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Date Permissions Signed


Date of Award


Document Type

Masters Thesis

Degree Name

Master of Science (MS)


Environmental Sciences

First Advisor

Homann, Peter S., 1953-

Second Advisor

Bunn, Rebecca

Third Advisor

Hooper, David U., 1961-


Ecosystem responses to temperature and moisture influence whether terrestrial ecosystems act as sources or sinks of atmospheric CO2, an important greenhouse gas. Soil respiration—defined here as microbial release of CO2 during decomposition—is a key process of CO2 release to the atmosphere. This study focused on the response of soil respiration to temperature, moisture, and their interaction, and developed quantitative models to describe the nature of this interactive effect. This study addressed several underexamined components of the temperature and moisture effect on C and N dynamics: organic soils, multiple soil layers, a broad range of moistures, and a relevant, lowtemperature range. Samples of upper and lower forest floor organic‐horizon layers were collected from a mature conifer stand on the Olympic Peninsula in Washington State. Two experiments were conducted in which the soil samples were incubated at four temperatures (5.8–19.4°C) for up to four months, during which respiration was measured repeatedly. Because suboptimal moistures were expected to limit soil respiration, one experiment examined low soil moisture contents (1.4‐fold as moisture increased from 100 to 220%, but was nearly constant at higher moistures. At the low moistures, the respiration response to moisture increased with increasing temperature. This respiration response was best described in regression models by a complex temperature–moisture interaction comprised of varying multiplicative effects. Long‐term global C budget models, such as CENTURY and Rothamsted, currently assume a simple interactive effect comprised of a constant multiplicative effect of temperature and moisture on soil respiration; the models might be improved by inclusion of a more complex interaction such as that observed in this study. However, further studies are first needed to refine the equation(s) for describing this interaction, and to determine whether a single equation can be used to adequately describe soil respiration in all soils and soil layers.






Western Washington University

OCLC Number


Subject – LCSH

Forest litter--Effect of temperature on--Northwest, Pacific; Forest litter--Moisture--Northwest, Pacific; Soil respiration--Effect of temperature on--Environmental aspects--Northwest, Pacific; Soil moisture--Environmental aspects--Northwest, Pacific; Carbon cycle (Biogeochemistry)--Environmental aspects; Climatic changes

Geographic Coverage

Northwest, Pacific




masters theses




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