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UBC Theses and Dissertations

Nitrogen cycling processes and microbial communities in reconstructed oil-sands soils Masse, Jacynthe


Covering 140,200 square km, the Athabasca Oil Sands deposit in Alberta is one of the largest single oil deposits in the world. Following surface mining, companies are required to restore soil-like profiles that can support the previous land capabilities. The overall objective of this thesis was to measure, compare and understand processes underlying nitrogen cycling rates and microbial communities in 20- to 30- year-old reconstructed oil-sands soils and in natural boreal-forest soils. The use of ¹⁵N tracer methods in combination with massively parallel sequencing techniques of the 16S and ITS genes identified key dissimilarities between reconstructed and natural boreal-forest soils. In reconstructed soils, NH₄⁺ was mainly cycled through the recalcitrant organic-N pool. In natural soils, NH₄⁺ was produced from the recalcitrant organic-N pool, but predominantly consumed in the labile organic-N pool, suggesting greater prominence of microbial N-cycling activity in the natural soils compared to the reconstructed soils. Reconstructed soils also produced more NO₃- than they immobilized it resulting in net nitrification rates. Prokaryotic and fungal β-diversity, but not α-diversity, differed between reconstructed and natural forest soils. Microorganisms associated with a copiotrophic lifestyle were more abundant in reconstructed soils, whereas microorganisms associated with an oligotrophic lifestyle were more abundant in natural forest soils. Vegetation cover was the main factor influencing prokaryotic and fungal α-diversity in reconstructed and natural forest soils. Nitrogen deposition, pH, soil nutrient content and plant cover influenced prokaryotic and fungal β-diversity. The results of this thesis deepen our understanding of the distinct pedological environments of oil-sands reconstructed soils and highlighted the importance of above- and below-ground interactions in reconstructed and natural ecosystems.

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