Abstract
Many of the world forests are affected by human activities such as forest fragmentation and introduction of exotic species. The goal of this research was to study the effects of forest fragmentation and exotic species introductions on populations and communities of ectomycorrhizal (EM) fungi. In the first study, I examined the genetic differentiation and effects of past forest fragmentation in populations of Suillus spraguei, a specific symbiont of eastern white pine (Pinus strobus) across northeastern United States. The population genetic analyses from microsatellite data revealed a broad panmictic population with no isolation by distance over the sampled area and no detectable effect of forest fragmentation. In the second and third study, I focus on the introduction of Pinus caribaea and exotic EM fungi to the island of Puerto Rico. In the second study, I examined the effects of species introduction on the population genetics of the exotic EM fungus Pisolithus tinctorius. For this, I developed and employed microsatellite markers and compared samples from Puerto Rico and the United States (native range). Evidence for a founder effect is supported by the reduced allelic richness when compared to samples from the United States. The population structure of P. tinctorius in Puerto Rico represents a genetic mosaic most likely associated with the movement of soil within the island followed by genetic drift. The third study focuses on the identification of the EM fungal community associated with three P. caribaea plantations and surrounding areas using field and soil bioassay experiments. Field experiments detected a low species diversity of EM fungi and reports five EM species for the first time on the island. Rhizopogon was identified as a key facilitator of pine establishment at all distances by both bioassay and field experiments. The distribution of Rhizopogon suggests the presence of dispersal vectors on the island such as exotic small mammals, anthropogenic activities, and weather-related disturbances. These studies demonstrate different scenarios of anthropogenic activities and their influence, or lack thereof, on the populations and communities of ectomycorrhizal fungi.