Climate change has led to more severe and more frequent fires, especially in the western US. Increases in burn severity are especially important, as this is a central factor for determining soil responses following fire, thereby affecting both vegetation recovery and water quality. This analysis is focused on changes to soil chemistry following two 2018 wildfires in lodgepole pine forests in Wyoming, USA. In July 2019, 0-5 cm and 5-10 cm depth soil samples were collected in low, moderate, and high severity burned areas, along with adjacent, unburned controls. Soil organic matter was extracted for chemical analyses including Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICR MS). Initial chemical analyses showed that dissolved organic carbon decreased with increasing severity in the 0-5 cm depth, but not the 5-10 cm depth. Conversely, nitrogen analyses show the highest concentration of dissolved organic nitrogen at low burn severities in the 0-5 cm depth. Complementary analysis of the FTICR MS data displays a decrease in the average mass, decreased O/C ratios, and increased double-bond equivalence of burned samples at the 0-5 cm depth relative to the unburned control, offering preliminary insights into the ways in which fire affects soil quality. All burned samples display a relative increase in CHNO, CHOS, and CHNOS compared to the controls, demonstrating a shift in chemical composition with fire that may be indicative of the specific transformations that soils undergo during heating. We are currently exploring the FTICR MS data to evaluate changes in dissolved organic matter quality while focusing on the CHNO fraction across the severity gradient, as nitrogen is relatively understudied compared to carbon in these systems. Further analysis into CHNO structural transformations in fire-affected soils will provide molecular insights for the formation of pyrogenic organic matter and enhance our understanding of nitrogen cycling in post-fire environments.

Identifying the role of fire severity on carbon and nitrogen cycling in high-elevation forest soils

ACS Fall 2021

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