Ecology of ectomycorrhizal fungi in mixed-conifer forests of California

This work is focused on understanding spatial and temporal patterns of ectomycorrhizal fungi in an old-growth Sierra Nevada forest (California, USA), and understanding how species respond to disturbance.; In the first study, the ectomycorrhizal root community was investigated for spatial and temporal patterns. Ectomycorrhizal roots were collected from soils (9 plots x 4 soil cores x 3 years) underneath stands composed primarily of Abies concolor or Abies magnifica. Dry root biomass was taken as a measure of abundance for each species of fungus within a core. Fungal community composition change was between years at small scales, primarily due to the turnover of one or two species in a plot. The fungal community, however, appeared more constant at larger scales.; In the second study, the spatial structure of the ectomycorrhizal fungi present in the resistant propagule community (RPC) was investigated. All of the fungal species colonizing A. concolor seedlings were also detected on the P. jeffreyi seedlings. P. jeffreyi seedlings, however, were colonized by a unique set of Rhizopogon spp. that collectively were very frequent. Two species of Rhizopogon, R. occidentalis and R. olivaceotinctus , were found to be common in the RPC, but absent from the fruiting and root-colonizing communities.; The third study attempted to refine estimates of the portion of roots that are colonized by fungi that form hypogeous sporocarps. DNA was isolated from: (1) sporocarps that were collected from throughout the region and that represented 27 hypogeous-fruiting genera, and (2) scat samples of Glaucomys sabrinus (northern flying squirrel) and Tamias speciosus (Lodgepole chipmunk) both of which are known mycophagists. DNA sequence analysis allowed direct comparison of these samples to the ectomycorrhizal root community from the first study. Fungi that can form hypogeous sporocarps made up 20% of the total species and 37% of the total biomass of the root community.; The last study investigated the ability of ectomycorrhizal propagules in the soil to colonize seedlings following heating of the soil. Soils collected from the same forest as the previous studies were treated by heating them up to temperatures known to cause spore germination in other fungi. The fungi that colonized seedlings planted into these soils were then collected and identified by DNA sequence analysis. The heat treatments had a significant effect on the composition of the fungi on the seedlings, and generally favored colonization by Rhizopogon spp. (Abstract shortened by UMI.)...