More than a stick in the mud: Eelgrass leaf and root bacterial communities are distinct from those on physical mimics

Summary We examine the role of physical structure vs. biotic interactions in structuring host-associated microbial communities on a marine angiosperm, Zostera marina, eelgrass. Across several months and sites, we compared microbiomes on physical mimics of eelgrass roots and leaves to those on intact plants. We find large, consistent differences in the microbiome of mimics and plants, especially on roots, but also on leaves. Key taxa that are more abundant on leaves have been associated with microalgal and macroalgal disease and merit further investigation to determine their role in mediating plant-microalgal-pathogen interactions. Root associated taxa were associated with sulfur and nitrogen cycling, potentially ameliorating environmental stresses for the plant. Our work identifies targets for future work on the functional role of the seagrass microbiome in promoting the success of these angiosperms in the sea. Originality-Significance Statement We show that eelgrass establishes a distinct microbial community from a physical mimic on both its leaves and roots. This is, to our knowledge, the first comparison of seagrass to a mimicked physical environment. Insights from our study establish bacterial targets for future functional studies of seagrass-microbiome interactions.