Fire effect on lipid composition and hydrophobicity of sandy soils

Low soil-water affinity and soil water repellence (SWR, hydrophobicity) prevents water from wetting or infiltrating soils in burnt and unburnt ecosystems, causing changes on their hydrology, geomorphology, geochemistry, and biochemistry. A wildfire may destroy, develop or enhance SWR in previously wettable or water-repellent soils (e.g., Doerr et al., 2009; Jordán et al., 2013 and references therein). Hydrophobicity is at least in part attributed to a lipid-like cover, rich in fatty acids (FAs). Recently, we have shown that FAs had a major role in the water repellency observed in sandy soils in Doñana National Park (DNP, SW-Spain) under trees (Quercus suber, Pinus pinea) and shrubs (Pteridium aquilinum, Halimium halimifolium) vegetation (Jiménez-Morillo et al., 2016). To get further insight into how fire affect the distribution of soil lipids and their role in SWR, a study was performed on different size fractions of a DNP sandy soil under Quercus suber cover. Two soil samples were taken, one in a burnt site and another in an adjacent unburnt (control) one, both having the same physiographic characteristics. SWR was determined using water-drop-penetration-time test in the <2 mm sieved (bulk) soils and in six size fractions: 1-2 mm, 0.5-1 mm, 0.25-0.5 mm, 0.1-0.25 mm, 0.05-0.1 mm and