The Below Ground View of Ectomycorrhizal Fungi in Three Conifer Communities

Thomas Roscoe Horton
Doctor of Philosophy in Plant Pathology
University of California, Berkeley
Professor Thomas D. Bruns, Chair

Abstract
Ectomycorrhizal fungi of Pinus muricata (bishop pine), Pseudotsuga menziesii (Douglas-fir) and Pinus radiata (monterey pine) were investigated. Fungi were identified from field collected roots utilizing PCR based methods. The frequency and abundance of ectomycorrhizae were used to measure the contribution of each fungal species to ectomycorrhizal communities.

In the first study, a stand of bishop pine and Douglas-fir was investigated. The most frequent and abundant fungi in the stand were generalists. Twelve of sixteen fungi, making up 90% of the ectomycorrhizal biomass, associated with both hosts. Rhizopogon parksii was the only host specific fungus, associating with Douglas-fir. Three remaining species of fungi were too infrequent to assess their specificity. The results indicate that individual fungi may have linked the competing tree hosts below ground.

In the second study, first year bishop pine seedlings establishing after a wildfire were investigated. The frequency of seedlings colonized by fungi in burned ectomycorrhizal forest and burned VAM coastal scrub was compared. Seedlings from both locations were colonized by VAM, dark septate and ectomycorrhizal fungi. Seedlings in the scrub were only colonized by two Rhizopogon spp. and Suillus pungens. In contrast, a diverse group of ectomycorrhizal fungi colonized seedlings in the forest, including three Amanita spp., the two Rhizopogon spp. found in the scrub, Russula brevipes, Tuber californicum, and a cantharelloid species. The results indicate that most of the ectomycorrhizal fungi did not disperse into the area after the fire but were resident as spores in the scrub and spores and hyphae in the forest.

Finally, the ectomycorrhizal community of monterey pine plantations growing at about 3500 m in Salinas, Ecuador was investigated. Suillus luteus sporocarp production in these plantations was estimated to be over 100 kg ha-1 yr-1, dry weight. Suillus luteus and T. terrestris were the only fungi observed as ectomycorrhizae in the plantations, each colonizing about 50% of the root tips down to 30 cm. These results indicate that the abnormally high S. luteus sporocarp production is correlated with, and may be a function of, a simplified ectomycorrhizal community in these plantations.