Fire effect on soil organic matter bulk and compound specific stable isotopes (¿13C, ¿D IRMS & Py-CSIA)

Abstract

The effect of a wildfire in the soil organic matter (SOM) isotopic signature was analysed in a comparative manner in fire-affected and nearby non-affected Arenosol from the Doñana National Park (Andalusia, SW Spain). The main vegetation was cork oak (Quercus suber) and the fire event occurred in the summer of 2012. Carbon and hydrogen stable isotopic analysis (¿13C and ¿D IRMS) was done in bulk (whole soil and particle-size fractions). In addition a detailed compound specific isotopic analysis of carbon (¿13C) and hydrogen (¿D) using direct pyrolysis (Py-CSIA) was also conducted in the same soil size fractions. Heat caused SOM dD and d13C fractionation both, in the bulk soil samples and in pyrolysis released specific compounds from different biogenic origin i.e. non-specific aromatics (alkylbenzenes and alkylphenols), fatty acids, lignin-derived methoxyphenols, N-bearing compounds from peptides and polysaccharide-derived structures. Particularly informative about the passage of fire where conspicuous shifts found in the isotopic signatures of hydrocarbon series (n-alkanes) with 14 to 28 carbon atoms chain length. The results will be discussed in relation to the meaning of the differences found in relation to SOM evolution and to the potential use of stable isotope fractionation as proxies to study the effect of fire in SOM.