Carbon in Flux: Measuring the Climate Sensitivity of Terrestrial Greenhouse Gas Uptake

Citation

Dion-Kirschner, Hannah Henning (2025) Carbon in Flux: Measuring the Climate Sensitivity of Terrestrial Greenhouse Gas Uptake. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/6pc2-ex86. https://resolver.caltech.edu/CaltechTHESIS:05312025-010337506

Abstract

The greenhouse gases carbon dioxide and methane exert a major control on Earth’s climate, and their accumulation in the atmosphere is tempered by biological uptake. These biological uptake processes—photosynthesis and methanotrophy—are key contributors to the carbon-climate system, but their sensitivity to ongoing environmental change remains uncertain. In this thesis, I investigate how the ecophysiology of methanotrophy and photosynthesis dictate their response to perturbations in atmospheric composition, temperature, and other environmental variables. In Chapter 1, I present the first comprehensive compilation of kinetic measurements of methanotrophy in soils, and use this dataset to explore how kinetic properties may provide additional constraints to improve global models of the soil methane sink. Chapter 2 is a study of soil methane uptake rates in California dryland ecosystems and their relationship to local climate, ecology, and edaphic properties. This study reveals unique characteristics of dry climate regions that contradict typical assumptions about soil methane cycling. In Chapter 3, I present a novel method for position-specific carbon isotope analysis of submilligram glucose samples by Orbitrap mass spectrometry, and an application of this method to glucose standards isolated from C3 and C4 plants. In Chapter 4, I apply this new method to cellulose-derived glucose from tree-ring samples. Measurements of trees grown in climate chambers show how 13C-PSIA can disentangle changes in temperature, soil moisture, and tree carbon allocation. Finally, in two appendices, I describe methodological progress toward field-portable measurements of sedimentary porewater methane and the kinetics of soil methane uptake. Taken together, this work makes progress toward a more nuanced understanding of biological greenhouse gas uptake processes and their sensitivity to climate change.

Thesis Files