Long-term resilience of mineral associated organic matter in soils of a Mediterranean forest burned in 1994 at different severities

Wildfires are a common disturbance in Mediterranean ecosystems; nevertheless, in temperate and higher latitude ecosystems the frequency and severity of wildfires increased because of prolonged heat waves, drought periods and changes in fire regime. High wildfire frequency and increased burned surface area may affect soil organic carbon (SOC) dynamics. In our study, we assessed the effects on different SOC pools (labile, intermediate and passive) in two areas of the Cadiretes Massif in Spain 28 years after a wildfire event. The area was burned at different severities (LS: low severity; HS: high severity) and were compared with a control (unburned) adjacent area. A physical fractionation method was used to isolate the OC and associated to dissolved organic carbon (DOC), particulate organic matter (POM) the mineral associated organic matter (MAOM). In addition, we used 13C NMR spectroscopy to get information about the quality of the different OC fractions. Results displayed that an increase in wildfire severity caused a decrease of SOC and N in the bulk soil. This was mainly observed in the labile fractions (DOC; POM). No differences were observed in the OC associated to the MAOM with the increase of the burning severity indicating that the OC protected in the mineral fraction was resilient towards wildfires.