Composition of soil lipids as semi-quantitative fire severity proxy

Poster presentado en el 5th International Conference of Fire Effects on Soil Properties (FESP5) Poster:P6 (2015)Fire effects on soil properties may be studied in laboratory simulation experiments, which help in differentiating fire intrinsic effects on soil organic matter (SOM) from those produced by inputs of organic matter from charred necromass after a fire. Chemical composition of soil lipid fraction comprises valuable information about environmental impact on soils i.e. effect of fire, reafforestation or cultivation. The present study simulates fire effects on topsoil from Central Spain: soil G is a Calcic Luvisol under barley from CSIC Experimental Farm 'La Higueruela', Toledo; soil R3 is a Mollic Cambisol under evergreen oak forest (Quercus pyrenaica), and soil R4 is an Ortieutric Cambisol on pine (Pinus pinaster) forest. Parent rock was limestone in site G and granite in R3 and R4. Soil samples were isothermally heated at 350 ºC for periods ranging from 0 to 660 seconds. Soil lipids were Soxhlet extracted with dichloromethane-methanol (3:1 v/v), methylated and injected in a GC/MS system fitted with an HP5 MS column. The concentrations of the major oxygen-containing lipid compounds i.e., alkanols, fatty acids and alkanoic diacids, were found poorly heat responsive. On the contrary, fire induced chain breakdowns in hydrocarbons. In fact unheated soil n-alkane series show maximum chain length ca. C31 with odd-C numbered chains dominance as typically produced by vascular plants. After heating, the carbon preference index (CPI) and average carbon length (ACL) systematically changed, leading to patterns with increased low molecular weight (1. The fire-induced rearrangement of alkane series that was consistent in the three soils studied and more intense in the G1 cultivated soil under barley, and least intense in the R3, as could correspond to a more refractory SOM in clay-humus complexes in the latter.Peer Reviewe