Microbial communities in arid region lakes are highly sensitive to salinity fluctuations, yet systematic comparisons of free-living (FL) and particle-attached (PA) bacteria along salinity gradients remain scarce. This study focuses on five lakes in the northwestern China, where salinity ranges from freshwater to brackish (0.17–13.88). Using 16S rRNA high-throughput sequencing, null model analysis, and co-occurrence network approaches, we investigated the diversity and driving mechanisms of FL and PA bacterial communities. Results show that: (1) PA communities exhibited significantly higher α-diversity than FL communities, with PA diversity decreasing as salinity increased, while FL diversity followed a U-shaped trend; (2) beta-dispersion analysis indicated that the spatial heterogeneity of PA communities was stronger compared to FL communities (P<0.001); (3) redundancy analysis (RDA) showed that salinity was the main factor controlling the differentiation of FL communities (35.5

Organic aggregates (OAs) serve as critical microhabitats for microbial activity in aquatic environments. However, the extent to which their source and particle size influence bacterial colonization and community succession remains poorly understood. To address this gap, we collected microbial community samples in August 2023 from two contrasting lakes: Lake Taihu, where OAs are predominantly algal-derived, and Lake Lihu, where OAs are largely macrophyte-derived. Using 15-day microcosm experiments, we examined how OA source and particle size (250, 1000, and 2360 μm) influence the composition and structure of particle-attached (PA) and free-living (FL) bacterial communities, analyzing a total of 105 samples. PA bacterial communities consistently exhibited higher α-diversity than FL communities (p < 0.01). OA source was a dominant factor shaping PA community composition, with algal-derived aggregates supporting greater phylogenetic diversity (p < 0.01), likely due to higher bioavailability of labile substrate. Although particle size had minimal impact on α-diversity (p > 0.05) and phylum-level structure, it significantly influenced β-diversity patterns (p = 0.001). Over the 15-day incubation, FL communities displayed marked temporal succession-initially dominated by Proteobacteria and Bacteroidota, followed by a more balanced phylum-level composition in later stages, including Verrucomicrobiota, Cyanobacteria, Planctomycetota, Actinobacteriota, and Patescibacteria. Co-occurrence network analysis further revealed that PA communities exhibited weaker interspecific associations than FL communities, suggesting reduced interaction complexity on particles. Together, these findings demonstrate that both the source and size of OAs act as ecological filters that shape the assembly and dynamics of PA and FL bacterial communities. This study provides novel experimental evidence for understanding microbial roles in organic matter degradation and algae-bacteria interactions in shallow freshwater ecosystems.

Abstract Over the past six decades, northwestern China has undergone a pronounced climatic transition from a “warm‐dry” to a “warm‐wet” regime, driving substantial shifts in lake water level (WL), salinity, and nutrient conditions. However, how this hydroclimatic transition restructures lake microbiomes and their functional potential remains poorly understood. Here, we used Lake Bosten, the largest inland lake in arid northwestern China, as a model ecosystem to examine the long‐term impacts of climate‐driven environmental change on microbial diversity, community assembly, network structure, and functional potential. We combined (1) meteorological and aquatic environmental records from 1958 to 2022, (2) decade‐separated field surveys of microbial communities (2010−2011 vs. 2021−2022) using amplicon sequencing and metagenomics, and (3) mesocosm experiments simulating projected future hydroclimatic conditions. Warm‐wet conditions influenced the Lake Bosten ecosystem through two main pathways: direct temperature effects and indirect WL mediated effects on hydrological connectivity and water chemistry. Field observations showed that the warm‐wet period was characterized by higher WL, lower salinity and total nitrogen, and increased bacterial and eukaryotic diversity. Community assembly shifted toward stronger homogeneous selection and weaker dispersal limitation in both bacterial and eukaryotic communities, consistent with enhanced hydrological connectivity. At the same time, both microbial domains showed reduced community stability, and their co‐occurrence networks exhibited lower complexity and structural stability. In contrast, broad metagenomic functional composition showed no significant shift despite pronounced taxonomic and network reorganization. Nitrogen cycling genes showed pathway‐specific redistribution, with enhanced nitrogen fixation and selected nitrification related genes but reduced nitrate reduction, denitrification, and dissimilatory nitrate reduction to ammonium (DNRA). Taxon‐function linkage further indicated that functional compensation was mainly mediated by replacement within bacterial functional guilds. Overall, our study links warm‐wet hydroclimatic change to altered water level, salinity, nutrient conditions, microbiome restructuring, cross domain network rewiring, and buffered functional potential in an arid lake.

Saucer-shaped sub-lakes in floodplains undergo strong seasonal changes in water level and connectivity, but their microbial responses and roles in nutrient cycling remain poorly understood. Here we show, using 28 lake units across Lake Poyang, China, that seasonal hydrological change is associated with distinct patterns of microbial stability and nutrient cycling in water and sediment. Core microbial taxa support both diversity and compositional stability, as their removal reduces both measures of community resistance. Functional shifts are stronger in water, where nitrogen cycling potential increases during the dry season while phosphorus uptake, assimilation, and storage potential declines. Sediment shows weaker seasonal reorganization, with moderate increases in downstream nitrogen reduction and a shift toward phosphorus regeneration and supply. Environmental variation is also associated with changes in core microbial community composition and nutrient cycling potential. Together, these findings show that seasonal hydrological change is accompanied by coordinated but contrasting microbial and nutrient cycling responses in water and sediment. Core taxa support seasonal microbial stability, while nitrogen and phosphorus cycling potentials show contrasting seasonal reorganization in water and sediment, according to a study of 28 floodplain lake units in Lake Poyang, China, using 16S rRNA gene sequencing and shotgun metagenomics.

Lakes are hotspots for natural methane (CH4) emissions. However, the microbial processes driving CH4 production in oxygenated surface waters remain unclear. We investigated CH4-producing microorganisms associated with organic aggregates (OAs) fractionated into four sizes (>112, 64-112, 5-64, and 0.2-5 μm) across five ecologically diverse lakes. Using qPCR and amplicon sequencing, we quantified methanogenic archaea (mcrA gene) and bacteria (phnJ gene) and identified their environmental drivers. Gene absolute abundances were significantly affected by the lake type, OAs size, and their interaction. Both mcrA and phnJ increased with lake trophic status, following a size-dependent pattern: decreasing from >112 to 64-112 μm, then increasing to peak in the 0.2-5 μm. Overall, mcrA absolute abundance (2.17-4.23 × 105 copies/mL) exceeded phnJ (0.98-1.16 × 105 copies/mL), particularly in the >112 and 0.2-5 μm fractions. Organic matter characteristics, nutrient levels, and physicochemical conditions collectively shaped microbial distributions. These findings support a dual-pathway for oxic methane production: (1) classical archaeal methanogenesis within anoxic microniches embedded in OAs, and (2) bacterial CH4 generation via methylphosphonate (MPn) degradation triggered by phosphorus limitation or algal-derived methylated substrates. This mechanistic framework explains persistent methane supersaturation in oxic waters and improves predictions of freshwater-methane emissions and carbon cycling under environmental change.

Solar irradiation can induce the breakdown of particulate or dissolved organic matter and cause the release of inorganic nutrients. Lakes in the arid and semi-arid regions of northwestern China are exposed to high levels of ultraviolet (UV) radiation, yet the photochemical release of inorganic nutrients from resuspended sediments remains largely unexplored. In this study, sediment suspensions in 15 lakes of northwestern China were exposed to simulated UV irradiation, and the photochemical release of ammonium (NH4+) and phosphate (PO43-) were investigated during the incubations. The release and compositional changes of dissolved organic matter (DOM) were also explored by measuring their UV-Visible absorption spectroscopy and three-dimensional fluorescence spectroscopy. Results showed that light irradiation induces NH4+ and PO43- releases from sediment suspensions from most lakes, with rates ranging from undetectable to 0.42 mg N L-1 d-1 and 0.012 mg P L-1 d-1, respectively. Light irradiation also induces compositional changes in the DOM pools of sediment suspensions, producing DOM with smaller molecular sizes and lower aromaticity compared to dark controls. The NH4+ photorelease was influenced by sedimentary particle size distribution and extractable DOM abundance, with finer particles and higher sediment organic matter content contributing to greater NH4+ release. The PO43- photorelease linked closely to the humification degree of sediment extractable DOM. These findings suggest that photochemical alterations of sedimentary organic matter may potentially influence nutrient dynamics in lakes of northwestern China, thereby highlighting the importance of integrating suspended particle-associated photoprocesses into nutrient management strategies for lakes.

Particulate phosphorus (PP) often constitutes a substantial proportion of the phosphorus pool in shallow eutrophic lakes. However, limited quantitative evidence exists regarding the role of PP in contributing to phosphorus loading and sustaining algal blooms in lake ecosystems. In this study, we conducted monthly field surveys throughout a full annual cycle to characterize the compositions and enzymatic hydrolysis rates of PP in Lake Taihu. Meanwhile, phosphorus budgets were constructed to clarify the contributions of PP to phosphorus loading and sustaining algal blooms. The results indicated that mean PP concentration was 0.098 +/- 0.050 mg P L-1, accounting for 66.9 % of total phosphorus. Algal blooms, riverine inputs, and sediment resuspension caused by wind-wave disturbances were identified as the predominant drivers of the spatiotemporal variation of PP. The maximum rates of PP enzymatic hydrolysis mediated by particulate alkaline phosphatase were induced by substrates availability and phosphorus limitation. Annual amount of PP hydrolysis exceeded other sources by 2-3 orders of magnitude. Path analysis further revealed that high concentrations and enzymatic hydrolysis rates of PP directly supported soluble reactive phosphorus concentrations. These findings indicated that PP biodegradation was critical for sustaining algal blooms as an internal recycling mechanism, providing theoretical insights into eutrophication persistence in shallow lake ecosystems.

Lake Chaohu, the fifth-largest freshwater lake in China, has been experiencing severe eutrophication and algal bloom problems. Owing to differences in trophic status, the lake is divided into two distinct regions. However, the sediment bacterial communities within the lake remain poorly understood. This study aims to fill this knowledge gap by comparing sediment bacterial communities between the two different lake regions using 16S rRNA gene amplicon sequencing. A total of 1,222,845 high-quality sequences were generated, encompassing 92 phyla and 3296 genera across 20 surface sediment samples. The results indicated that the pH, loss on ignition (LOI), and the total nitrogen (TN), total phosphorus (TP), and total organic carbon (TOC) concentration of sediments in the western region were significantly higher than those in the eastern region. Furthermore, bacterial alpha-diversity, beta-diversity, and community composition in the sediments exhibited marked differences between the two lake regions. The functional profiles of the bacterial populations also revealed statistically significant differences in predicted functional composition among the two different lake regions. Redundancy analysis (RDA) identified that TN, TP, and TOC are the primary factors influencing the variations of sediment bacterial communities between the two different lake regions. Overall, this study substantially advances our understanding of sediment microbial ecology in eutrophic freshwater lakes.

Recirculating aquaculture systems (RAS) have promising applications in aquaculture. Feed is recognized as a major source of input to the RAS, and feeding frequency will not only impact the performance of turbot, but will also impact the quality of the cultured water. In order to rationally manage feeding and reduce aquaculture pollution, this study investigated the effects of feeding frequency on the performance of turbot (Scophthalmus maximus), nitrogen removal (ammonia and nitrite) characteristics and microbial communities in biofilters. The experiment was designed with three treatment groups, which were categorized into feeding once/day (FF1), feeding twice/day (FF2) and feeding three times/day (FF3) for 30 days. The results indicated that weight gain rate (WGR) and specific growth rate (SGR) significantly increased (p < 0.05) in the FF2 group and FF3 group compared with the FF1 group. The feed conversion ratio (FCR) was significantly lower (p < 0.05) in the FF2 group and FF3 group than in the FF1 group. There was no significant change in condition factor (CF). Ammonia and nitrite concentration decreased and water quality fluctuated less as the feeding frequency increased. FF2 showed the highest ammonia and nitrite removal rates. Feeding frequency did not significantly affect biofilter alpha diversity, but significantly altered beta diversity. PICRUSt functional prediction analysis revealed that the relative abundance of functional genes for nitrogen metabolism (amoA, amoB, amoC, hao, nxrA and nxrB) was highest in FF2. Therefore, feeding frequency of twice/day not only benefits the performance of turbot but also stabilizes the water environment and improves the removal of ammonia nitrogen and nitrite in RAS. These results provide theoretical and practical basis for further water improvement by seawater RAS.

The oviduct gland of cartilaginous fish (sharks, skates, and chimeras) synthesizes a highly cross-linked biomaterial that forms a protective leathery egg case, commonly known as "mermaid's purses." Understanding the tissue structure of this organ is critical for elucidating the synthesis process of this promising material. In this study, we performed a histological investigation of the oviduct gland in an oviparous skate, Okamejei kenojei, using paraffin sectioning to generate three-dimensional morphological data. A total of 654 tissue sections were collected and made open source. Our results reveal that the oviduct gland of O. kenojei exhibits a typical zonal structure. The club and papillary zones account for 7.74% ± 7.58% of the gland, while the baffle zone, the largest region, comprises 25-30 layers of glandular ducts, including serous gland ducts (64.72% ± 5.86%) and mixed-type ducts (0.95% ± 1.74%), predominantly distributed along the lateral margins. The terminal zone represents the smallest region, accounting for 2.17% ± 0.54% of the gland. These findings enhance our understanding of the secretion mechanisms involved in the formation of this natural biomedical material. They also provide a foundation for further studies on marine biological histology and the development of biomimetic materials through comparisons with the oviduct glands of other cartilaginous fish.

Egg cases in oviparous cartilaginous fishes (sharks, rays, and chimaeras) exhibit diverse morphologies that are closely tied to species-specific reproductive adaptations. However, the diversity and formation mechanisms of these structures remain poorly understood. In this study, we performed a quantitative morphological analysis of egg cases from three species: Okamejei kenojei, Cephaloscyllium sarawakense, and Chiloscyllium plagiosum. The results demonstrated that the egg cases of these species could be distinguished using multiple morphological indices (p < 0.05), supporting species-specificity in egg case morphology. In these species, we observed that egg jelly initially envelops the egg case during early embryonic development and later dissolves, allowing seawater entry-suggesting a conserved reproductive strategy within Elasmobranchii. Furthermore, under artificial breeding conditions, observations of female O. kenojei showed that ovulation occurs before egg case secretion. Specifically, eggs reach the oviduct above the oviducal gland when about half of the egg case has formed. Immunohistochemical staining revealed estrogen and progesterone receptors in the oviductal gland cells. Interestingly, O. kenojei can produce malformed eggs with shark egg case-like features under captive breeding conditions. These findings provide new insights into the species-specificity, timing, and hormonal regulation of egg case formation in cartilaginous fishes, and lay a foundation for future research on their reproductive strategies.

Since the middle of the last century, China has experienced social-economic progress and climate transition, which have been strong triggers for the regime shift of lake ecosystem, threatening species coexistence, biodiversity and community persistence. Given the high vulnerability of ecosystems in arid and semi-arid north-west of China, anticipating their regime shifts can contribute to the development of effective interventions to maintain lake health. However, it is not known how and to what extent lake ecosystems have changed in this region. To fill this gap, we investigated the imprints in paleolimnological sedimental cores over the last 150 similar to 200 years in shallow Lake Bosten and deep Lake Sayram. Results showed that anthropogenic heavy metals showed a sudden increase along the sediment cores. In Lake Bosten, bacterial diversity, niche differentiation, and species interactions exhibited a stepwise shift from an alternative state to anther in a nonlinear manner, highlighting the existence of regime shift. In contrast, in Lake Sayram, the change in bacterial communities was more gradual. Compared with the two alternative states, network topology analysis revealed tighter bacterial interactions in the intermediate transitional phase, which implicates stable-unstable-stable progresses during the regime shift. Concurrently, the predominant deterministic processes in the two alternative states and stochastic processes in the transitional phase may reflect the important roles of stochasticity in triggering the regime shift. Overall, our study showed that anthropogenic activities lead to a regime shift in the shallow lake rather but not in the deep lake.

Cartilaginous fishes (sharks, skates and chimaeras) exhibit diverse behavioral patterns and unique endoskeleton, which provide insights into their ecological adaptations and evolution. However, research on the development of cartilaginous fish is still limited. To evaluate the relationship between embryonic behavior and cartilage development in cartilaginous fishes, the developing Okamejei kenojei was analyzed through behavioral, anatomical, and histological approaches, with an atlas of embryonic behavior and skeletal morphology. The result shows that the behavior of skate embryos evolves from early rhythmic movements to vigilance behavior to external stimuli. Data from Alcian blue and Alizarin red staining and histology sections showed that the vertebrae are the earliest regions to mineralize, with the mineralization process starting at the neural arch area and expanding along the body axis. In the anterior area, mineralized structures spread along the synarcual and neurocranium towards the pectoral fins and fin rays. Interestingly, a novel branching pattern of fin rays was observed in the pectoral fins of embryonic O. kenojei, characterized by the inward growth of the perichondrium into the cartilage element, potentially linked to the morphogenesis of the skate's pectoral fins. Additionally, this study provides a set of open-source morphological data for O. kenojei, which will serve as a valuable reference for marine animal conservation and evolutionary developmental biology.

Although the biogeographical pattern and mechanisms underlying microbial assembly have been well-explored in lentic ecosystems, the relevant scenarios in lotic ecosystems remain poorly understood. By sequencing the bacterial communities in bacterioplankton and biofilm, our study detected their distance-decay relationship (DDR), and the balance between deterministic and stochastic processes, along the Kaidu river in an arid and semi-arid region of northwest China. Our results revealed that bacterioplankton and biofilm had significantly contrasting community structures. The bacterioplankton communities showed a gradually decreasing trend in alpha-diversity from the headwater to the river mouth, contrasting with the alpha-diversity of biofilm communities which was constant along the river length. Both bacterioplankton and biofilm showed significant DDRs along the 500-km river corridor with the slope of the bacterioplankton DDR being steeper than that of the biofilm DDR, which implies a stronger biogeography of bacterioplankton than biofilm. Relative to biofilm communities, the species interactions formed a denser and more complex network in the bacterioplankton communities than in the biofilm communities. Our results also revealed that there was a transition of community assembly from deterministic to stochastic processes upstream to downstream, although both the bacterioplankton and biofilm communities were mainly regulated by deterministic processes within the entire river. All these empirical results expand our knowledge of microbial ecology in an arid and semi-arid lotic ecosystem.

Understanding the effects of warming on bacterial communities is essential for predicting microbial responses to climate change in aquatic ecosystems. However, the mechanisms through which warming influences bacterial diversity and stability in lake ecosystems remain poorly understood. To address this gap, we conducted a mesocosm experiment in Lake Bosten, a climate change hotspot, with three temperature scenarios (26 degrees C, 29 degrees C, and 32 degrees C), and investigated bacterial diversity, community composition, potential functions, and stability. Our findings revealed that temperature, time, and their interactions significantly reduced bacterial alpha-diversity (twoway ANOVA: P < 0.05). Warming altered bacterial potential metabolic functions, with decreases in methanotrophy and methylotrophy and increases in phototrophy and photoheterotrophy. Warming also increased species replacement within bacterial communities, indicating a dynamic shift in community composition. Network analysis indicated heightened complexity under higher temperatures but also a decrease in bacterial stability, evidenced by higher average variation degree (AVD), increased vulnerability, and reduced robustness. Overall, our study highlights the profound effects of warming on the ecological dynamics of lake bacterial communities, underscoring the need for further research to understand and mitigate the impacts of global climate change on aquatic ecosystems.

Cu catalysts with different compositions and different Cu and promoter contents were prepared by precipitation-gel method and studied for the selective hydrogenation of syngas or biomass-based diethyl malonate (DEM) to valuable 1,3-propanediol (1,3-PDO). The Ga-promoted 70Cu6Ga/SiO2 catalyst was found to exhibit the highest catalytic performance, achieving 100 % DEM conversion and 76.6 % 1,3-PDO selectivity under reaction conditions of 160 °C and 8 MPa H2. The 70Cu6Ga/SiO2 bimetallic catalyst also presented obviously better stability than that of the monometallic 70Cu/SiO2 catalyst in a continuous flow reactor over 180 h time-on stream. Characterization results showed that the incorporation of Ga increased the interaction between Cu and Ga species, hindered the full reduction of Cu2+ species, and thus increased the proportion of Cu+ and the number of Lewis acidic sites on the catalyst surface. The synergistic effect between Cu0 and Cu+ enhanced the adsorption and activation of ester carbonyl groups and their subsequent hydrogenation, eventually contributed to the outstanding performances of the CuGa/SiO2 bimetallic catalysts.

Wild populations of cartilaginous fish (sharks, skates, rays, and chimaeras) are encountering challenges. Here, we are unveiling genomic data and behavioral ecological records of Okamejei kenojei, a species listed in the IUCN Red List of Threatened Species, aiming to offer insights into the conservation and environmental adaptability of cartilaginous fish.