Distribution patterns and community assembly processes of eukaryotic microorganisms along an altitudinal gradient in the middle reaches of the Yarlung Zangbo River

Climate and biological factors jointly shape microbial community structure in the Yarlung Zangbo River during the dry season

Microorganisms are crucial components of aquatic ecosystems, playing key roles in biogeochemical cycles. Understanding microbial diversity and community assembly mechanisms is essential for river management and sustainable utilization of freshwater resources. However, the role of inter-microbial taxonomic group relationships in shaping community structures within high-altitude river ecosystems is unclear. This study utilizes high-throughput sequencing and bioinformatics analysis to describe the spatial dynamics of fungal and bacterial communities in the Yarlung Zangbo River at a broad environmental scale and to elucidate their community assembly mechanisms. The results indicate a significant distance-decay pattern in the fungal (p < 0.001) and bacterial (p < 0.001) communities of the Yarlung Zangbo River, with substantial differences in microbial taxonomic composition, diversity, and community structure across different regions (fungi ANOSIM R = 0.20, bacteria ANOSIM R = 0.63). Homogeneous selection predominated the community assembly of fungi (average: 67.4 %) and bacteria (average: 74.5 %) in aquatic environments. As altitude decreases, the influence of deterministic processes on fungal communities increases, while their influence on bacterial communities decreases. At the basin scale, the community structures of fungi and bacteria are mainly influenced by the degree of functional or ecological niche differentiation of another taxonomic group, as well as the hydrothermal conditions of the basin that vary with longitude. This study enhances the understanding of fungal and bacterial biogeographic patterns and community assembly mechanisms in plateau rivers, providing new perspectives for microbial ecological research in these ecosystems.

Similar but different assembly processes of bacterial and micro-eukaryotic communities in an urban river

Bacteria and micro-eukaryotes play important roles in river ecological systems. The processes that govern bacterial and micro-eukaryotic communities in urban rivers are still uncertain. The spatiotemporal characteristics and assembly processes of bacterial and micro-eukaryotic communities in the Xiangjianghe River were explored using 16 S and 18 S rRNA gene amplicon sequencing in the present study. The results indicate that the bacterial and micro-eukaryotic community composition exhibited distinct temporal and spatial variation. The topological characteristics of co-occurrence networks demonstrate that the bacterial and micro-eukaryotic community coexistence patterns vary significantly between the four seasons. Water temperature (WT) and oxidation-reduction potential (ORP) were detected as the most critical factors affecting bacterial and micro-eukaryotic community structure. The stochastic process (dispersal limitation) was the dominant assembly process for bacteria and micro-eukaryotes in all seasons. Deterministic and stochastic processes influenced the bacteria and micro-eukaryotes differently. Compared to bacteria, the values of niche breadth were relatively lower, and the proportion of deterministic processes was relatively higher in micro-eukaryotes. These results expand our understanding of spatiotemporal patterns, assembly mechanisms, and influencing factors of bacterial and micro-eukaryotic communities in urban rivers.

Deciphering Planktonic Bacterial Community Assembly in the Storage Reservoir of the Long-Distance Water Diversion Project

Storage reservoirs are crucial components of long-distance water diversion projects, where water diversion may lead to changes in microbial diversity and community structure. Seasonal variations also drive alterations in microbial communities. However, the way that microbes assemble under the combined effects of water diversion and seasonal variations in the storage reservoir has not been extensively studied. Jihongtan Reservoir is the terminal storage reservoir of the Yellow River to Qingdao Water Diversion Project (YQWD), which had an average annual water diversion period exceeding 290 days in recent years. In this study, 16S rDNA amplicon sequencing was used to investigate the seasonal dynamics and assembly of planktonic bacterial communities during the water diversion period in Jihongtan Reservoir. The results indicate that planktonic bacteria were able to maintain stable diversity across all four seasons, while the community structure underwent significant seasonal succession. Water temperature (WT) was found to be the primary driving environmental factor influencing the seasonal dynamic of planktonic bacterial communities. Co-occurrence network patterns of planktonic bacterial communities varied across different seasons, particularly in spring and winter. The spring network displayed the most complexity, showcasing the highest connectivity and greater stability. In contrast, the winter network was simpler, exhibiting lower local connectivity but higher global connectivity and lower stability. The analysis of the neutral community model and null model revealed that the relative importance of deterministic and stochastic processes in governing planktonic bacterial community assembly varies seasonally. Stochastic processes (dispersal limitation) are more prominent in spring, summer, and autumn, while deterministic processes (heterogeneous selection) play a greater role in winter. This study is essential for gaining a comprehensive understanding of the effects of water diversion projects and offers valuable references for the assessment of other similar projects.

Habitat-specific regulation of microbiota in long-distance water diversion systems

Long-distance water diversion projects typically utilize various hydro-engineering facilities, creating complex and dynamic habitats. However, the microbial dynamics of multi-trophic microorganisms during water diversion and their responses to different hydro-engineering habitats remain poorly understood. In this study, we investigated bacteria, fungi, protists, and metazoa across tunnels, reservoirs, and inverted siphon piping along the main and northern branches of the Yellow River Diversion Project into Shanxi, during spring, summer, and autumn. Our results showed that both seasonal factors and hydro-engineering facilities significantly influenced the composition and diversity of microbiota. Bacterial community composition remained relatively stable during water transport, while fungi, protists, and metazoa exhibited greater spatial variability and habitat specificity. Stochastic processes predominantly governed the community assembly of all microbial groups across all hydro-engineering habitats. The structural features of the main network modules within the co-occurrence networks of multi-trophic species were highly consistent across different seasons within the same habitat, indicating the stable adaptation of microbiota interactions to the same habitat. Patterns of intra-kingdom (within bacteria, fungi, protists, or metazoa) and inter-kingdom (between bacteria, fungi, protists, and metazoa) associations of microbiota in different habitats varied, reflecting specific adaptations of microorganisms to particular habitats and suggesting an important role for environmental filtering. Variance partitioning analysis revealed that environmental factors accounted for 34.21 % to 45.19 % of the variation in the four microbial taxa. Our findings reveal the ecological processes of microbial assembly and adaptation in large-scale water diversion projects, providing insights for project management and risk control.

Bt toxins alter bacterial communities and their potential functions in earthworm intestines

The accumulation and persistence of Bt toxins in soils from Bt plants and Bt biopesticides can result in ecological hazards. Earthworms are one of the most frequently used bioindicators for soil ecological monitoring, characterization, and risk assessment. However, the effects of Bt toxins on earthworm bacterial communities have conversely rarely been studied. Here, the dynamics of exposure to exogenous Bt toxins in earthworm intestines were investigated alongside the impacts of Bt toxins on intestinal bacterial community diversity, stability, and potential function. The intestinal concentration of water-dissolved Bt toxins drastically decreased with increased incubation time. Intestinal bacterial community compositions in earthworm intestines were affected by the concentration of Bt toxin that was added and incubation time. Moreover, lower bacterial community α diversity (i.e., based on Sobs and ACE indices) and significantly higher predicted relative abundances of microbial enzymes in the Bt toxin treatment compared with the control were observed alongside differences in bacterial taxonomic and functional compositional profiles after Bt toxin exposure. The observed changes were most strongly associated with variation in overall functional redundancy. Intestinal bacterial taxa probably played pivotal roles in the degradation and transformation of Bt toxins via nitrogen, phosphorus, and polysaccharide hydrolysis metabolic pathways. Although the application of Bt toxin led to lower intestinal community α diversity and stability after 14 days, these community characteristics were restored upon further incubation to 21 days. Thus, these results suggest that earthworm intestinal microbial communities confer strong resilience and the ability to adapt to Bt toxin stress. Consequently, persistent adverse effects of Bt toxins on intestinal microbiomes were not observed after earthworm exposure to Bt toxins.

Ca2+ enhanced the wastewater treatment performance of microalgal-bacterial consortia: Response of extracellular polymeric substances and bacterial communities

The technology of microalgae-bacteria consortia (MBC) for wastewater treatment is currently facing a variety of challenges. One of the main issues is the construction of structurally and functionally stable symbiont. Ca2+ may be involved in this process, but the underlying mechanism is not well understood. Here the response of MBC to the regulation of Ca2+ was systematically explored from the perspectives of extracellular polymeric substances (EPS) and bacterial communities. The results showed that the exogenous addition of Ca2+ (10-50 mM) not only promoted the production of extracellular polysaccharides and proteins of MBC, but also increased the proportion of some functional groups and components of EPS, such as CO and α-helix. The change of EPS characteristics was conducive to provide more sites for bining Ca2+, which in turn favored the formation of compact MBC via overcoming electrostatic repulsive effect. Besides, the supplementation of Ca2+ favored the recruitment of more EPS-producing bacteria (such as Rhodobacter, Pedobacter, Rhizorhapis, and Sphingopyxis) and indole acetic acid producing bacteria (such as Hydrogenophaga and Agromyces). The enrichment of these functional bacteria not only promoted the adhesion between bacteria and microalgae, but also promoted the growth of symbiotic microalgae, which contributed to the formation of stable large-sized MBC. The change in structure and function of MBC was ultimately reflected in the improved performance in treating municipal wastewater. The findings of this study provided insights into the mechanism underlying the enhanced performance of MBC for wastewater treatment under the influence of Ca2+.

The co-occurrence patterns and assembly mechanisms of microeukaryotic communities in geothermal ecosystems of the Qinghai-Tibet Plateau

Geothermal spring ecosystems, as extreme habitats, exert significant environmental pressure on their microeukaryotic communities. However, existing studies on the stability of microeukaryotic communities in geothermal ecosystems across different habitats and temperature gradients are still limited. In this study, we used high-throughput 18S rDNA sequencing in combination with environmental factor analysis to investigate the co-occurrence patterns, assembly mechanisms, and responses to environmental changes of microeukaryotic communities in sediment and water samples from 36 geothermal springs across different temperature gradients in southern Tibet. The results show that with increasing temperature, the network stability of microeukaryotic communities in sediments significantly improved, while the stability in water communities decreased. The assembly mechanisms of microeukaryotic communities in both sediment and water were primarily driven by undominant processes within stochastic processes. Latitude and longitude were the key factors influencing changes in sediment community composition, while water temperature and electrical conductivity were the major environmental factors affecting water community composition. Additionally, the stability of the geothermal community network was closely related to its response to external disturbances: sediment communities, being in relatively stable environments, demonstrated higher resistance to disturbances, whereas water communities, influenced by environmental changes such as water flow and precipitation, exhibited greater dynamic variability. These findings not only enhance our understanding of the ecological adaptability of microeukaryotic communities in geothermal springs but also provide valuable insights into how microorganisms in extreme environments respond to external disturbances. This is especially significant for understanding how microeukaryotic communities maintain ecological stability under highly dynamic and stressful environmental conditions.

Spatiotemporal distribution patterns and assembly mechanisms of eukaryotic plankton communities in Liujiaxia Reservoir at the northeastern edge of the Tibetan Plateau

Eukaryotic plankton are important parts of the aquatic ecosystem and their community composition and spatiotemporal distribution patterns are affected by environmental factors. The Liujiaxia Reservoir is located at the northeastern edge of the Tibetan Plateau and is a vital resource for communities and agriculture in the region. Revealing the plankton diversity and their correlation with environmental factors is essential for understanding the ecological processes and mechanisms by which plankton contribute to, and maintain the ecosystem function of, the Liujiaxia Reservoir and beyond. This study investigated the detailed spatiotemporal distribution patterns and assembly mechanisms of eukaryotic plankton communities in Liujiaxia Reservoir for three periods during 2021. Significant spatial and temporal variations of abundance and community distribution of eukaryotic plankton were demonstrated. In addition, environmental factors such as water transparency, total phosphorus, total nitrogen, ammonia nitrogen, and pH were confirmed to have the most significant impact on the distribution of these communities in the reservoir. The dominant eukaryotic plankton group was Pyrrophyta, and the species interactions were predominantly cooperative. The trophic level index indicated excellent overall water quality in the reservoir. Deterministic processes were demonstrated as the predominant factors governing the assembly of eukaryotic plankton communities. This study provides valuable insight into the eukaryotic plankton community structure in the Liujiaxia Reservoir and reveals the complex relationships between plankton communities, environmental factors, and water quality.IMPORTANCEBased on 18S rDNA high-throughput sequencing, the spatiotemporal distribution patterns and assembly mechanisms of eukaryotic plankton communities were investigated. This study provides valuable insight into the eukaryotic plankton community structure in the Liujiaxia Reservoir in the northeastern edge of the Tibetan Plateau, and the relationships between eukaryotic plankton communities, environmental factors, and water quality. Through the dynamic changes of these communities, the water quality of the reservoir was assessed to provide basic data for the protection of its biodiversity. The findings of the present study will help to improve knowledge and understanding of the ecological processes and mechanisms by which plankton contribute to ecosystem function in the Liujiaxia Reservoir and beyond.

Mechanisms Driving Seasonal Succession and Community Assembly in Sediment Microbial Communities Across the Dali River Basin, the Loess Plateau, China

Microorganisms are instrumental in river ecosystems and participate in biogeochemical cycles. It is thought that dynamic hydrological processes in rivers influence microbial community assembly, but the seasonal succession and community assembly of river sediments on the Loess Plateau remain unclear. This study used high-throughput sequencing technology (16S and ITS) and the neutral community model to analyze seasonal succession and the assembly processes associated with microbial communities in the Dali River, a tributary of the Yellow River on the Loess Plateau. The results showed that sediment bacterial and fungal community diversity indexes in non-flood season were 1.03-3.15 times greater than those in flood season. There were obvious variations between non-flood and flood seasons in sediment microorganisms. The similarities among all, abundant, and rare microbial communities decreased as geographical distance increased. Proteobacteria (52.5-99.6%) and Ascomycota (22.0-34.2%) were the primary microbial phyla in all, abundant, and rare microbial communities. Sediment ammonia nitrogen, water temperature, and sediment organic carbon significantly affected (p < 0.05) the structure of all, abundant, and rare sediment microorganism communities. The ecological networks for the bacterial community of non-flood season and fungal community of flood season had complex topological parameters. The bacterial community in river sediments was driven by deterministic processes, while the fungal community was dominated by stochastic processes. These results expanded understanding about sediment microbial community characteristics in rivers on the Loess Plateau and provided insights into the assembly processes and the factors driving microbial communities in river networks.

Distribution patterns and community assembly processes of bacterial communities across different sediment habitats of subsidence lakes

Subsidence lakes, formed due to extensive underground coal mining activities, present both ecological challenges and opportunities for alternative land use practices, such as photovoltaic power generation and aquaculture. However, the ecological consequences of these anthropogenic activities on bacterial communities within subsidence lakes remain largely unexplored. To address this knowledge gap, we conducted a comprehensive investigation of bacterial communities in two typical subsidence lake districts located in Huainan, Anhui Province, China. A total of 44 sediment samples were collected across four distinct habitats: photovoltaic zones (PV), aquaculture zones (AC), photovoltaic-aquaculture zones (PV_AC), and unimpacted zones (Natural). Bacterial communities were investigated using 16S rRNA gene sequencing and various statistical methods. Our results revealed that the α-diversity and network complexity of bacterial communities in PV, PV_AC, and AC habitats are significantly higher than habitats of Natural (P < 0.01). Specifically, the α-diversity is the highest in PV habitats, while the network complexity is the highest in AC habitats. The network stability is the highest in PV and PV_AC habitats, while it is the lowest in AC. There were also significant differences in community structure among different habitats, Nitrospirota in PV (31.9%) was higher than that in the other three habitats, the percentage of Firmicute in Natural (21.96%) and PV_AC (13.70%) was higher than other two habitats, Actinobacteriota has the highest proportion in AC (20.93%). Furthermore, stochastic processes dominate community assembly in PV, PV_AC, and AC habitats, it has the highest proportion in PV, particularly on dispersal limitation (DL). However, deterministic processes prevail in Natural habitats, particularly on heterogeneous selection (HeS). Collectively, these findings highlight the significant differences in sediment bacterial communities across various habitats in subsidence lakes. Our study provides valuable insights into understanding the ecological implications of different habitats in subsidence lake ecosystems.

Evidence of sewage discharge on the coalescence mechanism of aquatic microbial communities during high amplitude hydrological periods

Microbial community coalescence is a ubiquitous ecological process in various ecosystems. However, limited research has addressed the effects of the coalescence on microbial ecological processes and network structure, particularly in the context of sewage discharge during high amplitude hydrological periods. Employing 16S rRNA sequencing and species source tracking analysis, we investigated the coalescence pattern of bacterioplankton in the Chishui river and sewage across various hydrological periods. The results demonstrated that the downstream bacterioplankton mainly originated from the upstream water body, and the sewage discharge from the wastewater treatment plants (WWTPs) had less impact on the downstream bacterioplankton. In the low-water period, the bacterioplankton community showed significant coalescence, and the specialist species and functional taxa gathered in the downstream. Bacterioplankton displayed distinct ecological succession patterns after community coalescence, with notable variations in the abundance of dominant group. Bacterioplankton community assembly was dominated by stochastic processes in river and the sewage over different hydrological periods. The ecological networks exhibited the highest complexity in the high-water period, whereas their stability was most pronounced in the low-water period. Species diversity, as opposed to functional and phylogenetic diversity, might be a more accurate indicator to predict changes in microbial network structure. Our findings will provide new perspectives on the mechanisms of aquatic microbial community coalescence in natural environments.

Comparative analysis of community composition and network structure between phyllosphere endophytic and epiphytic fungal communities of Mussaenda pubescens

The phyllosphere constitutes a critical habitat for microorganisms, exerting profound influences on host vitality, developmental dynamics, reproductive functions, and stress resilience. However, the diversity and network structure of endophytic and epiphytic fungal communities within this microecosystem have not been thoroughly explored. In this investigation, high-throughput sequencing technologies were employed to assess the diversity, community composition, and network structure of endophytic and epiphytic fungal communities associated with Mussaenda pubescens across six geographically distinct locations in Southeast China. The results revealed significant differences in community composition and diversity between endophytic and epiphytic fungi, with pronounced geographical variation observed within these phyllosphere fungal communities. Network analysis indicated that epiphytic fungal networks possess enhanced complexity compared with their endophytic counterparts, although the latter exhibit greater network stability. Moreover, stochastic processes were identified as pivotal in shaping the composition of these fungal communities. This research substantially enriches our comprehension of the diversity and organizational mechanisms of phyllosphere fungal communities, providing novel insights into the modalities of species coexistence and the stability of community equilibrium within ecosystems.IMPORTANCEThis study employs high-throughput sequencing technologies to explore the fungal communities within the phyllosphere of Mussaenda pubescens across Southeast China, offering significant insights into plant mycobiome. It demonstrates geographical variations in these fungal communities, with epiphytic fungi exhibiting more complex interaction networks compared with the endophytic fungi. Crucially, the research indicates that stochastic processes play a substantial role in the composition of fungal communities. These findings enhance our comprehension of plant-associated microecosystems and underscore the intricate interplay of randomness in maintaining ecosystem stability and diversity.

Differential insights into the distribution characteristics of bacterial communities and their response to typical pollutants in the sediment and soil of large drinking water reservoir

In this study, a large drinking water reservoir (Fengshuba Reservoir) was chosen as a representative case, and the bacterial communities in the sediments and soils of Water-level fluctuating zone (WLFZ) as well as their responses to heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) were systematically investigated. The results indicated that the abundance and diversity of the bacterial community obviously changed with seasonal hydrological variations in sediments, and the absolute abundance and composition of bacteria community differed significantly between the sediment phase and soil phase. Bacteria with the ability to degrade pollutants rapidly proliferate and gain ascendancy in the soil phase, with Burkholderia-Caballeronia-Paraburkholderia (B-C-P) and Bradyrhizobium forming the core of the largest community. Furthermore, Co-occurrence network analysis indicated that a more stable bacterial community composition in the sediment phase. The community assembly pattern of bacteria in sediments exhibit a higher degree of stochasticity than that observed in soils of the WLFZ. Furthermore, the Spearman correlations found that the interaction between physicochemical factors, HMs, and PAHs with bacteria community was stronger in the soils of WLFZ. In total, the structural equation models indicated that PAHs were the main driver in altering the deterministic process of bacterial community in the sediment, while HMs and physicochemical factors had a greater effect on the bacteria community in the WLFZ. This study systematically revealed the differential characteristics of bacterial community and their response to typical pollutants between the sediments and soils of large drinking water reservoir.

Distinct strategies of microeukaryotic generalists and specialists in Qinghai-Tibet plateau sediment driven by salinity

Unraveling how microeukaryotic generalists and specialists assemble and coexist under environmental stress is central to our understanding of the mechanisms maintaining diversity. Here, we explored the biogeographical distributions of microeukaryotic generalists and specialists in lake surface sediments along a salinity gradient on the Qinghai-Tibet Plateau. We found that relative abundances of Chlorophyta (28.6 %) and Dinophyceae (9.5 %) were higher as habitat generalists than as specialists. Conversely, relative abundances of habitat specialists were higher in the Ciliophora (22.2 %) and Cercozoa (11.6 %) than those of generalists. Environmental adaptation analysis showed a broader niche threshold for generalists than for specialists, whereas a stronger phylogenetic signal for environmental factors was observed for specialists. Thus, increases in salinity had stronger effects on specialists than on generalists through environmental selection and diversification processes. However, null model analysis indicated stochastic processes were the primary drivers of both generalists and specialists. Network analysis revealed that with increasing salinity, specialists were more important than generalists in stabilizing networks. In addition, phylogenetic relatedness indicated that microeukaryotic generalists coexisted because of niche differences, whereas specialists coexisted because of average fitness similarity. Our study will help to predict microeukaryotic responses to environmental changes in aquatic ecosystems.

Remote sensing ecological index (RSEI) affects microbial community diversity in ecosystems of different qualities

Soil microorganisms are key to ecological environment stability, but climate change and human activities exacerbate ecological environment changes. Therefore, assessment of ecological environment quality impacts on microbial diversity is needed. The Tarim River is the largest inland river in China and plays a crucial role in supporting regional biodiversity, maintaining ecological balance, and preventing desertification. In this study, we used the Remote Sensing-based Ecological Index (RSEI) to assess the ecological quality of habitats in the Tarim River Basin and explore the effects of habitat quality (extreme, semi-extreme, and general) on the structural diversity of microbial (bacterial and fungal) communities, biogeographic patterns, co-occurrence networks, and community assembly processes. Study results show that soil physicochemical characteristics varied significantly with habitat quality; highly resilient microorganisms are more abundant in habitats with low ecological quality. RSEI affects changes in microbial communities, and the positive correlation ratio of the network is inversely proportional to RSEI. The interspecific relationships of microbial communities in the Tarim River Basin are dominated by positive correlations, and community assembly is strongly influenced by stochastic processes. RSEI directly affects soil microbial diversity, with its contribution to both bacterial and fungal diversity being 0.27. Total nitrogen (TN) also directly affects microbial diversity, with effects of 0.11 on bacteria and 0.07 on fungi, respectively. This study provides scientific evidence and technical support for understanding microbial diversity in environments and for the development of regional sustainable development policies.

Distinct influences of altitude on microbiome and antibiotic resistome assembly in a glacial river ecosystem of Mount Everest

The profound influences of altitude on aquatic microbiome were well documented. However, differences in the responses of different life domains (bacteria, microeukaryotes, viruses) and antibiotics resistance genes (ARGs) in glacier river ecosystems to altitude remain unknown. Here, we employed shotgun metagenomic and amplicon sequencing to characterize the altitudinal variations of microbiome and ARGs in the Rongbu River, Mount Everest. Our results indicated the relative influences of stochastic processes on microbiome and ARGs assembly in water and sediment were in the following order: microeukaryotes < ARGs < viruses < bacteria. Moreover, distinct assembly patterns of the microbiome and ARGs were found in response to differences in altitude, the latter of which shift from deterministic to stochastic processes with increasing differences in altitude. Partial least squares path modeling revealed that mobile genetic elements (MGEs) and viral β-diversity were the major factors influencing the ARG abundances. Taken together, our work revealed that altitude-caused environmental changes led to significant changes in the composition and assembly processes of the microbiome and ARGs, while ARGs had a unique response pattern to altitude. Our findings provide novel insights into the impacts of altitude on the biogeographic distribution of microbiome and ARGs, and the associated driving forces in glacier river ecosystems.

Microbial community assembly patterns at the species level in different parts of the medium temperature Daqu during fermentation

Medium-temperature Daqu (MT-Daqu) serves as a crucial saccharifying and fermentation agent in the production of strong-flavor Baijiu. Due to the spatial heterogeneity of solid fermentation, significant differences occurred in the fermentation state and appearance features in different parts of Daqu during fermentation. Currently, the understanding of the underlying mechanism behind this phenomenon remains limited. Here, we analyzed the microbial succession and assembly models and driving factors in different parts of MT-Daqu at the species level based on the PacBio single-molecule real-time sequencing technology. The results showed significantly different bacterial and fungal community compositions, successions, and interaction patterns in different parts of MT-Daqu. The bacterial community composition and succession model in the middle layer were similar to those in the core layer, whereas the fungal community composition and succession model in the surface layer were similar to those in the middle layer. The co-occurrence network analysis showed that microbial interaction is stronger in the middle and core layers than in the surface layer. Analyses based on both niche theory and neutral theory models indicated that deterministic processes predominantly governed the microbial community assembly and these processes played an increasingly important role from the surface to the core layer. Random forest analysis revealed that temperature was the primary endogenous factor driving the bacterial and fungal community assembly. The results of this study contribute to a better understanding of the microbial community in MT-Daqu and are helpful for the quality control of MT-Daqu fermentation.

Species pool and local assembly processes drive β diversity of ammonia-oxidizing and denitrifying microbial communities in rivers along a latitudinal gradient

Both regional species pool and local community assembly mechanism drive the microbial diversity patterns across geographical gradients. However, little has been done to separate their effects on the β diversity patterns of microbial communities involved in nitrogen (N) cycling in river ecosystems. Here, we use high-throughput sequencing of the archaeal amoA, bacterial amoA, nirK, and nirS genes, null model, and neutral community model to distinguish the relative importance of species pool and local assembly processes for ammonia-oxidizing and denitrifying communities in river wetlands along a latitudinal gradient in eastern China. Results indicated that the β diversity of the nirS-type denitrifying community co-varied with γ diversity and environmental heterogeneity, implying that regional species pool and heterogeneous selection explained variation in β diversity. However, the β diversity of ammonia-oxidizing and nirK-type denitrifying communities did not correlate with γ diversity and environmental heterogeneity. The continuous hump distribution of β deviation along the latitudinal gradient and the lower species dispersal rate indicated that the dispersal limitation shaped the variation in β diversity of ammonia-oxidizing and nirK-type denitrifying communities. Additionally, biotic interactions drove ammonia-oxidizing and nirS-type denitrifying communities by influencing species co-occurrence patterns. Our study highlights the importance of regional species pool and local community assembly processes in shaping geographical patterns of N-cycling microorganisms and extends knowledge of their adaptability to a continuously changing environment on a large scale.

Differential microbiome features in lake-river systems of Taihu basin in response to water flow disturbance

Introduction

In riverine ecosystems, dynamic interplay between hydrological conditions, such as flow rate, water level, and rainfall, significantly shape the structure and function of bacterial and microeukaryotic communities, with consequences for biogeochemical cycles and ecological stability. Lake Taihu, one of China's largest freshwater lakes, frequently experiences cyanobacterial blooms primarily driven by nutrient over-enrichment and hydrological changes, posing severe threats to water quality, aquatic life, and surrounding human populations. This study explored how varying water flow disturbances influence microbial diversity and community assembly within the interconnected river-lake systems of the East and South of Lake Taihu (ET&ST). The Taipu River in the ET region accounts for nearly one-third of Lake Taihu's outflow, while the ST region includes the Changdougang and Xiaomeigang rivers, which act as inflow rivers. These two rivers not only channel water into Lake Taihu but can also cause the backflow of lake water into the rivers, creating distinct river-lake systems subjected to different intensities of water flow disturbances.

Methods

Utilizing high-throughput sequencing, we selected 22 sampling sites in the ET and ST interconnected river-lake systems and conducted seasonally assessments of bacterial and microeukaryotic community dynamics. We then compared differences in microbial diversity, community assembly, and co-occurrence networks between the two regions under varying hydrological regimes.

Results and discussion

This study demonstrated that water flow intensity and temperature disturbances significantly influenced diversity, community structure, community assembly, ecological niches, and coexistence networks of bacterial and eukaryotic microbes. In the ET region, where water flow disturbances were stronger, microbial richness significantly increased, and phylogenetic relationships were closer, yet variations in community structure were greater than in the ST region, which experienced milder water flow disturbances. Additionally, migration and dispersal rates of microbes in the ET region, along with the impact of dispersal limitations, were significantly higher than in the ST region. High flow disturbances notably reduced microbial niche width and overlap, decreasing the complexity and stability of microbial coexistence networks. Moreover, path analysis indicated that microeukaryotic communities exhibited a stronger response to water flow disturbances than bacterial communities. Our findings underscore the critical need to consider the effects of hydrological disturbance on microbial diversity, community assembly, and coexistence networks when developing strategies to manage and protect river-lake ecosystems, particularly in efforts to control cyanobacterial blooms in Lake Taihu.

The enhanced neutral process with decreasing cell size: a study on phytoplankton metacommunities from the glacier-fed river of Qinghai-Xizang Plateau

The cell size of phytoplankton is an important defining functional trait that can serve as a driver and sentinel of phytoplankton community structure and function. However, the study of the assembly patterns and drivers of phytoplankton metacommunities with different cell sizes has not been widely carried out. In this study, we systematically investigated the biodiversity patterns, drivers, and assembly processes of the three phytoplankton cell sizes (micro: 20-200 μm; nano: 2-20 μm; pico: 0.2-2 μm) in the Za'gya Zangbo River from the source to the estuary using 18S rDNA amplicon sequencing. The results demonstrated that the alpha diversity and co-occurrence network complexity for all three sizes of phytoplankton increased to a peak downstream of the glacier sources and then decreased to the estuary. The nanophytoplankton subcommunity consistently had the highest alpha diversity and co-occurrence network complexity. On the other hand, total beta diversity followed a unimodal trend of decreasing and then increasing from source to estuary, and was dominated by species replacement components. In addition, deterministic processes driven mainly by physiochemical indices (PCIs) and biogenic elements (BGEs) dominated the assembly of micro- and nanophytoplankton subcommunities, whereas stochastic processes driven by geographical factors (GGFs) dominated the assembly of picophytoplankton subcommunities. The results explained the contradictions in previous studies of phytoplankton community assembly processes in highland aquatic ecosystems, elucidating the different contributions of deterministic and stochastic processes, and the complexity of compositional mechanisms in shaping the assembly of micro-, nano-, and picophytoplankton in this highland glacial river.

IMPORTANCE

The cell size of phytoplankton is a key life-history trait and key determinant, and phytoplankton of different cell sizes are differentially affected by ecological processes. However, the study of the assembly patterns and drivers of phytoplankton metacommunities with different cell sizes has not been widely carried out. We provide an in-depth analysis of phytoplankton community diversity across three cell sizes in the glacier-fed river, describing how the pattern of phytoplankton communities differs across cell sizes in response to geochemical gradients. The results show that the smaller phytoplankton (picophytoplankton) are relatively more influenced by dispersal-based stochastic processes, whereas larger ones (microphytoplankton and nanophytoplankton) are more structured by selection-based deterministic processes.

Unraveling the distribution pattern and driving forces of soil microorganisms under geographic barriers

The Altai Mountains (ALE) and the Greater Khingan Mountains (GKM) in northern China are forest regions dominated by coniferous trees. These geographically isolated regions provide an ideal setting for studying microbial biogeographic patterns. In this study, we employed high-throughput techniques to obtain DNA sequences of soil myxomycetes, bacteria, and fungi and explored the mechanisms underlying the assembly of both local and cross-regional microbial communities in relation to environmental factors. Our investigation revealed that the environmental heterogeneity in ALE and GKM significantly affected the succession and assembly of soil bacterial communities at cross-regional scales. Specifically, the optimal environmental factors affecting bacterial Bray-Curtis similarity were elevation and temperature seasonality. The spatial factors and climate change impact on bacterial communities under the geographical barriers surpassed that of local soil microenvironments. The assembly pattern of bacterial communities transitions from local drift to cross-regional heterogeneous selection. Environmental factors had a relatively weak influence on myxomycetes and fungi. Both soil myxomycetes and fungi faced considerable dispersal limitation at local and cross-regional scales, ultimately leading to weak geographical distribution patterns.IMPORTANCEThe impact of environmental selection and dispersal on the soil microbial spatial distribution is a key concern in microbial biogeography, particularly in large-scale geographical patterns. However, our current understanding remains limited. Our study found that soil bacteria displayed a distinct cross-regional geographical distribution pattern, primarily influenced by environmental selection. Conversely, the cross-regional geographical distribution patterns of soil myxomycetes and fungi were relatively weak. Their composition exhibited a weak association with the environment at local and cross-regional scales, with assembly primarily driven by dispersal limitation.

Biogeographic patterns and community assembly mechanisms of bacterial community in the upper seawater of seamounts and non-seamounts in the Eastern Indian Ocean

Seamounts are widespread underwater topographic features in the ocean that exert an influential role in shaping the microbial biogeographic distribution. Nevertheless, research on the differences in microbial biogeographic distribution between seamount and non-seamount upper water column is still lacking, particularly in the Indian Ocean where studies are limited. In the present study, a total of 45 seawater samples were collected from the water column (5-200 m) of seamounts (HS) and non-seamounts (E87 transect) regions in the Eastern Indian Ocean (EIO) for the analysis of microbial biogeographic patterns and community assembly processes. The results indicated that bacterial community diversity did not differ significantly between the HS and E87 transect regions; however, the community composition was significantly different. Additionally, bacterial community diversity, composition, as well as structure were more affected by depth than by region. Community diversity tended to increase with depth in E87 transect region, while it tended to decrease in HS region. A distance decay analysis also demonstrated that bacterial communities were more influenced by environmental and depth distances than geographic distances. In the assembly of bacterial communities on HS and E87 transect regions, as well as at different depths, stochastic processes, particularly dispersal limitation, were found to be predominant. These findings enhance our comprehension of bacterial community characteristics in the upper seawater of seamounts and non-seamounts regions in the EIO and offer insights into the assembly processes shaping microbial communities at varying depths.

IMPORTANCE

By comparing the bacterial diversity, composition, and structure in the upper seawater of seamount and non-seamount areas, we provide valuable insights into the influential role of seamounts in shaping microbial biogeography. The finding that the depth had a more significant impact on bacterial community characteristics than region underscores the importance of considering vertical stratification when examining microbial distributions. Moreover, the dominance of stochastic processes, particularly dispersal limitation, in governing community assembly across both seamount and non-seamount areas offers critical implications for the mechanisms underlying microbial biogeographic patterns in these dynamic ocean environments. This study expands the current knowledge and lays the groundwork for further investigations into the complex interactions between oceanographic features, environmental gradients, and microbial community dynamics in the Indian Ocean.

Community coalescence under variable hydrochemical conditions of the Chesapeake Bay shaped bacterial diversity and functional traits

Community coalescence related to bacterial mixing events regulates community characteristics and affects the health of estuary ecosystems. At present, bacterial coalescence and its driving factors are still unclear. The present study used a dataset from the Chesapeake Bay (2017) to address how bacterial community coalescence in response to variable hydrochemistry in estuarine ecosystems. We determined that variable hydrochemistry promoted the deterioration of water quality. Temperature, orthophosphate, dissolved oxygen, chlorophyll a, Secchi disk depth, and dissolved organic phosphorus were the key environmental factors driving community coalescence. Bacteria with high tolerance to environmental change were the primary taxa accumulated in community coalescence, and the significance of deterministic processes to communities was revealed. Community coalescence was significantly correlated with the pathways of metabolism and organismal systems, and promoted the co-occurrence of antibiotic resistance and virulence factor genes. Briefly, community coalescence under variable hydrochemical conditions shaped bacterial diversity and functional traits, to optimise strategies for energy acquisition and lay the foundation for alleviating environmental pressures. However, potential pathogenic bacteria in community coalescence may be harmful to human health and environmental safety. The present study provides a scientific reference for ecological management of estuaries.

Seasonal Dynamics of Eukaryotic Microbial Communities in the Water-Receiving Reservoir of the Long-Distance Water Diversion Project, China

Inter-basin water transfer projects, such as the Yellow River to Qingdao Water Diversion Project (YQWD), are essential for addressing water scarcity, but impact local aquatic ecosystems. This study investigates the seasonal characteristics of eukaryotic microbial communities in the Jihongtan Reservoir, the main water-receiving body of YQWD, over a one-year period using 18S rDNA amplicon sequencing. The results showed that the eukaryotic microbial diversity did not exhibit significant seasonal variation (p > 0.05), but there was a notable variance in the community structure (p < 0.05). Arthropoda and Paracyclopina, representing the most dominant phylum and the most dominant genus, respectively, both exhibited the lowest abundance during the winter. The Chlorophyta, as the second-dominant phylum, demonstrates its higher abundance in the spring and winter. The Mantel test and PLS-PM (Partial Least Squares Path Modeling) revealed that water temperature (WT), dissolved oxygen (DO), and pH influenced the seasonal dynamic of eukaryotic microbial communities significantly, of which WT was the primary driving factor. In addition to environmental factors, water diversion is likely to be an important influencing factor. The results of the co-occurrence network and robustness suggested that the spring network is the most complex and exhibits the highest stability. Moreover, keystone taxa within networks have been identified, revealing that these key groups encompass both abundant and rare species, with specificity to different seasons. These insights are vital for understanding the seasonal variation of microbial communities in the Jihongtan Reservoir during ongoing water diversions.

Application of Synchronous Evaluation-Diagnosis Model with Quantitative Stressor-Response Analysis (SED-QSR) to Urban Lake Ecological Status: A Proposed Multiple-Level System

Ecological integrity assessment and degradation diagnosis are used globally to evaluate the health of water bodies and pinpoint critical stressors. However, current studies mainly focus on separate evaluation or diagnosis, leading to an inadequate exploration of the relationship between stressors and responses. Here, based on multiple data sets in an urban lake system, a synchronous evaluation-diagnosis model with quantitative stressor-response analysis was advanced, aiming to improve the accuracy of evaluation and diagnosis. The weights for key physicochemical stressors were quantitatively determined in the sequence of NDAVIadj > CODMn > TP > NH4+-N by the combination of generalized additive model and structural equation modeling, clarifying the most significant effects of aquatic vegetation on the degradation of fish assemblages. Then, sensitive biological metrics were screened by considering the distinct contributions of four key stressors to alleviate the possible deviation caused by common methods. Finally, ecological integrity was evaluated by summing the key physicochemical stressors and sensitive biological metrics according to the model-deduced weights instead of empirical weights. Our system's diagnosis and evaluation results achieved an accuracy of over 80% when predicting anthropogenic stress and biological status, which highlights the great potential of our multiple-level system for ecosystem management.

Nonlinear responses of biofilm bacteria to alkyl-chain length of parabens by DFT calculation

Parabens can particularly raise significant concerns regarding the disruption of microbial ecology due to their antimicrobial properties. However, the responses of biofilm bacteria to diverse parabens with different alkyl-chain length remains unclear. Here, theoretical calculations and bioinformatic analysis were performed to decipher the influence of parabens varying alkyl-chain lengths on the biofilm bacteria. Our results showed that the disturbances in bacterial community did not linearly response to the alkyl-chain length of parabens, and propylparaben (PrP), with median chain length, had more severe impact on bacterial community. Despite the fact that paraben lethality linearly increased with chain length, the PrP had a higher chemical reactions potential than parabens with shorter or longer alkyl-chain. The chemical reactions potential was critical in the nonlinear responses of bacterial community to alkyl-chain length of parabens. PrP could impose selective pressure to disturb the bacterial community, because it had a more profound contribution to deterministic assembly process. Furthermore, N-acyl-homoserine lactones was also significantly promoted under PrP exposure, confirming that PrP could affect the bacterial community by influencing the quorum-sensing system. Overall, our study reveals the nonlinear responses of bacterial communities to the alkyl-chain lengths of parabens and provides insightful perspectives for the better regulation of parabens. ENVIRONMENTAL IMPLICATION: Parabens are recognized as emerging organic pollutants, which specially raise great concerns due to their antimicrobial properties disturbing microbial ecology. However, few study have addressed the relationship between bacterial community responses and the molecular structural features of parabens with different alkyl-chain length. This investigation revealed nonlinear responses of the bacterial community to the alkyl-chain length of parabens through DFT calculation and bioinformatic analysis and identified the critical roles of chemical reactions potential in nonlinear responses of bacterial community. Our results benefit the precise evaluation of ecological hazards posed by parabens and provide useful insights for better regulation of parabens.

Elevation-associated pathways mediate aquatic biodiversity at multi-trophic levels along a plateau inland river

Aquatic biodiversity plays a significant role in maintaining the ecological balance and the overall health of riverine ecosystems. Elevation is an important factor influencing biodiversity patterns. However, it is still unclear through which pathway elevation influences riverine biodiversity at different trophic levels. In this study, the elevation-associated pathways affecting aquatic biodiversity at different trophic levels were explored using structural equation modeling (SEM) and taking the Bayin River, China as the case. The results showed that the elevational patterns were different among aquatic organisms at different trophic levels. For macroinvertebrates and bacteria, the pattern was hump-shaped; while for phytoplankton and zooplankton, it was U-shaped. Building upon these observed elevational patterns, our investigation delved into the direct and indirect pathways through which elevation influences aquatic biodiversity. We found that elevation exerts an impact on aquatic biodiversity via indirect pathways. For all aquatic organisms investigated, the major pathway through which elevation influences biodiversity is mediated by water temperature and water quality. For aquatic organisms at higher trophic levels, like macroinvertebrates and zooplankton, the crucial pathway is also mediated by the landscape. The results of this study contributed to understanding the effects of elevation on aquatic organisms at different trophic levels and provided an important basis for the assessment of riverine biodiversity at large scales.

Undisclosed contribution of microbial assemblages selectively enriched by microplastics to the sulfur cycle in the large deep-water reservoir

The accumulation of microplastics in reservoirs due to river damming has drawn considerable attention due to their potential impacts on elemental biogeochemical cycling at the watershed scale. However, the effects of plastisphere communities on the sulfur cycle in the large deep-water reservoir remain poorly understood. Here, we collected microplastics and their surrounding environmental samples in the water and sediment ecosystems of Xiaowan Reservoir and found a significant spatiotemporal pattern of microplastics and sulfur distribution in this Reservoir. Based on the microbial analysis, plastic-degrading taxa (e.g., Ralstonia, Rhodococcus) involved in the sulfur cycle were enriched in the plastisphere of water and sediment, respectively. Typical thiosulfate oxidizing bacteria Limnobacter acted as keystone species in the plastisphere microbial network. Sulfate, oxidation reduction potential and organic matter drove the variations of the plastisphere. Environmental filtration significantly affected the plastisphere communities, and the deterministic process dominated the community assembly. Furthermore, predicted functional profiles related to sulfur cycling, compound degradation and membrane transport were significantly enriched in the plastisphere. Overall, our results suggest microplastics as a new microbial niche exert different effects in water and sediment environments, and provide insights into the potential impacts of the plastisphere on the sulfur biogeochemical cycle in the reservoir ecosystem.

Residual effects of chlorinated organic pollutants on microbial community and natural redox processes in coastal wetlands

Chlorinated organic pollutants (COPs) are common in flooded environments. To examine the residual status and effects of COPs on flooded environments, a survey of 7 coastal wetlands in Zhejiang, East China was conducted. Total COP concentrations detected from 95.69 to 412.76 ng g-1 dw. Gamma-HCH and o,p'-DDT posed the greatest risk with exceedance rates of 100% according to sediment quality guidelines. Samples with higher COP pollution had higher microbial diversity, more complex microbial networks, more deterministic community assembly processes and lower microbiome stability, indicating an improved soil function for balance cycle of substances, especially for COP degradation. Further analysis using quantitative real-time PCR suggested COP-dechlorination interacted with natural redox processes, especially sulfate reduction and methanogenesis. The positive correlation between CH4 and pentachlorobenzene indicated a potential increase in greenhouse gas emissions caused by COP pollution. Correlation between dsr gene and COPs demonstrated the ability of sulfate-reducing bacteria to degrade COPs. Particularly, facultative OHRB such as sulfate-reducing bacteria hold significant importance in the process of COP-dechlorination. This finding provides a reference for COP pollution remediation. Collectively, our study offers new insight into the residual effect of COPs in coastal wetlands and contributes to an improved understanding of bioremediation strategies for COP pollution.

Stochastic processes drive the diversity and composition of methanogenic community in a natural mangrove ecosystem

Methanogens are considered to be crucial components of mangrove ecosystems with ecological significance. However, understanding the assembly processes of methanogenic communities in mangrove ecosystems is relatively insufficient. In the current study, a natural mangrove in a protection zone was employed to investigate the diversity and assembly processes of methanogenic community by using amplicon high-throughput sequencing, a null model as well as a neutral community model. The results showed that methanogenic community in mangrove sediments were highly diverse, with the predominance of methylotrophic Methanolobus, and hydrogenotrophic Methanogenium, Methanospirillum. The diversity, composition, and gene abundance varied obviously across the mangrove sampling sites, whereas the measured environmental variables exhibited a negligible effect. Null model showed that the values of beta nearest-taxon index were mostly between -2 and 2, indicating that stochastic processes contributed more than deterministic processes driving the methanogenic community assembly in mangrove sediments. Neutral community model revealed a high estimated migration rate of methanogenic community, further substantiating the significance of stochastic processes. Among the keystone species identified in network analysis, methanogens affiliated to hydrogenotrophic Methanospirillum may have a crucial role in maintaining the structure and function of methanogenic community. Notably, these keystone species were almost unaffected by measured environmental factors, indicating that the methanogenic community in mangrove sediments is more likely to be affected by stochastic processes. This study deepens the understanding of the diversity and assembly of methanogenic community in mangrove sediments, and provides clues to maintain mangrove ecosystem functioning.

Tracking the source of antibiotic resistome in the stormwater network drainage in the presence of sewage illicit connections

Stormwater pipes are illicitly connected with sewage in many countries, which means that sewage enters stormwater pipes and the drainage is discharged to surface water without any treatment. Sewage contains more pathogens and highly risky antibiotic resistance genes (ARGs) than surface runoff. Therefore, sewage may alter the microbial and ARG compositions in stormwater pipe drainage, which in turn leads to an increased risk of resistance in surface water. However, the effects of sewage on ARGs in the drainage of stormwater networks have not been systematically studied. This study characterized the microbial and ARG composition of several environmental compartments of a typical stormwater network and quantified their contributions to those in the drainage. This network transported ARGs and microorganisms from sewage, sediments in stormwater pipes, and surface runoff into the drainage and thus into the river. According to metagenomic analysis, multidrug resistance genes were most abundant in all samples and the numbers and relative abundance of ARGs in the drainage collected during wet weather were comparable to that of sewage. The results of SourceTracker showed that the relative contribution of sewage was double that of rainwater and surface runoff in the drainage during wet weather for both microorganisms and ARGs. Desulfovibrio, Azoarcus, and Sulfuritalea were connected with the greatest number of ARGs and were most abundant in the sediments of stormwater pipes. Furthermore, stochastic processes were found to dominate ARG and microbial assembly, as the effects of high hydrodynamic intensity outweighed the effects of environmental filtration and species interactions. The findings of this study can increase our understanding of ARGs in stormwater pipe drainage, a crucial medium linking ARGs in sewage to environmental ARGs.

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.

Environmental gradients shape microbiome assembly and stability in the East China sea

Microbiomes play a key role in marine ecosystem functioning and sustainability. Their organization and stability in coastal areas, particularly in anthropogenic-influenced regions, however, remains unclear compared with an understanding of how microbial community shifts respond to marine environmental gradients. Here, the assembly and community associations across vertical and horizontal gradients in the East China Sea are systematically researched. The seawater microbial communities possessed higher robustness and lower fragmentation and vulnerability compared to the sediment microbiomes. Spatial gradients act as a deterministic filtering factor for microbiome organization. Microbial communities had lower phylogenetic distance and higher niche breadth in the nearshore and offshore areas compared to intermediate areas. The phylogenetic distance of microbiomes decreased from the surface to the bottom but the niche breadth was enhanced in surface and bottom environments. Vertical gradients destabilized microbial associations, while the community diversity was enhanced. Multivariate regression tree analysis and canonical correspondence analysis indicated that depth, distance from shore, nutrient availability, temperature, salinity, and chlorophyll a, affected the distribution and co-occurrence of microbial groups. Our results highlight the crucial roles of environmental gradients in determining microbiome association and stability. These results improve our understanding of the survival strategies/adaptive mechanisms of microbial communities in response to environmental variation and provide new insights for protecting the ecosystems and maintaining the sustainability of ecological functions.

Spatial and Temporal Characteristics of Phytoplankton Communities in Drinking Water Source Reservoirs in Shenzhen, China

Phytoplankton diversity and community characteristics are closely associated with aquatic environmental factors. Understanding these dynamics can provide insights into the ecological health of water bodies. We investigate the spatial and temporal characteristics of phytoplankton communities in 27 drinking water source reservoirs in Shenzhen, China. As a method, we collected samples during the dry season in 2021 and the wet season in 2022, analyzed the alpha and beta diversities of phytoplankton communities, and correlated these with the environmental factors. The results reveal that Cyanobacteria dominate the phytoplankton communities in the Shenzhen reservoirs. Phytoplankton diversity is greater during the dry season. The algal composition varies spatially, and the phytoplankton diversity tends to decrease with increasing eutrophication. A co-occurrence network analysis indicates denser and stronger correlations among phytoplankton nodes during the wet season than dry season. Reservoirs with moderate eutrophication levels exhibit denser nodes and stronger correlations compared to those with low or high eutrophication levels. The chemical oxygen demand, water temperature, pH, and total nitrogen are identified as key influencers of the phytoplankton community structure. Our results contribute to the enhanced understanding of the spatial and temporal dynamics of phytoplankton communities in reservoirs in South China and provides insights into the management and conservation of these drinking water reservoirs.