Conclusion
Although there is laboratory work yet to be completed, I can make preliminary conclusions about my four research questions.
1. Is microbial community composition, determined by phospholipid fatty acid (PLFA) analysis, different in rhizosphere versus bulk soil? Overall, microbial communities of the rhizosphere differed from bulk soil in clear-cut stands but not natural stands. No difference in natural stands indicates vegetation shifts from spruce to aspen, with climate change, will not have a large impact on the overall microbial community.
2. Does canopy type (aspen versus spruce) affect rhizosphere microbial community composition? To answer this question I will focus on natural stands. Overall rhizosphere microbial communities differed in natural aspen versus spruce stands. Of the five microbial groups investigated, only protists differed between natural aspen and spruce stands. Rhizosphere soils under spruce had significantly less protists than under aspen. Interestingly, no differences were found for fungi or gram(-) bacteria (microbes important for priming) in the rhizosphere across site type.
3. What effects will clear-cutting have on total PLFA and microbial community composition? Clear-cutting did not significantly affect total PLFA in bulk soil, but did significantly reduce total PLFA in the rhizosphere, even 17 years post-harvest. The loss of rhizosphere microbial biomass with clear-cutting could mean reduced CO2 emissions from clear-cut stands. In the rhizosphere, clear-cutting will change the microbial community of natural spruce stands (if the forest is left to natural succession, and spruce are replaced by aspen). Microbial communities of natural aspen stands were not significantly affected by clear-cutting. The same trend was observed for bulk soil.
4. Could observed changes in total PLFA and rhizosphere community composition with vegetation shifts alter soil respiration from priming? Unlikely. Total PLFA did not differ between natural aspen and spruce stands. Fungi and gram(-) bacteria abundance did not differ significantly between natural aspen and spruce stands. Given total PLFA and microbial group data, the role of soil microbial communities in boreal forest carbon losses may not be so critical as the literature suggests. Microbial community composition was affected by vegetation shifts, however not all PLFAs can be associated to microbial groups, so the overall effect on rhizosphere carbon remains unclear.
1. Is microbial community composition, determined by phospholipid fatty acid (PLFA) analysis, different in rhizosphere versus bulk soil? Overall, microbial communities of the rhizosphere differed from bulk soil in clear-cut stands but not natural stands. No difference in natural stands indicates vegetation shifts from spruce to aspen, with climate change, will not have a large impact on the overall microbial community.
2. Does canopy type (aspen versus spruce) affect rhizosphere microbial community composition? To answer this question I will focus on natural stands. Overall rhizosphere microbial communities differed in natural aspen versus spruce stands. Of the five microbial groups investigated, only protists differed between natural aspen and spruce stands. Rhizosphere soils under spruce had significantly less protists than under aspen. Interestingly, no differences were found for fungi or gram(-) bacteria (microbes important for priming) in the rhizosphere across site type.
3. What effects will clear-cutting have on total PLFA and microbial community composition? Clear-cutting did not significantly affect total PLFA in bulk soil, but did significantly reduce total PLFA in the rhizosphere, even 17 years post-harvest. The loss of rhizosphere microbial biomass with clear-cutting could mean reduced CO2 emissions from clear-cut stands. In the rhizosphere, clear-cutting will change the microbial community of natural spruce stands (if the forest is left to natural succession, and spruce are replaced by aspen). Microbial communities of natural aspen stands were not significantly affected by clear-cutting. The same trend was observed for bulk soil.
4. Could observed changes in total PLFA and rhizosphere community composition with vegetation shifts alter soil respiration from priming? Unlikely. Total PLFA did not differ between natural aspen and spruce stands. Fungi and gram(-) bacteria abundance did not differ significantly between natural aspen and spruce stands. Given total PLFA and microbial group data, the role of soil microbial communities in boreal forest carbon losses may not be so critical as the literature suggests. Microbial community composition was affected by vegetation shifts, however not all PLFAs can be associated to microbial groups, so the overall effect on rhizosphere carbon remains unclear.