| 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.;... |
