Just as in all higher organisms, plants are colonized by an impressive array of microbes. One such group of microbes, known as fungal endophytes, are found within all plants and do not cause symptoms of disease. Most fungal endophytes are currently classified as commensals or latent saprobes, yet this classification will likely change in the coming years as we come to further understand their ecological functions. I investigate fungal endophytes that associate with seed-free plants (e.g. ferns), but also conduct research in other host plants. Very few studies have examined fungal endophyte colonists in ferns. Due to their unique ecology and modes of reproduction, ferns may host many distinct fungal endophytes that play a key role in fern fitness and evolution. Some of my research projects are below:
Temporal turnover of fungal endophytes in ferns— I have conducted a temporal turnover survey in an effort to (i) clarify what fungal endophytes are commonly found in an abundant fern in Western North America, Polystichum munitum, and (ii) determine how the community composition of endophytes changes on a fine scale over time. In this project, I have sampled the same 20 plants in a population of P. munitum at the Oregon Coast Range monthly, for an entire growing season. This is the first project to leverage next generation sequencing technology (NGS) to examine endophyte community turnover on such a fine scale. I have found that when fern leaves first unfurl in the spring, they are colonized by endophytes in a patchy manner, but after one month, a highly competitive endophyte, Flagellospora fusarioides, comes to dominate the fungal community. The results of this project have broad applicability to agriculture since there is some interest in using endophytes as biological agents that benefit plants. As this project demonstrates, some endophytes are highly ephemeral in the presence of other competitive fungi, making their potential application futile when competitive fungi are present. Publications from this project are underway, so stay tuned!
Vertical transmission of fungal symbionts in ferns—Some fungal endophytes are vertically transmitted, from parent to offspring, in many seed plants. However, it is unknown if this also happens in spore-reproducing plants like ferns. I have found fungal DNA in fern gametophytes (haploid fern babies) that I have reared in sterile conditions from surface sterilized spores. Are these fungal endophytes that somehow colonize fern spores on the interior or are there recalcitrant fungi clinging to the spore surface? I am currently tracking the identity of endophytes found within the leaves of parent plants and within the gametophytes of resulting progeny to find out if they are the same fungal taxa. I am also examining the surface of sterilized spores with electron microscopy to see if fungal tissue is present. If vertical transmission is indeed occurring in fern spores, this could have a large implication regarding the evolution of plant-fungal symbioses in all spore-reproducing plants.
Spatial turnover of endophyte communities in ferns—Although we have learned over the past two decades that fungal endophytes are incredibly diverse and may play important ecological functions, there is little knowledge on the factors that structure their communities. In this spatial turnover project, I am examining fungal endophyte communities in the P. munitum fern host in four unique habitat types that exist within 200 km of each other: a rocky cliff at the Oregon Coast, a coniferous understory habitat in the Oregon Coast Range, a secondary succession site near the 1980 volcanic eruption of Mount Saint Helens, and a plot near the Mount Saint Helens site, but not impacted by the eruption. I aim to determine if the following factors play some role in structuring endophyte communities in this fern host:
1. Dispersal limitation
2. Abiotic habitat conditions/edaphic factors
3. The identity of neighboring plants growing in the same community
4. The identity of microbes found in host plants growing near target ferns
Influence of plant sexual dimorphism, herbivory, and edaphic factors on endophyte communities—For this project I have extended beyond fern hosts into endophyte communities found in Salix sitchensis (sitka willow). This is part of a long-term ecological study conducted on the Pumice Plain of Mount Saint Helens, a primary succession site impacted by the 1980 eruption, in conjunction with Dr. John Bishop from Washington State University. Here, several plots of S. sitchensis have been sexed, some have been treated with fertilizer, and some have had stem-boring weevils, a common herbivore on the Pumice Plain, excluded. We are currently looking into whether plant sex influences fungal endophyte communities. If this turns out to be the case, this will be the first example of the structuring of endophyte communities based on plant sexual dimorphism.