Date of Award:

5-2024

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Watershed Sciences

Committee Chair(s)

Trisha Atwood

Committee

Trisha Atwood

Committee

Bonnie Waring

Committee

Karen Beard

Committee

Tim Walsworth

Abstract

Soil holds more carbon (C) than the Earth's atmosphere and vegetation combined. Soil loses carbon through soil respiration and releases CO2 from the soil. The soil respiration rate can vary based on the chemistry of the plant litter inputs and physical factors, such as soil temperature and nutrient content. In Alaska's Yukon-Kuskokwim (YK) Delta, grazing by geese affects the chemistry of plants and the soil's physical qualities, thus altering the rate of soil respiration. Although we know that goose herbivory leads to changes in the rate of soil respiration, we know very little about how goose herbivory affects the inputs of plant roots. Roots are an important factor in soil respiration because roots contribute a substantial amount of C to the soil. This knowledge gap limits our ability to truly understand C cycling processes like root decomposition, which may influence soil respiration in the YK Delta.

To better understand how goose herbivory affects root C and soil respiration, we collected C. subspathacea root samples, a common sedge in the YK Delta, from either grazed or ungrazed habitats to understand if goose herbivory creates intraspecific differences in their morphological (specific root length, root volume and root surface area), chemical (carbon: nitrogen ratio, %C, %nitrogen, %phosphorus and ADF), and physiological traits (root exudates). Additionally, we created a laboratory experiment to assess how goose herbivory affects root decomposition and C loss using weekly CO2 efflux as a proxy for the decomposition rate. Within this experiment, we manipulated root treatment by using roots that were either exposed to aboveground grazing or not, feces deposition (present/absent), and temperature to simulate the range of effects aboveground herbivory has on plant litter and soil physicochemical properties.

In this study, we demonstrated that aboveground herbivory did not alter root morphology but affected root chemistry and exudation. Specifically, aboveground grazing led to lower C:N, higher %N, lower %C, %ADF (a measurement of cellulose and lignin), and a greater rate of root exudation. Although we did not see differences in root morphology, the differences in root chemistry and exudation are often associated with faster plant decomposition. Our root decomposition experiment confirmed that aboveground herbivory alters the rate of root decomposition and leads to increased C loss directly by altering indirectly by increasing soil temperatures and directly by altering root inputs. Our study demonstrates that aboveground herbivory can significantly alter root trait expression, which may increase the loss of C from the soil.

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Creative Commons License

Creative Commons Attribution-Noncommercial 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License

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