Diversity and Effects of the Fungal Endophytes of the Liverwort Marchantia polymorpha

Fungal endophytes are ubiquitous inhabitants of plants and can have a wide range of effects on their hosts, from pathogenic to mutualistic. These fungal associates are important drivers of plant success and therefore contribute to plant community structure. The majority of endophyte studies have focused on seed plants, but in order to understand the dynamics of endophytes at the ecosystem scale, as well as the evolution of these fungal associations, investigations are also necessary in earlier-diverging clades of plants, such as the non-vascular bryophytes (mosses, liverworts, and hornworts). This dissertation presents a survey of the diversity of fungal endophytes found in the liverwort Marchantia polymorpha L. and develops a gnotobiotic experimental system for testing the effects of these fungi on their liverwort host. The survey reveals a diverse community of fungi in M. polymorpha, with some fungi that are associated with this host across geographically distant sites. The laboratory experiments demonstrate that culturable endophytes of M. polymorpha can, in isolation, cause positive, negative, or neutral effects on host success and that these effects change in response to nutrient levels and the presence of multiple endophytes. The experimental system developed in this dissertation has great potential in the growing field of plant microbiota research to answer questions that range in scale from molecular mechanisms to ecosystem function.