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

Cascade effects of nutrient input on river microeukaryotic stability: habitat heterogeneity-driven assembly mechanisms

The assembly process and stability mechanism of microeukaryotes can reflect the health and sustainability of river ecosystems, and changes in land use types can alter biodiversity and affect ecosystem functions. Here, we used 18S rDNA amplicon sequencing technology to explore the effects of land use and dry and wet season changes on microeukaryotic species composition, community assembly, co-occurrence networks, and network stability, as well as the mechanisms driving observed changes. The total phosphorus concentration was 13.3 and 7.8 times higher and the total nitrogen concentration was 6.3 and 3.8 times higher in agricultural and urban river sections, respectively, than in forest river sections. Differences in land use types have created heterogeneity on river habitats and altered the distribution and species composition of microeukaryotes, reducing the number and diversity of endemic species in communities and simplifying the food web. High nitrogen and phosphorus inputs promoted the abundance of low-trophic-level species; ecosystem stability and population sizes were maintained by high trophic levels, which controlled the abundance of low trophic levels through predation and promoted nitrogen transformation. The high-nutrient environment reduced the niche breadth of species (>70 % dry season niche breadth contraction), thus promoting specialization; given that this placed these species at a disadvantage in the competition for resources, community stability decreased (60 %/40 % wet/dry season robustness reductions). The physical dilution effect of the river in the dry season was weakened, and the input of domestic sewage and agricultural return water promoted deterministic processes (71.43 % increased |βNTI|>2 in dry season). The environmental filtration effect in the wet season was still stronger than the physical dilution effect caused by the increase in river flow (neutral model R2 = 33.5 %). The input of large amounts of nutrients was the main driver of the decline in the stability of microeukaryotes (Total Effect = -0.62).

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.

Sequential decline in cyanobacterial, total prokaryotic, and eukaryotic responses to backward flow in a river connected to Lake Taihu

River ecosystems face escalating challenges due to altered flow regimes from human activities, such as urbanization with hydrological modifications. Understanding the role of microbial communities for ecosystems with changing flow regimes is still incomplete and remains at the frontier of aquatic microbial ecology. In particular, influences of riverine backward flow on the aquatic biota remain largely unknown. Therefore, we examined the impact of backward flow on the cyanobacterial, total prokaryotic, and eukaryotic communities in the Changdougang River, which naturally flows into Lake Taihu, through environmental DNA metabarcoding. We analyzed the differences in community diversity, assembly, and ecological network stability among groups under backward, weak, and forward flow direction conditions. Non-metric multidimensional scaling showed higher variations in communities of groups across flow direction conditions than seasonal groups. Variations in alpha and beta diversity showed that cyanobacterial and total prokaryotic communities experienced strong homogenization under backward flow conditions, whereas the ecological uniqueness of the eukaryotic community decreased. Assembly of the three flow-related communities was primarily governed by drift and dispersal limitation in stochastic processes. However, in the cyanobacterial community, homogeneous selection in deterministic processes increased from 22.79 % to 42.86 % under backward flow, aligning with trends observed in the checkerboard score (C-score). More importantly, the topological properties of ecological networks and the degree of average variation revealed higher stability in the cyanobacterial community compared to total prokaryotic and eukaryotic communities. Considering the variations in cohesion, the network stability in the cyanobacterial community decreased under backward flow. Our findings emphasize the distinct and sequentially diminishing responses of cyanobacterial, total prokaryotic, and eukaryotic communities to backward flowing rivers. This knowledge is crucial for maintaining ecological health of rivers, assessing the complex ecological impacts on hydrological engineering, and formulating sustainable water management strategies.

Impact of extreme rainfall and flood events on harmful cyanobacterial communities and ecological safety in the Baiyangdian Lake Basin, China

Globally, climate change has intensified extreme rainfall events, leading to substantial hydrological changes in aquatic ecosystems. These changes, in turn, have increased the frequency of harmful algal blooms, particularly those of cyanobacteria. This study examines cyanobacterial community dynamics in the Baiyangdian Lake Basin, China, after heavy rainfall and flooding events. The aim was to clarify how such extreme hydrological events affect cyanobacterial populations in floodplain ecosystems and assess related ecological risks. The results demonstrated a significant increase in cyanobacterial diversity, exemplified by an increase of the Shannon diversity index from an average of 1.72 to 2.1 (p < 0.05). Following heavy rainfall and subsequent flooding, the average relative abundance of cyanobacteria in the microbial community increased from 7.59 % to 9.62 %, along a notable rise in the abundance of harmful cyanobacteria. The community structure exhibited notable differences after flooding, showing an increase in species richness, but a decrease in community tightness and clustering, as well as a reduction in niche overlap among harmful cyanobacteria. Environmental factors such as dissolved oxygen, water temperature, and pH were identified as crucial predictors of harmful cyanobacterial community differences and abundance variations resulting from flooding. These findings provide a critical framework for predicting ecological risks associated with the expansion of bloom-forming cyanobacteria in large shallow lake basins, particularly under intensified rainfall and flooding events. This insight is essential to anticipate potential ecological disruptions in sensitive aquatic ecosystems.