Transformation of humic substances and functional groups of soil organic carbon after wildfire

The composition of humic substances and structural diversity of soil organic carbon (SOC) can be affected by wildfire. In this study, soil samples were collected after 1 year of no fire, low intensity of fire (dead trees <= 30%), moderate intensity of fire (dead trees 30-70%) and high intensity of fire (dead trees >= 70%). The amounts of humic acid (HA), fulvic acid (FA) and humin (Hu) were investigated, and the characteristics of SOC were analyzed by C-13 NMR spectroscopy too. The results showed that Hu decreased much more than HA and FA after fires, but it still contained more C than HA and FA. There was a positive correlation between the contents of SOC and Hu (R-2 = 0.96, p = 0.02). Aryl C of SOC decreased with the heavy intensity of fire, while alkyl C increased in converse. These results indicate that Hu loses more C than HA and FA with fires, while it is still the main component of SOC. The Alkyl C is more stable than aryl C in fires.