Characterisation of microbial eukaryotes and interactions in Arctic aquatic and terrestrial microbiomes

Abstract

Communities of microbes, often thriving under extreme environmental conditions, are the key drivers of biogeochemical cycles and the foundation of aquatic and terrestrial food chains in the Arctic. More recently, microorganisms have become integral to monitoring environmental change in the Arctic and global climate change. However, the diversity, trophic function, and biogeography of microbial eukaryotes are currently much less studied than prokaryotes in Arctic aquatic and terrestrial ecosystems. The research in this thesis aimed to characterise the diversity and interactions of microbial eukaryotes within aquatic and terrestrial microbial communities in the Arctic region. Through the application of eDNA metabarcoding and long-read sequencing, the diversity of microbial eukaryotes, often alongside prokaryotes, was assessed at the community level within Arctic freshwater and terrestrial microbial communities. Measurements of environmental conditions were collected alongside these community samples. Through comparison of microbial communities and environmental conditions, consistent trends appeared in the diversity, trophic function, distribution, and responsiveness of microbial eukaryotes to environmental change. The diversity of microbial eukaryotes and prokaryotes in freshwater benthic microbial mat communities were compared across a broad latitudinal gradient from the subarctic to the High Arctic (55 to 83°N). Microbial eukaryotic and prokaryotic richness decreased, in tandem with decreasing temperatures and shorter seasons of light availability, from the subarctic to the High Arctic. This represented the first identification of a latitudinal diversity gradient in Arctic freshwater microbial communities. Microbial eukaryotic diversity was further assessed in terrestrial, freshwater, and coastal microbial communities from the northern coastline of the terrestrial Canadian Arctic (83°N). This provided invaluable sequencing data from microbial communities in the Quttinirpaaq National Park, Nunavut, proximal to the region of thickest and oldest Arctic sea ice, designated the Last Ice Area. The highest diversity of microbial eukaryotes was identified in terrestrial microbial communities from water tracks. Differences in the diversity and ecological function of microbial eukaryotes were identified between distinct habitats within each environment, highlighting the strong influence of abiotic factors, particularly water and light availability and salinity, on determining small-scale biogeographical patterns of microbial eukaryotes. The implications of future environmental change for Ward Hunt Lake, the northernmost lake in the Canadian Arctic, were further explored by in situ nutrient enrichment microcosm experiments, to assess the influence of increased nutrient input from more hydrologically and biologically active catchments on microplantkon and microbial mat communities in the lake. Phosphorus enrichment was identified to significantly increase the relative abundance of heterotrophic protists, suggesting that future changes in lake nutrient conditions may modulate trophic interactions in the microbial communities within. These comparative analyses of microbial communities across different spatial scales revealed a consistent diversity of phototrophic and heterotrophic microbial eukaryotes in Arctic aquatic and terrestrial microbiomes. Moreover, these diverse microbial eukaryotic communities appear predominantly shaped by current environmental conditions. This implies that accelerating climatic and environmental change in the Arctic will have implications for microbial eukaryote diversity and distribution across Arctic ecosystems and foodwebs. The findings of this thesis highlight the importance of increased monitoring of microbial eukaryotic diversity in the Arctic.

Date of Award	11 Dec 2024
Original language	English
Awarding Institution	University of Bath
Supervisor	Edward Feil (Supervisor), Anne Jungblut (Supervisor), David Bass (Supervisor) & Warwick Vincent (Supervisor)