Examining the Legacy of Severe Fire on Soil Carbon Cycling in Montane Landscapes in and around the Hayman Burn, Colorado

As the climate continues to warm, the frequency and severity of wildfires are expected to increase, altering global carbon stocks. Microbial communities are important to carbon cycling and sequestration and increase the resiliency of ecosystems. However, the effects of wildfire on microbial communities and the subsequent impact this perturbation has on ecosystem carbon stocks remains poorly understood. Here we investigate soil microbial communities present in the 2002 Hayman burn in Colorado to determine microbes' role in building soil carbon stocks in a montane environment experiencing little post-fire recovery. Soil was collected along a geomorphic gradient of three burned watersheds and two unburned, nearby reference watersheds dominated by Ponderosa Pine. Soil respiration, measured in 6-week soil laboratory incubations, is not significantly different (p =0.79) between burned and unburned watersheds. However, carbon content in burned watershed soils is ~60% lower than unburned watersheds. Thus, soil organic matter (SOM) in burned watersheds is ~47% more bioavailable than unburned watersheds and is statistically significant (p =0.00034). Higher bioavailability could be due to soil organic matter quality or shifts in the microbial community. Comparison of the SOM and respired CO₂ δ¹³C will help partition preferential sources of carbon. Soil microbial community richness and diversity will be determined using 16S RNA gene sequencing. We hypothesize that burned watersheds will have soil microbial communities that are distinct from unburned locations, with potential specializations for utilization of carbon pools that are altered during fire. Microbial carbon processing could form a positive feedback cycle that inhibits the ability of carbon stocks to increase, which affects post-fire recovery as a larger fraction of SOM in burned soils is respired.