The increasing frequency and severity of wildfires pose a growing threat to soil microbial community, which plays a key role in soil health and functioning of the whole terrestrial ecosystem. The aim of this study was to assess the effects of high-severity wildfires, occurred during 2017 and 2023 summers within the Maiella National Park, on soil microbial communities of a beech forest and a pine forest. Specific goals were to analyse: i) the impact of the 2023 fire in relation to forest type (beech vs pine forests), and ii) the effect of fire frequency (1 vs. 2 fires in the period 2017- 2024) within the pine forest. On soil samples, collected in November 2024, microbial community performance was analysed in burned sites, compared to unburned controls, measuring microbial biomass, fungal biomass, potential respiration, N-acetyl-β-D-glucosaminidase activity, bacterial and fungal genetic diversity (richness and Shannon index). Significant reductions in microbial and fungal biomass, respiration, and fungal richness were observed in 2023-burned sites, compared to control, with higher negative effect generally observed in beech than in pine forest. However, only in the burned pine forest a negative impact on the bacterial richness was found. Data also showed higher negative effects with increasing fire frequency in the pine site affected by two fires (2017+2023), which exhibited significant decreases in microbial biomass, respiration and bacterial Shannon index, compared to site burned only once. Overall, data showed that 15 months after fire microbial community has not yet returned to its pre-fire state, and that the repeated fires, even six years later, can amplify negative impacts on microbial community.

Funded by the Project “BIOdiversita’ Specifica e Funzionale per la Resistenza, Resilienza e Recupero ai disturbi ed al cambiamento climatico [BIOSFeR3a]”, within the “National Biodiversity Future Center - NBFC PROJECT” (CUP B83C22002930006), Italian Ministry of University and Research.