Experimental summer fires do not affect fungal diversity but do shape fungal community composition in Mediterranean Pinus nigra forests

Abstract Background Fire regimes (in terms of frequency, severity, and intensity) in ecosystems are changing. Summer fires are occurring in Mediterranean forests more frequently and are more severe than spring or autumn fires. Soil microbial communities provide essential ecosystem services and are essential in post-fire recovery. However, to date, studies to determine the impact of summer fires on soil microbial communities have been limited. To explore how more severe fires may affect fungal diversity and community composition, we conducted an experimental summer fire in June 2019 at an experimental site that had been previously established in a pure stand of black pine ( Pinus nigra Arn.) in 2016 in the Cuenca Mountains in Spain (Central-Eastern Spain). Results Metabarcode DNA analyses of soil samples collected in three blocks (with three plots sampled in unburned and burned areas per block) in spring 2020 revealed that total soil fungi richness and diversity were not affected by summer burning; although no significant, summer burning did have a contrary influence on the most dominant fungal trophic groups. The relative abundance of ectomycorrhizal (ECM) fungi was negatively affected by burning, whereas saprotrophic fungi were positively affected by burning. Fire also had a significant effect on the composition of the total community and when analyzed by the trophic group. Multilevel pattern analysis showed that ECM fungi were significantly correlated with unburned plots. Physicochemical analyses revealed that there were no changes in the main edaphic variables measured. Conclusions The application of fire under more critical summer conditions (out of typical prescribed fire weather windows in Europe) did not produce significant differences in the diversity of the fungal community, being ECM fungi more sensitive to heat than other trophic groups. However, the composition of the fungal community differed significantly between burned and unburned plots. Overall, burned plots showed an adaptation to fire with a rapid proliferation of several pyrophilous genera that are able to improve soil conditions, which would enhance post-fire regeneration of the stand. These pioneering results can inform managers in conducting controlled summer fires to surrogate low to medium surface fire in Pinus nigra stands, knowing that the fungal diversity of the ecosystem is not affected, and thus the key ecological role of these organisms is not significantly harmed.