Recurrent wildfires disrupt soil microbial communities and increase soil carbon emissions in Atlantic shrublands

Poster and Abstract presented in the III SIBECOL & XVII AEET Meeting 2025. Abstract book 2- 6 June 2025 Pontevedra, Galicia (Spain)

Under the current human-induced global change, wildfires are becoming more frequent in many regions, altering ecosystem functioning. Fire-driven ecosystem imbalances can result in more carbon emitted, with positive feedback to global warming. Soil microbial communities are key drivers of ecosystem carbon fluxes, but their resilience to increasing fire recurrence remains poorly understood. We examined the effects of recurrent wildfires on soil microbial communities in shrublands of NW Spain (Allande, Principality of Asturias), where fires are typically human-driven. Soils (0–5 cm depth) with increasing fire recurrence (0–4 fires over 40 years) were incubated for 90 days. To stimulate the soil microbial response, ash was added (1/10 w/w to fresh soil) as a microbial substrate commonly found in fire-prone environments. Microbial activity was measured by basal respiration, and community composition (fungi and bacteria) analyzed by metabarcoding. Our results reveal profound shifts in microbial composition and functional response with increasing fire recurrence. Soils that remained unburned or burned once over the last 40 years exhibited similar microbial communities, whereas soils with higher fire recurrence (2–4 fires) showed higher alpha diversity and community dissimilarity. Ash addition amplified these differences, with the strongest response in soils observed with the highest fire recurrence. Elevated respiration rates in soils burned 4 times suggest accelerated mineralization of soil organic carbon. These results highlight that increased fire frequency disrupts microbial composition and carbon cycling, indicating vulnerability to carbon loss in fire-prone ecosystems. Understanding these dynamics is essential for predicting long-term soil resilience under changing fire regimes

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