Seminar: Investigating the ecology and biogeochemistry of fire effects on soil microbes

Abstract: Fires represent a fundamental ecological disturbance, with multifaceted effects on ecosystems above and belowground. Furthermore, fire regimes in many regions of the world are changing, often increasing in frequency or severity. While fire ecology is relatively well characterized for larger organisms, our understanding of microbial response to fires is still developing. Our lab studies the effects of fire on soil microbes, spanning from field studies in northern Canada to mechanistic laboratory studies and stable isotope-informed approaches. I will present elements of a fire ecology framework for soil bacteria, where we empirically identified fire-related traits in the lab, and then assessed their relative abundances in natural communities across a fire severity gradient in the boreal forest one and five years post-fire. In addition to combustion, fires also transform organic matter into pyrogenic organic matter. I will present results from our lab’s studies of the interactive effects of pyrogenic organic matter on soil microbes and their degradation of non-pyrogenic soil organic matter. High temporal-resolution CO₂ flux monitoring using custom-built instrumentation and ¹³C-labelled pyrogenic organic matter allow us to distinguish shifting mechanisms over time in a short-term soil incubation and to identify the bacterial taxa that degrade pyrogenic organic matter. Together, these studies help us understand how and why soil microbes respond to fire.