Habitat selection drives diatom community assembly and network complexity in sediment-laden riverine environments.

Microbial communities assemble stochastically and deterministically, but how different assembly processes shape diatom community structure across riverine habitats is unclear, especially in sediment-laden environments. In this study, we deciphered the mechanisms of riverine diatom community assembly in the water column and riverbed substrate with varying sediment concentrations. Water and sediment samples were collected from 44 sampling sites along the Yellow River mainstream during two seasons. Diatom communities were characterized based on high-throughput sequencing of the 18S ribosomal RNA genes coupled with multivariate statistical analyses. A total of 198 diatom species were taxonomically assigned, including 182 free-living and particle-attached species and 184 surface-sediment species. Planktonic communities were structurally different from benthic communities, with Cyclotella being dominant mainly in the middle and lower reaches of the river with higher sediment concentrations. Both stochastic and deterministic processes affected diatom community assembly in different habitats. Species dispersal was more important in the water than in the substrate, and this process was strengthened by increased sediment concentration across habitats. Diatom communities exhibited lower network complexity and enhanced antagonistic or competitive interactions between species in response to higher sediment concentrations compared with lower sediment concentrations mainly in the source region of the river. Differences in the species composition and community diversity of planktonic diatoms were closely correlated with the proportion of bare land area, nitrogen nutrients, precipitation, and sediment concentration. In particular, particle-attached diatoms responded sensitively to environmental factors. These findings provide strong evidence for sediment-mediated assembly and interactions of riverine diatom communities.

In-lake water turnover time shapes the distribution pattern of phytoplankton communities in a river-connected floodplain lake.

In floodplains, phytoplankton communities are mainly shaped by environmental heterogeneity, hydrological connectivity, and habitat diversity. However, it remains unclear how hydrological connectivity drives phytoplankton biodiversity in floodplain lakes. This study was carried out in the Dongting Lake connected to the Yangtze River to ascertain the response mechanisms of phytoplankton communities to different hydrological connectivity gradients. We quantified the hydrological connectivity between lake and river habitats using in-lake water turnover time, and identified its relationship with phytoplankton community structure. Changes in hydrological connectivity can lead to different hydrodynamic and environmental conditions, which have a direct or indirect impact on phytoplankton community structure in water environments. The results showed that spatiotemporal changes in the hydrological connectivity and water environment led to distinct spatial variation in phytoplankton community structure across the study area. α and ß diversity showed a consistent change law with the change of turnover time, and the diversity index gradually increased with the decrease of hydrological connectivity, reaching the maximum value at the moderate hydrological connectivity, and then gradually decreasing. The peak of ß diversity occurs earlier than the peak of α diversity during the decline of hydrological connectivity. This study demonstrates that in-lake water turnover time has a non-negligible impact on phytoplankton community distribution in river-connected lakes. Phytoplankton can maintain the highest α diversity and possibly ß diversity under moderate hydrological connectivity, which is crucial for maintaining aquatic biodiversity in floodplain lakes.

Characteristics of phytoplankton community and its influencing factors in the Yanhe River Basin, Northwest China.

Yanhe River is one of the important tributaries of the Yellow River, with a vital role in the maintenance of biodiversity and ecological conservation in the middle reaches of the Yellow River. In this study, we conducted a systematic aquatic ecological survey of the Yanhe River Basin in spring (April-May) and autumn (September-October) of 2021, with phytoplankton as indicator organism. A total of 33 sampling sections were selected in the mainstem, five first-class tributaries, and impounded water bodies (reservoir and check dam water bodies) of the Yanhe River Basin. The results showed that a total of 253 phytoplankton species, belonging to 7 phyla and 91 genera, were detected in the two surveys. Diatoms and green algae prevailed in spring (168 species), while diatoms and cyanobacteria dominated in autumn (179 species). The mean phytoplankton density and biomass were 316.07×104 cells·L-1 and 6.41 mg·L-1 in spring, and 69.56×104 cells·L-1 and 1.59 mg·L-1 in autumn, respectively. At the temporal scale, phytoplankton abundance in spring was higher than that in autumn. At the spatial scale, the phytoplankton abundance in the middle and lower reaches of the mainstream was higher than that in the upper reaches. Phytoplankton biomass in the impounded water bodies formed by dam interception was maintained at a high level, which was significantly higher than that in the mainstem and tributary water bodies in autumn. The phytoplankton diversity, as indicated by Shannon diversity index, Margalef richness index, and Pielou evenness index, in spring was greater than that in autumn. Phytoplankton diversity was greater in the trunk and tributary waters than that in impounded waters. The results of redundancy analysis showed that the key factors driving the phytoplankton community structure in spring were flow velocity, dissolved oxygen, nitrite nitrogen, and water depth. In contrast, the key driving factors in autumn were nitrate nitrogen, water depth, and dissolved oxygen.

Identification of Sodium- and Chloride-Sensitive Sites in the Slack Channel.

The Slack channel (KCNT1, Slo2.2) is a sodium-activated and chloride-activated potassium channel that regulates heart rate and maintains the normal excitability of the nervous system. Despite intense interest in the sodium gating mechanism, a comprehensive investigation to identify the sodium-sensitive and chloride-sensitive sites has been missing. In the present study, we identified two potential sodium-binding sites in the C-terminal domain of the rat Slack channel by conducting electrophysical recordings and systematic mutagenesis of cytosolic acidic residues in the rat Slack channel C terminus. In particular, by taking advantage of the M335A mutant, which results in the opening of the Slack channel in the absence of cytosolic sodium, we found that among the 92 screened negatively charged amino acids, E373 mutants could completely remove sodium sensitivity of the Slack channel. In contrast, several other mutants showed dramatic decreases in sodium sensitivity but did not abolish it altogether. Furthermore, molecular dynamics (MD) simulations performed at the hundreds of nanoseconds timescale revealed one or two sodium ions at the E373 position or an acidic pocket composed of several negatively charged residues. Moreover, the MD simulations predicted possible chloride interaction sites. By screening predicted positively charged residues, we identified R379 as a chloride interaction site. Thus, we conclude that the E373 site and the D863/E865 pocket are two potential sodium-sensitive sites, while R379 is a chloride interaction site in the Slack channel.SIGNIFICANCE STATEMENT The research presented here identified two distinct sodium and one chloride interaction sites located in the intracellular C-terminal domain of the Slack (Slo2.2, KCNT1) channel. Identification of the sites responsible for the sodium and chloride activation of the Slack channel sets its gating property apart from other potassium channels in the BK channel family. This finding sets the stage for future functional and pharmacological studies of this channel.

Selective Adsorption of Quercetin by the Sol-Gel Surface Molecularly Imprinted Polymer.

Quercetin, as one of the most biologically active natural flavonoids, is widely found in various vegetables, fruits and Chinese herbs. In this work, molecularly imprinted polymer (MIP) was synthesized through surface molecular imprinting technology with sol-gel polymerization mechanism on SiO2 at room temperature using quercetin as the template, SiO2 as the supporter, 3-aminopropyltriethoxysilane (APTES) as the functional monomer, and tetraethoxysilane (TEOS) as the cross-linker. The prepared MIP was characterized via scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR) and nitrogen adsorption measurements to validate its surface morphology, structure and functionality. SEM images revealed that the morphology of MIP was rough and spherical with the particle size of 260 nm larger than that of the support SiO2. In the FTIR spectra of MIP, the band around 1499 cm-1 and 2932 cm-1 were assigned to N-H and C-H groups, respectively. The results indicated that the imprinted polymer layers were grafted on the surface of SiO2 and the MIP had been successfully prepared. Since the specific surface area and pore volume of MIP were markedly higher than those of NIP and SiO2 and were 52.10 m2 g-1 and 0.150 cm3 g-1, respectively, it was evident that the imprinting process created corresponding imprinted cavities and porosity. The MIP for adsorbing quercetin was evaluated by static adsorption experiment. The results indicated that the adsorption equilibrium could be reached within 90 min and the maximum adsorption capacity was as high as 35.70 mg/g. The mechanism for adsorption kinetics and isotherm of MIP for quercetin was proved to conform the pseudo-second-order kinetics model (R2 = 0.9930) and the Freundlich isotherm model (R2 = 0.9999), respectively, revealing that chemical adsorption and heterogeneous surface with multilayer adsorption dominated. In contrast to non-imprinted polymer (NIP), the MIP demonstrated high selectivity and specific recognition towards quercetin whose selectivity coefficients for quercetin relative to biochanin A were 1.61. Furthermore, the adsorption capacity of MIP can be maintaining above 90% after five regeneration cycles, indicating brilliant reusability and potential application for selective adsorption of quercetin.

Versatile Melanin-Like Coatings with Hierarchical Structure toward Personal Thermal Management, Anti-Icing/Deicing, and UV Protection.

Superhydrophobic photothermal coatings are promising for multifunctional applications due to the efficient use of solar energy, but the current challenge is to seek one easy-to-prepare material with high photothermal performance. Herein, inspired by mussel adhesion and lotus leaf surfaces, we developed superhydrophobic photothermal coatings with hierarchical structure by depositing melanin-like polydopamine (PDA) and dip-coating polydimethylsiloxane (PDMS)/hydrophobic fumed silica (SiO2) sequentially. Benefitting from the efficient photothermal conversion performance of PDA, the coated fabric can rapidly warm up to 100 °C under 100 mW/cm2 sun irradiation. Meanwhile, the coatings show excellent superhydrophobic properties (WCA of 163°), which not only prevent the adhesion of the contaminant from maintaining a long-term and efficient photothermal performance but also help the fabric to own outstanding passive anti-icing and active deicing performances. Furthermore, the superhydrophobic properties of the coatings can be maintained after sandpaper abrasion, repeat tape-peeling, and ultrasonication. In addition, superior UV protection of the coatings can meet the long-term service conditions under outdoor sunlight. The PDA-based superhydrophobic photothermal coatings are believed to inspire new strategies for solar-driven multifunctional applications such as personal thermal management, anti-icing/deicing of variously shaped components, photothermal antibacterial, and so on.

Will a heavy sediment load affect responses of phytoplankton functional groups to aquatic environmental changes in different water body types?

Sediment, as a natural component of rivers, directly affects the abundance and function of phytoplankton by altering water physicochemical properties. Despite mounting evidence for the sensitivity of phytoplankton to environmental factors, the responses of phytoplankton functional groups to complex environmental changes in rivers with a heavy sediment load are still poorly understood. Herein, the effectiveness of phytoplankton functional groups was evaluated as an indicator of aquatic environmental changes in a heavily sediment-laden river. Samples were collected from 44 sites (22 free-flowing river sections and 22 man-made reservoir sections) with a mean annual sediment concentration of 4.69 kg m-3 in the Yellow River, China. A total of 31 phytoplankton functional groups were classified during spring (April-May) and autumn (September-October) in 2019. Groups C, MP, and D, which are well adapted to strong water disturbances and turbid habitats, showed distinct advantages over other groups. Despite no significant differences in many environmental variables between the river and reservoir sections, these variables (especially nitrogen nutrients) had remarkable effects on the phytoplankton community structure. The phytoplankton functional groups were sensitive to environmental changes even under sediment interference, although geo-climatic variables also exhibited non-trivial effects. The mean niche breadth of the abundant taxa (river: 11.16; reservoir: 7.93) was higher than that of the rare taxa (river: 5.64; reservoir: 4.86) in different water bodies. Thus, growth and diffusion of the abundant taxa played paramount roles in maintaining ecosystem stability. The results indicate that, in a large-scale sediment-laden river, phytoplankton functional groups can effectively indicate changes in the aquatic environment of either a free-flowing river or a man-made reservoir.

Disentangling the drivers of phytoplankton community composition in a heavily sediment-laden transcontinental river.

Phytoplankton play a crucial role in energy flow and carbon cycling in aquatic ecosystems; however, exploring the driving factors influencing phytoplankton, especially in heavily sediment-laden rivers, is challenging. We analyzed 704 samples from 44 sampling sites along the Yellow River to investigate the biogeographic, environmental, and anthropogenic impacts on the phytoplankton community composition. Using cluster analysis, we identified three different phytoplankton community compositions in Regions Ⅰ, Ⅱ, and Ⅲ, which were consistent with the three primary changes in the water-surface slope across the three regions. The sampling results showed that the Bacillariophyta primarily consisted of Navicula, Cyclotella, Synedra, Fragilaria, Gyrosigma, Diatoma, and Asterionella. In addition, representation by Chlorophyta was dominated by Chlamydomonas, Pandorina, Closteriopsis, and Closterium, while Phormidium was the dominant Cyanophyta genus. The variation partitioning results indicated that spatial factors (geographic distance) were the most important determinants of phytoplankton community succession. Additionally, our results highlighted that the influence of spatial and climatic factors on the succession of the phytoplankton community structure was much greater than that of the water quality. Compared to that in the free-flowing river, the phytoplankton biomass in the impoundment was much higher, and the phytoplankton community was dominated by Dinophyta, Chlorophyta, and Cyanophyta, primarily because of anthropogenic impacts. Based on the composition and biomass of phytoplankton communities in different regions, the phytoplankton community composition in the Yellow River was found to be primarily influenced by the erosion of the watershed and the inflow of tributaries rather than by limited in situ algae growth.

Geo-climatic factors weaken the effectiveness of phytoplankton diversity as a water quality indicator in a large sediment-laden river.

The study aims to determine whether phytoplankton diversity can be used as an indicator of water quality in large-scale sediment-laden rivers with heterogeneous environmental conditions. We hypothesized that environmental factors, such as sediment load, water surface slope, and precipitation, may impact the effectiveness of using phytoplankton diversity as a water quality indicator. To test this hypothesis, the Yellow River was selected for phytoplankton diversity and water quality assessments. We measured water quality parameters, calculated phytoplankton diversity indices, and collected data on geo-climatic variables at 130 sampling points in the Yellow River mainstream over two seasons (spring and autumn) in 2019. The results of the water quality assessment based on phytoplankton diversity indices were compared with those based on water quality index (WQI). Correlation analysis, multiple stepwise regression, distance-based redundancy analysis, and regression modeling were used to explore the biogeographical patterns and drivers of phytoplankton diversity. According to the WQI, the water quality gradually deteriorated from the source to the estuary of the river. Three biodiversity indices (Margalef, Pielou, and Shannon-Wiener) indicated that the water quality varied dynamically in the middle reaches of the river. The actual relationships between the biodiversity indices and WQI did not fit well with the standard curves of water quality classification based on the respective biodiversity indices and WQI. Variation partitioning analysis indicated that water quality parameters, such as sediment and nutrient load, were the dominant drivers of variation in phytoplankton diversity in most cases, with the contribution ranging from 11.0% to 25.7%. Geo-climatic factors, such as water surface slope and annual mean precipitation, also affected phytoplankton diversity, with the contribution reaching 27.8%. Therefore, in sediment-laden rivers with a large geographical span and complex environment, phytoplankton diversity cannot be used as a suitable water quality indicator, albeit it can reflect habitat changes to a certain extent.

In-situ fabrication of a novel anisotropic PC-matrix light-scattering materials containing spindle-shaped core-shell particles.

Polycarbonate (PC)/Poly(styrene-co-acrylonitrile) (SAN)-organic silica bead (OSB) anisotropic light-scattering materials containing novel spindle-shaped core-shell particles through simple, low-cost hot stretching methods are prepared in situ, which have excellent and easily tunable optical properties. The effects of OSB particle size, OSB mass fraction and stretching ratio on the morphology of the spindle-shaped core-shell particles and the scattering properties of PC/SAN-OSB composites were studied in detail. The results show that smaller particle size OSB and smaller draw ratio are more conducive to the production of spindle-shaped core-shell particles. And because of the multiple scattering effects of the spindle-shaped core-shell particles, they have a significant compensation effect on the pattern short-axis light-scattering range of the PC anisotropic materials while ensuring that the pattern long-axis direction light-scattering range is not impaired.