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.