Dr. Thea Whitman, University of Wisconsin – Madison – 10 November 2020

Soil microbes and fire ecology: Developing a belowground perspective


Global fire regimes are changing, with shifts in wildfire duration, frequency, and severity predicted for North American forests over the next 100 years. Additionally, in many ecosystems, prescribed fires are an important management tool. Fires can restructure plant and microbial communities within the ecosystem, which can have long-lasting effects on ecosystem functions. Fires can also cause dramatic losses or transformations of C stocks, through the combustion of biomass and organic soil horizons, as well as through the production of pyrogenic organic matter. However, these effects depend on fire severity. We have investigated the effects of fire on soil microbial communities (bacteria and fungi), in low-severity prescribed fires in Wisconsin, USA, as well as in an unprecedentedly extreme fire season in the boreal forest of Alberta and the Northwest Territories of Canada. Our approaches have included field surveys, laboratory experiments, and meta-analyses. Drawing on a range of studies, I will address the following questions: (1) What factors structure soil microbial communities post-fire? (2) Which specific taxa respond positively to fires? (3) What ecological strategies allow bacteria and fungi to thrive post-fire? We have found that in low-severity prescribed fires, shifts to microbial composition are minimal, and, to the extent that they occur, are largely restricted to the O horizon. Conversely, in northern Canadian boreal forests, we found that fires significantly changed fungal and bacterial communities in both organic and mineral horizons, with post-fire microbial communities being structured by vegetation community, moisture regime, pH, total carbon, and soil texture. We have identified specific taxa as “fire-responders” in both low- and high-severity fires (e.g., Massilia sp., Arthrobacter sp., Fusicladium sp., and Pennicilium sp.), some of which are also found in other fire-affected systems. However, organisms within the same genus may not respond to fires in the same way, highlighting that the characteristics that lead to post-fire success may not be well-conserved, even at the genus level or finer. To begin to understand these responses, we are taking a traits-based approach, where we seek to identify specific microbes that (a) survive fire, (b) grow quickly post-fire, or (c) thrive under post-fire conditions. Together, we strive to add to our collective understanding of wildfire and prescribed fire effects on soil microbes and the fundamental ecological processes they control.

Nature of Life seminars

Date       :   10 November 2020

Time       :   15.45 hours

Location:   Online