Using hierarchical stable isotope to reveal microbial food web structure and trophic transfer efficiency differences during lake melt season

Trophic transfer efficiency of microbial food webs differs in water and sediment in alpine wetlands across the Tibetan Plateau

The Tibetan Plateau contains the world's largest area of alpine wetlands, where coexisting water and sediment environments provide habitats for multitrophic microbial communities. However, the microbial food web (MFW) of coexisting water and sediment in wetland ecosystems and their responses to environmental changes remain unclear. In this study, we investigated MFWs (including archaea, bacteria, and eukaryotes) across 21 paired samples from alpine wetlands on the Tibetan Plateau along a salinity gradient. In both water and sediment, the MFWs exhibited enhanced predation and decreased mutualism with increasing salinity, with the total trophic transfer efficiency (TTE) community of bacteria, protists and metazoa increasing. The TTE of MFWs in sediment was higher than that in water, and the competition associations among species decreased while the cooperation associations increased. Compared to sediment, the MFWs in water were more complex and vulnerable. Salinity exerted top-down control on MFWs by directly influencing higher trophic levels (e.g., metazoa) in water. In contrast, salinity affected the MFWs through bottom-up effects by impacting lower trophic levels (heterotrophic archaea, heterotrophic bacteria) in sediment. Overall, this study provides new insights into understanding the trophic cycle and interactions of multi-trophic biological communities in coexisting water and sediment, and how MFWs adapt to environmental change.

Habitat-specific regulation of microbiota in long-distance water diversion systems

Long-distance water diversion projects typically utilize various hydro-engineering facilities, creating complex and dynamic habitats. However, the microbial dynamics of multi-trophic microorganisms during water diversion and their responses to different hydro-engineering habitats remain poorly understood. In this study, we investigated bacteria, fungi, protists, and metazoa across tunnels, reservoirs, and inverted siphon piping along the main and northern branches of the Yellow River Diversion Project into Shanxi, during spring, summer, and autumn. Our results showed that both seasonal factors and hydro-engineering facilities significantly influenced the composition and diversity of microbiota. Bacterial community composition remained relatively stable during water transport, while fungi, protists, and metazoa exhibited greater spatial variability and habitat specificity. Stochastic processes predominantly governed the community assembly of all microbial groups across all hydro-engineering habitats. The structural features of the main network modules within the co-occurrence networks of multi-trophic species were highly consistent across different seasons within the same habitat, indicating the stable adaptation of microbiota interactions to the same habitat. Patterns of intra-kingdom (within bacteria, fungi, protists, or metazoa) and inter-kingdom (between bacteria, fungi, protists, and metazoa) associations of microbiota in different habitats varied, reflecting specific adaptations of microorganisms to particular habitats and suggesting an important role for environmental filtering. Variance partitioning analysis revealed that environmental factors accounted for 34.21 % to 45.19 % of the variation in the four microbial taxa. Our findings reveal the ecological processes of microbial assembly and adaptation in large-scale water diversion projects, providing insights for project management and risk control.

Water quality drives the reconfiguration of riverine planktonic microbial food webs

The food web is a cycle of matter and energy within river ecosystems. River environmental changes resulting from human activities are increasingly threatening the composition and diversity of global aquatic organisms and the multi-trophic networks. How multiple environmental factors influence food web patterns among multi-trophic microbial communities in rivers remains largely unknown. Using water quality evaluation and meta-omics techniques, we investigated the composition, structure and interaction characteristics, and drivers of food webs of microorganisms (archaea, bacteria, fungi, protists, metazoa, viridiplantae and viruses) at multiple trophic levels in different water quality environments (Classes II, III, and IV). First, water quality deterioration led to significant changes in the composition of the microbial community at multiple trophic levels, which were represented by the enrichment of Euryarchaeota in the archaeal community, the increase of r-strategists in the bacterial community, and the increase of the proportion of predators in the protist community. Second, deteriorating water quality resulted in a significant reduction in the dissimilarity of community structure (homogenization of community structure in Class III and IV waters). Of the symbiotic, parasitic, and predatory networks, the community networks in Class II water all showed the most stable symbiotic, parasitic, and predatory correlations (higher levels of modularity in the networks). In Class III and IV waters, nutrient inputs have led to increased reciprocal symbiosis and decreased competition between communities, which may have the risk of a positive feedback loop driving a system collapse. Finally, inputs of phosphorus and organic matter could be the main drivers of changes in the planktonic microbial food web in the Fen River. Overall, the results indicated the potential ecological risks of exogenous nutrient inputs, which were important for aquatic ecosystem conservation.

Predation has a significant impact on the complexity and stability of microbial food webs in subalpine lakes

IMPORTANCE

As an important part of microbial food webs, protists transfer organic carbon and nutrients to higher trophic levels in aquatic ecosystems. Protist predation often influences the abundance and composition of bacterial communities. However, we still do not understand whether and how predation affects the complexity and stability of microbial food webs. This study assessed the seasonal dynamic characteristics and driving factors of microbial food webs in terms of complexity and stability. Our findings have implications for future surveys to reveal the effects of climate and environmental changes.