A Scoping Review of Bryophyte Microbiota: Diverse Microbial Communities in Small Plant Packages

Plant health depends not only on the condition of the plant itself but also on its diverse community of microbes, or microbiota. Just like the better-studied angiosperms, bryophytes (mosses, liverworts, and hornworts) harbor diverse communities of bacteria, archaea, fungi, and other microbial eukaryotes. Bryophytes are increasingly recognized as important model systems for understanding plant evolution, development, physiology, and symbiotic interactions. Much of the work on bryophyte microbiota in the past focused on specific symbiont types for each bryophyte group, but more recent studies have started to expand the view. Therefore, this review integrates studies of bryophyte microbes from both scopes to provide a holistic view of the existing research for each bryophyte group and on key themes. The systematic search also reveals the taxonomic and geographic biases in this field, including a severe underrepresentation of the tropics, very few studies on viruses or eukaryotic microbes beyond fungi, and overrepresentation of mycorrhizal fungi studies in liverworts. Such gaps may lead to errors in conclusions about evolutionary patterns in symbiosis. This analysis points to a wealth of future research directions that promise to reveal how the distinct life cycles and physiology of bryophytes interact with their microbiota.