Differences in diversity and community assembly processes between planktonic and benthic diatoms in the upper reach of the Jinsha River, China

New insights into the assembly processes of biofilm microbiota communities: Taking the world's largest water diversion canal as a case study

Systematic studies on the assembly process and drivers of biofilm microbiota communities are still limited. In this study, we used the artificial concrete channel of the world's largest interbasin water diversion project, the middle route of the South-to-North Water Diversion Project in China, as a model system to investigate the assembly mechanisms of biofilm microbiota communities. Our study revealed that water temperature (p < 0.001) and hydrodynamic disturbance (p < 0.05) significantly influenced biofilm biomass. The bacterial communities exhibited substantial spatial heterogeneity, whereas the eukaryotic communities presented pronounced spatial and seasonal variations (PERMANOVA, p < 0.05). Neutral model and null model analyses indicated that dispersal limitation and homogeneous selection (54.8 %-69.7 % in bacteria and 55.9 %-76.1 % in eukaryotes) predominantly governed community assembly. Deterministic effects such as hydrodynamic conditions and temperature strongly influence eukaryotes (homogeneous selection accounts for 63.9 % of eukaryotes in spring). The metacommunity network could be divided into five primary modules with key nodes, including many species from Proteobacteria, Chlorophyta, Bacillariophyta, and Cyanobacteria. Bacteria, such as Proteobacteria, Chlorophyta, Cyanobacteria, and Bacteroidota, act as connectors and a vital role in maintaining the coexistence of modules. Finally, we confirmed that physicochemical (hydrodynamic conditions, temperature, dissolved oxygen conductivity permanganate index), spatial, and biological factors have significant effects on both bacterial and eukaryotic communities as well as metacommunity networks. Our findings provide new insights into the different assembly processes and drivers of bacterial and eukaryotic communities in biofilms, which is highly important for water quality monitoring and sustainable water diversion.

Seasonal Variation in the β-Diversity of Periphytic Algae and Its Response to Landscape Patterns in the Chishui River, a Naturally Flowing Tributary of the Upper Yangtze River

Understanding biodiversity is essential for preserving the stability of river ecosystems. However, the impact of landscape configurations and seasonal variations on biodiversity within undammed river ecosystems remains unexplored. Therefore, we selected the Chishui River-a naturally flowing tributary of the upper Yangtze River-for a survey of periphytic algae. The present study focuses on the seasonal fluctuations in the β-diversity of periphytic algae within the Chishui River and its correlation with the surrounding landscape patterns. Our findings indicate that there is a substantial influence of seasonal variations on the community structure and β-diversity of these algae within the Chishui River ecosystem. Concurrently, we observed that the turnover component predominantly contributes to β-diversity. In light of these findings, we recommend that conservation measures be implemented across the entire Chishui River basin to safeguard the regional biodiversity. Redundancy analysis elucidated that water temperature, conductivity, and pH were the primary environmental drivers shaping the structure of periphytic algal communities. Furthermore, additional analyses using a random forest model indicated that landscape fragmentation and complexity were key determinants of β-diversity in algal communities. Notably, the number of landscape patches was strongly correlated with the β-diversity of periphytic algae. It is important to highlight that maintaining an optimal balance between the number of patches and their size is crucial for enhancing the ecosystem's capacity to preserve biodiversity. In summary, our findings provide insights into the interplay between biodiversity and land-use practices within complex riverine environments, thereby offering a scientific foundation for the conservation and management of these ecosystems.

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.

Species turnover and functional nestedness constitute the geographic patterns of stream diatoms in the Three Parallel Rivers region, China

Unraveling biodiversity patterns and their driving processes is paramount in ecology and biogeography. However, there remains a limited understanding regarding the underlying mechanisms of community assembly, particularly in alpine streams where significant elevation gradients and habitat heterogeneity exist. We investigated the patterns and drivers of beta diversity, explicitly focusing on taxonomic and functional diversity, in the three parallel rivers region in China. We employed a beta diversity partitioning approach to examine the turnover and nestedness components of beta diversity and further deconstructed the diatom community into attached and unattached groups. Our results revealed distinct diversity patterns and drivers for taxonomic and functional beta diversity. Specifically, taxonomic beta diversity was mainly driven by the turnover component affected by spatial processes, whereas functional beta diversity was dominated by the nestedness component affected by environmental processes. Furthermore, our analysis of the division of the whole communities demonstrated that the varying responses of benthic diatoms with different attached abilities to environmental filtering, dispersal limitation, and directional flow were the essential reasons for shaping the biodiversity patterns of species turnover and functional nestedness in the alpine stream. Our findings suggested that partitioning beta diversity and dividing the entire community can more deeply infer underlying community assembly processes, thereby providing valuable insights into understanding biodiversity patterns, drivers, and conservation strategies.

Diel variation of plankton in the highly impacted freshwater zone of Hooghly estuary in relation to ecological alteration

Plankton are promising ecological monitoring tool that responds quickly to any sort of aquatic ecological alteration, of which many of them are much susceptible to ecological variations. Therefore, monitoring shifts in plankton composition can indicate changes in water quality and aid to identify potential pollution sources. In the present study, the variation in plankton dynamics in relation to ecological variables were monitored in the freshwater zone of the Hooghly estuary from May 2020 to April 2021. The study was conducted in the interval of every six hours. i.e., at 6 A.M., 12 P.M., 6 P.M., and 12 A.M. The present finding revealed the occurrence of 54 phytoplankton and 20 zooplankton taxa/species. Diel variation revealed that among different time intervals, the highest abundance of phytoplankton was recorded 28,307 cells l-1 at 12 P.M, while the lowest was recorded 10,632 cells l-1 at 6 A.M. However, the highest zooplankton abundance was observed 804 ind l-1 at 6 A.M., and the lowest was recorded 156 ind l-1 at 6 P.M. The ANOVA (p < 0.05) analysis indicated significant diel variation for many planktonic genera. The CCA exhibited that most of the phytoplankton were influenced by multiple water quality variables such as temperature, turbidity, calcium, pH, salinity, DO, and nutrients. However, the majority of the zooplankton were affected by turbidity, total phosphorus, sulphate, calcium and available nitrogen. Significant seasonal variation in plankton composition has also been observed. The present study will help to determine the varying diel pattern of planktons in retort to alterations in the water quality parameters and varying ecological niches.

Hydrological disturbances enhance stochastic assembly processes and decrease network stability of algae communities in a highland floodplain system

Floodplains are hotspots for biodiversity research and conservation worldwide. Hydrological disturbances can profoundly influence the ecological processes and functions of floodplain systems by altering key biological groups such as algae communities. However, the impacts of flood disturbance on the assembly processes and co-occurrence patterns of algae communities in floodplain ecosystems are still unclear. To ascertain the response patterns of algae communities to flood disturbance, we characterized planktonic and benthic algae communities in 144 water and sediment samples collected from the Tibetan floodplain during non-flood and flood periods based on 23S ribosomal RNA gene sequencing. Results showed that planktonic algae exhibited higher diversity and greater compositional variations compared with benthic communities after flood disturbance. Flooding promoted algae community homogenization at horizontal (rivers vs. oxbow lakes) and vertical levels (water vs. sediment). Stochastic processes governed the assembly of distinct algae communities, and their ecological impacts were enhanced in response to flooding. In the non-flood period, dispersal limitation (81.78 %) was the primary ecological process driving algae community assembly. In the flood period, the relative contribution of ecological drift (72.91 %) to algae community assembly markedly increased, with dispersal limitation (22.61 %) being less important. Flooding reduced the interactions among algae taxa, resulting in lower network complexity and stability. Compared with the planktonic algae subnetworks, the benthic subnetworks showed greater stability in the face of flooding. Findings of this study broaden our understanding of how algae communities respond to hydrological disturbances from an ecological perspective and could be useful for the management of highland floodplain ecosystems.

Benthic diatom communities and a comparative seasonal-based ecological quality assessment of a transboundary river in Bangladesh

Seasonality can play a crucial role in altering water quality in tropical rivers, and as a benthic community, diatom can show seasonal variation and changes in ecological status. During the present study, the Trophic Diatom Index (TDI) and Water Quality Index (WQI) were used to determine the ecological status of a transboundary river, the Sari-Goyain River in Bangladesh. Samplings were carried out from upstream to downstream river sites in wet and dry seasons to observe the seasonal dynamics. The benthic diatom composition and physicochemical parameters showed seasonal variation in ecological water quality assessment. In the River, 42 different diatom species from 19 genera were recorded. The mean TDI values indicated an oligotrophic condition of the river in both seasons. But, the WQI values showed excellent and good water quality in the wet and dry seasons, respectively. So, the WQI was helpful in assessing seasonal variation of ecological water quality status in the Sari-Goyain River. For the long-term monitoring of the ecological status of the river, seasonal variation and WQI-based assessment should be considered.

Application of Phytoplankton Taxonomic α-Diversity Indices to Assess Trophic States in Barrier Lake: A Case of Jingpo Lake

Phytoplankton taxonomic α-diversity indices are useful tools to characterize the trophic states in freshwater ecosystems. However, the application of these indices to assess trophic states in large barrier lakes is rare, especially in China. To test the usefulness of phytoplankton taxonomic α-diversity indices in trophic state assessments, we investigated the taxonomic α-diversity-Comprehensive Trophic Level Index (TLI) relationships in the second largest alpine lava barrier lake (Jingpo Lake, China) in the rainy and dry season from 2017 to 2018. Based on a two-year dataset, we found that there was a significant difference in the phytoplankton community, α-diversity indices, and TLI dynamic between the rainy season and the dry season. First, there was significant variation in phytoplankton abundance, the Margalef index, and the Shannon-Wiener index in different hydrological periods (p < 0.05). Second, the mean TLI in the rainy season (44 ± 5) was higher than in the dry season (41 ± 5) (p < 0.05). Lastly, the response characteristics of the Margalef and Shannon-Wiener index with TLI were different in different hydrological periods, and the relationship between the Pielou evenness index and TLI was weak. This study highlights that phytoplankton taxonomic α-diversity indices are relevant tools in water quality assessments but selecting the fit index is necessary. The current study provides key information about phytoplankton community, α-diversity, and trophic states in the largest alpine lava barrier lake, and the results of the study will benefit water quality management and biodiversity conservation in barrier lakes.