Neutral community model explained 49% of bacterial community variance and immigration rate by the estimate of dispersal in HvC (Nm: 27,154) and HvL (Nm: 25,765), respectively. Null model showed stochastic factors governed the bacterial community assembly in HvC (66.67%) and HvL (87.28%). TP and pH were key factors affecting the bacterial community structure at the phylum level. More hubs and complex interactions among bacteria were observed in HvL than HvC. Function analysis showed bacterial community had important role in carbon, organic phosphorus, and nitrogen removal but phosphorus-starvation was detected in debris of H. verticillata. This study provides useful information for understanding the changes in nutrients and bacterial community in litter during H. verticillata decomposition and highlights the role of reed belts on retained plant litter to protect lake from pollution.

Interactions between water quality and microbes in epiphytic biofilm and superficial sediment of lake in trophic agriculture area

Epiphytic and superficial sediment biofilm-dwelling microbial communities play a pivotal role in water quality regulation and biogeochemical cycling in shallow lakes. However, the interactions are far from clear between water physicochemical parameters and microbial community on aquatic plants and in surface sediments of lake in trophic agriculture area. This study employed Illumina sequencing, Partial Least Squares Path Modeling (PLS-PM), and physico-chemical analytical methods to explore the interactions between water quality and microbes (bacteria and eukaryotes) in three substrates of trophic shallow Lake Cyohoha North, Rwanda. The Lake Cyohoha was significantly polluted with total phosphorus (TP), total nitrogen (TN), nitrate nitrogen (NO3-N), and ammonia nitrogen (NH3-N) in the wet season compared to the dry season. PLS-PM revealed a strong positive correlation (+0.9301) between land use types and physico-chemical variables in the rainy season. In three substrates of the trophic lake, Proteobacteria, Cyanobacteria, Firmicutes, and Actinobacteria were dominant phyla in the bacterial communities, and Rotifers, Platyhelminthes, Gastrotricha, and Ascomycota dominated in microeukaryotic communities. As revealed by null and neutral models, stochastic processes predominantly governed the assembly of bacterial and microeukaryotic communities in biofilms and surface sediments. Network analysis revealed that the microbial interconnections in Ceratophyllum demersum were more stable and complex compared to those in Eichhornia crassipes and sediments. Co-occurrence network analysis (|r| > 0.7, p < 0.05) revealed that there were complex interactions among physicochemical parameters and microbes in epiphytic and sediment biofilms, and many keystone microbes on three substrates played important role in nutrients removal, food web and microbial community stable. These findings emphasize that eutrophic water influence the structure, composition, and interactions of microbes in epiphytic and surface sediment biofilms, and provided new insights into the interconnections between water quality and microbial community in presentative substrates in tropical lacustrine ecosystems in agriculturally polluted areas. The study provides useful information for water quality protection and aquatic plants restoration for policy making and catchment management.

Toward an intensive understanding of sewer sediment prokaryotic community assembly and function

Prokaryotic communities play important roles in sewer sediment ecosystems, but the community composition, functional potential, and assembly mechanisms of sewer sediment prokaryotic communities are still poorly understood. Here, we studied the sediment prokaryotic communities in different urban functional areas (multifunctional, commercial, and residential areas) through 16S rRNA gene amplicon sequencing. Our results suggested that the compositions of prokaryotic communities varied significantly among functional areas. Desulfomicrobium, Desulfovibrio, and Desulfobacter involved in the sulfur cycle and some hydrolytic fermentation bacteria were enriched in multifunctional area, while Methanospirillum and Methanoregulaceae, which were related to methane metabolism were significantly discriminant taxa in the commercial area. Physicochemical properties were closely related to overall community changes (p < 0.001), especially the nutrient levels of sediments (i.e., total nitrogen and total phosphorus) and sediment pH. Network analysis revealed that the prokaryotic community network of the residential area sediment was more complex than the other functional areas, suggesting higher stability of the prokaryotic community in the residential area. Stochastic processes dominated the construction of the prokaryotic community. These results expand our understanding of the characteristics of prokaryotic communities in sewer sediment, providing a new perspective for studying sewer sediment prokaryotic community structure.

Community structures of mangrove endophytic and rhizosphere bacteria in Zhangjiangkou National Mangrove Nature Reserve

Bacterial communities play an important role in mangrove ecosystems. In order to gain information on the bacterial communities in mangrove species and rhizospheres grown in Zhangjiangkou National Mangrove Nature Reserve, this study collected root, branch, and leaf samples from five mangrove species as well as rhizosphere and non-rhizosphere samples and analyzed the community structure of endophytic bacteria and bacteria in rhizosphere and non-rhizosphere using Illumina high-throughput sequencing technique. Bacteria in 52 phyla, 64 classes, 152 orders, 295 families, and 794 genera were identified, which mainly belonged to Proteobacteria, Cyanobacteria, Actinobacteria, Firmicutes, Bacteroidetes, Fusobacteria, and Nitrospirota. At each taxonomic level, the community structure of the rhizosphere bacteria varied slightly with mangrove species, but endophytic bacteria differed greatly with plant species. The diversity indices of endophytic bacteria in branch and leaf samples of Acanthus ilicifolius were significantly lower, and endophytic bacteria in the plant tissues had higher abundance in the replication/repair and translation Clusters of Orthologous Genes functional categories but lower abundance in the carbohydrate metabolism category. This study helps to understand the community structure and diversity characteristics of endophytic and rhizosphere bacteria in different mangrove plants. Provide a theoretical basis for in-depth research on the functions of mangrove ecosystems.