Multi-scale Studies of Microbial Mats and Biocrusts: Integrating Remote Sensing with Field Investigations in Antarctica's McMurdo Dry Valleys

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.