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Item Phycosomal dynamics in xenic cultures of the alkalitolerant green Microalga chlorella sp. SLA-04(Montana State University - Bozeman, College of Agriculture, 2023) Miller, Isaac Robert; Chairperson, Graduate Committee: Matthew Fields; This is a manuscript style paper that includes co-authored chapters.The production of microalgal biomass and biofuel is an important component of the transition away from a petroleum-based economy. Industrial scale microalgal cultures are often xenic, meaning they are comprised of microalgae as well as a phycosome (i.e., microbiome). The microalgal field has begun to appreciate the ubiquity and potential influence of the phycosome, but there remains a critical need for comprehensive research to unravel the intricate metabolic and ecological relationships between microalgae and the respective phycosome that can be comprised of mainly bacteria but also other microorganisms (i.e., archaea, fungi, protists, viruses). Phycosome research is essential for potentially using these interactions to enhance the stability, productivity, and cost-efficiency of industrial microalgal cultivation. Chlorella sp. SLA-04 is an oleaginous, alkalitolerant microalga isolated from the alkaline Soap Lake (Washington, USA). Under alkaline conditions, SLA-04 can be grown to high biomass levels without reliance on the delivery of concentrated CO 2, an improvement in producing competitively priced biomass and biofuel. The high pH, high alkalinity systems are able to capture CO 2 directly from the air in open systems (e.g., raceway ponds) but the open systems can be dynamic in terms of stability and productivity. Despite growing knowledge of the importance of phycosomes in open production systems, little is known about how alterations to cultivation conditions can be used to maintain a xenic system with controllable outputs, especially under high pH, high alkalinity conditions. The work outlined in this dissertation employed long term temporal community studies, open outdoor raceway experiments, diel-cycle-resolved temporal sampling coupled with activity-based probing (bioorthogonal non-canonical amino acid tagging (BONCAT)), and quantitative measures of algal physiology to better understand the relationship between microalgal phenotype and the respective phycosomes. SLA-04 phycosome composition and culture physiology were consistent over time when maintained in xenic cultures under low and high alkalinity. When xenic cultures were used in successive open, outdoor raceway experiments, compositional community changes coincided with seasonal temperature and light shifts, providing evidence that abiotic and biological environmental stresses impact directly and indirectly SLA-04 productivity and phycosome composition. By employing temporally resolved sampling and probing the relationship between diel-cycle-dependent metabolism and the phycosome, we identified active bacterial populations that may play a role in culture productivity. Expanding beyond augmenting SLA-04 productivity, aggregation of xenic cultures was assessed as a quantifiable phenotype, uncovering a relationship between aggregation, taxonomic composition and algal growth conditions (i.e., alkalinity level). All together, these results represent an initial description of the ecology (e.g., composition, succession, activity) of alkaline microalgae cultures and provide methodology and perspective for future phycosome studies.Item Daily signals in nitrate processing provide a holistic perspective on stream corridor hydrologic and biogeochemical function(Montana State University - Bozeman, College of Agriculture, 2023) Foster, Madison Jo; Chairperson, Graduate Committee: Robert A. Payn; This is a manuscript style paper that includes co-authored chapters.Understanding interactive pathways of biogeochemical reaction and water movement in stream corridors is critical given the role stream corridors play in mitigating nitrate loading from agricultural watersheds. However, few studies consider the interactive effects of nitrate loading, riparian processing, and stream ecosystem processing, which may limit abilities to predict downstream nitrate delivery. Riparian groundwater inputs and stream ecosystem processing may vary due to daily cycles in evapotranspiration or stream ecosystem primary production. Recent advances in high-frequency monitoring of stream chemistry throughout the day exhibit potential to explore both hydrologic and biogeochemical influences on nitrate attenuation. In this thesis, I explore how diel variations in stream reach nitrate processing can provide holistic perspectives on the attenuation of nitrate along stream corridors within a watershed that is heavily influenced by agricultural land use. Nitrate processing is defined as the evident changes in nitrate concentration in parcels of water as they travel along a given reach of a stream, as measured from nitrate sensors located at the head and base of ca. 0.5 km reaches. To understand controls on diel variation in nitrate processing, we measured diel processing signals in agricultural headwater reaches in Central Montana, USA spanning variable atmospheric and flow conditions from March through August in 2020-2022. Across 168 days with valid data, most signals exhibited little diel variation (n = 106) and this lack of variation occurred most frequently during cooler and shorter days. In contrast, signals with greater variation were common during longer days, warmer temperatures, and lower flows (n = 62). This seasonal shift in patterns suggests that solar radiation and stream flow are primary controls on diel nitrate processing signals in these low-order reaches. In addition to diel variation, less overall nitrate attenuation in the study reach with direct inputs of high-nitrate upland waters suggest that the degree of hydrologic connection to upland aquifers influences apparent reach nitrate processing. This work highlights how understanding the drivers of diel processing signals may lead to a more holistic understanding of how multiple interacting processes in stream corridors influence nitrate delivery to downstream ecosystems.