Looking below: Climate Change and Microbial Communities in the Rhizosphere of Boreal Forest Soils.

Climate change threatens the boreal forest—the largest terrestrial store of carbon in the world. Given continued increases in mean annual temperature, will the boreal forest—currently a global carbon sink—continue to sequester carbon or become a carbon source and further exacerbate climate change?

This research attempts to elucidate the effects of climate change on carbon stability in boreal forest soils. We focused on the rhizosphere, a hotspot for microbial activity in soil, where priming could destabilize existing organic matter. We investigated microbial community response to expected vegetation shifts with climate change, which for Western Canada will correspond to a shift from white spruce to aspen. Rhizosphere samples were collected at the Ecosystem Management Emulating Natural Disturbance (EMEND) project in northern Alberta, Canada. Phospholipid fatty acid (PLFA) analysis was used to characterize microbial community composition and multiple substrate induced respiration (MSIR) to examine microbial community function. We compared undisturbed stands of aspen and spruce to investigate future vegetation shifts, and 17-year-old clear-cuts of both stand types where aspen is naturally regenerating.

Preliminary results revealed that the microbial communities of undisturbed spruce stands differed from aspen stands in both composition and function. Composition of the aspen rhizospheres differed between the two clear-cut stands, indicating a legacy effect of spruce in clear-cut spruce sites. While overall rhizosphere microbial communities did not differ from the bulk soil, differences were observed for specific PLFA chemical structures and MSIR substrates. Next steps include determining what observed differences in microbial community composition and function could mean for soil carbon flux. Additionally, measurement of PLFA isotopic ratios will allow us to examine how the source of carbon differs for rhizosphere and bulk soil microbes.