Linking historical vegetation to bacterial succession under the contrasting climates of the Tibetan Plateau

Understanding the relationship between historical vegetation and bacteria is critical for disentangling spatiotemporal variations in microbial communities. However, the utility of historical vegetation as indicated by the reconstruction proxies like n-alkanes to explain microbial succession has been understudied, especially regarding aquatic microbes living under contrasting climates. Here, we studied bacterial and n-alkane succession in sediment cores from Kusai Lake and Lugu Lake under contrasting climates, that is, the drier and colder climates and the warmer and wetter conditions, respectively, and further explored how bacterial communities are affected by historical vegetation. In both lakes, the Shannon diversity of bacteria and n-alkanes consistently and significantly (P < 0.05) decreased towards deep-depth sediments, and their compositional dissimilarity Bray-Curtis increased with depth changes, with slopes of 0.00048 and 0.00027 in Kusai and Lugu lakes, respectively. Furthermore, there was strong synchrony between bacteria and historical vegetation, which was underpinned by similar ecological processes such as environmental selection (e.g., climatic perturbations). Compared to Lugu Lake, however, both the Shannon diversity and compositions of bacteria or n-alkanes changed faster in Kusai Lake, which was influenced by abiotic factors such as the sediment Na and loss-on-ignition. Except for abiotic variables, we found that bacterial diversity and composition were also affected by n-alkane attributes such as the C27/C31, carbon preference index, Shannon diversity and composition in both lakes. In particular, n-alkane attributes generally exerted stronger effects on bacterial characteristics than abiotic variables. For example, n-alkane attributes showed strong direct effects on bacterial community composition, with path coefficients of 0.485 and 0.976 (P < 0.001) in Kusai and Lugu lakes, respectively, while abiotic variables had no direct effect. Thus, our findings provide new evidence that historical vegetation could substantially explain variations in bacterial communities across temporal scales.