The biogeography and co-occurrence network patterns of bacteria and microeukaryotes in the estuarine and coastal waters

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.

Spatiotemporal assembly and functional composition of planktonic microeukaryotic communities along productivity gradients in a subtropical lake

Microeukaryotes play crucial roles in the microbial loop of freshwater ecosystems, functioning both as primary producers and bacterivorous consumers. However, understanding the assembly of microeukaryotic communities and their functional composition in freshwater lake ecosystems across diverse environmental gradients remains limited. Here, we utilized amplicon sequencing of 18S rRNA gene and multivariate statistical analyses to examine the spatiotemporal and biogeographical patterns of microeukaryotes in water columns (at depths of 0.5, 5, and 10 m) within a subtropical lake in eastern China, covering a 40 km distance during spring and autumn of 2022. Our results revealed that complex and diverse microeukaryotic communities were dominated by Chlorophyta (mainly Chlorophyceae), Fungi, Alveolata, Stramenopiles, and Cryptophyta lineages. Species richness was higher in autumn than in spring, forming significant hump-shaped relationships with chlorophyll a concentration (Chl-a, an indicator of phytoplankton biomass). Microeukaryotic communities exhibited significant seasonality and distance-decay patterns. By contrast, the effect of vertical depth was negligible. Stochastic processes mainly influenced the assembly of microeukaryotic communities, explaining 63, 67, and 55% of community variation for spring, autumn, and both seasons combined, respectively. Trait-based functional analysis revealed the prevalence of heterotrophic and phototrophic microeukaryotic plankton with a trade-off along N:P ratio, Chl-a, and dissolved oxygen (DO) gradients. Similarly, the mixotrophic proportions were significantly and positively correlated with Chl-a and DO concentrations. Overall, our findings may provide useful insights into the assembly patterns of microeukaryotes in lake ecosystem and how their functions respond to environmental changes.

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

Eukaryotic microorganisms play an important role in the biogeochemical cycles of rivers. Dynamic hydrological processes in rivers are thought to influence the assembly processes of eukaryotic microbes, as well as affecting local geomorphology. These processes have not been extensively studied for eukaryotic river microbes in extreme environments on the Tibetan Plateau. This study used 18S rDNA gene amplification sequencing, a neutral community model, and a null model to analyze the spatial and temporal dynamics and assembly processes of eukaryotic microbial communities in the middle reaches of the Yarlung Zangbo River. We conducted analyses across wet and dry seasons, as well as varying altitudinal gradients. Our results showed that the diversity, structure, and taxonomic composition of eukaryotic microbial communities varied more with altitude than season, and the diversity of the communities first increased, then decreased, with increasing elevation. Distance-decay analysis showed that the correlation between eukaryotic microbial communities and environmental distance was stronger than the correlation between the microbial communities and geographical distance. Deterministic processes (homogeneous selection) dominated the construction of eukaryotic microbial communities, and water temperature, pH, and total phosphorus were the primary environmental factors that influenced the construction of eukaryotic microbial communities. These results expand our understanding of the characteristics of eukaryotic microbial communities in rivers on the Tibetan Plateau and provide clues to understanding the mechanisms that maintain eukaryotic microbial diversity in extreme environments.