Mat-forming ectomycorrhizal (EcM) fungi represent a prevalent constituent of many
temperate forest ecosystems and create dramatic changes in soil structure and
chemistry. EcM mat soil have been shown to have increased microbial respiration
rates and have been hypothesized to harbor unique assemblages of fungi and bacteria.
The objectives of this dissertation were to characterize and examine the fungal and
bacterial communities associated with EcM mats in old-growth forests of the H.J.
Andrews Experimental Forest located in the Oregon Cascades. Additionally, this
work assessed the application of traditional, emerging, and novel molecular sampling
techniques for determining microbial communities of environmental samples. This
research investigated the microbial communities associated with two common EcM
mat genera found in old-growth Douglas fir stands in the Pacific Northwest;
Piloderma (Atheliales, Basidiomycota) and Ramaria (Gomphales, Basidiomycota).
Soil samples were collected from Piloderma and Ramaria mats and surrounding non-
mat soil for molecular analysis of nucleic acids. First, a comparative study was
conducted to determine the most appropriate rDNA molecular sampling technique for
microbial community characterization. Two next-generation sequencing methods,
Roche 454 pyrosequencing and Illumina-based environmental sequencing, the latter
developed by the author, were compared to a more traditional sequencing approach,
i.e., Sanger sequencing of clone libraries. These findings informed the subsequent
sampling of the fungal ITS and bacterial 16S rDNA fragment with 454
pyrosequencing to determine the microbial communities within mat and non-mat soils.
Second, this work utilized a pyrosequencing approach to explore fungal community
structure in EcM mat and non-mat soils. This work concluded that differences in
microbial communities do exist between Piloderma mat, Ramaria mat, and non-mat
soils, but the differences are largely quantitative with relatively few distinct taxonomic
shifts in microbial constituents. Piloderma, Ramaria and Russula, in addition to being
the dominant taxa found on mycorrhizal root tips, were found to be the most abundant
taxa in bulk soils within their respective mat types or non-mat sample. The
background fungal communities within the EcM mats in this study exhibited
considerable taxonomic overlap with the exception of Piloderma vs. non-mat
comparisons; Russula species dominated nonmat soils but tended to be excluded or
significantly underrepresented in Piloderma mats. Lastly, this study explored the
bacterial communities associated with Piloderma and Ramaria mats using lower-
coverage 454-Jr pyrosequencing. Bacterial communities exhibited significant
structure as a function of mat-type, soil horizon and pH, but this finding should be
interpreted with respect to the nonrandom distribution of Piloderma-mats in the O-
horizon and the Ramaria-mats in the A-horizon, and the tendancy for EcM mats to be
more acidic than surrounding soils. Nonetheless, the total microbial (bacterial and
fungal) community was typically dominated by the mat-forming taxa, or Russula, in
the case of non-mat soils. While the presence of Piloderma mats did enrich or restrict
some bacterial groups, soil pH was also found to be a significant driver of bacterial
richness and taxonomic diversity. Fungal and bacterial richness were also found to be
positively related to one another, regardless of soil horizon or EcM mat type. This
work, taken together, contributes to the understanding of hyperdiversity and
heterogeneity of microbial communities of temperate forest soils and highlights the
potential for fungal and bacterial communities to be influenced by the presence of
EcM mats. / Graduation date: 2012
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/30044 |
| Date | 17 May 2012 |
| Creators | Hesse, Cedar N. |
| Contributors | Spatafora, Joseph W. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
| Relation | Forest Explorer |
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