Uncoupling of seagrass host selection and succession for microbial guilds in meadow chronosequence

Succession is an ecosystem building process in which a habitat and its community interact predictably by increasing diversity, habitat engineering, and ultimately reaching a climax community, where other ecological processes influence its dynamic. Key to succession is the establishment of primary producing habitat forming species, which drives niche differentiation leading to increasing diversity. Here, we use the primary colonizing and habitat forming seagrass, Halophila ovalis, to demonstrate that it drives bacterial succession in a meadow ecosystem, and its microbiome, both rhizoplane and phylloplane, are under host selection. Many of the characteristics attributed to plants for habitat modification are microbial processes such as nitrogen fixation and sulfide detoxification and succession is often extrapolated to such processes. To determine if succession (increasing diversity) or selection (reducing diversity) drives changes in diversity (16S rRNA gene) or habitat modifying processes (nifH, soxB, aprA, dsrA), molecular analysis was performed along chronosequences (as a proxy for succession) of seagrass patches. Bacterial communities were sampled within the meadow ecosystem and the microbiomes of H. ovalis (both rhizoplane and phylloplane). Genes involved in biogeochemical cycling are differentially impacted within the microbiome and meadow sediments, with only nifH under succession. All genes from all niches sampled for community analysis are under directional community trajectories, despite being subjected to distinct ecological processes, signifying that many ecological processes, including succession and host association, drive community assemblage.