| In this dissertation, I present three, cultivation-independent studies of high altitude soil microbial diversity within a molecular-phylogenetic framework. The goals of my research were to discover and expand the known diversity and distribution of novel microbial lineages, and to characterize microbial community structure and composition across extreme environmental gradients in alpine ecosystems.; First, I explored the microbial diversity of snowmelt-saturated, alpine tundra wet-meadow soil from Niwot Ridge, Colorado. This work revealed an abundance of novel, Chloroflexi-related bacterial lineages (six sub-phyla and one candidate sister phylum, AD3) present in 0°C, low-O2 subsurface soil. Subsequent examination of Niwot Ridge subalpine forest soil diversity also yielded novel bacterial lineages, including candidate phylum WPS-2. Locally, the novel Chloroflexi and candidate phyla AD3 and WPS-2 were found in soils with relatively long isothermal phases and seasonally moderate temperatures. These conditions arose under deep winter snowpack and at spring snowmelt.; Next, I expanded the known diversity and investigated the biogeography of the relatively low-abundance candidate phyla AD3 and WPS-2 using targeted gene surveys. In isothermal soil, depth structured AD3 and WPS-2 collections. AD3 dominated deeper alpine soils, suggesting an oligotrophic or microaerophilic lifestyle, while WPS-2 increased in abundance toward the soil surface, suggesting an aerobic niche, potentially at the soil-to-snowpack interface. Searching an array of samples, as well as mining legacy collections revealed that rare candidate phyla AD3 and WPS-2 have global distributions in exclusively terrestrial, including arctic and alpine soil, ecosystems.; Finally, I surveyed bacterial and eukaryotic diversity in soils collected near the summit of Socompa Volcano, Andes, where geothermal activity supports small islands of vegetation in an otherwise arid and barren, high-elevation landscape. Bacterial and eukaryotic assemblages from extremely dry Socompa soils exhibited an overabundance of closely related lineages, suggesting habitat filtering for desiccation or UV-resistance. Communities associated with undisturbed geothermal areas hosted a diverse assortment of bacteria and eukaryotes, including candidate phyla AD3 and WPS-2, a wide array of algal lineages and a clade of novel metazoans. As suggested by a distinct soil organic delta 13C signature, this unique and isolated autotrophic community may fix carbon of volcanic origin. |
