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TES: Modelling Microbes to Predict Post-Fire Carbon Cycling in the Boreal Forest across Burn Severities

Active Dates 8/15/2020-12/14/2024
Program Area Environmental Systems Science
Project Description
Boreal forests hold between 370-1720 Pg carbon (C) above- and belowground, making them a major stock of C globally. In North American boreal ecosystems, wildfire is the primary stand-replacing disturbance, and fires are projected to increase in frequency and severity in the future. Fires have direct effects on C stocks due to immediate losses during combustion, but also have indirect effects, through the modification of soil properties and remaining soil C, the response of vegetation communities, and changes to soil microbial communities and their activities. Changes to fire frequency and severity could affect each of these processes, and changes to fire severity or frequency have, indeed, been associated with changes in soil C storage. However, data quantifying these effects are sparse, and our understanding of the mechanisms driving them remains limited.

Recent advances in Earth system model (ESM) representations of soil C cycling, such as the Carbon, Organisms, Rhizosphere and Protection in the Soil Environment (CORPSE) model, have included an emphasis on explicitly representing the system in an increasingly mechanistically accurate way. In particular, this has included: representing both physically protected and unprotected C; distinguishing between rhizosphere and bulk soil; representing microbes as dead or living, or as different functional types, among other developments. Because of their mechanistic nature, these models may be better prepared to represent the effects of wildfires on soil C dynamics than most current ESMs. Standard ESMs generally do not represent complex feedbacks between fire, vegetation, soils, microbes, and climate. Rather, they usually represent fires only in terms of their frequency and impacts on vegetation biomass pools, and predict that the above-ground community follows a well- known trajectory over time, with no new steady states other than those functionally similar to the previous state.

We propose to determine whether linking belowground microbial community composition, size, and activity to aboveground properties of burn severity and plant community composition (upland jack pine and upland spruce) allows us to better model post-fire soil CO2 fluxes using the CORPSE model. We will use an integrated modelling-experimental approach, with mechanistic laboratory experiments designed to inform models of three hierarchical levels of complexity. Our objectives are as follows:

Objective 1. Quantify changes in C fluxes, microbial biomass, and microbial community composition, after simulated fires in intact soil cores across a burn severity gradient.
Objective 2. Develop and evaluate adaptations to the CORPSE model to better represent post-fire SOC dynamics across a burn severity gradient using data from Objective 1 across a hierarchy of model complexity: (1) no explicit microbial representation; (2) community-level microbial traits characterized by single scalable parameters – maximum growth rate, CUE, and total microbial biomass; (3) microbes characterized as an assemblage of multiple functional groups with different traits constrained by the observed experimental data across the microbial community.
Objective 3. Test the capacity of the adapted CORPSE model (Objective 2) to predict CO2 flux rates in burned cores from new sites.

Wildfires in boreal ecosystems represent a globally significant ecological process that is expected to be sensitive to climate change, but is currently insufficiently understood and represented in models. We propose fundamental, mechanism-based and model-driven research in a globally important system with basic relevance for environmental change, addressing current modelling challenges. It will help advance understanding of Earth’s biogeochemical systems and climate while developing insights into terrestrial cycling of C and nutrients, and their feedbacks with Earth’s climate system, thus strengthening scientific knowledge in ecology, biology, and biogeochemistry.
Award Recipient(s)
  • University of Wisconsin, Madison (PI: Whitman, Thea)