Differentiation of the Foliar Microbiomes From Co-Occurring Grass Species Reflects Their Recency of Invasion

Above-ground microbial communities associated with non-native invasive plants are infrequently characterized, particularly during the early stages of an invasion event. This study compared the foliar fungal and bacterial microbiomes of two co-occurring invasive grasses found in the Mid-Atlantic United States, recently introduced Oplismenus undulatifolius and long-established Microstegium vimineum. Amplicon sequencing was used to characterize endophytic communities collected from replicate plots within two field sites, and microbial community diversity, composition, and structure were contrasted between hosts. Despite occupying the same niche space, these invasive grasses carried significantly different microbial communities. Oplismenus supported lower within-sample fungal diversity and greater among-sample heterogeneity than Microstegium, while differences in bacterial communities were weaker and depended on the diversity metric examined. Null model analyses suggested that assembly processes were host- and microbial kingdom-specific. The differences observed between hosts may have resulted from several non-exclusive mechanisms but were generally consistent with an incomplete establishment of stable host-associated symbioses by the more recent invader. Differential abundance analyses also identified multiple host-associated fungal and bacterial lineages, including increased representation of Glomerellales, Pleosporales, and Rhizobiales in Oplismenus. The results of this study contribute to our understanding of co-occurring invasive weed communities and provide insight into the formation of an emerging, invasive Oplismenus microbiome.