Fungal endophyte communities in the temperate fern Polystichum munitum show early colonization and extensive temporal turnover

PREMISE OF THE STUDY: Fungal endophytes have been shown to colonize all land plants, yet surprisingly little attention has been given to their community composition in ferns. We examined the diversity and temporal turnover of fungal endophytes in foliar tissue of the temperate western sword fern, Polystichum munitum, comparing taxa in newly emerged leaflets and in the same fronds after 1 mo of exposure in the field. METHODS: Utilizing next-generation sequencing, we sampled pinnae from P. munitum in spring, 2-3 d after they emerged. We additionally sampled pinnae 30 d later from the same fern blades. From these samples, we sequenced fungal DNA to characterize the initial colonization and temporal turnover of endophytes in the host. KEY RESULTS: We demonstrate that P. munitum is abundantly colonized by endophytes in newly emerged foliar tissue. However, 1 mo later, the community composition undergoes a marked shift: the overall richness of endophytes increases, but the evenness of the community wanes as a single taxon, Flagellospora fusarioides, comes to dominate. CONCLUSIONS: We conclude that P. munitum hosts a variety of fungal endophyte taxa, similarly to other land plants. However, the rapid shift of the endophyte community we report is an unprecedented observation. Therefore, we further conclude that repeated sampling should be the standard in endophyte studies, because single sampling events are not sufficient to capture the dynamic nature of these cryptic microfungi.