Uncovering the role of biogeography, resources, food web composition and time during microbial primary succession.

Ecological succession is shaped by multiple processes that operate simultaneously across spatial and temporal scales. While classical succession theory generally focuses on a single trophic level within a single location, often in plants or other macroscopic organisms, recent efforts have extended this framework to microorganisms across multiple ecological dimensions. The aquatic micro-ecosystem within the pitcher plant, Sarracenia purpurea, provides a natural model of primary succession replicated across a continental latitudinal gradient. Using this model system, we investigated how biogeography, food web structure and resource availability influenced bacterial succession. Over 12 weeks, we repeatedly sampled bacterial communities from seven sites spanning the latitudinal range of S. purpurea and characterized communities using 16S rRNA gene sequencing. Both taxonomic and phylogenetic diversity increased over succession. These diversity patterns were not explained by temporal changes in food web composition, resources or environmental conditions, although pH, water volume, latitude and midge abundance, each influenced diversity independently of time. Latent Dirichlet allocation models identified six compositional groups with distinct temporal and biogeographic signatures. Early-successional groups were enriched in putative diazotrophs, while late-successional groups contained metabolically diverse taxa adapted to low-oxygen conditions. Our findings show that microbial primary succession in S. purpurea is shaped by time, biogeography and pitcher-scale environmental filters.