Date of Award:

5-2017

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Wildland Resources

Committee Chair(s)

Helga Van Miegroet

Committee

Helga Van Miegroet

Committee

Astrid Jacobson

Committee

Michelle Baker

Committee

John Stark

Committee

Jeff Hatten

Abstract

Soil organic carbon (SOC) positively affects many soil properties (e.g., fertility and water holding capacity), and the amount of carbon (C) in soil exceeds the amount in the atmosphere by about three times. Forest soils store as much C as is found in trees. Tree species differ in their effect on SOC pools. Quaking aspen forests in the Western US often store more stable SOC in the mineral soil than nearby conifers. During the last decades a decline in aspen cover, often followed by conifer encroachment, has been documented. A shift from aspen to conifer overstories may negatively affect the amount and properties of SOC. In this dissertation, I aimed to evaluate the mechanisms that drive the higher SOC pools under aspen compared to conifers. I found that the amount of detritus produced by both forest types could not explain the observed differences. Aspen foliage dissolved organic carbon (DOC) was, however, retained in soil more than conifer DOC, and soils with aspen SOC retained new C more in general. This suggests that it is the chemistry of aspen detritus rather than the amount that drives the higher SOC pools. Root- and foliage-specific biomarkers, identified in this dissertation, could help us elaborate on the source of stable SOC in future studies. The observed SOC differences between aspen and conifers do not represent a general trend between hardwoods and conifers worldwide, suggesting that the factors affecting SOC differ from place to place.

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