Heating-Induced Changes in Content and Molecular Characteristics of Pyrogenic Dissolved Organic Matter across Soil Types

Wildfires remarkably alter the quantity and quality of dissolved organic matter (DOM) that regulates postfire biogeochemical processes and environmental quality. However, it remains unclear how the heating-induced percent changes (%HIC) in DOM quantity and quality differ among soil types on a wide geographic scale. Here, we used dissolved organic carbon (DOC) quantification, absorption, and fluorescence spectroscopies, and Fourier transform ion cyclotron resonance mass spectrometry to investigate the variations in %HIC in DOM quantity and quality of Chinese soil reference materials after heating at 250 and 400 °C. Our results reveal that as soil pH increased, %HIC in DOC content increased, while %HIC in aromaticity-related indices of DOM decreased for both heating temperatures. Moreover, the %HIC in DOM biolability and contents of aliphatics increased with soil pH for 250 °C heating but remained relatively stable for 400 °C heating. Results suggest that compared to those in acidic soil-dominated forests, wildfires in alkaline soil-dominated forests may cause greater DOM content and biolability in soils, which may facilitate postfire microbial recovery. These findings deepen our understanding of the site-specific impacts of wildfires on DOM and the subsequent implications for biogeochemical cycling and environmental quality across different geographic regions.