Thesis

Understanding microalgal composition and contributions in Antarctic glacial meltwater through rbcL sequencing

Microbial mats are found globally in dynamic aquatic environments. Visually different morphotypes (orange-red and black-green) also show different rates of nitrogen fixation and biogeochemical activity. Glacial meltwater communities in the McMurdo Dry Valleys (MDV) of Antarctica present unique opportunities to study microbial mats, due to limited grazing effects and their sensitivity to climate change. Microscopy has yielded a poor understanding of species composition and diversity. I sought to address this limited understanding through deep sequencing of photosynthetic genes such as cbbL, and the 16S rRNA V4 hypervariable region. A total of 15 transects from five valleys were used, with samples representing stream-associated (submerged) or transiently wetted (hyporheic) transect points. While stream position is a clear driver of mat morphotype, morphotype was not associated with microbial community composition. Microbial mat communities exhibit temporal shifts in relative abundance, but not diversity of microorganisms present. We propose that unique mat morphotypes are not distinct communities, but rather a continuum of the same overall community ranging from submerged to hyporheic habitats. As such, microalgal mats have the potential for morphotypic and biogeochemical functional plasticity with changing hydrogeological conditions.

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