Fire Damage to the Soil Bacterial Structure and Function Depends on Burn Severity: Experimental Burnings at a Lysimetric Facility (Medforecotron)

The soil microbiota is vulnerable to burning; however, it shows some resilience. No indices have yet been developed to assess fire damage related to soil biota. We evaluated the biological soil indices recorded by a Biolog EcoPlate System in a Mediterranean ecosystem. The experiment was carried out in an outdoor forest lysimeter facility (MedForECOtron), where we simulated burns with different burn severities. Burning increased the metabolic diversity of bacteria and most C-substrate utilization groups. Soil organic matter, phosphorus, electric conductivity, and calcium increased with increasing burn severity. Microbial richness and activity, as well as the integrated capacity of soil microbes to use a C source, lowered by burning, but recovered 6 months later. The functional diversity and amount of the C source used by microbes immediately increased after fire, and values remained higher than for unburned soils. We evaluated the changes in the vulnerability and resilience of fire-adapted ecosystems to improve their adaptive forest management. We found that the high burn severity reduced microbial richness, functional diversity, and the C source utilization of soil microbes (marked vulnerability to high temperatures), which recovered in the short term (high resilience). These results help to understand the main mechanisms of the effects of wildfire on semi-arid Mediterranean ecosystems, whose field validation will be helpful for fire prevention planning and restoration of burned areas.