Browsing by Subject "bryophyte"

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.

Bryophytes, by their haploid dominant life cycle, possess several unique qualities ideal for study of mating patterns. In particular, the possibility of intragametophytic selfing in some species, and the vegetative propagation of gametes allow for a unique window into the haploid stage that is intractable in other groups. Despite these advantages, there have been relatively few studies on mating patterns bryophytes in natural populations. Sphagnum (peatmoss) is an excellent case study in the interactions between sexual condition, ecology, and mating patterns. In the first Chapter, we use microsatellites to characterize the genetic diversity and mating patterns in fourteen species of Sphagnum, diverse in sexual condition (separate vs combined sexes in the haploid stage) and ecology (microhabitat variance along the water table). We find that genetic diversity and mating patterns are related only in species with separate sexes, that sexual condition and ecology have interacting effects on inbreeding coefficients, and that inbreeding depression is not a common phenomenon in Sphagnum. In the second Chapter, we conduct an intensive survey of one population of Sphagnum macrophyllum, to detect whether variance in haploid fecundity and mating success is related to diploid fitness. We find a relationship between mating success and fecundity (a signal of sexual selection), and fitness of the diploid generation is connected to the parentage of the haploid generation. Finally, in Chapter 3 we use phylogenetic comparative methods to track the phylogenetic signal in microhabitat preference in Sphagnum. We find extremely fast rates of evolution along the micronutrient gradient, but high phylogenetic signal along a hydrological gradient. Given that Sphagnum species living high above the water table have reduced water availability, phylogenetic signal in the hydrological gradient has macroevolutionary implications for mating systems in Sphagnum.