Long-term effects of nitrogen and phosphorus fertilization on ectomycorrhizal diversity of 18-year-old western hemlock (Tsuga heterophylla) on northern Vancouver Island

This thesis explores the diversity of ectomycorrhizae of western hemlock (Tsuga heterophylla) in nutrient-poor environments and the role of fertilization on the ectomycorrhizal fungal community. In Chapter One, the thesis provides an introduction to mycorrhizal fungi and to my research site, a cedar-hemlock ecosystem on northern Vancouver Island where forest regeneration has been problematic. The first chapter continues with a review of previous studies of mycorrhizae from the same research site and of western hemlock. Chapter Two presents the results of my study on the effects of nitrogen and phosphorus fertilization on ectomycorrhizal species composition and diversity. Nitrogen fertilization typically reduces ectomycorrhizal diversity within the first two years of its application. Less is known about the long-term influence of fertilization. In this research, ectomycorrhizal diversity and community composition were compared among three fertilization treatments in plots of 18-year old western hemlock from northern Vancouver Island, Canada. Of nine plots, three were unfertilized controls. Six plots were fertilized in 1987 and 1997; three with 300 kg/ha urea (N); and three with the kg/ha N plus 100 kg/ha P (N + P). Four sets of 100 ectomycorrhizal root tips were sampled per plot and used for random clone libraries of amplified ITS regions using fungal specific primers ITSIF and TW13. Fungal species were identified from sequenced clones using fast parsimony analysis. Assuming that clones with > 97% identity were conspecific, 99 species were detected among 1004 clones sequenced. Fungal diversity was high and not significantly different across treatments. Species composition differed significantly in N + P plots compared to control plots or plots that received N alone. The presence of Cenococcum geophilum spl0 and Dermocybe cinnamomea were correlated with control and N plots, whereas the presence of Cenococcum geophilum sp8 and sp9, and Cortinarius spl8 and spl9 were correlated with N + P plots. Chapter Three of this thesis discusses limitations of a molecular approach to detecting fungal diversity, and ideas for future research to help elucidate the ecological roles of ectomycorrhizal fungi. This thesis contributes new knowledge about the diversity of western hemlock's ectomycorrhizal fungi and shows that N + P fertilization used in forest management has resulted in a long-lasting change in the ectomycorrhizal fungal community composition.Science, Faculty ofBotany, Department ofGraduat