Evolution of lake microbial structure and function under climatic and anthropogenic forcings: Insights from sedimentary ancient DNA.

Structure and function of lake microorganisms are sensitive to environmental disturbances; yet their differential responses to climatic and anthropogenic forcings over centennial scales remain poorly understood. Here, we analyzed a sediment core from Lake Daihai in northern China, combining metagenomics and stable isotope analyses. Our results revealed that microbial community assembly was dominated by deterministic processes, whereas stochasticity increased notably after 1850, coinciding with the termination of the Little Ice Age and intensified human impacts. Notably, microbial community structure evolved at a rate approximately one order of magnitude faster than community function. This decoupling was mediated by functional redundancy associated with bacterial keystone taxa, ultimately resulting in more negative sedimentary carbon and nitrogen isotopic compositions nearly a century later. Gene-level functional redundancy further buffered ecosystem function variability across biological scales. Collectively, our findings integrate omics and geochemical approaches to advance the understanding of lake ecological evolution under complex multi-forcing regimes.