Primary productivity is a fundamental ecosystem process driven by vascular plants in most terrestrial ecosystems and by microbes in more extreme ecosystems. In dense associations, microbial organisms can form visually conspicuous layers on sediment, soil, and rock surfaces, called microbial mats and biological soil crusts (i.e., biocrusts). Both microbial mats and biocrusts consist of cyanobacteria, moss, diatoms, and green algae, and also support diverse heterotrophic taxa. These communities exist in harsh environments worldwide such as hypersaline environments, tundra ecosystems, and hot and cold deserts where they are foundational taxa, providing most of the primary production and nitrogen fixation, as well as promoting cohesion and stability to soil surfaces. In the McMurdo Dry Valleys of Antarctica, microbial mats are the main source of fixed carbon in lentic and lotic environments, but their contribution to soil carbon and nitrogen cycling has not been systematically examined. In my dissertation, I investigated the relationships between microbial mats and the soil environments in which they occur. Using a combination of field surveys, soil analyses, and remote sensing, my objectives were to examine the influence of microbial mats and biocrusts on underlying soils and model the main drivers of their distribution and abundance. In Chapter 2, I investigated the relationships between underlying soil chemistry and microbial mat distribution, composition, and function in the Taylor Valley, finding that microbial mats enrich underlying soils, contributing to soil organic carbon and nitrogen. In Chapter 3, I assessed the spectral detectability of patchy biocrusts using multispectral satellite imagery to examine the environments in which biocrusts occur, finding that spectral unmixing of satellite imagery can successfully detect the presence of biocrust and its association with seasonal snow patches. As a direct continuation, in Chapter 4, I created a habitat suitability model using machine learning algorithms to determine the distribution and abundance of biocrusts in the Lake Fryxell basin. I found that biocrusts contribute a significant amount of carbon to the surface soil in the Lake Fryxell basin, with biocrust presence primarily driven by snow frequency, moisture content, and salinity. This dissertation contributes to ongoing questions about the sources of energy fueling soil food webs and regional carbon balance in the Taylor Valley, and how we can use remote sensing techniques for researching these critical soil communities in the dynamic Antarctic landscape. / Doctor of Philosophy / Photosynthesis is the process where plants and other organisms use sunlight to transform carbon dioxide into chemical energy. This is crucial because it provides the energy and nutrients that support all other life forms. In this dissertation, I focused on colonial microorganisms, which are the main primary producers in extreme environments, like deserts. I used a combination of field surveys and satellite imaging to study these organisms in the McMurdo Dry Valleys, Antarctica, which is a harsh polar desert environment that lacks vascular plants. Microbes colonize the surface of soil and form mm-cm thick microbial mats and biological soil crusts (called biocrusts). These organisms are found within the glacial-melt streams that flow on and off for only a few weeks each year, and they also occur on the stream margins and other periodically wet areas like near snow patches. This dissertation investigates the ecological importance of microbial mats and biocrusts, the ability to measure where they are using satellite imagery, and how much organic material they contribute to the broader landscape. Field work in the McMurdo Dry Valleys and laboratory analyses were required for each of these chapters. In Chapter 2, I investigated the relationships between microbial mats and the soils below them, and I found that microbial mats increase the organic matter and nutrient content in the soils. In Chapter 3, I assessed whether satellite imagery could be used to study the presence of sparse biocrusts and examined the environments in which biocrusts occur. I discovered that satellite imagery can successfully detect the presence of biocrust and that biocrusts occurred near melting snow patches. Lastly, in Chapter 4, I created models to determine where biocrusts occur in the Lake Fryxell basin and why biocrusts occur in those areas. I found that biocrusts occur over a significant area of the Lake Fryxell basin, containing a lot of organic material, and that biocrusts thrive in wet areas near snow patches where the soils are less salty. This dissertation contributes to ongoing questions about the sources of nutrients fueling soil food webs and contributing to the amount of organic material in the McMurdo Dry Valleys, and how we can use satellite imagery for monitoring these important soil communities in the changing Antarctic landscape.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/121090 |
| Date | 06 September 2024 |
| Creators | Power, Sarah Nicole |
| Contributors | Biological Sciences, Barrett, John E., Thomas, Valerie Anne, Salvatore, Mark, Hotchkiss, Erin R., Carey, Cayelan C. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | Creative Commons Attribution 4.0 International, http://creativecommons.org/licenses/by/4.0/ |
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