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UBC Theses and Dissertations

Nutrient effects on metabolic rate in a changing world : a multiscale approach Davis, Kaleigh


As climate change warms the planet, ecosystems require increasing amounts of resources to meet increasing metabolic demand. Understanding whether resource supply will meet this increasing demand is central to predicting and mitigating the ecological effects of warming. Photosynthesis drives the global biological carbon pump and is, as such, a major focus of climate modelling research. In my dissertation, I completed three novel research projects that explore how nutrient supply affects photosynthetic rates in a wide range of ecological systems. First, I tested the hypothesis that there may be broad and predictable effects of warming on resource supply by focusing on a major global source of bioavailable nitrogen: nitrogen fixation. I used theory and data synthesis to understand how rates of nitrogen fixation change with warming across diverse ecological systems. I found that, on average, nitrogen fixation is more temperature-sensitive than photosynthesis, but temperature sensitivity varies across systems. Next, I conducted a lab experiment to test whether this broad-scale pattern could be observed in a simple, two-species phytoplankton system. I also tested the hypothesis that, because of its high temperature-sensitivity, nitrogen fixation can buffer photosynthesis against nitrogen limitation with warming by providing sufficient nitrogen to meet photosynthetic demand. I found that nitrogen fixation did support photosynthesis and growth in nitrogen-limited conditions, but this effect was weak and photosynthetic productivity remained nitrogen limited in the presence of nitrogen fixation. Finally, I conducted a field experiment to understand the role of nutrient limitation in the recovery of eelgrass ecosystems in Eeyou Istchee, Quebec, in order to inform decision-making for local communities. I found that light availability, rather than nutrient availability, is likely limiting eelgrass production in this system. Altogether, I learned when and how nutrient supply influenced photosynthetic productivity in a few specific systems and generated new predictions for how nitrogen supply via nitrogen fixation may influence photosynthesis with warming.

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