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The ecology of boreal forest floor microbial communities in relation to environmental factors Open Access


Other title
Type of item
Degree grantor
University of Alberta
Author or creator
Swallow, Mathew J B
Supervisor and department
Quideau, Sylvie A (Renewable Resources)
Examining committee member and department
Foght, Julia (Biological Science)
Macdonald, Ellen (Renewable Resources)
Spence, John (Renewable Resources)
Adl, Sina (Soil Science)
Department of Renewable Resources
Soil Science
Date accepted
Graduation date
Doctor of Philosophy
Degree level
Soil microbial communities in boreal forests are structured by complex interactions among many factors operating simultaneously on large and small spatial scales. Of particular note in the boreal mixedwood, the microbial communities under trembling aspen and white spruce forest floors are distinct. This thesis highlights linkages that connect ecosystem characteristics observable on the landscape with microscopic processes occurring within boreal forest floors. As indicated by phospholipid fatty acid (PLFA) and multi-substrate induced respiration analysis, prescribed burning after harvest did not alter microbial community structure or function in aspen, spruce and mixedwood stand. Instead, community structure was related to the pre-harvest overstory and local topography, with communities under aspen being different than those under similarly structured spruce and mixedwood canopies but in sites located at lower landscape positions. Microbial communities in spruce forest floor were similar regardless of the amount of moisture retained throughout the incubation, while in aspen, community structure depended on the level of moisture. Microbial community response to moisture in aspen and spruce was linked to different physical properties and subsequently, the pore habitat, inherent to the two forest floors. Microbial community structure in aspen leaf litter inoculated with forest floor bacteria is altered when ciliates are present. Ciliates moderated the growth of gram negative bacteria, potentially grazed on fungi and promoted bacteria that consumed plant auxins. However, I learned that PLFA analysis may not be a suitable method to detect ciliates as ciliate lipid biomarkers were either absent or not correlated with ciliate abundance. Forest floor microbial communities are shaped by the pore habitat, which in turn is generated by the litter of the plant community and predatory activity of protozoa. However, being aquatic organisms, protozoa can function only when suitable water filled pore habitat is available. On the landscape these processes depend on factors such as topography to redistribute moisture. Under these circumstances, differences between the physical properties of aspen and spruce forest floors manifest and influence the microbial communities residing within them.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Swallow, M., Quideau, S.A., MacKenzie, M.D., Kishchuk, B.E. 2009. Microbial community structure and function: the effect of silvicultural burning and topographic variability in northern Alberta. Soil Biology and Biochemistry 41, 770-777.

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