Environmental factors and stochasticity affect the fungal community structures in the water and sediments of Hulun Lake, China

Climate and Environmental Variables Drive Stream Biofilm Bacterial and Fungal Diversity on Tropical Mountainsides

High mountain freshwater systems are particularly sensitive to the impacts of global warming and relevant environmental changes. Microorganisms contribute substantially to biogeochemical processes, yet their distribution patterns and driving mechanism in alpine streams remain understudied. Here, we examined the bacterial and fungal community compositions in stream biofilm along the elevational gradient of 745-1874 m on Mt. Kilimanjaro and explored their alpha and beta diversity patterns and the underlying environmental drivers. We found that the species richness and evenness monotonically increased towards higher elevations for bacteria, while were non-significant for fungi. However, both bacterial and fungal communities showed consistent elevational distance-decay relationships, i.e., the dissimilarity of assemblage composition increased with greater elevational differences. Bacterial alpha diversity patterns were mainly affected by chemical variables such as total nitrogen and phosphorus, while fungi were affected by physical variables such as riparian shading and stream width. Notably, climatic variables such as mean annual temperature strongly affected the elevational succession of bacterial and fungal community compositions. Our study is the first exploration of microbial biodiversity and their underlying driving mechanisms for stream ecosystems in tropical alpine regions. Our findings provide insights on the response patterns of tropical aquatic microbial community composition and diversity under climate change.

Dry and wet seasonal variations of the sediment fungal community composition in the semi-arid region of the Dali River, Northwest China

Microbial communities play an important role in water quality regulation and biogeochemical cycling in freshwater ecosystems. However, there has been a lack of research on the seasonal variation of sediment microorganisms in the sediments of small river basins in typical semi-arid region. In this study, high-throughput DNA sequencing was used to investigate the fungal community and its influencing factors in the sediment of the Dali River in the dry and wet seasons. The results showed that there were obvious seasonal differences in fungal alpha diversity. The diversity and richness of fungi in the dry season were greater than that in the wet season, but the evenness of fungi in the dry season was lower than that in the wet season. In addition, Ascomycota and Basidiomycota were the most important phyla in the Dali River fungal community, but their distributions showed clear seasonal differences. In the dry season, the relative abundance of Ascomycota and Basidiomycota were 12.34-46.42% and 17.59-27.20%, respectively. In the wet season, the relative abundances of these two phyla were 24.33-36.56% and 5.75-12.26%, respectively. PICRUSt2 was used to predict the metabolic function of fungal community in the sediment, and it was found that at the first level, the proportion of biosynthesis in the dry season was higher than that in the wet season. The ecological network structure showed that the fungal community in the wet season was more complex and stable than that in the dry season. The characteristic fungi in the dry season sediment were chytrid fungi in the family Rhizophydiaceae and the order Rhizophydiales, whereas those in the wet season sediment were in the orders Eurotiales and Saccharomycetales. Canonical correspondence analysis (CCA) showed that the physicochemical properties of water and sediment together explained a greater proportion of the dry-season fungal community changes than of the wet-season changes. In the dry season, temperature and ammonia nitrogen in the water were the main factors affecting the change of fungal community, whereas in the wet season, total nitrogen concentration of the water, electrical conductivity, total organic carbon and available phosphorus of the sediment, pH, and temperature were the main factors affecting the changes in fungal community composition. The results of this study enhanced our understanding of microbial communities in semi-arid river ecosystems, and highlight the importance of the management and protection in river ecosystems.

Strong bacterial stochasticity and fast fungal turnover in Taihu Lake sediments, China

Understanding the assembly and turnover of microbial communities is crucial for gaining insights into the diversity and functioning of lake ecosystems, a fundamental and central issue in microbial ecology. The ecosystem of Taihu Lake has been significantly jeopardized due to urbanization and industrialization. In this study, we examined the diversity, assembly, and turnover of bacterial and fungal communities in Taihu Lake sediment. The results revealed strong bacterial stochasticity and fast fungal turnover in the sediment. Significant heterogeneity was observed among all sediment samples in terms of environmental factors, especially ORP, TOC, and TN, as well as microbial community composition and alpha diversity. For instance, the fungal richness index exhibited an approximate 3-fold variation. Among the environmental factors, TOC, TN, and pH had a more pronounced influence on the bacterial community composition compared to the fungal community composition. Interestingly, species replacement played a dominant role in microbial beta diversity, with fungi exhibiting a stronger pattern. In contrast, stochastic processes governed the community assembly of both bacteria and fungi, but were more pronounced for bacteria (R2 = 0.7 vs. 0.5). These findings deepen the understanding of microbial assembly and turnover in sediments under environmental stress and provide essential insights for maintaining the multifunctionality of lake ecosystems.